CN109694486B - Preparation method of 100% gamma-phase PVDF film - Google Patents
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- C08J2327/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers
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Abstract
The invention relates to a preparation method of a 100% gamma-phase PVDF film, which comprises the following steps: subjecting a modified illite obtained by subjecting an illite to a surface activation treatment to a first mixing treatment with a PVDF pellet; performing film forming treatment on the first mixed treatment product; drying the film forming treatment product; subjecting the dried processed product to a melting process to eliminate a heat history; and (3) carrying out isothermal crystallization treatment on the molten treatment product at the temperature of 158-168 ℃ so as to obtain the gamma-phase PVDF film. The method can prepare 100% gamma-phase PVDF materials, has the advantages of high crystallization rate, high efficiency and low cost, and is suitable for large-scale popularization and application.
Description
Technical Field
The invention relates to the field of materials, in particular to a preparation method of a 100% gamma-phase PVDF film, and more particularly relates to a preparation method of a gamma-phase PVDF film and application of modified illite in preparation of the gamma-phase PVDF film.
Background
Polyvinylidene fluoride (PVDF) is a typical polymorphic polymer having five different crystal forms, α, β, γ, δ, and ∈. The gamma crystal form PVDF has excellent piezoelectricity, pyroelectricity and ferroelectricity due to the special molecular conformation, and a polymer with electric performance is used as a new intelligent material and can be applied to the intelligent material fields of sensors, actuators, energy collectors and the like. However, the existing method or conditions for preparing 100% gamma-phase polyvinylidene fluoride material are harsh, the crystal growth rate is slow, or the cost is too high, which is not beneficial to popularization and application.
Therefore, the method for preparing 100% gamma phase polyvinylidene fluoride material needs further research.
Disclosure of Invention
The present application is based on the discovery and recognition by the inventors of the following facts and problems:
the preparation of the gamma crystal form PVDF is currently divided into two types, wherein one type is a gamma crystal form generated by low-rate nucleation in the process of high-temperature crystallization, and the gamma crystal form usually coexists with an alpha phase generated by high-rate nucleation; the other is that the alpha crystal form obtains the gamma crystal form through solid-solid phase transformation. The former is mainly annealed at high temperature, or polyvinylidene fluoride is blended with other polymers or fillers (carbon nano tube, graphene, silicon dioxide, potassium bromide and nano montmorillonite) to promote the formation of a gamma polar phase, but the reaction conditions are harsh, and 100% gamma phase materials are not easy to form; the latter requires a long time to complete the solid-solid phase transition. In conclusion, the prior art is difficult to directly and rapidly prepare the 100% gamma-phase polyvinylidene fluoride material.
Based on the problems, the inventor surprisingly discovers through a large amount of experimental researches that from pure PVDF of an alpha phase, only a very small amount (0.05 wt% -10.0 wt%) of organically modified illite needs to be added, and 100% gamma phase PVDF material with rapid nucleation growth (POM characterization results show that a certain amount of organically modified illite can grow to a full view after isothermal crystallization for 10min at a certain temperature) can be prepared through melting recrystallization at a certain temperature (158 ℃ -168 ℃), and the illite used in the method is low in price (800-1500 yuan/ton), rich in resources and suitable for mass low-cost production.
To this end, in a first aspect of the invention, a method is provided for preparing a gamma phase PVDF film. According to an embodiment of the invention, the method comprises: subjecting a modified illite obtained by subjecting illite to a surface activation treatment to a first mixing treatment with PVDF pellets; performing film forming treatment on the first mixed treatment product; drying the film forming treatment product; subjecting the dried processed product to a melting process to eliminate a heat history; subjecting the melt-processed product to isothermal crystallization at a temperature of 158 to 168 ℃, such as 159, 160, 161, 162, 163, 164, 165, 166 or 167 ℃, so as to obtain the gamma-phase PVDF film. The meaning of the film formation process, the elimination of the heat history, and the isothermal crystallization may be understood according to the conventional explanation in the art. The film forming process can be performed by directly dropping the film on the silicon wafer and the infrared silicon wafer, and the volume of the mixed solution which is removed by the liquid removing gun is determined according to the concentration of the specific polymer blend and the required substrate area, for example, 100 mu L of the mixed solution (with the concentration of 10 mg/ml) is dropped on a substrate of 13mm × 13mm according to the embodiment of the invention, and the average film thickness is 2 mu m. The meaning of eliminating the thermal history is to eliminate various crystal forms formed by the high molecular polymer through melting treatment, so that the high molecular polymer is in an original random arrangement state on a microscopic level, and the subsequent recrystallization process is facilitated. Isothermal crystallization refers to the crystallization process under constant temperature conditions, and is one of the commonly used experimental methods for studying and characterizing the crystallization behavior of high polymers. Illite, a TOT structure (two layers of silicon-oxygen tetrahedrons plus one layer of aluminum-oxygen octahedra) layered silicate, is currently essentially unexplored as having an effect on the crystallization properties of polymers. The inventors found that the temperature of the isothermal crystallization treatment is closely related to the structure of the prepared gamma-phase PVDF film: if the temperature of isothermal crystallization treatment is too low, only PVDF in alpha phase or PVDF mixed with alpha phase and gamma phase can be generated; if the temperature of isothermal crystallization treatment is too high, the nucleation of polymer crystals is difficult, and the formation of gamma-phase PVDF is not facilitated, and the temperature of isothermal crystallization treatment is 158-168 ℃, the conformation of PVDF gamma-phase is formed in a kinetic and thermodynamic manner. Furthermore, the method provided by the embodiment of the invention can be used for preparing 100% gamma-phase PVDF material, and is high in crystallization rate, high in efficiency, low in cost and suitable for large-scale popularization and application.
