Preparation method and application of charge self-recovery electret composite porous membrane

Abstract

The present invention belongs to the technical field of electret porous membranes, and specifically discloses a method for preparing a charge self-restoring electret composite porous membrane and its application, comprising the following steps: S1, dispersing water-soluble particles and polytetrafluoroethylene particles in a curable polymer liquid in a certain proportion, and obtaining a mixed solution A after uniform mixing; S2, preparing a lower porous membrane by an electrostatic spinning method; S3, dispersing the mixed solution A obtained by S1 on the upper surface of the lower porous membrane obtained by S2 for high-temperature curing, and preparing an upper porous membrane on the lower porous membrane; S4, subjecting the upper porous membrane obtained by S3 to a high-temperature water bath to obtain a composite porous membrane; S5, corona charging the composite porous membrane obtained by S4 to obtain an electret composite porous membrane. The present invention adopts the above-mentioned method for preparing a charge self-restoring electret composite porous membrane and its application, which is simple to operate and has stable properties, and solves the problem that traditional electret porous membranes are easily ineffective and difficult to apply in high-humidity environments and water conditions.

Description

Technical Field

[0001] The invention relates to the technical field of electret porous films, and in particular to a preparation method and application of a charge self-recovery electret composite porous film. Background Art

[0002] Electret refers to a dielectric material that can store space charge and dipole charge for a long time. It is often used to manufacture electret generators, electret filter membranes, etc. Therefore, electret has a wide range of important applications in the field of energy and environment. An important indicator for measuring the performance of electret is the stability of its stored charge.

[0003] However, most electret materials are space charge electrets, and most of the stored charges are located on the surface of the electret film, which is easily affected by external interference. For example, when it comes into contact with water, the retained charge will be lost quickly and cannot be automatically restored.

[0004] In the prior art, the invention patent with publication number CN113783462A discloses a microcapsule electret self-generating device and its preparation method, which assembles polytetrafluoroethylene, uncured polydimethylsiloxane and self-made charged microcapsules and then solidifies them, and assembles them with upper and lower electrodes to realize electret self-generating. However, the device has the defects of fine upper and lower electrodes and microcapsule structures, high preparation cost, and the device relies on a single-layer microcapsule structure for power generation, which is easy to deform under the action of external force, resulting in unstable effect.

[0005] The invention patent with publication number CN106863994A discloses a charge self-recovery electret film, which stably stores charge through a hot-pressed groove structure, so that it can still achieve charge self-recovery under external interference. However, the electret film is very dense, not breathable, has a small application range, and the charge recovery only depends on the electric dipole generated by the groove structure under corona charging, which makes it difficult to ensure a high charge recovery ability. Summary of the invention

[0006] The purpose of the present invention is to provide a preparation method and application of a charge self-recovery electret composite porous membrane, which is simple to operate, has good charge recovery performance, and is stable in nature. After the external moisture interference disappears, the surface charge can be automatically restored, and the charge recovery rate reaches 80-95%. The problem that traditional electret porous membranes are easy to fail and difficult to apply in high humidity environments and water conditions can be effectively solved.

[0007] To achieve the above object, the present invention provides a method for preparing a charge self-recovery electret composite porous film, comprising the following steps:

[0008] S1. Dispersing water-soluble particles and polytetrafluoroethylene particles in a curable polymer liquid in a certain proportion, and mixing them evenly to obtain a mixed solution A;

[0009] S2, preparing the lower porous membrane by electrospinning;

[0010] S3, dispersing the mixed solution A obtained in S1 on the upper surface of the lower porous membrane obtained in S2 and curing it at high temperature to prepare an upper porous membrane on the lower porous membrane;

[0011] S4, placing the upper porous membrane obtained in S3 in a high-temperature water bath to obtain a composite porous membrane;

[0012] S5. Perform corona charging on the composite porous film obtained in S4 to obtain an electret composite porous film.

[0013] Preferably, in S1, the curable polymer liquid is polydimethylsiloxane; the water-soluble particles are one or both of anhydrous glucose and sodium chloride particles, and the particle size range of the water-soluble particles is 0.1-1000 μm; the particle size range of the polytetrafluoroethylene particles is 0.2-1.6 μm.

[0014] Preferably, in S1, the mass fractions of the water-soluble particles and the polytetrafluoroethylene particles are both 15-35wt%.

