CN112852078B - Method for preparing polyvinylidene fluoride based piezoelectric foam part based on selective laser sintering - Google Patents

Method for preparing polyvinylidene fluoride based piezoelectric foam part based on selective laser sintering Download PDF

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CN112852078B
CN112852078B CN202110047669.6A CN202110047669A CN112852078B CN 112852078 B CN112852078 B CN 112852078B CN 202110047669 A CN202110047669 A CN 202110047669A CN 112852078 B CN112852078 B CN 112852078B
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polyvinylidene fluoride
foaming
pvdf
laser sintering
temperature
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CN112852078A (en
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陈宁
杨程
王琪
刘鹏举
张楚虹
华正坤
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Sichuan University
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    • C—CHEMISTRY; METALLURGY
    • 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
    • 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
    • C—CHEMISTRY; METALLURGY
    • 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
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/0066—Use of inorganic compounding ingredients
    • C—CHEMISTRY; METALLURGY
    • 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
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/0066—Use of inorganic compounding ingredients
    • C08J9/0071—Nanosized fillers, i.e. having at least one dimension below 100 nanometers
    • C—CHEMISTRY; METALLURGY
    • 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
    • C08J2203/00—Foams characterized by the expanding agent
    • C08J2203/06—CO2, N2 or noble gases
    • C—CHEMISTRY; METALLURGY
    • 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
    • C08J2203/00—Foams characterized by the expanding agent
    • C08J2203/08—Supercritical fluid
    • C—CHEMISTRY; METALLURGY
    • 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
    • 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
    • C08K2201/00—Specific properties of additives
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    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
    • C08K3/24—Acids; Salts thereof
    • 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
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/34—Silicon-containing compounds
    • 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
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/34—Silicon-containing compounds
    • C08K3/36—Silica

Abstract

The invention provides a method for preparing a polyvinylidene fluoride piezoelectric foam part based on selective laser sintering. According to the invention, the beta crystal form content of polyvinylidene fluoride in the preparation process is maintained and further improved through the limitation of the supercritical carbon dioxide kettle pressure foaming method process parameters and the coordination effect with selective laser sintering, the compression modulus of the PVDF-based piezoelectric foam product prepared by the method can reach 1.44MPa under the condition of adding inorganic filler, and the maximum piezoelectric output is 20.9V.

Description

Method for preparing polyvinylidene fluoride based piezoelectric foam part based on selective laser sintering
Technical Field
The invention belongs to the technical field of polyvinylidene fluoride piezoelectric foam products, and particularly relates to a method for preparing a polyvinylidene fluoride piezoelectric foam product based on selective laser sintering.
Background
In recent years, green energy has attracted more and more attention due to the defects of environmental pollution and non-renewable property of the traditional energy. Mechanical energy, one of green energy sources, widely exists in nature, but is difficult to be effectively utilized, and one of the key technical problems is the power-electricity conversion efficiency. Therefore, how to improve the power-electricity conversion efficiency is a difficult problem to be solved urgently.
The piezoelectric material has wide application in the aspect of force-electricity conversion, and the piezoelectric coefficient of polyvinylidene fluoride (PVDF) in known polymers is the highest (d33 ≈ 20 to-34 pC/N). The beta crystal form has the highest piezoelectric performance, and the methods for improving the content of the beta crystal mainly comprise cold stretching, solid phase extrusion and grinding. Nowadays, PVDF is widely researched and utilized in the fields of sensing, energy storage and the like due to its unique piezoelectric property, good flexibility and machinability, but the research and application of existing PVDF in the piezoelectric direction is mainly focused on two-dimensional films, and the research on three-dimensional parts is rare.
The reason is that the prior three-dimensional piezoelectric foam part is generally formed primarily by adopting a thermoforming method such as a die pressing method, an injection molding method and the like in the prior art, but the content of beta crystal form of the product is reduced in the preparation process of the thermoforming process. For example, in the molding method, a polymer raw material is placed in a required mold, the melting is carried out at a temperature higher than the melting point (generally 200-220 ℃, the fluidity of PVDF is good at the moment, and the molding effect is good), and the PVDF is formed after melting, wherein the crystal form mainly comprises a stable alpha crystal form, and most of the electrically activated crystal form-beta crystal form is converted into the alpha crystal form, so the piezoelectric performance of the PVDF is obviously influenced. The injection molding method also has the problems, and also needs to customize a specific mold according to the requirements of the product, so that the production cost is high and the process is complex.
In addition, the conventional three-dimensional part manufacturing method often has the disadvantages of long design time consumption and high manufacturing cost when facing to the increasingly updated technical development requirements, particularly the actual requirements of various shapes and complex structures of the power-electricity conversion device, so that the popularization and development of the piezoelectric foam product with the complex structure prepared by the conventional method are restricted to a certain extent. In recent years, with the development of 3D printing technology, its processing advantages are continuously highlighted, including easy printing of complex structures, short product design period, less material consumption of additive manufacturing process, and the like. Therefore, the preparation of the piezoelectric foam product with a complex structure is realized through a 3D printing technology, and the application and development of the electric conversion are greatly promoted.