According to an embodiment of the present invention, the method may further include at least one of the following additional technical features:
according to an embodiment of the invention, the modified illite has a mass fraction of 0.05 to 10.0%, such as 0.07, 0.09, 0.1, 0.3, 0.5, 0.7, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 6.0, 7.0, 8.0 or 9.0%. It is to be noted that the mass fraction of the modified illite (for example a PVDF film containing 0.1%, 0.5%, 1.0%, 2.0% or 5.0% by weight of the organized illite according to the examples of the invention) is the ratio of the mass of the modified illite to the sum of the masses of the modified illite and of the PVDF pellets. The inventors have found that if the mass fraction of the modified illite is too low, it is not possible to prepare a PVDF material having 100% of the γ phase, and if the mass fraction of the modified illite is too high, it will not only hinder the crystallization of PVDF and reduce the crystallinity of PVDF, but also interfere with the performance of the γ phase PVDF material. Therefore, when the mass fraction of the modified illite is 0.05-10.0%, the PVDF material with 100% of gamma phase can be prepared according to the method provided by the embodiment of the invention, the crystallization rate is higher, the efficiency is higher, and the dosage of the modified illite is less.
According to the embodiment of the invention, the mass fraction of the modified illite is 0.1-5%. The inventor finds that when the mass fraction of the modified illite is 0.1-5%, the PVDF material with 100% of gamma phase can be prepared by the method provided by the embodiment of the invention, the crystallization rate is higher, the efficiency is higher, and the dosage of the modified illite is less.
According to embodiments of the invention, the first mixed treatment product has a mass volume concentration of 1 to 50mg/mL, such as 2, 3, 4, 5, 7, 9, 10, 13, 15, 17, 19, 20, 25, 30, 35, 40, or 45mg/mL. It is noted that the mass-to-volume concentration of the first mixed treatment product (e.g., the concentration of the blending solution according to an embodiment of the present invention is 5mg/mL, 10mg/mL, 20mg/mL, 40mg/mL, or 50 mg/mL) refers to the ratio of the sum of the masses of the modified illite and the PVDF pellet to the volume of the organic solvent. The inventor finds that if the mass volume concentration of the first mixed treatment product is too low, the rate of preparing the PVDF material is slow, and the efficiency is low; if the mass volume concentration of the first mixed treatment product is too high, the organic solvent cannot sufficiently dissolve the PVDF pellets and disperse the modified illite. Therefore, when the mass volume concentration of the first mixed treatment product is 1-50 mg/mL, the PVDF granules can be fully dissolved by the organic solvent and the modified illite can be dispersed, and further, the PVDF material with 100% gamma phase can be prepared and obtained by the method provided by the embodiment of the invention, and the crystallization rate is higher and the efficiency is higher.
According to the embodiment of the invention, the mass volume concentration of the first mixed processed product is 5-20 mg/mL. The inventor finds that when the mass volume concentration of the first mixed treatment product is 5-20 mg/mL, the organic solvent can fully dissolve PVDF granules and disperse modified illite, and further, the method according to the embodiment of the invention can prepare 100% gamma-phase PVDF material, and has faster crystallization rate and higher efficiency.
According to an embodiment of the invention, the first mixing treatment is carried out at a temperature of 60 to 100 ℃, such as 70, 80, 90 ℃. The inventors found that if the temperature of the first mixing treatment is too low, it is not possible to sufficiently dissolve the PVDF pellets and disperse the modified illite; if the temperature of the first mixing process is too high, the structure of the raw material may be damaged. Therefore, when the first mixing treatment is carried out at the temperature of 60-100 ℃, the organic solvent can fully dissolve PVDF granules and disperse modified illite without damaging the structure of the raw material, and further, the method provided by the embodiment of the invention can prepare 100% gamma-phase PVDF material, and has the advantages of higher crystallization rate and higher efficiency.
According to an embodiment of the present invention, the first mixing process is performed in an organic solvent including at least one selected from the group consisting of N, N-dimethylformamide, dimethylacetamide, and N-methylpyrrolidone.
According to an embodiment of the present invention, the modified illite is provided in a form suspended in the organic solvent.
According to an embodiment of the present invention, before performing the first mixing process, further includes: the modified illite suspension is sonicated. Further, the modified illite is more uniformly dispersed in the organic solvent.
According to an embodiment of the invention, the melting process is performed at 200-220 ℃, such as 205, 210, 215 ℃ in order to eliminate the thermal history.
According to the embodiment of the invention, after the melting treatment and before the isothermal crystallization treatment, the melting treatment product is subjected to rapid cooling treatment so as to reach the isothermal crystallization treatment temperature. The temperature after the rapid cooling treatment is the isothermal crystallization temperature. Wherein, the rapid cooling treatment refers to cooling at the speed as fast as possible, and the cooling rate is about 20 ℃/s to 50 ℃/s.
