CN111961246B - Supercritical fluid foaming method for porous PVDF with high beta crystal content - Google Patents
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- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/04—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent
- C08J9/12—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent by a physical blowing agent
- C08J9/122—Hydrogen, oxygen, CO2, nitrogen or noble gases
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- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/0014—Use of organic additives
- C08J9/0028—Use of organic additives containing nitrogen
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- C—CHEMISTRY; METALLURGY
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- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2203/00—Foams characterized by the expanding agent
- C08J2203/06—CO2, N2 or noble gases
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- C08J2203/00—Foams characterized by the expanding agent
- C08J2203/08—Supercritical fluid
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- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- 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
- C08J2327/02—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 not modified by chemical after-treatment
- C08J2327/12—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 not modified by chemical after-treatment containing fluorine atoms
- C08J2327/16—Homopolymers or copolymers of vinylidene fluoride
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- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K5/00—Use of organic ingredients
- C08K5/16—Nitrogen-containing compounds
- C08K5/17—Amines; Quaternary ammonium compounds
- C08K5/19—Quaternary ammonium compounds
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K5/00—Use of organic ingredients
- C08K5/16—Nitrogen-containing compounds
- C08K5/34—Heterocyclic compounds having nitrogen in the ring
- C08K5/3442—Heterocyclic compounds having nitrogen in the ring having two nitrogen atoms in the ring
- C08K5/3445—Five-membered rings
Abstract
The invention discloses a supercritical fluid foaming method of porous PVDF with high beta crystal content, which comprises the following steps: firstly, uniformly mixing PVDF and a modifier, then granulating, putting the granules into a die with a certain length-diameter ratio, and then placing the die into a high-pressure reaction kettle to carry out foaming molding through supercritical fluid to obtain a porous product. According to the invention, a proper modifier is selected, so that the foaming condition of the PVDF raw material and the content of beta crystals in the PVDF can be improved, and the PVDF material is endowed with excellent piezoelectric conversion performance, and the product prepared by the method can be used as a flexible piezoelectric mechanical energy collecting device, a piezoelectric sensor, a piezoelectric driver and the like, so as to be used in the fields of new energy, pressure sensing, artificial intelligence and the like.
Description
Technical Field
The invention relates to the field of supercritical fluid foaming processes, in particular to a supercritical fluid foaming method of porous PVDF with high beta crystal content under high temperature and high pressure.
Background
Supercritical fluid foaming is a physical foaming and forming technology, is a microcellular foaming and forming technology, has the advantages of low cost, environmental protection, simple and convenient operation, high efficiency, realization of complex structure and the like, and is used as a replacement method for producing a specific microcellular structure of a solvent-free functional polymer in multiple fields. Among the foaming techniques commonly used in the existing polymer foam materials and products, such as a phase separation method, a template method, a foaming agent method and the like, supercritical foaming is a physical foaming forming technique, wherein a supercritical fluid is used as a physical foaming agent, which not only provides safer and more responsible for the environment, but also is one of ideal methods for preparing controllable and uniform cellular materials. The polymer can realize the required micropore structure in a high-pressure reaction kettle filled with supercritical fluid only by regulating and controlling proper parameters such as pressure, temperature, time and the like.
PVDF has the advantages of high mechanical strength, good chemical resistance, good radiation resistance, low permeability, excellent impact resistance, toughness and the like, and has wide application in the fields of chemical industry, electronic appliances, buildings and the like. In terms of chemical properties, PVDF is a semi-crystalline polymer with a complex and diverse structure and has five different crystal forms, wherein beta-PVDF has the strongest electrical activity, has good application in emerging piezoelectric mechanical energy collection, piezoelectric sensors, piezoelectric drivers and the like, and has great development potential in emerging high-end fields such as artificial intelligence and the like.
beta-PVDF is generally obtained by a mechanical stretching method, an electric field polarization method, a radiation grafting method, or the like. At present, the following problems exist in the technology for preparing the high beta-crystal PVDF porous material by supercritical fluid foaming: (1) the supercritical fluid foaming is generally foaming at a temperature around the melting point of PVDF, and more stable alpha crystals can be easily obtained after cooling, and no electric activity exists; therefore, additive-assisted foaming is needed to improve the content of the beta phase, but the beta phase content of the method still cannot meet the requirement of the PVDF piezoelectric device industry on the polar phase (more than or equal to 80 percent); (2) the supercritical foaming temperature is high, so that the deformation amount of the material is large, and the molding quality in the foaming process is poor. (3) The influence of parameters such as temperature, pressure release time and speed in the foaming process on the formation of the polar phase is complex, so that the controllable preparation of the high-polarity porous PVDF cannot be realized, and the existing requirements cannot be met.
