Polyvinylidene fluoride film based on cross-linking reaction, preparation method and application

Abstract

The application belongs to the field of polymer films, and discloses a cross-linking reaction-based polyvinylidene fluoride film, a preparation method and application, which comprises the following steps: mixing cyclohexanone, polyvinylidene fluoride and polyoxyethylene diamine to obtain a mixed solution; solidifying the mixed solution into a film to obtain a blended polyvinylidene fluoride film; and performing cross-linking reaction on the blended polyvinylidene fluoride film to obtain a cross-linked polyvinylidene fluoride film, and culturing the cross-linked polyvinylidene fluoride film at 150-165 DEG C to obtain a polyvinylidene fluoride film with a high gamma crystal content. Through detection and comparison, it is found that the gamma phase crystalline content in the cross-linking reaction-based polyvinylidene fluoride film is obviously increased, and the alpha phase crystalline content is significantly reduced. The cross-linking reaction-based polyvinylidene fluoride film can replace traditional filler methods, aluminum oxide template methods and high-temperature culture methods, the preparation method is simple in process and convenient in operation, the polyvinylidene fluoride is endowed with the ability to obtain gamma crystals at low temperature and for a short time, and the polyvinylidene fluoride can be widely applied in the fields of pressure sensors, lithium ion batteries, automobile motors and high-temperature-resistant thermistor devices.

Description

Technical Field

[0001] This invention belongs to the field of polymer films, and relates to a polyvinylidene fluoride film based on crosslinking reaction, its preparation method, and its application. Background Technology

[0002] Polyvinylidene fluoride (PVDF), as a unique polymer material, has always attracted much attention due to its excellent dielectric and ferroelectric properties. It not only possesses a high dielectric constant and low dielectric loss, making it a promising material for applications in capacitors and dielectric materials, but also exhibits significant ferroelectricity, displaying a unique hysteresis loop characteristic under an electric field. Furthermore, PVDF possesses good chemical stability and mechanical strength, and is easily processed into various shapes. These superior properties make PVDF a promising candidate for applications in electronics, energy, smart materials, and many other fields.

[0003] Polyvinylidene fluoride (PVDF) is a polycrystalline semi-crystalline polymer, with three most common crystalline forms: α-crystalline, β-crystalline, and γ-crystalline. α-crystalline PVDF possesses excellent mechanical properties and is used in electronics, chemicals, and solar energy devices. β-crystalline and γ-crystalline PVDF exhibit good piezoelectric and ferroelectric effects and are widely used in transducers across various fields, such as varistors and humidity sensors, and can be applied in storage devices and smart appliances.

[0004] Currently, the preparation of polyvinylidene fluoride (PVDF) with high gamma-form content faces numerous challenges. The main reason lies in the relatively complex preparation process, requiring precise control of multiple process parameters to ensure stable crystal form transformation. Furthermore, this process often necessitates high incubation temperatures, which not only increases energy consumption but also places higher demands on equipment. More significantly, even under optimized conditions, the preparation of PVDF with high gamma-form content requires a considerable amount of time, greatly limiting its efficiency for large-scale production and application. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a polyvinylidene fluoride film based on crosslinking reaction, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing polyvinylidene fluoride (PVDF) films based on crosslinking reactions, comprising: mixing cyclohexanone, PVDF, and polyoxyethylene diamine to obtain a mixed solution; curing the mixed solution into a film to obtain a blended PVDF film; subjecting the blended PVDF film to a crosslinking reaction to obtain a crosslinked PVDF film and culturing it at 150–165°C to obtain a PVDF film with high γ-crystalline content.

[0008] Optionally, the step of mixing cyclohexanone, polyvinylidene fluoride, and polyoxyethylene diamine to obtain a mixed solution includes: adding polyvinylidene fluoride to cyclohexanone to obtain a polyvinylidene fluoride solution; and adding polyoxyethylene diamine to the polyvinylidene fluoride solution to obtain a mixed solution.