According to an embodiment of the invention, the surface activation treatment comprises: carrying out second mixing treatment on the illite, dilute hydrochloric acid and a cationic surfactant; filtering the second mixed treatment product to obtain filter residue; and drying the filter residue, wherein the filter residue after drying is the modified illite. The method provided by the embodiment of the invention can be used for preparing the PVDF material with 100% gamma phase, and has the advantages of higher crystallization rate and higher efficiency.
According to an embodiment of the invention, the mass ratio of said cationic surfactant to said illite is (1-10): 100, such as 2:100,3:100,4:100,5:100,6:100,7:100,8:100 or 9:100. it is noted that the mass concentration (e.g. 3wt%, 5wt%, 6wt% or 8wt% CTAB according to the examples of the present invention) refers to the ratio of the mass of the cationic surfactant to the mass of illite. The inventor finds that if the mass concentration of the cationic surfactant is too low, alkyl chains on the surface of illite can be reduced, so that the induction effect of the modified illite on a polar phase is influenced, and the prepared modified illite cannot obtain 100% gamma-phase PVDF material after being mixed with pure alpha-phase PVDF; if the mass concentration of the cationic surfactant is too high, repeated washing is needed so as to remove the excessive cationic surfactant completely, so that not only is the raw material wasted, but also the performance of the product is adversely affected by a large amount of unreacted cationic surfactant; in addition, because potassium ions exist among illite layers, the potassium ions are just embedded into cavities formed by oxygen atom grids among adjacent crystal layers, and 12 oxygens are coordinated with the potassium ions around the illite layers, the interlaminar binding capacity is strong, the cation exchange capacity of the illite is 10-40 milliequivalents per 100mg, when 15wt% of surfactant is used, the inventor finds that the oil absorption rate and the contact angle change are not very different compared with 10wt% through oil absorption rate and contact angle tests, namely, the fact that the concentration of the surfactant is continuously increased has little influence on promoting compatibility of the illite and the polymer, the ion exchange capacity is saturated, and the electrical performance of the product is also adversely affected due to the existence of the redundant surfactant in the system. Therefore, the inventor finds that 100% gamma-phase PVDF materials which can rapidly nucleate and grow can be prepared by mixing a very small amount of modified illite obtained by the method according to the embodiment of the invention with pure PVDF of an alpha phase and performing melt recrystallization under a certain condition, the illite used in the preparation method is low in price, rich in resources and suitable for mass low-cost production, and the method not only greatly improves the crystallization rate of the PVDF materials, but also expands the application field of the illite.
According to an embodiment of the invention, the mass ratio of said cationic surfactant to said illite is (3 to 8): 100. the inventor finds that the mass ratio of the cationic surfactant to the illite is (3-8): at 100, the method can prepare 100% gamma-phase PVDF material, and has the advantages of higher crystallization rate and higher efficiency.
According to an embodiment of the present invention, the cationic surfactant comprises at least one selected from the group consisting of cetyltrimethylammonium bromide, octadecyltrimethylammonium bromide, didodecyldimethylammonium bromide.
According to an embodiment of the invention, the temperature of the second mixing process is 60 to 100 ℃, such as 70, 80 or 90 ℃. The inventors found that if the temperature of the second mixing process is too high, the structure of the raw material may be damaged; if the temperature of the second mixing treatment is too low, the reaction proceeds slowly, and illite cannot be sufficiently modified. Therefore, the illite can be effectively modified when the temperature of the second mixing treatment is 60-100 ℃, so that the PVDF material with 100% of gamma phase can be prepared according to the embodiment of the invention, the crystallization rate is higher, and the efficiency is higher.
According to an embodiment of the invention, the illite is provided in a form suspended in water.
According to an embodiment of the present invention, before the surface activation treatment, the method further comprises subjecting the illite suspension to ultrasonic treatment. Further, the dispersion of illite in water is more uniform.
In a second aspect of the invention, the inventionThe invention proposes the use of a modified illite obtained by a surface activation treatment as described in any one of the preceding paragraphs, for the preparation of a gamma-phase PVDF film. Illite, a TOT structure (two layers of silicon-oxygen tetrahedrons plus one layer of aluminum-oxygen octahedra) layered silicate, is currently essentially unexplored as having an effect on the crystallization properties of polymers. The inventors have for the first time found that very small amounts of the modified illite obtained by the surface activation treatment described in any of the above can be used to prepare 100% gamma phase PVDF material, possibly due to the partial positive CH of PVDF 2 The ion-dipole interaction between the dipoles and the negatively charged clay nanolayers induces the formation of polar gamma conformations.