Disclosure of Invention
The invention aims to: aiming at the defects in the prior art, the supercritical fluid foaming method of the porous PVDF (polyvinylidene fluoride) with high beta-crystal content is provided, has the advantages of simple process, high polar phase content (more than 96%) of the PVDF material, flexible structure design, high flexibility, high mechanical energy collection efficiency and the like, and can meet the application of the method in the aspect of preparing flexible intelligent materials by using an intelligent manufacturing technology.
The technical scheme adopted by the invention is as follows:
a supercritical fluid foaming method of porous PVDF with high beta crystal content comprises the following steps:
a. uniformly mixing PVDF particles and a modifier to form a mixture;
b. drying the mixture, and then granulating to obtain granules;
c. and (3) placing the particles in a high-pressure reaction kettle, and foaming and forming pores by using supercritical fluid at high temperature to obtain the porous material.
According to the invention, the PVDF material is modified by the modifier, and the positive charge of the cation or non-ionic liquid modifier in the ionic liquid modifier and the-CF bond of the PVDF have strong ion-dipole interaction at high temperature, so that a high-content beta crystalline phase can be still obtained under the high-temperature and high-pressure supercritical fluid environment, and the preparation of the high-beta-crystalline-content porous PVDF flexible piezoelectric device by supercritical fluid foaming is realized.
In addition, the modifier is added in the invention, so that the melting point and the crystallinity of PVDF can be regulated and controlled, the foaming condition of PVDF is improved, and a high-quality, flexible and complex-pore-structure foam part can be obtained; on the other hand, the modifier can be retained or removed according to the application requirements of the material after foaming is finished, and the crystallinity and the polar phase content of the PVDF foam are regulated and controlled.
Further, the modifier is an ionic liquid or a nonionic liquid containing positive charges. The PVDF and the modifier can be mixed by a solution mixing method or a direct banburying mixing method. When the ionic liquid is used as a modifier, the ionic liquid is washed away and recovered after the product is obtained; when the nonionic liquid is used as the modifier, the product is directly obtained.
Further, the ionic liquid is 1-methylimidazole nitrate, 1-methylimidazole dihydrogen phosphate, 1-ethyl-3-methylimidazole tetrafluoroborate, 1-ethyl-3-methylimidazole diethyl phosphate, 1-butyl-2, 3-dimethylimidazole chloride, 1-butyl-3-methylimidazole hexafluorophosphate, 1-butyl-3-methylimidazole tetrafluoroborate, 1, 3-bis (2,4, 6-trimethylphenyl) imidazole chloride, 1-octyl-3-methylimidazole hexafluorophosphate, 1, 2-dimethyl-3-butylimidazole hexafluorophosphate, 1-butyl-4-methylpyridine chloride hydrochloride, 1-hexyl-3-methylimidazole hexafluorophosphate, 1-ethyl-3-methylimidazole dihydrogen phosphate, 1-butyl-3-methylimidazole hydrogen chloride, 1-ethyl-3-methylimidazole hydrogen phosphate, or mixtures thereof, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-n-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-ethyl-3-methylimidazolium acetate, 1, 2-dimethyl-3-ethylimidazolium bromide, 1-methyl-3-butylimidazolium nitrate or 1-ethyl-3-methylimidazolium tetrachloroferrate; the nonionic liquid is cetyl trimethyl ammonium bromide, dodecyl dimethyl benzyl ammonium chloride, bis-decyl dimethyl ammonium chloride, ammonium bisulfate, tetraphenyl phosphorus bromide, sodium dodecyl sulfate, sodium dodecyl sulfonate or sodium dodecyl benzene sulfonate.
Further, the mass ratio of the ionic liquid to the PVDF is 1-2:10, preferably 1.5: 10; the mass ratio of the nonionic liquid to the PVDF is 1-4:100, preferably 3: 100.
Further, the particles are placed in a high-pressure reaction kettle for supercritical fluid foaming.
Furthermore, the foaming temperature in the supercritical foaming process is 140-.
The porous PVDF material with high beta crystal content is prepared by the method.
The porous PVDF material with high beta crystal content is applied to the preparation of piezoelectric devices, wherein the piezoelectric devices comprise mechanical energy collecting devices, sensors, drivers and the like.