Selective Laser Sintering (SLS) is used as a branch of 3D printing, powder is used as a raw material, no shearing and no flowing are generated in the processing process, and a part with a complex structure can be designed. In addition, SLS does not need to be supported in the forming process, so that a complex post-treatment process is omitted, and the production efficiency is improved.
Therefore, if a selective laser sintering technology is used for constructing a PVDF piezoelectric foam part with high piezoelectric performance, the development research and the industrial application of the mechanical-electrical conversion technology are facilitated.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a method for preparing a PVDF-based piezoelectric foam product based on selective laser sintering, which maintains and further improves the beta crystal form content of polyvinylidene fluoride in the preparation process by limiting the technological parameters of a supercritical carbon dioxide kettle pressure foaming method and cooperating with selective laser sintering, and the PVDF-based piezoelectric foam product prepared by the method has the compression modulus of 0.98MPa under the condition of not adding inorganic filler and the maximum piezoelectric output of 7.8V, and has the compression modulus of 1.44MPa and the maximum piezoelectric output of 20.9V under the condition of adding the inorganic filler.
In order to achieve the purpose, the invention adopts the technical scheme formed by the following technical measures.
A method for preparing a PVDF-based piezoelectric foam part based on selective laser sintering comprises the following steps in parts by weight:
(1) preparing polyvinylidene fluoride powder suitable for selective laser sintering or polyvinylidene fluoride/inorganic filler mixed powder;
(2) uniformly mixing 100 parts of polyvinylidene fluoride powder or polyvinylidene fluoride/inorganic filler mixed powder prepared in the step (1) with 0.1-0.5 part of a flow aid, and performing a selective laser sintering process to obtain a finished product, namely a laser sintered product; wherein, the technological parameters of the selective laser sintering are as follows: preheating temperature is 150-160 ℃, laser scanning speed is 8000-9600 mm/s, laser scanning power is 10-40W, laser scanning times are 1-2 times, laser scanning distance is 0.1-0.3 mm, and powder spreading layer thickness is 0.1-0.3 mm;
(3) preparing the laser sintering part obtained in the step (2) into a PVDF-based foam part by adopting a supercritical carbon dioxide kettle pressure foaming method; wherein, the supercritical carbon dioxide kettle pressure foaming method comprises the following process parameters: the pressure in the foaming process is 7-16 MPa, the foaming temperature is 150-170 ℃, and the pressure maintaining time is 30-60 min;
(4) and (4) polarizing the PVDF-based foamed part obtained in the step (3) at the temperature of 80-100 ℃ to obtain the PVDF-based piezoelectric foamed part.
The polyvinylidene fluoride powder suitable for selective laser sintering in step (1) is generally selected conventionally from polyvinylidene fluoride powders suitable for selective laser sintering in the prior art, and those skilled in the art can select an appropriate particle size of polyvinylidene fluoride according to specific selective laser sintering equipment. In order to better illustrate the invention and provide a reference technical scheme, in the step (1), polyvinylidene fluoride powder with the particle size of 60-250 μm is selected from polyvinylidene fluoride powder or polyvinylidene fluoride raw material is crushed into polyvinylidene fluoride powder with the particle size of 60-250 μm, and the polyvinylidene fluoride powder is dried for later use.
Furthermore, the polyvinylidene fluoride raw material is pulverized into polyvinylidene fluoride powder with the particle size of 60-250 μm, and the polyvinylidene fluoride powder can be processed by the existing conventional pulverizing equipment such as a jaw crusher, a planetary ball mill and a freezing ball mill. In order to better illustrate the invention, the invention provides a specific mode for giving reference, wherein the grinding treatment is that the powder is subjected to cryogenic grinding by a freezing grinder, the grinding temperature is-120 to-60 ℃, and then the obtained powder is sieved by a 100-mesh screen to obtain the powder with the particle size of 60 to 120 mu m.
The polyvinylidene fluoride/inorganic filler mixed powder suitable for selective laser sintering in the step (1), wherein the inorganic filler mainly comprises an inorganic filler which is suitable for a selective laser sintering process and has functionality such as further enhanced piezoelectric performance or/and further enhanced mechanical performance. The skilled person will be able to select the appropriate type of inorganic filler based on the state of the art and the actual industrial conditions. In order to better illustrate the invention and to provide a technical solution that can be implemented by reference, the inorganic filler mainly comprises BaTiO3PZT, ZnO, boron nitride, and the like.
Preferably, in order toThe piezoelectric property and the mechanical property of the PVDF-based piezoelectric foam part are further improved, and the inorganic filler is preferably BaTiO3And the addition amount of the inorganic filler is 3-20 wt% of the total amount. Further preferably, the addition amount of the inorganic filler is 15 to 20 wt%.
It is noted that the addition amount of the inorganic filler in the polyvinylidene fluoride/inorganic filler mixed powder should not be more than 20 wt%, which depends on that the addition of the inorganic filler in the step (3) by the supercritical carbon dioxide kettle-pressure foaming method can hinder the foaming process, and the excessive addition can lead to incomplete appearance of the product. Generally speaking, on the premise that the addition amount of the inorganic filler is not higher than 20 wt%, 0.1-0.5 part of the polyvinylidene fluoride/inorganic filler mixed powder added with the flow assistant completely meets the fluidity required in the selective laser sintering process.