In a third aspect of the invention, a method of making a gamma phase PVDF film is provided. According to an embodiment of the invention, the method comprises: suspending illite in water, and carrying out ultrasonic treatment on the illite suspension; and carrying out second mixing treatment on the illite suspension subjected to ultrasonic treatment, dilute hydrochloric acid and a cationic surfactant at the temperature of 60-100 ℃, wherein the mass ratio of the cationic surfactant to the illite is 3:100 to 8:100, the surfactant comprises at least one selected from the group consisting of cetyltrimethylammonium bromide, octadecyltrimethylammonium bromide, didodecyldimethylammonium bromide; filtering the second mixed treatment product to obtain filter residue; drying the filter residue, wherein the filter residue after drying is modified illite; suspending the modified illite in an organic solvent comprising at least one selected from the group consisting of N, N-dimethylformamide, dimethylacetamide, N-methylpyrrolidone, and sonicating the modified illite suspension; carrying out first mixing treatment on the modified illite suspension subjected to ultrasonic treatment and PVDF granules at the temperature of 60-100 ℃, wherein the mass volume concentration of a first mixed treatment product is 5-20 mg/mL, the mass fraction of the modified illite is 0.1-5%, and the first mixing treatment is carried out in the organic solvent; performing film forming treatment on the first mixed treatment product; drying the film forming treatment product; carrying out melting treatment on the dried product at the temperature of 200-220 ℃ so as to eliminate heat history; subjecting the melt-processed product to a rapid cooling treatment so as to reach 158-168 ℃, and subjecting the melt-processed product to an isothermal crystallization treatment at a temperature of 158-168 ℃ so as to obtain the gamma-phase PVDF film. The method provided by the embodiment of the invention can be used for preparing the PVDF material with 100% gamma phase, and has the advantages of higher crystallization rate and higher efficiency.
Drawings
FIG. 1 is a schematic representation of an X-ray diffractometer (XRD) characterization of a PVDF material containing different mass fractions of organic illite according to an embodiment of the present invention, wherein line 1 represents pure PVDF, and lines 2/3/4 represent PVDF materials containing 0.5wt%/1.0wt%/2.0wt% of organic illite, respectively, as compared to pure PVDF having only alpha phase diffraction peaks, indicating that the PVDF added with the appropriate mass fraction of organic illite has only gamma phase diffraction peaks;
FIG. 2 is a schematic representation of an in situ Fourier transform infrared (SITU-FTIR) spectrum of a PVDF material containing 0.5wt% of organic illite crystallized isothermally at 165 ℃ until crystallization is complete according to an embodiment of the invention, showing that only gamma-phase crystal form exists from the beginning to the end of crystallization at an appropriate temperature without generating alpha-phase;
FIG. 3 is a schematic representation of Differential Scanning Calorimeter (DSC) characterization of a PVDF material containing 2.0wt% of organoillite at 165 ℃ for isothermal crystallization until crystallization is complete, according to an embodiment of the invention, showing that only a melting peak of a gamma-phase crystal form exists from the beginning of crystallization to the completion of crystallization at an appropriate temperature for isothermal crystallization, and no alpha-phase is generated;
FIG. 4 is a schematic representation of in-situ polarization microscope (POM) characterization showing that selective melting at 180 deg.C/183 deg.C after isothermal crystallization at 165 deg.C for 5 hours of PVDF material containing 1.0wt% of organic illite according to the embodiments of the present invention, the selective melting result shows that only gamma-phase crystal form exists until crystallization is completed at the suitable temperature, no alpha-phase is generated, and crystallization is initiated at 6-8 hours compared to isothermal crystallization of pure PVDF at the same temperature, the nucleation and growth rate of gamma-phase are significantly increased,
wherein: a represents a schematic diagram of a PVDF material containing 1.0wt% of organic illite when subjected to isothermal crystallization at 165 ℃ for 5h, B represents a schematic diagram of an in-situ polarization microscope (POM) for selective melting at 180 ℃ after 5h of isothermal crystallization, and C represents a schematic diagram of an in-situ polarization microscope (POM) for selective melting at 183 ℃ after 5h of isothermal crystallization;
FIG. 5 is a schematic representation of Atomic Force (AFM) characterization of 2.0wt% organic illite-containing PVDF material crystallized isothermally at 160 ℃ until crystallization is complete according to an embodiment of the present invention, which shows that only gamma phase flat-on crystal form exists and alpha phase of typical lamella twisted edge-on and flat-on alternately appearing ring structure does not exist when crystallized isothermally at a suitable temperature until crystallization is complete;
FIG. 6 is a schematic diagram of in-situ melting infrared rays at 160 ℃,170 ℃,175 ℃ and 178 ℃ respectively after isothermal crystallization of a polyvinylidene fluoride composite film added with 1.0wt% of modified illite at 140 ℃ for 10min according to an embodiment of the invention.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are illustrative and intended to explain the present invention and should not be construed as limiting the present invention.
It should be noted that, unless otherwise specified, the solvents, reagents or raw materials used in the present invention are commercially available, and the names and meanings of each solvent, reagent or raw material are understood according to the conventional explanations in the art.
The invention aims to provide a method for preparing a 100% polar gamma-phase PVDF crystal film at low cost. It is another object of the present invention to provide a method for promoting rapid nucleation and growth of gamma phase crystals. Another object of the present invention is to provide a method for using illite in the field of controlling polymer crystallization. The invention also discloses the application of the PVDF crystal film in piezoelectric, thermoelectric and ferroelectric devices.
The invention is realized by the following technical scheme, and the method for preparing the low-cost rapid nucleation growth 100% gamma-phase PVDF film comprises the following technologies: firstly, mixing illite and a cationic surfactant to prepare organic illite, then preparing a PVDF solution containing 0.1-5.0 wt% of organic illite, after the solutions are completely mixed, adopting a drop film method, drying in vacuum to prepare a film, and then carrying out isothermal crystallization at 158-168 ℃ for a period of time until the crystallization is complete, thus obtaining the 100% gamma-phase PVDF film.