In summary, due to the adoption of the technical scheme, the invention has the beneficial effects that:
1. according to the invention, the porous PVDF with high beta-crystal content is effectively obtained under the environment of high-temperature and high-pressure supercritical fluid through the strong ion-dipole interaction of cations in the modifier and-CF bonds, so that the PVDF-based piezoelectric material has good piezoelectric performance;
2. after the modifier is added, PVDF is easier to foam, the foaming processing characteristic and the dimensional stability are obviously improved, and the piezoelectric conversion performance is greatly improved;
3. the raw materials used in the invention have wide sources and low cost, and PVDF is used as general commercial plastics and has excellent physical and chemical properties; the ionic liquid as a green modifier has the characteristics of environmental protection and recyclability;
4. the porous PVDF with high beta crystal content obtained by the supercritical foam molding technology can be well suitable for piezoelectric mechanical energy collecting materials, piezoelectric sensors, piezoelectric drivers and the like, and is used in the fields of new energy, pressure sensing, artificial intelligence and the like.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
FIG. 1 shows pure PVDF and PVDF/1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquids ([ C ] before foaming2mim][BF4]) And DSC testing of cetyl trimethylammonium bromide (CTAB) PVDF;
FIG. 2 shows PVDF, PVDF/[ C ] after foaming2mim][BF4]And PVDF infrared testing of CTAB;
FIG. 3 shows PVDF/[ C ] after foaming2mim][BF4]SEM photograph of the composite;
FIG. 4 shows the addition of [ C ] separately2mim][BF4]And (3) carrying out piezoelectric voltage test on the PVDF piezoelectric device foamed by the ionic liquid and the CTAB modifier.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting, i.e., the embodiments described are only a few, but not all, embodiments of the invention. The components of embodiments of the present invention that are generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.
Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without making any creative effort, shall fall within the protection scope of the present invention.
It is noted that relational terms such as "first" and "second," and the like, may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or device that comprises the element.
The features and properties of the present invention are described in further detail below with reference to examples.
Example 1
The supercritical fluid foaming method of porous PVDF with high beta crystal content provided by the preferred embodiment of the invention comprises the following specific steps:
firstly, uniformly dispersing 1-ethyl-3-methylimidazole tetrafluoroborate in a Dimethylformamide (DMF) solvent, then adding PVDF particles, uniformly stirring at a constant temperature until PVDF is completely dissolved, and then drying in a vacuum oven until the solvent is completely removed; cutting into small particles, placing the particles in a die with a certain length-diameter ratio, and placing the particles in a high-pressure reaction kettle for supercritical CO2Foaming and pore-forming, wherein the foaming temperature is 145 ℃, the foaming time is 5h, the foaming pressure is 12MPa, and the pressure relief rate is less than 2 s.
Example 2
The supercritical fluid foaming method of porous PVDF with high beta crystal content provided by the preferred embodiment of the invention comprises the following specific steps:
firstly, dissolving 1-methylimidazole nitrate in a dimethylacetamide (DMAc) solvent, then adding PVDF, stirring at a constant speed until the PVDF is completely dissolved, and then drying in a vacuum oven until the solvent is completely removed; cutting into small particles, placing the particles in a die with a certain length-diameter ratio, and placing the particles in a high-pressure reaction kettle to obtain supercritical N2Foaming and pore forming are carried out at the foaming temperature ofThe foaming time is 2h at 150 ℃, the foaming pressure is 15MPa, and the pressure relief rate is less than 5 s.
Example 3
The supercritical fluid foaming method of porous PVDF with high beta crystal content provided by the preferred embodiment of the invention comprises the following specific steps:
firstly, dissolving CTAB in a dimethyl sulfoxide (DMSO) solvent, adding PVDF particles, uniformly stirring at a constant temperature until PVDF is completely dissolved, and then drying in a vacuum oven until the solvent is completely removed; cutting into small particles, placing the particles in a die with a certain length-diameter ratio, and placing the particles in a high-pressure reaction kettle to obtain supercritical N2、CO2And (3) foaming and pore-forming by using the mixed gas, wherein the foaming temperature range is 160 ℃, the foaming time is 1h, the foaming pressure is 20MPa, and the pressure relief rate is less than 5 s.
The supercritical foaming apparatus used in the above examples 1-3 was a high pressure reactor, model number SLM-250/SLM-50 (Beijing Shijisenlang laboratory instruments Co., Ltd.).
Experimental example 1
The sample prepared in example 1 was subjected to structural characterization: the melting point (Tm) and crystallinity (X) of the sample were measured by Differential Scanning Calorimetry (DSC)c) (sample mass about 7mg, temperature range 30-200 ℃, temperature ramp rate 10 ℃/min, nitrogen atmosphere) by infrared spectroscopy (FT-IR) to identify the crystal structure of PVDF (Nicolet is50, Thermo Fisher, USA) with a resolution of 4cm-14000-400cm by ATR mode analysis-1Representative bands within the range and the phase content was calculated quantitatively.
FIG. 1 is a DSC curve showing the decrease in the crystallinity of PVDF and the crystallinity χ of pure PVDF modified by ionic liquidc52.20%, and after the content of the ionic liquid is increased to 10 wt%, the crystallinity chicAbout 41%, decrease by about 11.2%, and when CTAB content is 3 wt%, crystallinity χc41.2 percent, the crystallinity is reduced by 11.0 percent, and the absorption and the temperature adjustment of the supercritical fluid are facilitated due to the reduction of the crystallinity;
fig. 2 is an FTIR test spectrum, and the result shows that the beta-phase content of the PVDF after foaming is 13.5%, the beta-phase content of the PVDF after ionic liquid modification can reach 97.38%, and the beta-phase content of the CTAB modified PVDF is 97.0%, which provides strong material support for the supercritical foaming PVDF-based piezoelectric flexible device.
