Flexible, high-strength composite piezoelectric fiber film, and preparation method and application thereof

Abstract

The present application relates to a kind of flexible, high-strength composite piezoelectric fiber film and its preparation method and application, including dissolving PVDF or its copolymer in solvent, obtain first solution;Strong dipole moment asymmetric polar inorganic metal salt is dissolved in solvent, obtain second solution;First solution and second solution are mixed evenly, add multifunctional biobased polymer, ultrasonic stirring until forming uniform composite spinning solution, electrospinning, obtain composite piezoelectric fiber film.The fiber film of the present application fuses the mechanical strength and chemical stability of PVDF and its copolymer and the flexibility and water absorption of biobased polymer.Meanwhile, the introduction of inorganic metal salt can play the role of beta phase nucleating agent in the crystallization process of electrospun PVDF, enhance the piezoelectric output performance of electrospun PVDF nanometer piezoelectric composite film, improve the mechanical properties of fiber film by metal coordination effect of metal ion and hydroxyl or carboxyl on biobased polymer, widen the application potential in the field of sensor, battery separator, antibacterial coating etc..

Description

Technical Field

[0001] This invention relates to the field of fiber film preparation technology, specifically to a flexible, high-strength composite piezoelectric fiber film, its preparation method, and its applications. Background Technology

[0002] Fiber films are materials made of fibrous materials and possess film-like properties, typically exhibiting a certain degree of flexibility and strength. These films can be made from natural fibers (such as cellulose and chitosan) or synthetic fibers (such as polyester and polyurethane). Fiber films have wide applications in various fields, including packaging, environmental protection, biomedicine, and electronics. Currently, the most widely used matrix material is PVDF. PVDF has excellent chemical resistance, resisting the erosion of various chemicals, including acids, alkalis, and organic solvents. This allows PVDF films to be used in corrosive environments, such as chemical plants, laboratories, and other industrial applications. Furthermore, they possess good electrical insulation properties, making them suitable for electronic and electrical applications, such as cable insulation, sensor materials, and battery separators.

[0003] However, the vast majority of fiber films are made by mixing PVDF with other reinforcing phase materials, which gives the composite fiber film better mechanical and piezoelectric properties.

[0004] Chinese patent application CN202211211515.7 discloses a PVDF piezoelectric thin film and its preparation method. This invention involves dissolving PVDF in an organic solvent to obtain a PVDF solution, coating the PVDF solution onto a glass substrate, drying it, and then cooling it to form a PVDF film. The film is then uniaxially stretched and polarized to generate a polarized PVDF thin film. A PEDOT:PSS aqueous solution is then vacuum spin-coated, and finally dried at 70–100°C to obtain the PVDF piezoelectric thin film. While this method improves the piezoelectric properties of the PVDF piezoelectric thin film, the process for improving its piezoelectric properties is complex, and the overall mechanical stability of the film cannot be guaranteed.

[0005] Chinese patent application number 201911177706.4 discloses a composite piezoelectric film and its preparation method. This invention utilizes pure natural plant nanocellulose fibers, Mxene, and polyvinylidene fluoride as raw materials, and prepares a nanocellulose / PVDF composite film with strong piezoelectric properties through processes such as mechanical mixing, drying, and high-voltage polarization. This method requires mechanical mixing and high-voltage polarization to prepare the composite film with strong piezoelectric properties, making the process cumbersome and unsuitable for large-scale production applications.

[0006] Therefore, it is necessary to provide a simple and low-cost method for preparing flexible composite fiber films with a dual interpenetrating network structure that combines excellent mechanical and piezoelectric properties to solve the above technical problems. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies in preparing PVDF-based piezoelectric films, which involve complex processes and difficulties in simultaneously improving both mechanical and piezoelectric properties, this invention provides a flexible, high-strength composite piezoelectric fiber film, its preparation method, and its applications. This invention utilizes electrospinning combined with in-situ construction technology, employing a multifunctional bio-based polymer and a strong dipole moment asymmetric polar inorganic metal salt as reinforcing phases, with PVDF or its copolymers as the matrix phase, to prepare a flexible, high-strength composite piezoelectric fiber film. The multifunctional bio-based polymer used in this invention exhibits excellent adhesive properties; adding it to the mixed solution improves the tensile strength and tear resistance of the film, making it more durable during use. The strong dipole moment asymmetric polar inorganic metal salt not only serves as a conductive filler but also improves the mechanical properties and thermal stability of the composite material.