In the present invention, the amphiphilic agent for modifying illite is chosen from cationic surfactants, in some embodiments: cetyl trimethyl ammonium bromide, stearyl trimethyl ammonium bromide, didodecyldimethylammonium bromide, and the like.
In the present invention, the solvent for dissolving the polymer is an organic solvent, and in some embodiments, the organic solvent is: n, N-Dimethylformamide (DMF), dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), or a mixed solvent of optionally two solvents, and the like.
In the present invention, the polymer blend solution is at a concentration of 1mg/mL to 50mg/mL, and in some embodiments at a concentration of 5mg/mL to 20mg/mL.
In the present invention, the thickness of the prepared film can be adjusted to be between 200nm and 10 μm, in some embodiments 500nm to 8 μm, and in other embodiments 1 μm to 5 μm.
In the invention, the electromagnetic stirring temperature and the stirring time, and the drying temperature and the drying time of the vacuum oven need to be selected reasonably.
The invention also discloses a mechanism for inducing PVDF to generate a gamma polar phase by the organic illite. Partial positive CH with mechanism of PVDF 2 The ion-dipole interaction between the dipoles and the negatively charged clay nanolayers induces the formation of polar gamma conformations.
The specific method comprises the following steps:
1. preparation method of organic modified illite
Firstly, carrying out ultrasonic treatment on illite, then placing the illite on an electromagnetic stirrer at a certain temperature for stirring, slowly adding a hydrochloric acid dilute solution and a certain mass fraction of cationic surfactant, stirring for a certain time, and standing for activation to complete the reaction. And (3) carrying out vacuum filtration on the suspension, alternately washing the suspension by using deionized water and absolute ethyl alcohol for multiple times in the process of vacuum filtration to remove unreacted ions, drying the suspension by using a vacuum oven, grinding, sieving and bottling the modified silicate clay. The organic modified illite prepared by the invention is preferably stirred at the temperature of 60-100 ℃, and the preferred cationic surfactant is cetyl trimethyl ammonium bromide, octadecyl trimethyl ammonium bromide, didodecyl dimethyl ammonium bromide and the like. Preferably, the surfactant concentration is from 1wt% to 10wt%, more preferably from 3wt% to 8wt%.
2. Preparation method of organic illite/PVDF (polyvinylidene fluoride) composite film
Weighing a certain mass of organic modified illite in a certain amount of solvent, adding weighed PVDF granules after ultrasonic dispersion, and mixing the solution by using an electromagnetic stirrer with a certain temperature and a certain rotating speed. After complete mixing, a dropping film method (a liquid transfer gun transfers liquid to a silicon wafer substrate of 13mm. Times.13mm) is adopted, and the film is prepared after drying by a vacuum oven. The solvent used for dissolving the polymer is a conventional solvent, preferably: n, N-Dimethylformamide (DMF), dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), or a mixed solvent of optionally two solvents, and the like. The mass fraction of the added modified illite is 0.05-10.0 wt%, and the mass fraction of the added modified illite is preferably 0.1-5 wt%. The concentration of the polymer blend solution is 1mg/mL to 50mg/mL, preferably 5mg/mL to 20mg/mL. The solution is preferably mixed at a stirring temperature of 60 ℃ to 100 ℃. The thickness of the prepared film can be adjusted between 200nm and 10 μm, preferably 500nm to 8 μm, and more preferably 1 μm to 4 μm.
The prepared sample is kept at 200-220 ℃ for 10min so as to eliminate heat history, and then is subjected to isothermal treatment at a specific temperature between 158-168 ℃ for a certain time by rapid cooling until crystallization is complete. The samples were characterized by X-ray diffractometry (XRD), polarization microscopy (POM), fourier transform infrared spectroscopy (FTIR), differential Scanning Calorimetry (DSC) and Atomic Force (AFM), respectively.
The technical effects are as follows: the invention provides a preparation method of 100% gamma-phase PVDF material, which is simple to operate, can be prepared in large yield and is low in cost. From pure PVDF of alpha-phase, only a very small amount (0.1 wt% -5.0 wt%) of organically modified illite needs to be added, and the PVDF material of 100% gamma-phase with rapid nucleation growth (POM characterization result is that isothermal crystallization for 10min at a certain temperature can grow the field of view by adding a certain amount of organically modified illite) can be prepared by melt recrystallization at a certain temperature (158 ℃ -168 ℃). The illite used in the method is low in price and suitable for mass production with low cost.
The invention will be further illustrated with reference to specific examples.
Example 1
The first step is the preparation of modified illite from cetyltrimethylammonium bromide (CTAB). 10g of illite was added to 150mL of deionized water, sonicated for 2h, and then placed on an 80 ℃ electromagnetic stirrer to stir, during which 4mL (0.1 mol/L) of dilute hydrochloric acid solution and 5wt% CTAB were slowly added to the clay suspension. The mixed solution is electromagnetically stirred for 2 hours at the temperature of 80 ℃, and is kept stand for 24 hours to completely activate the reaction. The suspension was filtered under vacuum and washed repeatedly with deionized water and absolute ethanol 3 times alternately to ensure removal of CTAB free on the illite surface. Then drying in a vacuum oven at 70 ℃ for 24h, taking out, grinding, sieving and bottling the dried organic modified illite.
