CN103113602A - Method for preparing high-oriented gamma phase polyvinylidene fluoride PVDF thin film - Google Patents

Abstract

A method for preparing a highly oriented γ-phase polyvinylidene fluoride PVDF film, the steps are: 1) Firstly, heat and keep the solution-cast film of polyvinylidene fluoride PVDF to eliminate the heat history, and heat the polyvinylidene fluoride PVDF film at 50°C/min Rapidly cool down to 160-170°C; 2) Use a polymethylsiloxane plate to apply pressure to the melt to apply shear stress, stand at 160-170°C, and find that the crystallization form is α at 160-163°C Crystal form, annealing in this temperature range can change from α-crystal phase to γ-crystal phase; at 164-167°C, the crystal nucleus is α-crystal nucleus, and at 168-170°C, the crystallization form is γ-crystal form; Microscope, scanning electron microscope and infrared spectrometer are used to characterize the crystallization process of the melt in the shear stress field and the crystal structure after the crystallization is completed. The process is simple and easy, and it solves the problem that the pure γ-phase PVDF film cannot be obtained by isothermal crystallization. Preparation of γ-phase PVDF film with high purity, high degree of orientation and excellent thermodynamic properties.

Description

A method for preparing highly oriented γ-phase polyvinylidene fluoride PVDF film

technical field

The invention belongs to the technical field of polyvinylidene fluoride PVDF film preparation, and in particular relates to a method for preparing highly oriented γ-phase polyvinylidene fluoride PVDF film.

Background technique

Polyvinylidene fluoride PVDF combines the characteristics of general-purpose resins and fluororesins. In addition to good high temperature resistance, chemical corrosion resistance, oxidation resistance, radiation resistance, and weather resistance, it also has piezoelectricity, dielectricity, Special properties such as pyroelectricity are currently the second largest products in the output of fluorine-containing plastic films.

The diverse performance of PVDF is closely related to its complex and variable crystal structure (α, β, γ, δ, and ε are equal), and various crystal forms can be transformed into each other under certain conditions. However, people generally pay attention to the three crystal forms of α, β, and γ. The α crystal form obtained by melt crystallization belongs to the monoclinic crystal system, and the molecular chain is in the TGTG' conformation. Since the dipole polarity of the molecular chain is opposite and does not show polarity, PVDF of this crystal form can only be used as an ordinary plastic. The β crystal form belongs to the orthorhombic crystal system, the molecular chain is an all-trans TTT conformation, and the polar zigzag chain conformation makes the PVDF of this crystal form show strong electrical properties. Another important crystal form of PVDF is the γ crystal form, and its molecular chain is in the TTTGTTTG' conformation. The crystal of this crystal form has the same ferroelectric effect as the β crystal, and has great application value in the high-tech field as a pyroelectric material. .

However, the γ crystal phase needs a small degree of undercooling to be obtained. Through melting high-temperature crystallization or high-temperature annealing methods, even at a small degree of undercooling due to the low nucleation and growth rates, a large amount of γ cannot be obtained. crystalline phase, and α crystalline phase also exists in large quantities; the method of successfully preparing γ-type PVDF nanoarray whiskers by anodized alumina template solution infiltration method, due to high technical requirements, high price, and little use value; and adding a small amount The gamma films obtained by nucleating agents such as KBr have low crystallinity and melting point. There are also some methods for preparing gamma thin films, such as micro-imprinting technology, which also have the disadvantages of the above-mentioned methods. Based on this, the present invention aims to explore a simple and easy preparation method of PVDF film with high γ phase content.

Contents of the invention

In order to overcome the deficiencies of the above-mentioned prior art, the object of the present invention is to provide a method for preparing a highly oriented γ-phase polyvinylidene fluoride PVDF film.

In order to achieve the above object, the technical solution adopted in the present invention is: a method for preparing a highly oriented γ-phase polyvinylidene fluoride PVDF film, comprising the following steps:

1) First, heat the solution-cast film of polyvinylidene fluoride to 195-205°C for 10 minutes to eliminate the heat history, and then rapidly cool the polyvinylidene fluoride PVDF film to 160-170°C at a rate of 50°C/min;

2) Use a polymethylsiloxane plate to apply a pressure of 10 ⁴ to 10 ⁵ Pa to apply a shear stress to the melt at a shear rate of 0.4 to 2.0 m/s, and stand at 160 to 170 °C for 48 to 168 hours, and then Observe the crystallization process of the melt in the shear stress field and the crystal structure after crystallization under a polarizing microscope. It is found that the crystallization form is α-crystal form at 160-163°C, and the α-crystal form phase to γ-form can occur after annealing in this temperature range. The transformation of the crystal form; at 164-167°C, the crystal nucleus is the α crystal nucleus. In this temperature range, the excess energy promotes the phase transformation of the α crystal form to the γ crystal form while growing, and the phase change speed Greater than the growth rate of the α crystal form, when the phase transition front catches up with the growth front, the α crystal form stops growing, and then begins to grow the γ crystal form; the crystalline form at 168-170°C is the γ crystal form;

3) Analyze the crystal structure and morphology of the columnar crystals after crystallization by infrared spectrum FTIR, scanning electron microscope SEM, transmission electron microscope TEM, differential scanning calorimeter DSC and other characterization methods to verify the crystallization of the columnar crystals. type.