[0009] Optionally, the polyvinylidene fluoride solution contains polyvinylidene fluoride at a mass concentration of 3% to 10%.

[0010] Optionally, in the mixed solution, the mass fraction of polyoxyethylene diamine is 5% to 15% of polyvinylidene fluoride.

[0011] Optionally, the step of adding polyoxyethylene diamine to the polyvinylidene fluoride solution to obtain a mixed solution includes: adding polyoxyethylene diamine to the polyvinylidene fluoride solution at 40-50°C and stirring at 1000-5000 r / min to obtain a mixed solution.

[0012] Optionally, the step of curing the mixed solution into a film includes: dropping the mixed solution onto a glass slide and curing it into a film in a vacuum oven at 90–120°C.

[0013] Optionally, the crosslinking reaction of the blended polyvinylidene fluoride film includes: performing a crosslinking reaction on the blended polyvinylidene fluoride film at 180–300°C.

[0014] Optionally, obtaining the cross-linked polyvinylidene fluoride film and culturing it at 150–165°C includes: obtaining the cross-linked polyvinylidene fluoride film and culturing it at 150–165°C for 4–18 hours.

[0015] In a second aspect, the present invention provides a polyvinylidene fluoride film based on a crosslinking reaction, wherein the polyvinylidene fluoride film is prepared by the above-described method for preparing polyvinylidene fluoride films based on crosslinking reactions.

[0016] In a third aspect, the present invention provides an application of the above-mentioned polyvinylidene fluoride thin film based on crosslinking reaction in the preparation of thermistor devices.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] This invention discloses a method for preparing polyvinylidene fluoride (PVDF) films based on a cross-linking reaction. First, a mixed solution of PVDF and polyoxyethylene diamine is prepared using cyclohexanone as a solvent. The solvent in the mixed system is then evaporated, and a further cross-linking reaction is carried out, followed by cultivation at 150–165°C to obtain a PVDF film with high γ-phase crystal content. Comparative analysis revealed that in the PVDF film with added polyoxyethylene diamine, the γ-phase crystal content was significantly increased, while the α-phase crystal content was significantly decreased. This invention prepares PVDF films with high γ-phase crystal content through a cross-linking reaction, requiring a low cultivation temperature. This method can replace traditional processes involving filler addition and long-term high-temperature cultivation. The preparation method is simple, convenient, and can rapidly obtain a high content of γ-phase crystals. Attached Figure Description

[0019] Figure 1 The Fourier transform infrared spectra of polyvinylidene fluoride with different degrees of crosslinking in this embodiment of the invention are shown.

[0020] Figure 2 The Fourier transform infrared spectra of polyvinylidene fluoride dielectric composite films cultured at 155°C for different times, according to an embodiment of the present invention.

[0021] Figure 3 This is a γ-ray polarization image of a cross-linked polyvinylidene fluoride film cultured at 155°C for 4 hours according to an embodiment of the present invention.

[0022] Figure 4 The image shows the γ-ray polarization pattern of a cross-linked polyvinylidene fluoride film with a mass ratio of 10 wt% of polyoxyethylene diamine to polyvinylidene fluoride and cultured at 155°C for 4 hours, according to an embodiment of the present invention.

[0023] Figure 5 The graph shows the γ-crystal content (calculated using Fourier transform infrared spectroscopy data) of the cross-linked polyvinylidene fluoride film cultured at 155°C for 4 hours according to an embodiment of the present invention.

[0024] Figure 6 The X-ray diffraction spectra of polyvinylidene fluoride with different degrees of crosslinking are shown in the embodiments of the present invention. Detailed Implementation

[0025] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0026] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0027] The present invention will now be described in further detail with reference to the accompanying drawings:

[0028] In one embodiment of the present invention, a method for preparing polyvinylidene fluoride (PVDF) films based on cross-linking reactions is provided. Specifically, it is a method for preparing PVDF films with high γ-crystalline content based on cross-linking of polyoxyethylene diamine and PVDF, which has the characteristics of low cultivation temperature, short time and easy industrialization.

