Oriented PVDF (Polyvinylidene Fluoride) / multi-fluorine polymer composite film with high triboelectric property for eliminating cavity defects through hot pressing and preparation and application of oriented PVDF / multi-fluorine polymer composite film

Abstract

The invention discloses a high-triboelectric-property oriented PVDF (Polyvinylidene Fluoride) / multi-fluorine polymer composite film capable of eliminating cavity defects through hot pressing as well as a preparation method and application of the oriented PVDF / multi-fluorine polymer composite film. The method comprises the following steps: firstly, preparing an initial composite membrane of PVDF (Polyvinylidene Fluoride) and multi-fluorine polymer nanoparticles through blending; then 2-4 times of hot stretching orientation treatment is carried out at 100 DEG C, and interface cavity defects are generated due to filler rigidity while beta phase formation is induced; and finally, carrying out hot pressing for 1 minute at 120-170 DEG C under 2.5-12.5 MPa. According to the hot pressing process, the cavity defect is effectively eliminated, meanwhile, the beta-phase orientation structure and the high crystallinity are successfully reserved, and the technical problem that defect elimination and orientation keeping are difficult to be compatible is solved. The obtained composite film has high compactness, high dielectric constant and excellent triboelectricity performance, the open-circuit voltage of the composite film can reach 170 V, and the composite film is suitable for a triboelectricity negative electricity layer of a high-performance friction nanometer generator.

Description

Technical Field

[0001] This invention relates to the field of functional polymer materials technology, specifically to a high triboelectric oriented PVDF / polyfluoropolymer composite film with high triboelectric properties obtained by hot pressing to eliminate cavity defects, its preparation method, and its application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Triboelectric nanogenerators (TENGs), as an emerging energy harvesting technology, have broad application prospects in the fields of micro-nano energy and self-driven sensing. The selection and performance of triboelectric materials are crucial. Polyvinylidene fluoride (PVDF) has been extensively studied due to its excellent piezoelectricity and triboelectronetics, but its triboelectric charge density still has room for improvement. Polyfluoropolymers are among the most electronegative materials, and using them as fillers in composites with PVDF is an effective strategy to enhance the performance of PVDF-based TENGs.

[0004] Currently, PVDF / polyfluoropolymer composite membranes are commonly prepared using a blending method. To further improve the crystallinity of PVDF and the β-phase content, the composite membrane is often subjected to a stretching and orientation treatment.

[0005] For example, the patent specification with publication number CN114300612A discloses a method for inducing the preparation of PVDF thin films based on lead zirconate titanate, PVDF thin films and their applications. Lead zirconate titanate is used as the β phase induction site of PVDF thin films to prepare high-purity PVDF thin films, which are applied in multiple fields such as piezoelectric crystal filters, triboelectric nanogenerators, sensors, brakes and biological applications.

[0006] For example, the patent specification with publication number CN108948398A discloses a flexible piezoelectric composite film and its preparation method. Nano-SiO2 particles are added to PVDF, and a high-ratio uniaxial stretching method is used to promote crystal phase transformation and increase the content of β phase in PVDF material. Then, conductive silver paste electrodes are coated on both sides of the film, and the material is polarized under high voltage to give the material better piezoelectric properties.

[0007] However, because the polyfluoropolymer particles remain rigid at the stretching temperature and cannot stretch and deform synchronously with the PVDF matrix, a large number of micro- and nano-scale voids are generated at the interface between the polyfluoropolymer particles and the PVDF matrix. These defects severely weaken the dielectric strength of the composite film, becoming channels for charge leakage, and reduce the mechanical integrity of the film, ultimately leading to a significant decrease in the output performance of the TENG.

[0008] Current technologies lack effective methods to eliminate interfacial cavity defects introduced by the tensile flow difference between rigid fillers and PVDF while maintaining the stretched and oriented structure of PVDF, which significantly reduces the electrical performance of composite films. Furthermore, the non-orientation of electric dipoles caused by the disordered arrangement of molecular chains in conventional PVDF hot-pressed films also degrades their electrical performance. Therefore, developing a method for preparing composite films that simultaneously achieves both PVDF polymer chain orientation and good interfacial bonding has become a pressing technical problem in this field. Summary of the Invention

[0009] To address the aforementioned technical problems and shortcomings in this field, this invention provides a high-triboelectric-performance oriented PVDF / polyfluoropolymer composite film with cavity defects eliminated by hot pressing, along with its preparation method and applications. By synergistically enhancing the composite film's performance through polyfluoropolymer nanoparticle composite, hot stretching orientation, and hot pressing, this invention solves problems such as weak intrinsic triboelectric negativity, low β-phase content, and interfacial cavity defects caused by modulus differences after hot stretching orientation in existing PVDF-based composite films. This invention significantly enhances the triboelectric negativity, β-phase content, structural density, and stability of the composite film, thereby substantially improving its triboelectric output performance.