[0015] Preferably, in S2, the electrospinning method is specifically:

[0016] According to a certain ratio, polytetrafluoroethylene solution and polyethylene oxide are mixed to prepare spinning solution A, and polyamic acid solution is used as spinning solution B. Spinning solution A and spinning solution B are used for double-needle electrospinning, and high-temperature sintering is performed to obtain a polymer fiber membrane with a thickness of 10~100μm and a pore size range of 50~100μm, wherein the electrospinning voltage is 25kV, and the spinning solution injection speed is 0.1~1ml•min -1 .

[0017] Preferably, in S3, the dispersion is performed by spin coating or press coating, and the thickness of the upper porous membrane is 10-100 μm.

[0018] Preferably, in S3, the high temperature curing temperature is 50-90° C. and the time is 3-5 hours.

[0019] Preferably, in S3, the pore size range of the upper porous membrane is 100-2000 μm.

[0020] Preferably, in S4, the temperature of the high temperature water bath is 50-80° C., and the time is 52-80 hours.

[0021] Preferably, in S5, the corona charging is performed by placing a polarization needle directly at the center of the upper porous membrane, with a voltage of -5 to -15 kV and a distance of 3 to 5 cm.

[0022] To achieve the above objectives, the present invention also provides a method for preparing a charge self-recovery electret composite porous membrane, and uses the prepared electret composite porous membrane in recyclable particle filtration membranes and piezoelectric materials in high humidity environments.

[0023] Therefore, the present invention adopts the above-mentioned method for preparing the charge self-recovery electret composite porous film and its application, and the beneficial effects are as follows:

[0024] (1) The present invention uses polydimethylsiloxane and polytetrafluoroethylene with greatly different charge storage capacities. During corona charging, the charge is more concentrated on the interface of polytetrafluoroethylene particles embedded in the upper porous membrane and the surface of polytetrafluoroethylene fibers in the lower porous membrane. When in contact with moisture, the internal charge can remain stable. After the moisture interference disappears, the internal charge migrates to the surface, realizing automatic charge recovery.

[0025] (2) The present invention uses polytetrafluoroethylene and polyimide. Polytetrafluoroethylene contains a strong polar CF bond. When polytetrafluoroethylene is used as the doping particles of the upper porous membrane and the main material of the lower porous membrane, it can stably store charges after corona charging. In addition, by doping with polyimide with high mechanical strength, the mechanical strength of the lower porous membrane is further increased while ensuring the charge storage capacity.

[0026] (3) The present invention utilizes a high-temperature water bath method to remove water-soluble particles in the upper porous membrane, thereby achieving more convenient and accurate pore creation on the polymer fiber membrane; after corona charging, the pores inside the electret composite porous membrane form electric dipoles, which can store a larger amount of charge than a non-porous membrane; after the moisture interference disappears, the electric dipoles in the internal pores can also absorb the charge in the air to promote automatic charge recovery.

[0027] (4) The electret composite porous membrane prepared by the present invention has the characteristics of both a moisture-resistant electret material and a porous material, and can be used as an electret filter membrane in the field of industrial particle filtration. At the same time, it can also be used as a porous piezoelectric material in a high humidity environment.

[0028] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the structure and charge distribution of an embodiment of a charge self-recovery electret composite porous membrane of the present invention;

[0030] Figure 2 1 is a scanning electron microscope image of an embodiment of a charge self-recovery electret composite porous membrane of the present invention, wherein (a) is an upper porous membrane, and (b) is a lower porous membrane;

[0031] Figure 3It is a schematic diagram of charge distribution of an embodiment of a charge self-recovery electret composite porous membrane of the present invention when immersed in deionized water;

[0032] Figure 4 It is a schematic diagram of charge distribution after the surface moisture interference of a charge self-recovery electret composite porous membrane embodiment of the present invention disappears;

[0033] Figure 5 The graphs are surface potential decay diagrams of a charge self-recovery electret composite porous membrane embodiment of the present invention, wherein (a) is a surface potential-time decay diagram, and (b) is a surface potential-cycle number decay diagram.

[0034] Reference numerals

[0035] 100, lower porous membrane; 200, upper porous membrane; 300, deionized water. DETAILED DESCRIPTION

[0036] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0037] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0038] like Figure 1 As shown, an electret composite porous membrane with charge self-recovery function includes a lower porous membrane 100 and an upper porous membrane 200, and both the lower porous membrane 100 and the upper porous membrane 200 store space charges and electric dipoles. Figure 2 As shown, (a) is a scanning electron microscope image of the upper porous membrane 200. The upper porous membrane 200 is a non-dense membrane, and holes are generated on the surface. The pore sizes are all less than 100 μm, and it has a certain permeability; (b) is a scanning electron microscope image of the lower porous membrane 100. The lower porous membrane 100 is a non-dense membrane, and holes are generated on the surface. The pore sizes are all less than 100 μm. Compared with the upper porous membrane 200, its porosity is larger.