Generally, the particle size of the polyvinylidene fluoride powder in the step (1) of the invention is 60-250 μm, which is mainly suitable for selective laser sintering in the subsequent steps, and a person skilled in the art can select the suitable particle size of the polyvinylidene fluoride powder according to the used selective laser sintering equipment.
Generally, the particle size of the inorganic filler in step (1) of the present invention is 300 to 500 μm or is consistent with the particle size of the polyvinylidene fluoride powder, so that the inorganic filler is suitably stirred, mixed and dispersed in the polyvinylidene fluoride powder.
Wherein the above polyvinylidene fluoride is consistent with the polyvinylidene fluoride selection used in the prior art for 3D printing, for better illustration of the present invention and to provide a specific means of selection reference, the polyvinylidene fluoride is selected from the model FR906 having a molecular weight of 300000g/mol, a density of 1.79g/mol, and a melting point of 172 ℃.
Generally, before the selective laser sintering in step (2), the raw material needs to be dried, mainly to prevent the polyvinylidene fluoride from being affected by moisture during storage before use, and those skilled in the art can refer to the conventional usage of polyvinylidene fluoride to apply the method of the present invention after drying. In order to better illustrate the present invention and provide a reference embodiment, when the amount of polyvinylidene fluoride is less than 1000g under laboratory conditions, the drying is performed for 8-24 h at a temperature of 30-100 ℃.
Wherein, the flow auxiliary agent in the step (2) is a conventional flow auxiliary agent for selective laser sintering, and comprises nano silicon dioxide, talcum powder and the like.
Generally speaking, in the step (2), the polyvinylidene fluoride powder or the polyvinylidene fluoride/inorganic filler mixed powder is uniformly mixed with the flow aid, in order to uniformly disperse the flow aid in the polyvinylidene fluoride powder or the polyvinylidene fluoride/inorganic filler mixed powder to play a role in increasing the overall processing fluidity, when the dosage of the polyvinylidene fluoride is lower than 1000g under a laboratory condition, the polyvinylidene fluoride powder or the polyvinylidene fluoride/inorganic filler mixed powder is placed in a mixer after the flow aid is added, and is mixed for 3-5 min at the rotating speed of 800 r/min-2000 r/min.
It should be noted that, although the prior art also has a process scheme for 3D printing a polyvinylidene fluoride product, in order to more suitably perform the foaming treatment on the polyvinylidene fluoride product obtained by selective laser sintering in the subsequent step by the supercritical carbon dioxide kettle pressure foaming method, the inventor of the present invention confirms and defines the process parameters of selective laser sintering through comparative experiments. Wherein, the preheating temperature is lower than 140 ℃ to cause serious warping in the sintering process, thereby causing serious deformation of the final product, and the preheating temperature is higher than 180 ℃ to cause powder bed agglomeration to influence the precision and the definition of the sintered product, so that the powder is difficult to recover and clean; laser power lower than 10W can make internal pores larger, which is beneficial to later CO2But the interlayer strength of the product is lower, the laser power is higher than 40W, although the interior of the product is more compact, the CO is caused2The penetration is difficult, thereby affecting the piezoelectric performance of the polarized component.
It is worth mentioning that, a person skilled in the art can prepare PVDF-based piezoelectric foam parts with different specifications by a selective laser sintering technology, but in order to make the cell distribution of the piezoelectric foam more uniform during the foaming process, the solid structure thickness of the laser sintered part is preferably controlled to be 2-2.5 mm.
The inventor of the invention finds out through contrast experiments that when the laser sintering part prepared by selective laser sintering is used for supercritical carbon dioxide kettle pressure foaming treatment, the pressure is lower than 7MPa, which causes insufficient carbon dioxide diffusion, the content of beta crystals in polyvinylidene fluoride is lower, the number of cells is less, and the piezoelectric property of the final product is affected; pressures above 16MPa can affect the stability of the experimental apparatus. And the foaming temperature lower than 150 ℃ can cause the system strength to be too high, influence the diffusion of carbon dioxide in the material, and the foaming temperature higher than 170 ℃ can easily cause the cell wall strength to be too low, cause the collapse, and even cause the melting and degradation of the material. Therefore, the invention is based on experimental facts, the pressure of the foaming process in the step (3) is limited to be 7-16 MPa, and the foaming temperature is 150-170 ℃.
In particular, at the same temperature, the CO increases with the saturation pressure2The gas state is changed into the supercritical state, the solubility of the catalyst in a polyvinylidene fluoride matrix is greatly improved, and more CO is generated2The bubble nucleation effect is achieved, and the number of the bubbles is greatly increased; as saturation pressure continues to increase, further increase in blowing agent solubility promotes cell nucleation, but CO used for foaming2The total amount can not satisfy the growth of a large number of original nucleation points, so that the growth time of the cells is short, the size of the cells is small, and a small and dense cell structure is easy to obtain.