The beneficial effects of the present invention are:

PVDF can generate columnar crystals with high degree of orientation and high nucleation density in the shear stress field. Studies have shown that in the stress field, the nucleation rate of the melt is significantly increased. Therefore, when the temperature is close to the melting point of PVDF, due to the effect of the shear stress field, the nucleation rate and nucleation density of PVDF are significantly increased, and its growth rate is also slightly increased. When the shear density is high enough, PVDF columnar crystal thin films can be obtained in a short time even if the degree of undercooling is small. Then, the morphology, structure and performance of the crystal surface were studied by FTIR, scanning electron microscope SEM, transmission electron microscope TEM, and differential scanning calorimeter DSC characterization methods of the films crystallized at different degrees of supercooling to verify the column crystal form. The biggest advantage of this patent is that the process is simple and easy to implement, the crystal melting point in the film is high, and the γ-column crystal content of the prepared PVDF film basically reaches 100%, which solves the problem that the pure γ-phase PVDF film cannot be obtained by isothermal crystallization.

Detailed ways:

Below in conjunction with specific embodiment the present invention is described in further detail.

Embodiment one

A method for preparing highly oriented γ-phase polyvinylidene fluoride PVDF film, comprising the following steps:

1) First, heat the polyvinylidene fluoride PVDF solution-cast film to 200°C for 10 minutes to eliminate the heat history, and then rapidly cool the polyvinylidene fluoride PVDF film to 170°C at a rate of 50°C/min;

2) Use a polymethylsiloxane plate to apply a pressure of 10 ⁵ Pa to the melt at a shear rate of 1.5m/s to apply a shear stress to the melt, and stand at 170°C for 96 hours to obtain a γ-phase PVDF film. Observe the crystallization process of the melt in the shear stress field and the crystal structure after crystallization under a microscope;

3) Analyze the crystal structure and morphology of the columnar crystals after crystallization by infrared spectrum FTIR, scanning electron microscope SEM, transmission electron microscope TEM, differential scanning calorimeter DSC and other characterization methods to verify the crystallization of the columnar crystals. type.

The results showed that the columnar crystals crystallized at 170℃ for 96h were in the γ crystal form, and a γ crystal PVDF thin film was obtained.

Embodiment two

A method for preparing highly oriented γ-phase polyvinylidene fluoride PVDF film, comprising the following steps:

1) First, heat the solution-cast film of polyvinylidene fluoride to 205°C for 10 minutes to eliminate the heat history, and then rapidly cool the polyvinylidene fluoride PVDF film to 165°C at a rate of 50°C/min;

2) Use a polymethylsiloxane plate to apply a pressure of 10 ⁵ Pa to the melt at a shear rate of 2.0m/s to apply a shear stress to the melt, and stand at 165°C for 72 hours to obtain a γ-phase PVDF film. Observe the crystallization process of the melt in the shear stress field and the crystal structure after crystallization under a microscope;

3) Analyze the crystal structure and morphology of PVDF columnar crystals by means of FTIR infrared spectroscopy, scanning electron microscope SEM, transmission electron microscope TEM, and differential scanning calorimeter DSC to verify the crystal form of columnar crystals after crystallization .

The results show that the crystal nucleation at 165℃ is α crystal nuclei, and the phase transformation from α to γ crystal form occurs simultaneously when the α crystal grows. When the phase transition rate exceeds the growth rate, the α crystal form stops growing and the γ crystal form begins to grow. After crystallization for 72 hours, PVDF film with full γ phase was obtained.

Embodiment Three

A method for preparing highly oriented γ-phase polyvinylidene fluoride PVDF film, comprising the following steps:

1) First, heat the polyvinylidene fluoride PVDF solution-cast film to 195°C for 10 minutes to eliminate the heat history, and then rapidly cool the polyvinylidene fluoride PVDF film to 160°C at a rate of 50°C/min;

2) Use a polymethylsiloxane plate to apply a pressure of 10 ⁵ Pa to the melt at a shear rate of 0.6m/s to apply a shear stress to the melt, and stand at 160°C for 48 hours to obtain an α-phase PVDF film with a crystallization of 2 After continuing to anneal at 160°C for 120 hours, a γ-phase thin film after α phase transition was obtained, and the crystallization process of the melt in the shear stress field and the crystal structure after crystallization were observed under a polarizing microscope;

3) Analyze the crystal structure and morphology of the columnar crystals after crystallization by infrared spectrum FTIR, scanning electron microscope SEM, transmission electron microscope TEM, differential scanning calorimeter DSC and other characterization methods to verify the crystallization of the columnar crystals. type.

The results show that crystal nucleation at 160°C is α crystal nuclei, annealing at this temperature for 120 hours after crystallization for 48 hours, and a γ phase PVDF film after α phase transformation is obtained. The melting temperature of the γ phase PVDF film obtained in this example is higher than that in the example The melting temperature of the γ-phase PVDF film obtained in 1 and 2 is about 8-12°C higher.