[0010] The specific technical solution is as follows: In a first aspect, the present invention provides a method for preparing a high-triboelectric-performance oriented PVDF / polyfluoropolymer composite film by eliminating cavity defects through hot pressing, comprising: Provide initial composite membranes containing PVDF and polyfluoropolymers; The initial composite film is subjected to thermal stretching and orientation treatment to obtain a stretched film with a β-phase orientation structure but with interfacial cavity defects. The stretched film is subjected to hot pressing to obtain the high triboelectric oriented PVDF / polyfluoropolymer composite film with cavity defects eliminated by hot pressing.

[0011] Furthermore, the polyfluoropolymer is in the form of nanoparticles.

[0012] The polyfluoropolymer preferably includes one or more of polytetrafluoroethylene (PTFE), perfluoroethylene propylene (FEP), polychlorotrifluoroethylene (PCTFE), and soluble polytetrafluoroethylene (PFA).

[0013] This invention precisely selects polyfluoropolymer nanoparticles and utilizes the strong electronegativity and molecular chain structure similarity of polyfluoropolymers to not only provide directional induction for the formation of PVDF β phase (the β phase content can be increased by more than 15% compared to pure PVDF stretched film), but also simultaneously enhances the intrinsic triboelectric negativeness of the composite film, achieving a functional synergy of β phase induction, electronegativity enhancement, and interface enhancement.

[0014] The preferred mass ratio of PVDF to polyfluoropolymer is 1:0.05~0.2.

[0015] The preferred method for forming the initial composite membrane is blending, which ensures uniform particle dispersion and a smooth initial membrane structure.

[0016] The preferred method for preparing the initial composite membrane includes: adding PVDF and polyfluoropolymer to a solvent and stirring to form a uniform slurry; spreading the slurry, drying it, and demolding it to obtain the initial composite membrane.

[0017] In the method for preparing the initial composite membrane, the solvent preferably includes DMF (N,N-dimethylformamide).

[0018] In the method for preparing the initial composite membrane, the stirring time is preferably 6 hours.

[0019] The thermal stretching orientation treatment can induce the PVDF molecular chain aggregation state to transform towards high crystallinity, high β phase content, and highly oriented arrangement. Furthermore, the thermal stretching orientation treatment is a uniaxial orientation thermal stretching treatment.

[0020] The preferred temperature for the hot stretching and orientation treatment is 100°C.

[0021] The stretching ratio of the heat-stretching orientation treatment is preferably 2 to 4 times the original length.

[0022] Preferably, the hot stretching orientation treatment involves holding the material at a temperature for 5 minutes after stretching it to a set length.

[0023] Preferably, after the thermal stretching and orientation treatment is completed, the material is cooled to room temperature while maintaining tension.

[0024] This invention involves hot-pressing the stretched composite film to eliminate interfacial cavities and voids caused by modulus differences, thereby improving the overall density and dielectric constant of the composite film while preserving its orientation structure, high crystallinity, and β-phase content to the maximum extent.

[0025] The hot pressing process is preferably performed for 1 minute.

[0026] The pressure for the hot pressing treatment is preferably 2.5~12.5 MPa.

[0027] The hot pressing temperature is 120~170℃.

[0028] Preferably, after the hot pressing process is completed, the material is cooled to room temperature while maintaining pressure.

[0029] This invention employs a three-step process of blending, stretching, and hot pressing: First, polyfluoropolymer nanoparticles are blended to utilize the interfacial interaction between the particles and the PVDF matrix, providing β-phase induction sites for subsequent stretching and orientation. Then, uniaxial hot stretching with controllable temperature and rate is used to directionally induce the orientation of PVDF molecular chains and increase the β-phase content. Finally, hot pressing is performed to eliminate interfacial cavity defects while maximizing the preservation of the orientation structure and high crystallinity, thus overcoming the technical contradiction of orientation loss during defect elimination.