Under the same saturation pressure, when the temperature is increased, the melt strength of the system can be obviously reduced, the relatively low melt strength is beneficial to the growth of the existing bubble nucleus, and the size of the formed bubble is larger; but the melt strength also plays an important role in the stabilization stage of the cell structure, and when the foaming temperature is too high, the cell wall strength is low, and the external pressure cannot be borne, so that the cells collapse.
Further, in order to obtain a PVDF-based foamed part with appropriate cell density and cell size and better mechanical properties, the pressure of the foaming process in the step (3) is preferably 10-16 MPa, and the foaming temperature is preferably 160-170 ℃.
It is worth to be noted that, in the process of development, the inventor of the present invention also finds that, in the pressure maintaining process, the pressure maintaining temperature and time also have a great influence on the crystal form of the final product, and even influence on the final piezoelectric output performance. When the pressure maintaining temperature is more than 150 ℃ or the pressure maintaining time is more than 90min, the crystal form of the product obtained through infrared test is mostly gamma crystal form, so that the piezoelectric performance is not improved when the pressure maintaining temperature is too high or the pressure maintaining time is too long.
Therefore, in order to enable the piezoelectric foam of the final product to have the characteristics of excellent piezoelectric performance and easy use, the pressure maintaining time in the step (3) is 30-60 min, and the pressure maintaining temperature is 35-45 ℃; further preferably, the pressure maintaining time in the step (3) is 30-45 min, and the pressure maintaining temperature is 35-45 ℃.
In summary, in order to obtain piezoelectric foam with better piezoelectric output, the characteristics of small and uniform foam pore size and large foam pore density should be satisfied as much as possible, so that a larger mechanical deformation is generated when the piezoelectric foam is subjected to the same stress, and a certain mechanical strength is required, therefore, it is further preferable that the process parameters of the supercritical carbon dioxide kettle pressure foaming method in step (3) are as follows: the pressure in the foaming process is 10-16 MPa, the foaming temperature is 160-167 ℃, the pressure maintaining time is 30-45 min, and the pressure maintaining temperature is 35-45 ℃.
Tests show that according to the technical scheme of the invention, under the condition of not adding inorganic filler, the prepared PVDF-based piezoelectric foam part has the cell size of 60-105 mu m and the cell density of 2.2 multiplied by 10 at most6Per cm3The optimum value of the compression modulus is 0.98 MPa.
Tests show that according to the technical scheme of the invention, under the condition of adding the inorganic filler, the prepared PVDF-based piezoelectric foam part has the cell size of 30-90 mu m and the cell density of 1.2 multiplied by 10 at most7Per cm3The optimum value of the compression modulus is 1.44 MPa.
Generally speaking, the polarization in the step (4) is a conventional process step for preparing a piezoelectric product, in order to better illustrate the present invention, and to provide a preferred technical scheme, the polarization in the step (4) is performed in an oil bath, conductive silver paste is uniformly coated on two sides of the foam, then the foam is placed under an electrode column, and is completely soaked in a silicone oil bathtub at 80-100 ℃, the polarization voltage is slowly increased, and the leakage current is observed to prevent the foam from being broken down. In order to obtain the maximum boost piezoelectric output, the polarization voltage should be as high as possible, and the polarization time should be as long as possible, therefore, the process parameters of polarization in step (4) are preferably: the temperature is 80-90 ℃, the polarization voltage is 3-4 KV, and the polarization time is 30-60 min.
It is important to point out that the beta crystal form content of the polyvinylidene fluoride in the preparation process is further improved through the process parameter limitation of the supercritical carbon dioxide kettle pressure foaming method and the coordination with the selective laser sintering. The selective laser sintering process is limited and selected in the step (2), the temperature of the workpiece in the process does not reach the melting point of polyvinylidene fluoride, the beta crystal form cannot be converted to the more stable alpha crystal form, the content of the beta crystal form is kept to a certain extent, and the process conditions of the supercritical carbon dioxide kettle pressure foaming method are also strictly limited in the step (3), so that the laser sintering workpiece is equivalent to slowly and mechanically stretching the skeleton forming the cells due to the expansion of gas in the foaming process, the conversion to the beta crystal form is further promoted under the action of mechanical stretching, and the PVDF-based piezoelectric foam workpiece with higher content of the beta crystal form is obtained, the piezoelectric performance is further improved and is higher than the upper limit of the piezoelectric performance of the product prepared based on the traditional thermal forming mode.
According to the technical scheme of the invention, the prepared PVDF-based piezoelectric foam part is used for infrared and piezoelectric performance tests, and under the condition of not adding inorganic filler, the beta crystal form content is 76.2%, the beta crystal content is improved by nearly 30% compared with that of an unfoamed sintered part, the open-circuit voltage can be up to 7.8V, and the short-circuit current can be up to 100nA, which are respectively 3 times and 2 times of that of the unfoamed sintered part.
When the inorganic filler is 20 wt% of barium titanate, the beta crystal form content is 80.6%, the beta crystal form content is improved by nearly 40% compared with that of an unfoamed sintered product, the open-circuit voltage can be up to 20.9V, and the short-circuit current can be up to 262nA, which are respectively 5 times and 3 times of that of the unfoamed sintered product.