Experimental example 2
The sample prepared in example 1 is quenched and broken in liquid nitrogen, or a foam sample is cut along the cross section by a single-sided blade, and is sprayed with gold, and the cell structure of the foam is observed by using an InspectF scanning electron microscope of FEI company of America, so that an SEM picture of the section of the cellular material is obtained, and the acceleration voltage is5 KV. FIG. 3 is a SEM photograph of a cross-sectional structure of a cellular material, in which cells are uniformly distributed, the diameter of the cells is 30-50 μm, and the whole structure of the cells is small and dense, which is beneficial to improving the piezoelectric output of PVDF.
Experimental example 3
Characterization of piezoelectric properties
The piezoelectric performance test was performed using a linear motor and Labview system, in which electrodes were attached to both sides of the sample prepared in examples 1 and 3, the linear motor applied a force to the sample, and a charge was introduced into an electrometer (Keithley 6514) through a wire connection and converted into a visible electrical signal.
As shown in FIG. 4, the open circuit voltage of pure PVDF is 0.8V, and after the ionic liquid and CTAB are modified, the open circuit voltage reaches 2.8V and 2.85V respectively, which are improved by 3.5 times and 3.56 times. The improvement of the output performance benefits from the formation of the high beta crystalline phase of PVDF, and the results also show that the PVDF material obtained by the preparation method is effective for collecting and utilizing potential mechanical energy.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (8)
1. A supercritical fluid foaming method of porous PVDF with high beta crystal content is characterized by comprising the following steps:
a. uniformly mixing PVDF particles and a modifier to obtain a mixture;
b. drying the mixture and then granulating;
c. and (3) placing the particles into a high-pressure reaction kettle, and carrying out supercritical fluid foaming at high temperature to obtain the porous material.
2. The supercritical fluid foaming method of porous PVDF with high beta crystal content as claimed in claim 1, wherein the fluid is CO2、N2、NH3One or more of ethylene, ethane, propane, n-pentane, propylene, methanol and water.
3. The supercritical fluid foaming process of porous PVDF with high beta crystal content as claimed in claim 1, wherein the modifier is ionic liquid or non-ionic liquid containing charge.
4. The method for supercritical fluid foaming of porous PVDF with high beta crystal content as claimed in claim 3, wherein the ionic liquid is 1-methylimidazole nitrate, 1-methylimidazole dihydrogen phosphate, 1-ethyl-3-methylimidazole tetrafluoroborate, 1-ethyl-3-methylimidazole diethyl phosphate, 1-butyl-2, 3-dimethylimidazole chloride, 1-butyl-3-methylimidazole hexafluorophosphate, 1-butyl-3-methylimidazole tetrafluoroborate, 1, 3-bis (2,4, 6-trimethylphenyl) imidazole chloride, 1-octyl-3-methylimidazole hexafluorophosphate, 1, 2-dimethyl-3-butylimidazole hexafluorophosphate, 1-ethyl-3-methylimidazole hexafluorophosphate, 1-butyl-4-methylchloridate, 1-hexyl-3-methylimidazolium hexafluorophosphate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-n-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-ethyl-3-methylimidazolium acetate, 1, 2-dimethyl-3-ethylimidazolium bromide, 1-methyl-3-butylimidazolium nitrate or 1-ethyl-3-methylimidazolium tetrachloroferrate; the non-ionic liquid is cetyl trimethyl ammonium bromide, dodecyl dimethyl benzyl ammonium chloride, didecyl dimethyl ammonium chloride, ammonium bisulfate, tetraphenyl phosphorus bromide, sodium dodecyl sulfate, sodium dodecyl sulfonate or sodium dodecyl benzene sulfonate.
5. The supercritical fluid foaming method of porous PVDF with high beta crystal content as claimed in claim 3, wherein the mass ratio of the ionic liquid to PVDF is 1-2:10, and the mass ratio of the non-ionic liquid to PVDF is 1-4: 100.
6. The supercritical fluid foaming method of porous PVDF with high beta-crystal content as claimed in claim 1, wherein the foaming temperature is 140-160 ℃, the foaming pressure is 10-20MPa, the foaming time is 1-5h, and the pressure release rate is less than 2s during the supercritical fluid foaming process.
7. The porous PVDF material with high beta crystal content prepared by the method of any one of claims 1-6.
8. Use of the porous PVDF material with high beta crystal content as claimed in claim 7 in the preparation of piezoelectric devices.
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