[0029] Specifically, the method for preparing polyvinylidene fluoride film based on crosslinking reaction of the present invention includes the following steps:

[0030] S1: Mix cyclohexanone, polyvinylidene fluoride and polyoxyethylene diamine to obtain a mixed solution.

[0031] S2: The mixed solution is cured into a film to obtain a blended polyvinylidene fluoride film.

[0032] S3: The blended polyvinylidene fluoride film is subjected to a crosslinking reaction to obtain a crosslinked polyvinylidene fluoride film, which is then cultured at 150-165℃ to obtain a polyvinylidene fluoride film with high γ crystal content.

[0033] This invention discloses a method for preparing polyvinylidene fluoride (PVDF) films based on a cross-linking reaction. First, a mixed solution of PVDF and polyoxyethylene diamine is prepared using cyclohexanone as a solvent. The solvent in the mixed system is then evaporated, and a further cross-linking reaction is carried out, followed by cultivation at 150–165°C to obtain a PVDF film with high γ-phase crystal content. Comparative analysis revealed that in the PVDF film with added polyoxyethylene diamine, the γ-phase crystal content was significantly increased, while the α-phase crystal content was significantly decreased. This invention prepares PVDF films with high γ-phase crystal content through a cross-linking reaction, requiring a low cultivation temperature. This method can replace traditional processes involving filler addition and long-term high-temperature cultivation. The preparation method is simple, convenient, and can rapidly obtain a high content of γ-phase crystals.

[0034] In one possible implementation, mixing cyclohexanone, polyvinylidene fluoride, and polyoxyethylene diamine to obtain a mixed solution comprises: adding polyvinylidene fluoride to cyclohexanone to obtain a polyvinylidene fluoride solution; and adding polyoxyethylene diamine to the polyvinylidene fluoride solution to obtain a mixed solution.

[0035] In one possible implementation, the polyvinylidene fluoride solution contains a polyvinylidene fluoride mass concentration of 3% to 10%.

[0036] Explanatoryly, the mass fraction ratio of polyvinylidene fluoride (PVDF) to cyclohexanone determines the uniformity of the film; as the proportion of PVDF gradually increases, the uniformity of the film gradually decreases.

[0037] In one possible implementation, the mass fraction of polyoxyethylene diamine in the mixed solution is 5% to 15% of polyvinylidene fluoride.

[0038] In one possible implementation, the step of adding polyoxyethylene diamine to the polyvinylidene fluoride solution to obtain a mixed solution includes: adding polyoxyethylene diamine to the polyvinylidene fluoride solution at 40-50°C and stirring at 1000-5000 r / min to obtain a mixed solution.

[0039] For example, the stirring can be done using magnetic stirring.

[0040] In one possible implementation, curing the mixed solution into a film includes: dropping the mixed solution onto a glass slide and curing it into a film in a vacuum oven at 90–120°C.

[0041] In one possible implementation, the crosslinking reaction of the blended polyvinylidene fluoride film includes: performing a crosslinking reaction on the blended polyvinylidene fluoride film at 180–300°C.

[0042] In one possible implementation, obtaining the cross-linked polyvinylidene fluoride film and culturing it at 150–165°C includes: obtaining the cross-linked polyvinylidene fluoride film and culturing it at 150–165°C for 4–18 hours.

[0043] In another embodiment of the present invention, a polyvinylidene fluoride film based on a crosslinking reaction is provided, which is prepared by the above-described method for preparing a polyvinylidene fluoride film based on a crosslinking reaction.

[0044] Specifically, this cross-linked polyvinylidene fluoride (PVDF) film exhibits a high gamma-ray crystal content. The presence of this high gamma-ray crystal content significantly enhances the piezoelectric and thermoelectric properties of the PVDF film, resulting in superior response characteristics and sensitivity in electronic devices such as sensors and actuators. Secondly, the high gamma-ray crystal content of the PVDF film provides better thermal stability and mechanical strength, enabling it to maintain stable performance under high temperatures and harsh environments, thus extending its service life. Furthermore, this high gamma-ray crystal content PVDF film also possesses excellent chemical stability, resisting the corrosive effects of various chemicals and broadening its application areas.