The invention has the following beneficial effects:
(1) the technical scheme of the invention is that a polyvinylidene fluoride piezoelectric foam product is prepared based on selective laser sintering and supercritical carbon dioxide foaming technologies, and the cell structure is optimized through the optimized combination of process conditions, so that the polyvinylidene fluoride piezoelectric foam with higher piezoelectric output and certain mechanical strength is obtained after polarization, and the defects that most of the existing piezoelectric parts are concentrated on a two-dimensional film, the composition structure is single, the flexibility is lacked, the output electric energy is small, and the stable energy storage is difficult are overcome.
(2) Because the invention adopts selective laser sintering as the forming method, the invention can design a complex structure and accurately control the appearance of an initial workpiece, and the special pore structure generated in the sintering process is beneficial to CO2Diffusion, the dwell time has been reduced than compression molding, has promoted production efficiency.
(3) The method of the invention adopts carbon dioxide as the foaming agent, is safe, environment-friendly and pollution-free, has no residue after foaming, can greatly reduce the final influence of the foaming agent, greatly improve the purity of the foam, and meet the fields of sensing, biomedicine and the like with strict requirements on impurity content.
(4) The technical scheme of the invention has mature process conditions, is suitable for continuous production and has excellent market popularization value.
Drawings
FIG. 1 is an electron microscope image of a laser sintered article prepared in step (2) of example 1 of the present invention.
FIG. 2 is a photograph of a sample of a laser sintered article (center) obtained in step (2) and a PVDF piezoelectric foam article (right) obtained in step (4) of example 1 of the present invention.
FIG. 3 is an electron microscope image of the cross section of a PVDF piezoelectric foam part prepared in example 1 of the present invention. Obviously, the PVDF piezoelectric foam part prepared by the technical scheme of the invention has uniform foam pore size and distribution.
FIG. 4 is a comparison graph of the laser sintered product obtained in step (2) and the PVDF foamed product obtained in step (3) in example 1 of the present invention obtained by infrared test, and it is clearly shown that the characteristic peak of the beta crystal form of the PVDF foamed product foamed in step (3) is 840cm-1The peak intensity is obviously increased, which shows that the content of the beta crystal form is increased.
Fig. 5 is a comparison graph of infrared tests of the PVDF foam product prepared in step (3) and the laser sintered product obtained in step (2) under different foaming temperatures in examples 2 to 5 of the present invention, and it is obvious that the content of β crystal in the product increases with the increase of the foaming temperature.
FIG. 6 is a graph showing the open circuit voltage of PVDF piezoelectric foam parts prepared in examples 2 to 5 of the present invention. In the figure, under the same conditions, the left line is before polarization in step (4), and the right line is the PVDF piezoelectric foam part obtained after polarization in step (4), so that the piezoelectric output is obviously further increased after polarization.
FIG. 7 is a diagram showing short-circuit current of PVDF piezoelectric foam parts prepared in examples 2 to 5 of the present invention. In the figure, under the same conditions, the left line is before polarization in step (4), and the right line is the PVDF piezoelectric foam part obtained after polarization in step (4), so that the piezoelectric output is obviously further increased after polarization.
FIG. 8 is a comparison graph of the infrared test of the PVDF foam product prepared in step (3) and the laser sintering product obtained in step (2) under different foaming pressure conditions in examples 1, 4, 6 to 7 of the invention, and it is obvious that the content of beta crystal in the product increases with the increase of the foaming pressure.
FIG. 9 is a graph showing open circuit voltages of the PVDF foam parts obtained in step (3) and the laser sintered parts obtained in step (2) in examples 1, 4, 6 to 7 of the present invention. In the figure, under the same conditions, the left line is before polarization in step (4), and the right line is the PVDF piezoelectric foam part obtained after polarization in step (4), so that the piezoelectric output is obviously further increased after polarization.
FIG. 10 is a short-circuit current diagram of the PVDF foam part prepared in step (3) and the laser sintered part obtained in step (2) in examples 1, 4, 6 to 7 of the present invention. In the figure, under the same conditions, the left line is before polarization in step (4), and the right line is the PVDF piezoelectric foam part obtained after polarization in step (4), so that the piezoelectric output is obviously further increased after polarization.
FIG. 11 is a graph of the energy storage application of the PVDF piezoelectric foam obtained in example 1 of the present invention, and it is clearly shown that the PVDF piezoelectric foam obtained can charge a 40 μ F50V capacitor to 3.51V within 275 s.
FIG. 12 shows BaTiO prepared in example 8 of the present invention3Open circuit voltage versus short circuit current plots for PVDF piezoelectric foam parts. It is evident that the output current and voltage increase significantly after the addition of the inorganic filler.
FIG. 13 shows BaTiO prepared in example 9 of the present invention3Open circuit voltage versus short circuit current plots for PVDF piezoelectric foam parts. It is evident that the output current and voltage increase significantly after the addition of the inorganic filler.
FIG. 14 shows BaTiO prepared in example 10 of the present invention3Open circuit voltage versus short circuit current plots for PVDF piezoelectric foam parts. It is evident that the output current and voltage increase significantly after the addition of the inorganic filler.