[0008] The objective of this invention can be achieved through the following technical solutions:

[0009] One objective of this invention is to provide a method for preparing a flexible, high-strength composite piezoelectric fiber film, comprising the following steps:

[0010] S1. Dissolve PVDF or its copolymer in a solvent to obtain a first solution; dissolve a strong dipole moment asymmetric polar inorganic metal salt in a solvent to obtain a second solution;

[0011] S2. Mix the first and second solutions evenly, add the multifunctional bio-based polymer, sonicate and continue stirring until a uniform composite spinning solution is formed;

[0012] S3. Electrospinning is performed on the composite spinning solution to obtain a flexible, high-strength composite piezoelectric fiber film.

[0013] Further, in S1, the solvent is one of the following combinations of solvents:

[0014] ① A mixed solvent prepared from tetrahydrofuran and N,N-dimethylformamide in a mass ratio of (2-8):(8-2);

[0015] ②A mixed solvent prepared from toluene and tetrahydrofuran, with a mass ratio of (2-8):(8-2);

[0016] ③ A mixed solvent prepared from N,N-dimethylformamide and dichloromethane, with a mass ratio of (2-8):(8-2);

[0017] ④ A mixed solvent prepared from N,N-dimethylformamide and acetone in a mass ratio of (2-8):(8-2).

[0018] Further, in S1, the PVDF or its copolymer satisfies at least one of the following conditions:

[0019] ①The molecular weight of the PVDF or its copolymer is between 200,000 and 1,000,000;

[0020] ②The PVDF or its copolymer is selected from any one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-fluorinated polymer (PVDF-HFP), polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) or polyvinylidene fluoride-vinyl chloride fluoride (PVDF-CTFE);

[0021] ③ The mass concentration of the PVDF or its copolymer is 70% to 90%;

[0022] ④ The PVDF or its copolymer is dissolved in the solvent by adding PVDF or its copolymer to the solvent and stirring for 1 to 6 hours under a constant temperature water bath at 60°C.

[0023] Furthermore, in S1, the strong dipole moment asymmetric polar inorganic metal salt satisfies at least one of the following conditions:

[0024] ①The strong dipole moment asymmetric polar inorganic metal salt includes one or more of CuCl2·2H2O, FeCl2·4H2O, CoCl2·6H2O, NiCl2·6H2O, SnCl2·2H2O, and FeCl3·6H2O.

[0025] ②The inorganic salt mass concentration in the strong dipole moment asymmetric polar inorganic metal salt solution is 0.5% to 5%.

[0026] Furthermore, in S2, the multifunctional bio-based polymer satisfies at least one of the following conditions:

[0027] ①The multifunctional bio-based polymer includes one or more of cellulose nanocrystals, cellulose nanofibers, methylcellulose, carboxymethylcellulose, sodium alginate, gelatin and chitosan.

[0028] ②The mass ratio of the multifunctional bio-based polymer to the PVDF or its copolymer is (0.02~0.1):1.

[0029] Furthermore, in S2, the power of the ultrasound is 50W to 100W, the frequency is 20kHz to 1MHz, and the processing time is 1h to 3h; the stirring time is 9h to 12h.

[0030] Further, in S3, the electrospinning specifically involves: injecting the composite spinning solution into a syringe and placing it in an electrospinning device to adjust the spinning parameters for stable spinning; collecting the spun fiber film; and drying it to obtain a flexible, high-strength composite piezoelectric fiber film. The syringe can be 10mL, 20mL, or 50mL.