[0045] The following specific embodiments illustrate the method for preparing polyvinylidene fluoride films based on crosslinking reactions according to the present invention.

[0046] Example 1

[0047] Step 1: Using cyclohexanone as a solvent, prepare a 3% (w / w) polyvinylidene fluoride (PVDF) solution. Then, add polyoxyethylene diamine to the PVDF solution at 45°C and magnetically stir at 4000 rpm until homogeneous, obtaining a mixed solution. The mass fraction of polyoxyethylene diamine is 5% of the PVDF.

[0048] Step 2: Drop the mixed solution from Step 1 onto a glass slide and cure it into a film in a vacuum oven at 90°C to obtain a blended polyvinylidene fluoride film.

[0049] Step 3: Place the blended polyvinylidene fluoride film obtained in Step 2 in an oven at 180°C for crosslinking reaction to obtain a crosslinked polyvinylidene fluoride film.

[0050] Step 4: The cross-linked polyvinylidene fluoride film obtained in Step 3 is cultured at 150°C for 18 hours to obtain a polyvinylidene fluoride film with high γ-crystal content.

[0051] Example 2

[0052] Step 1: Using cyclohexanone as a solvent, prepare a 7% (w / w) polyvinylidene fluoride (PVDF) solution. Then, add polyoxyethylene diamine (POD2) to the PVDF solution at 50°C and magnetically stir at 1000 rpm until homogeneous, obtaining a mixed solution. The POD2 contains 5% (w / w) of the PVDF.

[0053] Step 2: Drop the mixed solution from Step 1 onto a glass slide and cure it into a film in a vacuum oven at 100°C to obtain a blended polyvinylidene fluoride film.

[0054] Step 3: Place the blended polyvinylidene fluoride film obtained in Step 2 in an oven at 240°C for crosslinking reaction to obtain a crosslinked polyvinylidene fluoride film.

[0055] Step 4: The cross-linked polyvinylidene fluoride film obtained in Step 3 is cultured at 155°C for 10 hours to obtain a polyvinylidene fluoride film with high γ-crystal content.

[0056] Example 3

[0057] Step 1: Using cyclohexanone as a solvent, prepare a 10% (w / w) polyvinylidene fluoride (PVDF) solution. Then, add polyoxyethylene diamine to the PVDF solution at 55°C and magnetically stir at 2000 r / min until homogeneous, obtaining a mixed solution. The mass fraction of polyoxyethylene diamine is 10% of the PVDF.

[0058] Step 2: Drop the mixed solution from Step 1 onto a glass slide and cure it into a film in a vacuum oven at 110°C to obtain a blended polyvinylidene fluoride film.

[0059] Step 3: Place the blended polyvinylidene fluoride film obtained in Step 2 in an oven at 300°C for crosslinking reaction to obtain a crosslinked polyvinylidene fluoride film.

[0060] Step 4: The cross-linked polyvinylidene fluoride film obtained in Step 3 is cultured at 160℃ for 8 hours to obtain a polyvinylidene fluoride film with high γ crystal content.

[0061] Example 4

[0062] Step 1: Using cyclohexanone as a solvent, prepare a 10% (w / w) polyvinylidene fluoride (PVDF) solution. Then, add polyoxyethylene diamine to the PVDF solution at 55°C and magnetically stir at 2000 r / min until homogeneous, obtaining a mixed solution. The mass fraction of polyoxyethylene diamine is 15% of the PVDF.

[0063] Step 2: Drop the mixed solution from Step 1 onto a glass slide and cure it into a film in a vacuum oven at 110°C to obtain a blended polyvinylidene fluoride film.