FIG. 15 shows BaTiO prepared in example 11 of the present invention3Open circuit voltage versus short circuit current plots for PVDF piezoelectric foam parts. It is evident that the output current and voltage increase significantly after the addition of the inorganic filler.
FIG. 16 shows BaTiO compounds prepared in examples 8, 9, 10 and 11 of the present invention3Energy storage application diagram of PVDF piezoelectric foam part, it is obvious that BaTiO is obtained3the/PVDF piezoelectric foam part can charge a 40 mu F50V capacitor to 4.98V in 180s at most.
Detailed Description
The invention is further illustrated by the following examples in conjunction with the accompanying drawings. It should be noted that the examples given are not to be construed as limiting the scope of the invention, and that those skilled in the art, on the basis of the teachings of the present invention, will be able to make numerous insubstantial modifications and adaptations of the invention without departing from its scope.
In the following examples and comparative examples, the sample was quenched after being immersed in liquid nitrogen for 8min for sample morphology analysis (INSPECT F, FEI, Japan), the quenched section was vacuum-sprayed with gold, and the powder morphology, the section morphology after SLS sintering, the section cell morphology, the density, and the like were observed by SEM at an acceleration voltage of 20kV during the test. Average cell diameter and cell density were calculated using the Nano-Measurer software. The calculation formula of the cell density is as follows:
Figure BDA0002897965940000081
where N is the number of cells in the SEM micrograph, A is the area of the micrograph, and M is the magnification factor.
FT-IR (Nicolet 6700 Fourier transform infrared spectrometer of Thermo Scientific company in USA) can determine different crystal forms and each crystal form content of PVDF, so that conversion of crystal forms in laser sintering and supercritical foaming processes can be judged. Testing a sample with the thickness of not more than 2mm in an ATR mode, wherein the scanning range is 4000-400 cm-1Scanning times of 32 times and resolution of 4cm-1. The relative beta phase fraction (F (beta)) is estimated according to Lambert-Beer's law and can be expressed by the following formula
Figure BDA0002897965940000082
A alpha and A beta are samples at 766cm respectively-1And 840cm-1The absorption peak height of the sample, K alpha and K beta are the absorption coefficient of the sample at the corresponding wave number respectively, and K alpha is 6.1 multiplied by 104cm2mol-1，Kβ＝7.7×104cm2mol-1。
DSC (American TA Q20) can measure the crystallinity and melting point change of PVDF in the sintering process and the supercritical foaming process. Test procedure approximately 7mg of sample was loaded into a crucible, and the temperature was raised from 40 ℃ to 220 ℃ and then lowered to 40 ℃ at a rate of 10 ℃/min, and the crystallinity Xc was calculated as follows:
Figure BDA0002897965940000083
ΔH100％melting enthalpy, Δ H, for complete crystallization of polymersmThe enthalpy of fusion is determined by DSC. For PVDF,. DELTA.H100％＝105J/g。
The piezoelectric performance test (NTI AG HS 01-37X 166) is to coat the conductive silver adhesive on both sides of the test wafer uniformlyAnd after drying, loading high-voltage polarization in a silicon oil bath by using a corona polarization instrument. After polarization, double-sided conductive aluminum foils are adhered to the front and back sides of the workpiece, and the workpiece is connected to an iron plate of an experimental device and is positioned right opposite to the impact head. Passing through a linear motor at 5m/s2The sheet is impacted, the generated electric signal is amplified and output to a computer, and finally the open-circuit voltage and the short-circuit current of the workpiece can be obtained. Note that the open-circuit voltage in the following embodiments does not correspond to the maximum value in the open-circuit voltage diagram in the drawings of the specification, but is obtained by subtracting the minimum value from the maximum value in the drawings, and the short-circuit current corresponds to the maximum value shown in the drawings.
In the following examples and comparative examples, polyvinylidene fluoride was chosen as type FR906, which has a molecular weight of 300000g/mol, a density of 1.79g/mol and a melting point of 172 ℃.
It is noted that the electron microscope images and the infrared test images in the drawings are selected from the PVDF foam product obtained in the step (3) of the example as a sample for testing, because the PVDF piezoelectric foam product is permeated with oil after being polarized in the step (4), which is not beneficial for testing, but it should be noted that the influence of polarization on the micro-morphology and the infrared test result is negligible.
Example 1
The embodiment comprises the following steps in parts by weight:
(1) crushing a polyvinylidene fluoride raw material into polyvinylidene fluoride powder with the particle size of 60-250 mu m, and drying for later use;
(2) 100 parts of polyvinylidene fluoride powder for standby in the step (1) and a flow additive of nano SiO20.1 part of the mixture is uniformly mixed, and the product is prepared by a selective laser sintering process to obtain a laser sintering product; wherein, the technological parameters of the selective laser sintering are as follows: preheating temperature is 155 ℃, laser scanning speed is 9600mm/s, laser scanning power is 40W, laser scanning times are 1 time, laser scanning interval is 0.1-0.3 mm, and powder layer spreading thickness is 0.1 mm;
(3) preparing the laser sintering part obtained in the step (2) into a PVDF foam part by adopting a supercritical carbon dioxide kettle pressure foaming method; wherein, the supercritical carbon dioxide kettle pressure foaming method comprises the following process parameters: the pressure in the foaming process is 16MPa, the foaming temperature is 165 ℃, the pressure maintaining time is 30min, and the pressure maintaining temperature is 45 ℃;
(4) polarizing the PVDF foam part obtained in the step (3) to obtain a PVDF piezoelectric foam part; wherein, the polarization technological parameters are as follows: the temperature is 80 ℃, the polarization voltage is 4KV, and the polarization time is 30 min.