[0031] The spinning parameters are as follows: receiving distance 8-15cm, drum speed 150-800r / min, liquid flow rate 0.5-5ml / h, spinning voltage 8-12kv, humidity 30-50%, and spinning time 1-3h.

[0032] Furthermore, the drying specifically comprises one of the following operations:

[0033] ① Place the prepared fiber film in a dry environment with a humidity of 30-40% to remove excess moisture;

[0034] ② Place the prepared fiber film in a low-temperature oven and dry it at 40-50℃ to remove excess moisture.

[0035] The second objective of this invention is to provide a flexible, high-strength composite piezoelectric fiber film, which is prepared by the method described above, and the composite fiber film has a double interpenetrating network structure inside.

[0036] The third objective of this invention is to apply the flexible, high-strength composite piezoelectric fiber film described above in the preparation of sensors, battery separators, antibacterial coatings, etc.

[0037] Mechanism of action:

[0038] This invention enhances the mechanical stability and ductility of composite piezoelectric fiber films through physical entanglement and hydrogen bonding between PVDF or its copolymers and bio-based polymers rich in hydroxyl or carboxyl functional groups. Strong dipole moment asymmetric polar inorganic metal salts, oriented as electric dipoles, act as β-phase nucleating agents during the electrospinning of PVDF or its copolymers, significantly enhancing the piezoelectric output of the composite piezoelectric fiber film. Furthermore, the inorganic metal salt ions undergo coordination reactions with the bio-based polymers rich in hydroxyl or carboxyl functional groups to form a chemical cross-linked network, which is then tightly bonded to the PVDF or its copolymer network through hydrogen bonds, ion-dipole interactions, and other mechanisms, ultimately forming a double interpenetrating network flexible, high-strength composite piezoelectric fiber film. When the composite fiber film is subjected to external forces, the synergistic effect of the double interpenetrating network effectively disperses stress, thereby improving the overall performance of the composite piezoelectric fiber film. Finally, a flexible, high-strength composite piezoelectric fiber film was prepared by electrospinning combined with in-situ construction. Compared with traditional piezoelectric film forming methods such as "coating method", it can obtain a composite piezoelectric fiber film with excellent mechanical and piezoelectric properties simply and efficiently by simultaneously stretching and electric field polarizing polymer jets from widely available raw materials, which has great application prospects.

[0039] Compared to existing technologies, this invention uses a mixed solvent. Unlike single solvents, which have limited solubility for different substances, mixed solvents combine the solubility characteristics of multiple solvents, making PVDF or its copolymers, as well as strongly dipole-moment asymmetric inorganic metal salts, easier to dissolve. This prevents reactions between inorganic salts and PVDF or multifunctional bio-based polymers that could lead to gelation, thus maintaining the uniform dispersion of raw materials in the solution for a longer period, which is beneficial for subsequent electrospinning operations. Furthermore, by changing the composition ratio of the mixed solvent, parameters such as the polarity, boiling point, and evaporation rate of the solvent system can be flexibly adjusted, modifying the rheological properties of the solution. This, in turn, affects the crystallization behavior, phase separation degree, and intermolecular interactions of the PVDF or its copolymer composite spinning solution during film formation, ultimately achieving precise control over the piezoelectric properties, mechanical properties, thermal stability, and other aspects of the composite piezoelectric fiber membrane material. Attached Figure Description

[0040] Figure 1 This is a flowchart illustrating the overall preparation process of the present invention;

[0041] Figure 2 This is a scanning electron microscope image of the flexible, high-strength composite piezoelectric fiber film prepared in Example 1. Detailed Implementation

[0042] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0043] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. Unless otherwise specified, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0044] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0045] Example 1:

[0046] This embodiment provides a method for preparing a flexible, high-strength composite piezoelectric fiber film with a dual interpenetrating network structure, the steps of which are as follows:

[0047] (1) N,N-dimethylformamide (DMF) and acetone were mixed in a mass ratio of 2:5 to obtain a mixed solvent. PVDF was then gradually added to the mixed solvent, and the mixture was stirred at 500 rpm for 1 hour in a 60°C constant temperature water bath using an electromagnetic stirrer until the PVDF was completely dissolved, resulting in a homogeneous PVDF solution with a mass concentration of 88%. FeCl3·6H2O was added to the mixed solvent to obtain a 3% inorganic salt solution, which was then added to the dissolved PVDF solution and stirred again to ensure homogeneity. Finally, weighed carboxymethyl cellulose was added, and the mixture was ultrasonically treated for 1 hour, followed by stirring for 12 hours to obtain a composite spinning solution with a carboxymethyl cellulose mass concentration of 3%.