[0064] Step 3: Place the blended polyvinylidene fluoride film obtained in Step 2 in an oven at 300°C for crosslinking reaction to obtain a crosslinked polyvinylidene fluoride film.

[0065] Step 4: The cross-linked polyvinylidene fluoride film obtained in Step 3 is cultured at 165°C for 4 hours to obtain a polyvinylidene fluoride film with high γ-crystal content.

[0066] See Figure 1Fourier transform infrared (FTIR) spectra of polyvinylidene fluoride (PVDF) films with different degrees of crosslinking and high γ-morph content after incubation at 155 °C for 4 hours are shown. Wherein, P represents pure PVDF film; 5%-P indicates a mass ratio of polyoxyethylene diamine to PVDF of 5:100 with crosslinking; 10%-P indicates a mass ratio of polyoxyethylene diamine to PVDF of 10:100 with crosslinking; and 15%-P indicates a mass ratio of polyoxyethylene diamine to PVDF of 15:100 with crosslinking.

[0067] See Figure 2 Fourier transform infrared spectra of polyvinylidene fluoride (PVDF) films with a mass ratio of 5:100 of polyoxyethylene diamine and PVDF, after crosslinking reaction and cultivation at 155 °C for different times, are shown.

[0068] Combination Figure 1 and 2 It can be seen that a large number of γ polar crystal forms can be obtained from cross-linked polyvinylidene fluoride films after culturing at 155℃ for 4 hours, that is, polyvinylidene fluoride films with high γ crystal form content can be obtained.

[0069] See Figure 3 The image shows the crystal morphology of polyvinylidene fluoride (PVDF) under a polarizing microscope after incubation at 155°C for 4 hours. See also... Figure 4 The crystal morphology of polyvinylidene fluoride (PVDF) films with a mass ratio of 10:100 (PVDIamine to PVDF) after crosslinking and incubation at 155°C for 4 hours is shown under a γ-polarizing microscope. Crosslinking significantly affects the crystal morphology of PVDF. PVDF films incubated at 155°C for 4 hours exhibit obvious birefringence and consist of periodic lamellar structures, while the crystals formed by the crosslinked PVDF films show weaker birefringence and consist of curled lamellar crystals.

[0070] See Figure 5 The figure shows the γ-crystal content of cross-linked polyvinylidene fluoride (PVDF) films after incubation at 155°C for 4 hours (calculated using Fourier transform infrared spectroscopy data). It indicates that the γ-phase crystal content of PVDF films with a mass ratio of 5:100 of polyoxyethylene diamine and PVDF reaches 90% after cross-linking and incubation at 155°C for 4 hours. While the γ-phase crystal content decreases with increasing cross-linking degree, it remains higher than that of pure PVDF.

[0071] See Figure 6The X-ray diffraction spectrum of cross-linked polyvinylidene fluoride (PVDF) films cultured at 155 °C for 4 hours is shown. Pure PVDF exhibits significant α-phase crystallization characteristic absorption peaks, including (100), (020), and (110). Cross-linked PVDF, on the other hand, exhibits significant γ-phase crystallization characteristic absorption peaks, including (020) and (110). Wherein, P represents pure PVDF film; 5%-P indicates a mass ratio of polyoxyethylene diamine to PVDF of 5:100, with cross-linking occurring; 10%-P indicates a mass ratio of polyoxyethylene diamine to PVDF of 10:100, with cross-linking occurring; and 15%-P indicates a mass ratio of polyoxyethylene diamine to PVDF of 15:100, with cross-linking occurring.

[0072] Comparative testing revealed that, under the same crystallization incubation temperature and time, the γ-phase crystal content of polyvinylidene fluoride (PVDF) films based on cross-linking reactions was significantly increased. Furthermore, the cross-linking reaction-based PVDF film preparation method can replace traditional filler methods, alumina template methods, and high-temperature incubation methods; moreover, the preparation method is simple, easy to operate, and readily applicable.