The PVDF piezoelectric foam part finally obtained is a test sample with the thickness of 3mm, and through testing, the average diameter of cells is 65.20 mu m, and the cell density is 2.2 multiplied by 106Per cm3The compression modulus is 0.98MPa, the beta crystal form content is 76.2%, the crystallinity is 47.2%, the maximum open-circuit voltage can reach 6.5V, the maximum short-circuit current can reach 85nA, the maximum open-circuit voltage after polarization can reach 7.8V, and the maximum short-circuit current can reach 102 nA.
Example 2
The embodiment comprises the following steps in parts by weight:
(1) crushing a polyvinylidene fluoride raw material into polyvinylidene fluoride powder with the particle size of 60-250 mu m, and drying for later use;
(2) 100 parts of polyvinylidene fluoride powder for standby in the step (1) and a flow additive of nano SiO20.1 part of the mixture is uniformly mixed, and the product is prepared by a selective laser sintering process to obtain a laser sintering product; wherein, the technological parameters of the selective laser sintering are as follows: preheating temperature is 155 ℃, laser scanning speed is 9600mm/s, laser scanning power is 40W, laser scanning times are 1 time, laser scanning interval is 0.1-0.3 mm, and powder layer spreading thickness is 0.1 mm;
(3) preparing the laser sintering part obtained in the step (2) into a PVDF foam part by adopting a supercritical carbon dioxide kettle pressure foaming method; wherein, the supercritical carbon dioxide kettle pressure foaming method comprises the following process parameters: the pressure in the foaming process is 14MPa, the foaming temperature is 161 ℃, the pressure maintaining time is 30min, and the pressure maintaining temperature is 45 ℃;
(4) polarizing the PVDF foam part obtained in the step (3) to obtain a PVDF piezoelectric foam part; wherein, the polarization technological parameters are as follows: the temperature is 80 ℃, the polarization voltage is 4KV, and the polarization time is 30 min.
The PVDF piezoelectric foam part finally obtained is a test sample with the thickness of 3mm, and tests show that the average diameter of the cells is 61.70 microns, the wall thickness of the cells is 40.41 microns, the compression modulus is 8.85MPa, the beta crystal form content is 59.4%, the crystallinity is 40.6%, the maximum open-circuit voltage can reach 2.1V, and the maximum short-circuit current can reach 42 nA. After polarization, the maximum open-circuit voltage can reach 3.3V, and the maximum short-circuit current can reach 50nA
Example 3
The embodiment comprises the following steps in parts by weight:
(1) crushing a polyvinylidene fluoride raw material into polyvinylidene fluoride powder with the particle size of 60-250 mu m, and drying for later use;
(2) 100 parts of polyvinylidene fluoride powder for standby in the step (1) and a flow additive of nano SiO20.1 part of the mixture is uniformly mixed, and the product is prepared by a selective laser sintering process to obtain a laser sintering product; wherein, the technological parameters of the selective laser sintering are as follows: preheating temperature is 155 ℃, laser scanning speed is 9600mm/s, laser scanning power is 40W, laser scanning times are 1 time, laser scanning interval is 0.1-0.3 mm, and powder layer spreading thickness is 0.1 mm;
(3) preparing the laser sintering part obtained in the step (2) into a PVDF foam part by adopting a supercritical carbon dioxide kettle pressure foaming method; wherein, the supercritical carbon dioxide kettle pressure foaming method comprises the following process parameters: the pressure in the foaming process is 14MPa, the foaming temperature is 163 ℃, the pressure maintaining time is 30min, and the pressure maintaining temperature is 45 ℃;
(4) polarizing the PVDF foam part obtained in the step (3) to obtain a PVDF piezoelectric foam part; wherein, the polarization technological parameters are as follows: the temperature is 80 ℃, the polarization voltage is 4KV, and the polarization time is 30 min.