[0039] The mechanism of charge self-recovery function: Figure 3 As shown in FIG. 3 , when the electret porous membrane is disturbed by external water, that is, when the electret porous membrane is soaked in deionized water 300, the surface charge is lost. Figure 4 As shown, when the surface moisture interference disappears, that is, when the electret porous membrane leaves the deionized water 300, the charges of the pores inside the electret porous membrane and the charges of the underlying porous membrane 100 will spontaneously transfer to the surface, so that the surface charge is automatically restored, which has the advantages of large charge storage capacity and strong resistance to external interference.

[0040] Embodiment 1

[0041] A method for preparing an electret composite porous film with charge self-recovery function comprises the following steps:

[0042] S1. Add polytetrafluoroethylene particles with a particle size of 1.2 μm and anhydrous glucose particles into polydimethylsiloxane, wherein the mass fraction of the anhydrous glucose particles and the polytetrafluoroethylene particles is 20 wt % each, and mix well to obtain a mixed solution A.

[0043] S2. 60 wt% polytetrafluoroethylene solution is mixed with 1.52 wt% polyethylene oxide to prepare spinning solution A, 25 wt% polyimide precursor polyamic acid solution is used as spinning solution B, spinning solution A and spinning solution B are used for double-needle electrospinning, and then high-temperature sintering is performed to remove polyethylene oxide and convert polyamic acid into polyimide to obtain a lower porous membrane 100, wherein the electrospinning voltage is 25 kV, and the spinning solution injection speed is 0.1 ml•min -1 The spinning time is 4h and the high temperature sintering temperature is 390℃.

[0044] S3, the mixed solution A obtained in S1 is dispersed on the upper surface of the lower porous membrane 100 obtained in S2 by spin coating, and cured at high temperature to prepare the upper porous membrane 200 on the lower porous membrane 100. The high temperature curing temperature is 70° C. and the time is 4 hours.

[0045] S4, placing the upper porous membrane 200 obtained in S3 in a high-temperature water bath to remove the internal glucose and obtain a composite porous membrane, wherein the temperature of the high-temperature water bath is 60° C. and the duration is 76 hours.

[0046] S5, corona charging the composite porous film obtained in S4 to obtain an electret composite porous film. The corona charging voltage used is -10 kV, and the polarization needle is directly facing the center of the upper porous film 200, with a distance of 5 cm.

[0047] Embodiment 2

[0048] A method for preparing an electret composite porous film with charge self-recovery function comprises the following steps:

[0049] S1. Add polytetrafluoroethylene particles with a particle size of 0.2 μm and anhydrous glucose particles into polydimethylsiloxane, wherein the mass fraction of the anhydrous glucose particles and the polytetrafluoroethylene particles is 25 wt % each, and mix well to obtain a mixed solution A.

[0050] S2. 60 wt% polytetrafluoroethylene solution is mixed with 1.52 wt% polyethylene oxide to prepare spinning solution A, 25 wt% polyimide precursor polyamic acid solution is used as spinning solution B, spinning solution A and spinning solution B are used for double-needle electrospinning, and then high-temperature sintering is performed to remove polyethylene oxide and convert polyamic acid into polyimide to obtain a lower porous membrane 100, wherein the electrospinning voltage is 25 kV, and the spinning solution injection speed is 1 ml•min -1 The spinning time is 5h and the high temperature sintering temperature is 390℃.

[0051] S3, the mixed solution A obtained in S1 is dispersed on the upper surface of the lower porous membrane 100 obtained in S2 by spin coating, and cured at high temperature to prepare the upper porous membrane 200 on the lower porous membrane 100. The high temperature curing temperature is 80° C. and the time is 4 hours.

[0052] S4, placing the upper porous membrane 200 obtained in S3 in a high-temperature water bath to remove the internal glucose and obtain a composite porous membrane, wherein the temperature of the high-temperature water bath is 60° C. and the duration is 76 hours.

[0053] S5, corona charging the composite porous film obtained in S4 to obtain an electret composite porous film. The corona charging voltage used is -10 kV, and the polarization needle is directly facing the center of the upper porous film 200, with a distance of 3 cm.