[0073] In another embodiment of the present invention, an application of the above-mentioned polyvinylidene fluoride film based on crosslinking reaction in the preparation of thermistor devices is provided.

[0074] Specifically, polyvinylidene fluoride (PVDF) films based on cross-linking reactions exhibit good thermal stability, mechanical strength, and chemical resistance due to their high γ-crystalline content, and also possess unique electrical properties, making them an ideal choice in many high-end technology fields.

[0075] This cross-linked polyvinylidene fluoride (PVDF) film has shown great application potential in the field of pressure sensors. Its high sensitivity and stable electrical properties enable precise sensing and response to minute pressure changes, providing reliable assurance for precision measurement and control. Simultaneously, in the lithium-ion battery field, this film, used as a battery separator or packaging material, effectively improves battery safety and lifespan due to its excellent high-temperature resistance and chemical stability. Furthermore, this PVDF film is widely used in environments requiring high temperatures and mechanical stress, such as automotive motors. Its excellent wear resistance and anti-aging properties ensure the stability and reliability of motors under prolonged high-speed operation. Most notably, this high-gamma-crystalline PVDF film plays a crucial role in the fabrication of high-temperature thermistor devices. Its unique characteristic of significantly changing electrical properties with temperature enables thermistor devices to accurately sense and respond to temperature changes, providing a high-precision and high-stability solution for temperature control and monitoring.

[0076] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing polyvinylidene fluoride (PVDF) films based on cross-linking reactions, characterized in that, include: Cyclohexanone, polyvinylidene fluoride, and polyoxyethylene diamine were mixed to obtain a mixed solution; The mixed solution was cured into a film to obtain a blended polyvinylidene fluoride film; The blended polyvinylidene fluoride film was subjected to a crosslinking reaction to obtain a crosslinked polyvinylidene fluoride film, which was then cultured at 150~165℃ to obtain a polyvinylidene fluoride film with high γ crystal content. The step of mixing cyclohexanone, polyvinylidene fluoride, and polyoxyethylene diamine to obtain a mixed solution includes: Polyvinylidene fluoride was added to cyclohexanone to obtain a polyvinylidene fluoride solution; Polyoxyethylene diamine was added to a polyvinylidene fluoride solution to obtain a mixed solution; The polyvinylidene fluoride solution contains 3% to 10% polyvinylidene fluoride by mass. In the mixed solution, the mass fraction of polyoxyethylene diamine is 5% to 15% of polyvinylidene fluoride; The process of obtaining the cross-linked polyvinylidene fluoride film and culturing it at 150-165°C includes: Cross-linked polyvinylidene fluoride films were obtained and cultured at 150-165℃ for 4-18 hours.

2. The method for preparing polyvinylidene fluoride film based on crosslinking reaction according to claim 1, characterized in that, The step of adding polyoxyethylene diamine to a polyvinylidene fluoride solution to obtain a mixed solution includes: Polyoxyethylene diamine is added to a polyvinylidene fluoride solution at 40-50°C and stirred at 1000-5000 r / min to obtain a mixed solution.

3. The method for preparing polyvinylidene fluoride film based on crosslinking reaction according to claim 1, characterized in that, The step of solidifying the mixed solution into a film includes: The mixed solution is dropped onto a glass slide and cured into a film in a vacuum oven at 90~120℃.

4. The method for preparing polyvinylidene fluoride film based on crosslinking reaction according to claim 1, characterized in that, The crosslinking reaction of the blended polyvinylidene fluoride film includes: The blended polyvinylidene fluoride film was subjected to a crosslinking reaction at 180~300℃.

5. A polyvinylidene fluoride film based on a cross-linking reaction, characterized in that, The polyvinylidene fluoride film is prepared using the polyvinylidene fluoride film preparation method based on crosslinking reaction as described in any one of claims 1 to 4.

6. The application of the polyvinylidene fluoride thin film based on cross-linking reaction as described in claim 5 in the preparation of thermistor devices.

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