[0030] In a second aspect, the present invention provides a high triboelectric performance oriented PVDF / polyfluoropolymer composite film prepared by the method for eliminating cavity defects by hot pressing as described in the first aspect, which is a high triboelectric performance oriented PVDF / polyfluoropolymer composite film with cavity defects eliminated by hot pressing.

[0031] The composite film prepared by this invention is a high-performance composite triboelectric thin film that can effectively eliminate PVDF interface defects while maintaining the orientation structure. It has a highly dense structure, excellent dielectric properties, and significantly improved triboelectric negative output performance, and is suitable for the manufacture and application of high-performance triboelectric energy harvesting devices and self-powered wearable devices.

[0032] Thirdly, the present invention provides the application of the high triboelectric performance oriented PVDF / polyfluoropolymer composite film with cavity defects eliminated by hot pressing as described in the second aspect in a triboelectric nanogenerator. Further, the high triboelectric performance oriented PVDF / polyfluoropolymer composite film with cavity defects eliminated by hot pressing is used as or for fabricating a triboelectric negative layer.

[0033] Fourthly, the present invention provides a triboelectric nanogenerator comprising the high triboelectric performance oriented PVDF / polyfluoropolymer composite film with cavity defects eliminated by hot pressing as described in the second aspect. Further, the high triboelectric performance oriented PVDF / polyfluoropolymer composite film with cavity defects eliminated by hot pressing serves as or is used to fabricate a triboelectric negative layer.

[0034] Existing technical problems: First, existing PVDF-based composite films as triboelectric anode materials have the following limitations: their intrinsic triboelectric negative charge is weak and the β phase content is low, making it difficult to meet the output requirements of high charge density; after thermal stretching and orientation, the difference in modulus can easily lead to interface cavity defects, which can damage the charge transport path or dielectric environment, resulting in reduced triboelectric output stability and increased dielectric constant fluctuation.

[0035] Compared with the prior art, the beneficial effects of this invention are as follows: 1) The stretch-hot-press composite membrane of the present invention has both an oriented structure and a defect-free feature, achieving a 6-fold improvement in output performance compared to the untreated composite membrane; 2) The composite membrane of this invention has a triboelectric negative charge output performance: the open circuit voltage reaches 170 V, which meets the charge output requirements of high-performance triboelectric energy harvesting devices; 3) Dielectric properties of the composite film of the present invention: the dielectric constant is increased to 12.8 (at 1 kHz frequency), which is suitable for dielectric-related functional devices. Attached Figure Description

[0036] Figure 1 This is a process flow diagram of the preparation method in a specific embodiment of the present invention.

[0037] Figure 2 The open-circuit voltage of the TENG output of the stretch-hot-press composite films prepared by different polyfluoropolymers in Examples 1-4 is given.

[0038] Figure 3 The images shown are scanning electron microscope (SEM) images of the untreated composite film in the comparative examples (i), the stretch-oriented film in Example 1 (ii), and the stretch-hot-pressed composite film in Example 1 (iii).

[0039] Figure 4 Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), and dielectric constant plots of the composite films prepared in Example 1 and the comparative examples are shown.

[0040] Figure 5 This is a comparison chart of the output open-circuit voltages of the initial composite film, the stretched oriented film, and the stretched-hot-pressed composite film obtained at different stages of the process in Example 1. Detailed Implementation

[0041] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0042] Unless otherwise specified, the operating methods in the following examples are generally performed under conventional conditions or as recommended by the manufacturer.

[0043] For the detailed implementation process of the composite membrane preparation, please refer to [link to specific implementation details]. Figure 1 First, an initial PVDF / polyfluoropolymer nanoparticle composite film was prepared by blending process. Then, the initial composite film was subjected to uniaxial orientation hot stretching treatment to induce the PVDF molecular chain aggregation state to transform into high crystallinity, high β phase content and high orientation arrangement. Next, the stretched composite film was subjected to hot pressing treatment under specific temperature and pressure conditions to eliminate interfacial cavities and void defects while retaining the orientation structure.

[0044] Example 1: 1. Add 1 g of PVDF powder and 0.15 g of PTFE powder to 10 mL of DMF and stir for 6 hours to prepare a slurry.

[0045] 2. Apply the slurry to a glass plate with a scraper, dry it in an oven at 80°C for 6 hours, and then remove the film to obtain the initial composite film.

[0046] 3. The initial composite film is uniaxially stretched to 4 times its original length at 100℃, held at that temperature for 5 minutes, and then rapidly cooled to obtain a stretched oriented film.