[0054] Experimental Testing

[0055] The electret composite porous membrane (PTFE-PDMS porous membrane) obtained in Example 1 was installed on the air filter as a recyclable particle filter membrane, and a particle counter and a differential pressure gauge were connected to both ends of the filter to detect the filtration efficiency and pressure drop. After filtering for a period of time, the electret composite porous membrane was soaked in water for cleaning. Figure 5 As shown in (a), the surface charge is annihilated by water, and then taken out and dried. The internal charge of the electret composite porous membrane will spontaneously migrate to the surface, causing the surface charge to automatically recover.

[0056] The electret composite porous membrane (PDMS-PTFE composite membrane) obtained in Example 2 was taken out after being immersed in water for 10 seconds, and its surface potential could still be restored to 95% of the original value. Figure 5 As shown in (b), the surface charge can still be stably restored to more than 80% of the initial value after multiple cycles.

[0057] The composite electret porous film obtained in Example 2 was prepared into a piezoelectric device. When a certain pressure was applied, the electret composite porous film could output a short-circuit current when in contact with the electrode. After being soaked in water, compared with the normal electret material, which loses its charge when it encounters water, the device ensures a certain proportion of current output due to the charge self-recovery property of the electret composite porous film.

[0058] Therefore, the present invention adopts the above-mentioned preparation method and application of the charge self-recovery electret composite porous membrane, which is simple to operate, has good charge recovery performance, and stable properties. After the external moisture interference disappears, its surface charge can be automatically restored, and the charge recovery rate reaches 80~95%. It can effectively solve the problem that traditional electret porous membranes are easy to fail and difficult to use in high humidity environments and water conditions.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing a charge self-recovery electret composite porous membrane, characterized in that: The following steps are involved: S1. Dispersing water-soluble particles and polytetrafluoroethylene particles in a curable polymer liquid in a certain proportion, and mixing them evenly to obtain a mixed solution A; S2, preparing the lower porous membrane by electrospinning; S3, dispersing the mixed solution A obtained in S1 on the upper surface of the lower porous membrane obtained in S2 and performing high temperature curing at a temperature of 50-90° C. to prepare an upper porous membrane on the lower porous membrane; S4, placing the upper porous membrane obtained in S3 in a high temperature water bath at a temperature of 50-80° C. to obtain a composite porous membrane; S5, performing corona charging on the composite porous film obtained in S4 to obtain an electret composite porous film; In S1, the curable polymer liquid is polydimethylsiloxane; the water-soluble particles are one or both of anhydrous glucose and sodium chloride particles, and the particle size range of the water-soluble particles is 0.1-1000 μm; the particle size range of the polytetrafluoroethylene particles is 0.2-1.6 μm; In S2, the electrospinning method is specifically: According to a certain ratio, polytetrafluoroethylene solution and polyethylene oxide are mixed to prepare spinning solution A, and polyamic acid solution is used as spinning solution B. Spinning solution A and spinning solution B are used for double-needle electrospinning, and high-temperature sintering is performed to obtain a polymer fiber membrane with a thickness of 10~100μm and a pore size range of 50~100μm, wherein the electrospinning voltage is 25kV, and the spinning solution injection speed is 0.1~1ml•min -1 .

2. The method for preparing a charge self-recovery electret composite porous membrane according to claim 1, characterized in that: In S1, the mass fractions of the water-soluble particles and the polytetrafluoroethylene particles are both 15-35wt%.

3. The method for preparing a charge self-recovery electret composite porous membrane according to claim 1, characterized in that: In S3, the dispersion is performed by spin coating or press coating, and the thickness of the upper porous membrane is 10-100 μm.

4. The method for preparing a charge self-recovery electret composite porous membrane according to claim 1, characterized in that: In S3, the high temperature curing time is 3 to 5 hours.

5. The method for preparing a charge self-recovery electret composite porous membrane according to claim 1, characterized in that: In S3, the pore size range of the upper porous membrane is 100-2000 μm.

6. The method for preparing a charge self-recovery electret composite porous membrane according to claim 1, characterized in that: In S4, the high temperature water bath time is 52 to 80 hours.

7. The method for preparing a charge self-recovery electret composite porous membrane according to claim 1, characterized in that: In S5, the corona charging is performed by placing a polarization needle directly at the center of the upper porous membrane, with a voltage of -5 to -15 kV and a distance of 3 to 5 cm.

8. Application of an electret composite porous membrane prepared by the method for preparing a charge self-recovery electret composite porous membrane according to any one of claims 1 to 7 in a recyclable particle filter membrane and a piezoelectric material in a high humidity environment.

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