Claims (4)

1. a method for preparing high orientation γ phase polyvinylidene fluoride PVDF film, is characterized in that, includes following steps:

1) at first the solution-cast film heating to 195 of polyvinylidene difluoride (PVDF) PVDF～205 ℃ insulation 10min are eliminated thermal histories, subsequently polyvinylidene difluoride (PVDF) PVDF film is cooled to rapidly 160～170 ℃ with the speed of 50 ℃/min;

2) utilize the polymethyl siloxane plate to apply 10 ⁴～10 ⁵Pa pressure applies shear-stress with the shearing rate of 0.4～2.0m/s to melt, standing 48～168h under 160～170 ℃, crystalline structure after the crystallisation process of melt and crystallization are completed in polarized light microscopy Microscopic observation shear stress field, discovery is alpha-crystal form at 160～163 ℃ of lower Crystal types, through annealing under this temperature field, the alpha-crystal form transformation of γ crystal formation phase in opposite directions can occur; Be the α nucleus at 164～167 ℃ of lower crystallization nucleus, transformation mutually to the γ crystal formation when impelling alpha-crystal form growing, energy unnecessary under this temperature field is occuring, and phase velocity is greater than the alpha-crystal form speed of growth, when the transition front catch up with growth front, alpha-crystal form stops growing, and γ crystal formation then begins to grow; 168～170 ℃ of Crystal types are the γ crystal formation;

3) cylindrulite after crystallization is adopted the characterization methods such as infrared spectra FTIR, scanning electronic microscope SEM, transmission electron microscope TEM, differential scanning calorimeter DSC analyze crystalline structure and the pattern of PVDF cylindrulite, with the crystal formation of checking cylindrulite.

2. a kind of method for preparing high orientation γ phase polyvinylidene fluoride PVDF film according to claim 1, is characterized in that, includes following steps:

1) at first the solution-cast film heating to 200 of a polyvinylidene difluoride (PVDF) PVDF ℃ insulation 10min is eliminated thermal history, subsequently polyvinylidene difluoride (PVDF) PVDF film is cooled to rapidly 170 ℃ with the speed of 50 ℃/min;

2) utilize the polymethyl siloxane plate to apply 10 ⁵Pa pressure applies shear-stress with the shearing rate of 1.5m/s to melt, and standing 96h under 170 ℃ can obtain γ phase PVDF film, the crystalline structure after the crystallisation process of melt and crystallization are completed in polarized light microscopy Microscopic observation shear stress field;

3) adopt infrared spectra FTIR, scanning electronic microscope SEM, transmission electron microscope TEM, differential scanning calorimeter DSC characterization method to analyze crystalline structure and the pattern of PVDF cylindrulite to the cylindrulite after crystallization, with the crystal formation of checking cylindrulite.

3. a kind of method for preparing high orientation γ phase polyvinylidene fluoride PVDF film according to claim 1, is characterized in that, includes following steps:

1) at first the solution-cast film heating to 205 of a polyvinylidene difluoride (PVDF) PVDF ℃ insulation 10min is eliminated thermal history, subsequently polyvinylidene difluoride (PVDF) PVDF film is cooled to rapidly 165 ℃ with the speed of 50 ℃/min;

2) utilize the polymethyl siloxane plate to apply 10 ⁴Pa pressure applies shear-stress with the shearing rate of 2.0m/s to melt, and standing 72h under 165 ℃ can obtain γ phase PVDF film, the crystalline structure after the crystallisation process of melt and crystallization are completed in polarized light microscopy Microscopic observation shear stress field;

3) adopt infrared spectra FTIR, scanning electronic microscope SEM, transmission electron microscope TEM, differential scanning calorimeter DSC characterization method to analyze crystalline structure and the pattern of PVDF cylindrulite to the cylindrulite after crystallization, with the crystal formation of checking cylindrulite.

4. a kind of method for preparing high orientation γ phase polyvinylidene fluoride PVDF film according to claim 1, is characterized in that, includes following steps:

1) at first the solution-cast film heating to 195 of a polyvinylidene difluoride (PVDF) PVDF ℃ insulation 10min is eliminated thermal history, subsequently polyvinylidene difluoride (PVDF) PVDF film is cooled to rapidly 160 ℃ with the speed of 50 ℃/min;

2) utilize the polymethyl siloxane plate to apply 10 ⁵Pa pressure applies shear-stress with the shearing rate of 0.6m/s to melt, standing 48h under 160 ℃, can obtain α phase PVDF film, crystallization continues after 2 days after annealing 120h at 160 ℃ of temperature, obtain the γ phase film after the phase transformation of α phase, the crystalline structure after the crystallisation process of melt and crystallization are completed in polarized light microscopy Microscopic observation shear stress field;

3) adopt infrared spectra FTIR, scanning electronic microscope SEM, transmission electron microscope TEM, differential scanning calorimeter DSC characterization method to analyze crystalline structure and the pattern of PVDF cylindrulite to the cylindrulite after crystallization, with the crystal formation of checking cylindrulite.