[0047] 4. Place the stretched and oriented film in a hot press and hot press it at 140°C and 7.5 MPa for 1 minute. Then, hold the pressure and cool it to room temperature to obtain the final stretched-hot-pressed composite film.

[0048] 5. Assemble the final stretched-hot-pressed composite membrane with the nylon membrane into a contact-separation TENG and measure its electrical output performance.

[0049] Example 2: 1. Add 1 g of PVDF powder and 0.05 g of FEP powder to 10 mL of DMF and stir for 6 hours to prepare a slurry.

[0050] 2. Apply the slurry to a glass plate with a scraper, dry it in an oven at 80°C for 6 hours, and then remove the film to obtain the initial composite film.

[0051] 3. The initial composite film is uniaxially stretched to twice its original length at 100℃, held at that temperature for 5 minutes, and then rapidly cooled to obtain a stretched oriented film.

[0052] 4. Place the stretched and oriented film in a hot press and hot press it at 120°C and 2.5 MPa for 1 minute. Then, hold the pressure and cool it to room temperature to obtain the final stretched-hot-pressed composite film.

[0053] 5. Assemble the final stretched-hot-pressed composite membrane with the nylon membrane into a contact-separation TENG and measure its electrical output performance.

[0054] Example 3: 1. Add 1 g of PVDF powder and 0.2 g of PCTFE powder to 10 mL of DMF and stir for 6 hours to prepare a slurry.

[0055] 2. Apply the slurry to a glass plate with a scraper, dry it in an oven at 80°C for 6 hours, and then remove the film to obtain the initial composite film.

[0056] 3. The initial composite film is uniaxially stretched to 4 times its original length at 100℃, held at that temperature for 5 minutes, and then rapidly cooled to obtain a stretched oriented film.

[0057] 4. Place the stretched and oriented film in a hot press and hot press it at 170°C and 12.5 MPa for 1 minute. Then, hold the pressure and cool it to room temperature to obtain the final stretched-hot-pressed composite film.

[0058] 5. Assemble the final stretched-hot-pressed composite membrane with the nylon membrane into a contact-separation TENG and measure its electrical output performance.

[0059] Example 4: 1. Add 1 g of PVDF powder and 0.1 g of PFA powder to 10 mL of DMF and stir for 6 hours to prepare a slurry.

[0060] 2. Apply the slurry to a glass plate with a scraper, dry it in an oven at 80°C for 6 hours, and then remove the film to obtain the initial composite film.

[0061] 3. The initial composite film is uniaxially stretched to 3 times its original length at 100℃, and then rapidly cooled after holding at this temperature for 5 minutes to obtain a stretched oriented film.

[0062] 4. Place the stretched and oriented film in a hot press and hot press it at 150°C and 5 MPa for 1 minute. Then, maintain the pressure and cool it to room temperature to obtain the final stretched-hot-pressed composite film.

[0063] 5. Assemble the final stretched-hot-pressed composite membrane with the nylon membrane into a contact-separation TENG and measure its electrical output performance.

[0064] Comparative example: 1. Add 1 g of PVDF powder and 0.15 g of PTFE powder to 10 mL of DMF and stir for 6 hours to prepare a slurry.

[0065] 2. Apply the slurry to a glass plate with a scraper, dry it in an oven at 80°C for 6 hours, and then remove the film to obtain an untreated composite film.

[0066] 3. Assemble the untreated composite membrane and nylon membrane into a contact-separation TENG and measure its electrical output performance.

[0067] Results analysis: like Figure 2 As shown in Examples 1-4, the TENG output open-circuit voltage of the stretched-hot-pressed composite membranes prepared with different fluorinated fillers is shown. The results show that the output voltage of PVDF / PFA is 30 V, the output voltage of PVDF / PCTFE is 60 V, the output voltage of PVDF / FEP is 110 V, and the output voltage of PVDF / PTFE is 170 V. This indicates that polyfluorinated nanoparticles improve the output performance of PVDF, and PTFE has the best reinforcing effect.

[0068] Figure 3SEM images of the composite film prepared for comparison, the stretched oriented film and the stretched-hot-pressed composite film prepared in Example 1 show that the stretched film has a significant orientation structure and cavity defects of polyfluorinated particles along the stretching direction. After hot pressing, the stretched-hot-pressed composite film still maintains a significant orientation structure, while the cavity defects have been eliminated by the continuous PVDF phase filled during the secondary hot processing. This indicates that the composite film finally prepared in Example 1 has both high orientation and defect elimination characteristics.