[0048] (2) Inject the composite spinning solution into a 20mL syringe and place it in an electrospinning device. The spinning parameters are: receiving distance 15cm, roller speed 500r / min, liquid flow rate 1ml / h, spinning voltage 12kv, humidity 31%, and spinning time 1h to obtain a composite fiber film.

[0049] (3) The composite fiber film obtained in step (2) is further dried in a low temperature oven at 40 degrees Celsius to remove excess moisture and obtain a flexible composite piezoelectric fiber film with a double interpenetrating network structure.

[0050] Scanning electron microscope (SEM) images of the flexible composite piezoelectric fiber thin film with a dual interpenetrating network structure are shown below. Figure 2As shown in the figure, the composite nanofibers have a uniform diameter and no beaded structure is formed, indicating that the prepared composite spinning solution has good spinnability. Furthermore, no obvious beads or surface defects were observed in the fibers, indicating that FeCl3·6H2O and carboxymethyl cellulose are uniformly distributed on the fiber surface, giving it excellent mechanical stability and piezoelectricity.

[0051] Example 2:

[0052] This embodiment provides a method for preparing a flexible composite piezoelectric fiber film with a dual interpenetrating dual network structure, the steps of which are as follows:

[0053] (1) Tetrahydrofuran and N,N-dimethylformamide (DMF) were mixed in a mass ratio of 2:5 to obtain a mixed solvent. PVDF-HFP was then gradually added to the mixed solvent, and the mixture was stirred at 500 rpm for 1 hour in a 60°C constant temperature water bath using an electromagnetic stirrer until PVDF-HFP was completely dissolved, resulting in a homogeneous PVDF-HFP solution with a mass concentration of 75%. FeCl3·6H2O was added to the mixed solvent to obtain a 3% inorganic salt solution, which was then added to the dissolved PVDF-HFP solution and stirred again to ensure homogeneity. Finally, weighed sodium alginate was added, and the mixture was ultrasonically treated for 1 hour, followed by stirring for 12 hours to obtain a composite spinning solution with a sodium alginate mass concentration of 3%.

[0054] (2) Inject the composite spinning solution into a 20mL syringe and place it in an electrospinning device. The spinning parameters are: receiving distance 15cm, roller speed 800r / min, liquid flow rate 1ml / h, spinning voltage 12kv, humidity 31%, and spinning time 1h to obtain a composite fiber film.

[0055] (3) The fiber film obtained in step (2) is further dried in a low temperature oven at 40 degrees Celsius to remove excess moisture and obtain a flexible composite piezoelectric fiber film with a double interpenetrating network structure.

[0056] After testing the prepared flexible composite piezoelectric fiber film with a double interpenetrating network structure, it was found that it had an elongation at break of 170.7% under mechanical property testing, while the elongation at break of pure PVDF fiber film under the same conditions was 112.8%. Analysis showed that the presence of FeCl3·6H2O and sodium alginate significantly improved the mechanical properties of the polymer, thereby increasing the mechanical strength of the composite piezoelectric fiber film.