The second step is solution blending to prepare a PVDF film containing 2.0wt% of organic illite. 6mg of the organic illite was weighed out into 30mL of dimethylacetamide (DMAc), ultrasonically dispersed for 2h, 294mg of PVDF pellets were weighed out and put into an Erlenmeyer flask, the concentration of the blended solution was 10mg/mL, and the mixture was stirred magnetically at 100 ℃ for 4h to complete mixing. And (3) directly dripping the film on a silicon wafer and an infrared silicon wafer (100 mu L of mixed solution is dripped to a substrate of 13mm × 13mm, and the average film thickness is 2 mu m), and then drying in a vacuum oven at 90 ℃ for 24h to prepare the PVDF/CTAB-Illite film.
The prepared sample is kept at 210 ℃ for 10 minutes to eliminate heat history, and is quickly cooled to 165 ℃ for isothermal treatment for a certain time until crystallization is complete. Characterized by an X-ray diffractometer (XRD) and a Differential Scanning Calorimeter (DSC), respectively.
As a result: referring to line 4 in fig. 1 and fig. 3, the method can rapidly prepare 100% gamma phase PVDF material.
Example 2
The first step was the preparation of octadecyl trimethyl ammonium bromide (STAB) modified illite. 10g of illite was added to 150mL of deionized water, sonicated for 2h, then placed on a 60 ℃ electromagnetic stirrer and stirred, during which 4mL (0.1 mol/L) of dilute hydrochloric acid solution and 3wt% of CTAB were slowly added to the clay suspension. The mixed solution is electromagnetically stirred for 2 hours at the temperature of 60 ℃, and is kept stand for 24 hours to completely activate the reaction. The suspension was filtered under vacuum and washed repeatedly with deionized water and absolute ethanol 3 times in alternation to ensure removal of the STAB free on the illite surface. Then drying in a vacuum oven at 60 ℃ for 24h, taking out, grinding, sieving and bottling the dried organic modified illite.
The second step is solution blending to prepare a PVDF film containing 0.1wt% of organic illite. 0.25mg of the organic illite was weighed out in 50mL of N, N-Dimethylformamide (DMF), ultrasonically dispersed for 2 hours, 249.75mg of PVDF pellets were weighed out and put into a conical flask, the concentration of the blended solution was 5mg/mL, and the mixture was stirred magnetically at 60 ℃ for 2 hours to complete mixing. And (3) directly dripping the film on a silicon wafer and an infrared silicon wafer (50 mu L of mixed solution is dripped to a substrate of 13mm × 13mm, and the average film thickness is 500 nm), and then drying in a vacuum oven at 90 ℃ for 24h to obtain the PVDF/STAB-Illite film.
The prepared sample is kept at 210 ℃ for 10 minutes to eliminate heat history, and is subjected to isothermal treatment at 168 ℃ for a certain time by rapid cooling until crystallization is complete. Characterized by X-ray diffractometer (XRD), polarization microscope (POM), fourier transform infrared spectroscopy (FTIR), differential Scanning Calorimeter (DSC) and Atomic Force (AFM), respectively.
As a result: the method can rapidly prepare 100% gamma-phase PVDF material.
Example 3
The first step is the preparation of cetyltrimethylammonium bromide (CTAB) modified illite. 10g of illite was added to 150mL of deionized water, sonicated for 2h, and then placed on a 70 ℃ electromagnetic stirrer and stirred, during which 4mL (0.1 mol/L) of dilute hydrochloric acid solution and 5wt% CTAB were slowly added to the clay suspension. The mixed solution is electromagnetically stirred for 2 hours at the temperature of 70 ℃, and is kept stand for 24 hours to completely activate the reaction. The suspension was suction filtered under vacuum and washed repeatedly with deionized water and absolute ethanol 3 times to ensure removal of CTAB free on the illite surface. Then drying in a vacuum oven at 70 ℃ for 24h, taking out, grinding, sieving and bottling the dried organic modified illite.
The second step is solution blending to prepare a PVDF film containing 0.5wt% of organic illite. 1.5mg of the organic illite was weighed out into 30mL of N-methylpyrrolidone (NMP), ultrasonically dispersed for 2 hours, 298.5mg of PVDF pellets were weighed out and put into a conical flask, the concentration of the blending solution was 10mg/mL, and the mixture was stirred magnetically at 70 ℃ for 4 hours to complete mixing. And (3) directly dripping the film on a silicon wafer and an infrared silicon wafer (50 mu L of mixed solution is dripped to a substrate of 13mm × 13mm, and the average film thickness is 1 mu m), and then drying in a vacuum oven at 90 ℃ for 24h to prepare the PVDF/CTAB-Illite film.
The prepared sample is kept at 210 ℃ for 10 minutes to eliminate the heat history, and is subjected to isothermal treatment at 165 ℃ for a certain time by rapid cooling until the crystallization is complete. Characterized by X-ray diffractometer (XRD) and fourier transform infrared spectroscopy (FTIR), respectively.
As a result: referring to line 2 in fig. 1 and fig. 2, the method can rapidly prepare 100% gamma phase PVDF material.