[0069] like Figure 4 As shown, Fourier transform infrared spectroscopy and differential thermal analysis reveal that the content of the polar β phase in the stretched-hot-pressed composite film increased from 84.74% in the untreated composite film to 98.27% after a fourfold stretch. The crystallinity increased from 42.70% in the untreated composite film to 64.14% in the stretched composite film, subsequently decreasing to 61.32% after hot pressing. This indicates that hot pressing retained most of the original stretched-oriented crystallized structural characteristics, corresponding to the preservation of the electric dipole orientation structure within the composite film. The dielectric constant at 1 kHz increased from 7.6 to 12.8. This demonstrates that after molecular orientation and defect elimination, the internal structure of the composite film shifted towards a direction beneficial to electrical performance (increased polar phase, high electric dipole orientation, and disappearance of low-dielectric-constant, high-loss cavity defects).

[0070] Figure 5 The triboelectric output performance of the composite film at different stages of the process in Example 1 was measured. The voltage decreased from 28 V for the untreated composite film (no orientation and no cavity defects) to 15 V for the stretched oriented film (structural orientation with a large number of cavity defects), and then increased to 170 V for the stretched-hot-pressed composite film (structural orientation and no cavity defects), with an increase rate of more than 6 times. This indicates that the stretched-hot-pressing process, which has both structural orientation and no cavity defects, is very suitable for preparing electrically functional PVDF composite materials with high triboelectric output performance.

[0071] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A method for preparing a high-triboelectric-performance oriented PVDF / polyfluoropolymer composite film by eliminating cavity defects through hot pressing, characterized in that, include: Provide initial composite membranes containing PVDF and polyfluoropolymers; The initial composite film is subjected to thermal stretching and orientation treatment to obtain a stretched film with a β-phase orientation structure but with interfacial cavity defects. The stretched film is subjected to hot pressing to obtain the high triboelectric oriented PVDF / polyfluoropolymer composite film with cavity defects eliminated by hot pressing.

2. The method for preparing a high-triboelectric-performance oriented PVDF / polyfluoropolymer composite film by eliminating cavity defects through hot pressing according to claim 1, characterized in that, The polyfluoropolymer is in the form of nanoparticles.

3. The method for preparing a high triboelectric performance oriented PVDF / polyfluoropolymer composite film by eliminating cavity defects through hot pressing according to claim 1, characterized in that, The polyfluoropolymer includes one or more of polytetrafluoroethylene (PTFE), perfluoroethylene propylene (FEP), polychlorotrifluoroethylene (PCTFE), and soluble polytetrafluoroethylene (PFA).

4. The method for preparing a high triboelectric performance oriented PVDF / polyfluoropolymer composite film by eliminating cavity defects through hot pressing according to claim 1, characterized in that, The mass ratio of PVDF to polyfluoropolymer is 1:0.05~0.

2.

5. The method for preparing a high triboelectric performance oriented PVDF / polyfluoropolymer composite film by eliminating cavity defects through hot pressing according to claim 1, characterized in that, The initial composite film is formed by blending.

6. The method for preparing a high triboelectric performance oriented PVDF / polyfluoropolymer composite film by eliminating cavity defects through hot pressing according to claim 1, characterized in that, The method for preparing the initial composite membrane includes: adding PVDF and polyfluoropolymer to a solvent and stirring to form a uniform slurry; spreading the slurry, drying it, and demolding it to obtain the initial composite membrane.

7. The method for preparing a high triboelectric performance oriented PVDF / polyfluoropolymer composite film by eliminating cavity defects through hot pressing according to claim 1, characterized in that, The temperature of the hot stretching orientation treatment is 100℃, and the stretching ratio of the hot stretching orientation treatment is 2 to 4 times the original length. After stretching to the set length, the temperature is maintained for 5 minutes.

8. The method for preparing a high triboelectric performance oriented PVDF / polyfluoropolymer composite film by eliminating cavity defects through hot pressing according to claim 1, characterized in that, The hot pressing process takes 1 minute, the pressure is 2.5~12.5 MPa, and the temperature is 120~170℃.

9. The application of the high triboelectric performance oriented PVDF / polyfluoropolymer composite film with cavity defects eliminated by hot pressing, prepared by the preparation method according to claim 1, in triboelectric nanogenerators.

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