[0057] Example 3:

[0058] This embodiment provides a method for preparing a flexible fiber film with a dual network structure, the steps of which are as follows:

[0059] (1) N,N-dimethylformamide (DMF) and acetone were mixed in a ratio of 2:5 to obtain a mixed solvent. PVDF-CTFE was then gradually added to the mixed solvent, and the mixture was stirred at 500 rpm for 1 hour in a 60°C constant temperature water bath until the PVDF-CTFE was completely dissolved, resulting in a homogeneous PVDF-CTFE solution with a mass concentration of 90%. CuCl2·2H2O was added to the mixed solvent to obtain a 4% inorganic salt solution, which was then added to the dissolved PVDF-CTFE solution and stirred again to ensure homogeneity. Finally, the weighed cellulose nanocrystals were added, and the mixture was ultrasonically treated for 1 hour, followed by stirring for 12 hours to obtain a composite spinning solution with a cellulose nanocrystal mass concentration of 1%.

[0060] (2) Inject the composite spinning solution into a 20mL syringe and place it in an electrospinning device. The spinning parameters are: receiving distance 15cm, roller speed 600r / min, liquid flow rate 1ml / h, spinning voltage 12kv, humidity 31%, and spinning time 1h to obtain a composite fiber film.

[0061] (3) The fiber film obtained in step (2) is further dried in a low temperature oven at 40 degrees Celsius to remove excess moisture and obtain a flexible composite piezoelectric fiber film with a double interpenetrating network structure.

[0062] Using the flexible composite piezoelectric fiber film with the double interpenetrating network structure prepared above to assemble a flexible sensor, the test showed that the maximum output voltage of the sensor under the action of an external force of 10N at 30% relative humidity, 5Hz, was 12.20V, which is 7.6 times that of the pure PVDF nanofiber flexible sensor, and the sensor performance was stable.

[0063] Example 4:

[0064] This embodiment provides a flexible fiber film with a dual-network structure and its preparation method, the steps of which are as follows:

[0065] (1) Tetrahydrofuran and N,N-dimethylformamide (DMF) were mixed in a ratio of 2:5 to obtain a mixed solvent. Then, 80% PVDF-TrFE was gradually added to the mixed solvent. The mixture was stirred at 500 rpm for 1 hour in a constant temperature water bath at 60 degrees Celsius until the PVDF-TrFE was completely dissolved, resulting in a homogeneous PVDF-TrFE solution with a mass concentration of 80%. CuCl2·2H2O was added to the mixed solvent to obtain a 3% inorganic salt solution, which was then added to the dissolved PVDF-TrFE solution and stirred again to ensure homogeneity. Finally, weighed gelatin was added, and the mixture was ultrasonically treated for 1 hour, followed by stirring for 12 hours to obtain a composite spinning solution with a gelatin mass concentration of 1%.

[0066] (2) Inject the composite spinning solution into a 20mL syringe and place it in an electrospinning device. The spinning parameters are: receiving distance 15cm, roller speed 800r / min, liquid flow rate 1ml / h, spinning voltage 12kv, humidity 31%, and spinning time 1h to obtain a composite fiber film.

[0067] (3) The composite fiber film obtained in step (2) is further dried in a low temperature oven at 40 degrees Celsius to remove excess moisture and obtain a flexible composite piezoelectric fiber film with a double interpenetrating network structure.

[0068] The preparation method of the flexible composite piezoelectric fiber film with a double interpenetrating network structure of the present invention has been verified to be simple, low-cost, easy to mold, and has a short reaction time, making it very suitable for large-scale production. The obtained flexible composite piezoelectric fiber film with a double interpenetrating network structure combines the mechanical strength and chemical stability of PVDF and its copolymers with the flexibility and water absorption of bio-based polymers, forming a multifunctional composite material. Simultaneously, the introduction of inorganic metal salts acts as a β-phase nucleating agent during the electrospun PVDF crystallization process, significantly enhancing the piezoelectric output performance of the electrospun PVDF nanocomposite piezoelectric film, thereby broadening its application potential in sensors, battery separators, antibacterial coatings, and other fields.