Example 4
The first step is the preparation of modified illite from didodecyldimethylammonium bromide (DDAB). 10g of illite was added to 150mL of deionized water, sonicated for 2h, and then placed on an 80 ℃ electromagnetic stirrer to stir, during which 4mL (0.1 mol/L) of dilute hydrochloric acid solution and 6wt% CTAB were slowly added to the clay suspension. The mixed solution is electromagnetically stirred for 2 hours at the temperature of 80 ℃, and is kept stand for 24 hours to completely activate the reaction. The suspension was filtered under vacuum and washed repeatedly with deionized water and absolute ethanol 3 times in alternation to ensure removal of DDAB free on the illite surface. Then the mixture is dried in a vacuum oven at 90 ℃ for 24 hours and taken out, and the dried organic modified illite is ground, sieved and bottled.
The second step is solution blending to prepare a PVDF film containing 1.0wt% of organic illite. Weighing 4mg of organic Illite in 20mL of dimethylacetamide (DMAc), ultrasonically dispersing for 2h, weighing 396mg of PVDF granules, adding into a conical flask, mixing the solution with the concentration of 20mg/mL, electromagnetically stirring for 4h at 80 ℃ to completely mix, directly dripping 50 mu L of the mixed solution on a silicon wafer and an infrared silicon wafer (dripping the mixed solution to a substrate of 13mm × 13mm, wherein the average film thickness is 2 mu m), and drying for 24h in a vacuum oven at 80 ℃ to obtain the PVDF/DDAB-Illite film.
The prepared sample is kept at 210 ℃ for 10 minutes to eliminate the heat history, and is subjected to isothermal treatment at 163 ℃ for a certain time by rapid cooling until the crystallization is complete. Characterized by X-ray diffractometer (XRD) and polarization microscope (POM), respectively.
As a result: referring to line 3 in fig. 1 and fig. 4, the method can rapidly prepare 100% gamma phase PVDF material.
Example 5
The first step is the preparation of modified illite from didodecyldimethylammonium bromide (DDAB). 10g of illite was added to 150mL of deionized water, sonicated for 2h, then placed on a 90 ℃ electromagnetic stirrer and stirred, during which 4mL (0.1 mol/L) of dilute hydrochloric acid solution and 5wt% CTAB was slowly added to the clay suspension. The mixed solution is stirred electromagnetically for 2h at the temperature of 90 ℃, and is kept stand for 24h to ensure that the reaction is completely activated. The suspension was suction filtered under vacuum and washed repeatedly with deionized water and absolute ethanol 3 times to ensure removal of DDAB free on the illite surface. Then the mixture is dried in a vacuum oven at 50 ℃ for 24 hours and taken out, and the dried organic modified illite is ground, sieved and bottled.
The second step is the solution blending to prepare a PVDF film containing 2.0wt% of organic illite. 16mg of the organic illite was weighed out in 20mL of dimethylacetamide (DMAc), dispersed ultrasonically for 2h, 784mg of PVDF pellets were weighed out and put into an Erlenmeyer flask, the concentration of the blend solution was 40mg/mL, and the mixture was stirred magnetically at 90 ℃ for 4h to complete mixing. And (3) directly dripping the film on a silicon wafer and an infrared silicon wafer (50 mu L of mixed solution is dripped to a substrate of 13mm × 13mm, and the average film thickness is 4 mu m), and then drying in a vacuum oven at 80 ℃ for 24h to obtain the PVDF/DDAB-Illite film.
The prepared sample is kept at 210 ℃ for 10 minutes to eliminate heat history, and is subjected to isothermal treatment at 160 ℃ for a certain time by rapid cooling until crystallization is complete. Characterized by Atomic Force (AFM).
As a result: referring to fig. 5, it can be seen that the method can rapidly prepare 100% gamma phase PVDF material.
Example 6
The first step is the preparation of modified illite from cetyltrimethylammonium bromide (CTAB). 10g of illite was added to 150mL of deionized water, sonicated for 2h, and then placed on a 100 ℃ electromagnetic stirrer and stirred, during which 4mL (0.1 mol/L) of dilute hydrochloric acid solution and 8wt% CTAB were slowly added to the clay suspension. The mixed solution is stirred electromagnetically for 2h at the temperature of 100 ℃, and is kept stand for 24h to ensure that the reaction is completely activated. The suspension was suction filtered under vacuum and washed repeatedly with deionized water and absolute ethanol 3 times to ensure removal of CTAB free on the illite surface. Then drying in a vacuum oven at 70 ℃ for 24h, taking out, grinding, sieving and bottling the dried organic modified illite.
The second step is solution blending to prepare a PVDF film containing 5.0wt% of organic illite. 25mg of the organic illite was weighed out in 10mL of dimethylacetamide (DMAc), ultrasonically dispersed for 2h, 475mg of PVDF pellets were weighed out and put into an Erlenmeyer flask, the concentration of the blended solution was 50mg/mL, and the mixture was stirred magnetically at 100 ℃ for 4h to complete mixing. The PVDF/CTAB-Illite film was prepared by dropping 80. Mu.L of the mixed solution directly onto a silicon wafer and an infrared silicon wafer (average thickness 8 μm on a 13mm. Times.13mm substrate) and then drying in a vacuum oven at 80 ℃ for 24 h.
The prepared sample is kept at 210 ℃ for 10 minutes to eliminate heat history, and is subjected to isothermal treatment at 158 ℃ for a certain time by rapid cooling until crystallization is complete. Characterized by X-ray diffractometry (XRD), polarization microscopy (POM), fourier transform infrared spectroscopy (FTIR), differential Scanning Calorimetry (DSC), and Atomic Force (AFM), respectively.
As a result: the method can be used for quickly preparing 100% gamma-phase PVDF materials.
Comparative example 1
The experimental procedure is the same as in example 4, except that the isothermal crystallization temperature is 140 ℃.
Results and conclusions:
after the polyvinylidene fluoride composite film added with 1.0wt% of modified illite is subjected to isothermal crystallization at 140 ℃ for 10min, the in-situ melting infrared spectrogram at 160 ℃,170 ℃,175 ℃ and 178 ℃ respectively refers to fig. 6. The infrared absorption peaks in fig. 6 show that only the alpha phase can be generated during isothermal crystallization at 140 ℃, and the gamma crystal form of PVDF can be generated only by isothermal crystallization at a relatively high and proper temperature range.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or to implicitly indicate the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless explicitly specified otherwise.
In the description of the specification, reference to the description of "one embodiment," "some embodiments," "an example," "a specific example," or "some examples" or the like means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Moreover, various embodiments or examples and features of various embodiments or examples described in this specification can be combined and combined by one skilled in the art without being mutually inconsistent.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (14)
1. A method for preparing a gamma-phase PVDF film is characterized by comprising the following steps:
subjecting a modified illite obtained by subjecting an illite to a surface activation treatment to a first mixing treatment with a PVDF pellet; the mass fraction of the modified illite is 0.05-10.0%; the surface activation treatment comprises: carrying out second mixing treatment on the illite, dilute hydrochloric acid and a cationic surfactant; filtering the second mixed treatment product to obtain filter residue; drying the filter residue, wherein the filter residue after drying is the modified illite; the mass ratio of the cationic surfactant to the illite is 1:100 to 10:100, respectively; the temperature of the second mixing treatment is 60 to 100 ℃;
performing film forming treatment on the first mixed treatment product; the first mixing treatment is carried out at the temperature of 60-100 ℃; the mass volume concentration of the first mixed treatment product is 1-50mg/mL;
drying the film forming treatment product;
subjecting the dried processed product to a melting process to eliminate a heat history;
and (3) carrying out isothermal crystallization treatment on the melt-processed product at the temperature of 158-168 ℃ so as to obtain the gamma-phase PVDF film.
2. The method according to claim 1, wherein the mass fraction of the modified illite is 0.1 to 5%.
3. The method according to claim 1, wherein the concentration by mass is 5 to 20mg/mL.
4. The method according to claim 1, wherein the first mixing treatment is performed in an organic solvent including at least one selected from the group consisting of N, N-dimethylformamide, dimethylacetamide and N-methylpyrrolidone.
5. The method of claim 1 wherein the modified illite is provided in a form suspended in an organic solvent.
6. The method of claim 1, further comprising, prior to performing the first mixing process: the modified illite suspension is sonicated.
7. The process according to claim 1, wherein the melt processing is carried out at 200 to 220 ℃.
8. The method of claim 1, further comprising subjecting the melt-processed product to a rapid cooling process after the melting process and before the isothermal crystallization process to achieve the isothermal crystallization process temperature.
9. The method according to claim 1, characterized in that the mass ratio of the cationic surfactant to the illite is 3:100 to 8:100.
10. the method of claim 1, wherein the cationic surfactant comprises at least one member selected from the group consisting of cetyltrimethylammonium bromide, octadecyltrimethylammonium bromide, didodecyldimethylammonium bromide.
11. The method of claim 1 wherein the illite is provided in suspension in water.
12. The method of claim 1, further comprising subjecting the illite suspension to sonication prior to the surface activation treatment.
13. Use of a modified illite obtained by a surface activation treatment as defined in the preparation process according to any one of claims 1, 11 or 12, for the preparation of a gamma-phase PVDF film.
14. A method for preparing a gamma-phase PVDF film is characterized by comprising the following steps:
suspending illite in water, and carrying out ultrasonic treatment on the illite suspension;
and (3) carrying out second mixing treatment on the illite suspension subjected to ultrasonic treatment, dilute hydrochloric acid and a cationic surfactant at the temperature of 60-100 ℃, wherein the mass ratio of the cationic surfactant to the illite is 3:100 to 8:100, the surfactant comprises at least one selected from the group consisting of cetyltrimethylammonium bromide, octadecyltrimethylammonium bromide, didodecyldimethylammonium bromide;
filtering the second mixed treatment product to obtain filter residue;
drying the filter residue, wherein the filter residue after drying is modified illite;
suspending the modified illite in an organic solvent comprising at least one selected from the group consisting of N, N-dimethylformamide, dimethylacetamide and N-methylpyrrolidone, and subjecting the modified illite suspension to ultrasonication;
carrying out first mixing treatment on the modified illite suspension subjected to ultrasonic treatment and PVDF granules at the temperature of 60-100 ℃, wherein the mass volume concentration of a first mixed treatment product is 5-20 mg/mL, the mass fraction of the modified illite is 0.1-5%, and the first mixing treatment is carried out in the organic solvent;
performing film forming treatment on the first mixed treatment product;
drying the film forming treatment product;
carrying out melt processing on the dried product at the temperature of 200-220 ℃ so as to eliminate the thermal history;
and (3) carrying out quick cooling treatment on the melt processing product to reach 158-168 ℃, and carrying out isothermal crystallization treatment on the melt processing product at the temperature of 158-168 ℃ to obtain the gamma-phase PVDF film.
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