[0069] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a flexible, high-strength composite piezoelectric fiber film, characterized in that, Includes the following steps: S1. Dissolve PVDF or its copolymer in a solvent to obtain a first solution; dissolve a strong dipole moment asymmetric polar inorganic metal salt in a solvent to obtain a second solution; S2. Mix the first and second solutions evenly, add the multifunctional bio-based polymer, sonicate and continue stirring until a uniform composite spinning solution is formed; S3. Electrospinning of the composite spinning solution to obtain a flexible, high-strength composite piezoelectric fiber film. In S1, the strong dipole moment asymmetric polar inorganic metal salt satisfies the following condition: ①The strong dipole moment asymmetric polar inorganic metal salt includes one or more of CuCl2·2H2O, FeCl2·4H2O, CoCl2·6H2O, NiCl2·6H2O, SnCl2·2H2O, and FeCl3·6H2O; ② The inorganic salt mass concentration in the strong dipole moment asymmetric polar inorganic metal salt solution is 0.5%~5%; In S2, the multifunctional bio-based polymer satisfies the following conditions: ①The multifunctional bio-based polymer includes one or more of cellulose nanocrystals, cellulose nanofibers, methylcellulose, carboxymethylcellulose, sodium alginate, gelatin and chitosan; ② The mass ratio of the multifunctional bio-based polymer to the PVDF or its copolymer is (0.02~0.1):1; The composite piezoelectric fiber film has a dual interpenetrating network structure inside.

2. The method for preparing a flexible, high-strength composite piezoelectric fiber film according to claim 1, characterized in that, In S1, the solvent is one of the following combinations of solvents: ①A mixed solvent prepared from tetrahydrofuran and N,N-dimethylformamide in a mass ratio of (2-8): (8-2); ②A mixed solvent prepared from toluene and tetrahydrofuran, with a mass ratio of (2-8): (8-2); ③ A mixed solvent prepared from N,N-dimethylformamide and dichloromethane, with a mass ratio of (2-8): (8-2); ④ A mixed solvent prepared from N,N-dimethylformamide and acetone, with a mass ratio of (2-8): (8-2).

3. The method for preparing a flexible, high-strength composite piezoelectric fiber film according to claim 1, characterized in that, In S1, the PVDF or its copolymer satisfies the following conditions: ①The molecular weight of the PVDF or its copolymer is between 200,000 and 1,000,000; ②The PVDF or its copolymer is selected from any one of polyvinylidene fluoride, polyvinylidene fluoride-fluorinated polymer, polyvinylidene fluoride-trifluoroethylene, or polyvinylidene fluoride-vinyl chloride fluoride; ③ The mass concentration of the PVDF or its copolymer is 70%~90%; ④ The PVDF or its copolymer is dissolved in the solvent by adding PVDF or its copolymer to the solvent and stirring for 1 to 6 hours under a constant temperature water bath at 60°C.

4. The method for preparing a flexible, high-strength composite piezoelectric fiber film according to claim 1, characterized in that, In S2, the ultrasonic power is 50W~100W, the frequency is 20kHz~1MHz, and the processing time is 1h~3h; the stirring time is 9h-12h.

5. The method for preparing a flexible, high-strength composite piezoelectric fiber film according to claim 1, characterized in that, In S3, the electrospinning specifically involves: injecting the composite spinning solution into a syringe and placing it in an electrospinning device, adjusting the spinning parameters to stabilize the spinning process, collecting the spun fiber film, and drying it to obtain a flexible, high-strength composite piezoelectric fiber film. The spinning parameters are as follows: receiving distance 8~15cm, drum speed 150~800r / min, liquid flow rate 0.5~5ml / h, spinning voltage 8~12kv, humidity 30~50%, and spinning time 1~3h.

6. The method for preparing a flexible, high-strength composite piezoelectric fiber film according to claim 5, characterized in that, The drying process specifically includes one of the following operations: ① Place the prepared fiber film in a dry environment with a humidity of 30-40% to remove excess moisture; ② Place the prepared fiber film in a low-temperature oven and dry it at 40-50℃ to remove excess moisture.

7. A flexible, high-strength composite piezoelectric fiber film, characterized in that, It is prepared by the preparation method described in any one of claims 1-6.

8. The application of the flexible, high-strength composite piezoelectric fiber film as described in claim 7 in the preparation of sensors, battery separators, and antibacterial coatings.

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