The PVDF piezoelectric foam piece is a test sample with the thickness of 3mm, and through tests, the average diameter of the cells is 67.64 microns, the wall thickness of the cells is 32.32 microns, the compression modulus is 6.13MPa, the beta crystal form content is 61.1%, the crystallinity is 43.8%, the maximum open-circuit voltage can reach 3.5V, and the maximum short-circuit current can reach 51 nA. After polarization, the maximum open-circuit voltage can reach 4.4V, and the maximum short-circuit current can reach 60nA
Example 4
The embodiment comprises the following steps in parts by weight:
(1) crushing a polyvinylidene fluoride raw material into polyvinylidene fluoride powder with the particle size of 60-250 mu m, and drying for later use;
(2) 100 parts of polyvinylidene fluoride powder for standby in the step (1) and a flow additive of nano SiO20.1 part of the mixture is uniformly mixed, and the product is prepared by a selective laser sintering process to obtain a laser sintering product; wherein, the technological parameters of the selective laser sintering are as follows: preheating temperature is 155 ℃, laser scanning speed is 9600mm/s, laser scanning power is 40W, laser scanning times are 1 time, laser scanning interval is 0.1-0.3 mm, and powder layer spreading thickness is 0.1 mm;
(3) preparing the laser sintering part obtained in the step (2) into a PVDF foam part by adopting a supercritical carbon dioxide kettle pressure foaming method; wherein, the supercritical carbon dioxide kettle pressure foaming method comprises the following process parameters: the pressure in the foaming process is 14MPa, the foaming temperature is 165 ℃, the pressure maintaining time is 30min, and the pressure maintaining temperature is 45 ℃;
(4) polarizing the PVDF foam part obtained in the step (3) to obtain a PVDF piezoelectric foam part; wherein, the polarization technological parameters are as follows: the temperature is 80 ℃, the polarization voltage is 4KV, and the polarization time is 30 min.
The PVDF piezoelectric foam piece is a test sample with the thickness of 3mm, and through tests, the average diameter of the cells is 76.97 microns, the wall thickness of the cells is 18.82 microns, the compression modulus is 2.87MPa, the beta crystal form content is 61.6%, the crystallinity is 47.1%, the maximum open-circuit voltage can reach 4.5V, and the maximum short-circuit current can reach 72 nA. After polarization, the maximum open-circuit voltage can reach 5.5V, and the maximum short-circuit current can reach 80nA
Example 5
The embodiment comprises the following steps in parts by weight:
(1) crushing a polyvinylidene fluoride raw material into polyvinylidene fluoride powder with the particle size of 60-250 mu m, and drying for later use;
(2) 100 parts of polyvinylidene fluoride powder for standby in the step (1) and a flow additive of nano SiO20.1 part of the mixture is uniformly mixed, and the product is prepared by a selective laser sintering process to obtain a laser sintering product; wherein, the technological parameters of the selective laser sintering are as follows: preheating temperature of 155 ℃, laser scanning speed of 9600mm/s, laser scanning power of 40W and laser scanning times1 time, the laser scanning interval is 0.1-0.3 mm, and the powder spreading layer is 0.1mm thick;
(3) preparing the laser sintering part obtained in the step (2) into a PVDF foam part by adopting a supercritical carbon dioxide kettle pressure foaming method; wherein, the supercritical carbon dioxide kettle pressure foaming method comprises the following process parameters: the pressure in the foaming process is 14MPa, the foaming temperature is 167 ℃, the pressure maintaining time is 30min, and the pressure maintaining temperature is 45 ℃;
(4) polarizing the PVDF foam part obtained in the step (3) to obtain a PVDF piezoelectric foam part; wherein, the polarization technological parameters are as follows: the temperature is 80 ℃, the polarization voltage is 4KV, and the polarization time is 30 min.
The PVDF piezoelectric foam part finally obtained is a test sample with the thickness of 3mm, and through tests, the average diameter of the cells is 138.77 microns, the wall thickness of the cells is 8.19 microns, the compression modulus is 2.12MPa, the beta crystal form content is 69.5%, the crystallinity is 48.1%, the maximum open-circuit voltage can reach 2.5V, and the maximum short-circuit current can reach 21 nA. After polarization, the maximum open-circuit voltage can reach 3.4V, and the maximum short-circuit current can reach 30nA
Example 6
The embodiment comprises the following steps in parts by weight:
(1) crushing a polyvinylidene fluoride raw material into polyvinylidene fluoride powder with the particle size of 60-250 mu m, and drying for later use;
(2) 100 parts of polyvinylidene fluoride powder for standby in the step (1) and a flow additive of nano SiO20.1 part of the mixture is uniformly mixed, and the product is prepared by a selective laser sintering process to obtain a laser sintering product; wherein, the technological parameters of the selective laser sintering are as follows: preheating temperature is 155 ℃, laser scanning speed is 9600mm/s, laser scanning power is 40W, laser scanning times are 1 time, laser scanning interval is 0.1-0.3 mm, and powder layer spreading thickness is 0.1 mm;
(3) preparing the laser sintering part obtained in the step (2) into a PVDF foam part by adopting a supercritical carbon dioxide kettle pressure foaming method; wherein, the supercritical carbon dioxide kettle pressure foaming method comprises the following process parameters: the pressure in the foaming process is 10MPa, the foaming temperature is 165 ℃, the pressure maintaining time is 30min, and the pressure maintaining temperature is 45 ℃;
(4) polarizing the PVDF foam part obtained in the step (3) to obtain a PVDF piezoelectric foam part; wherein, the polarization technological parameters are as follows: the temperature is 80 ℃, the polarization voltage is 4KV, and the polarization time is 30 min.
The PVDF piezoelectric foam part finally obtained is a test sample with the thickness of 3mm, and the test sample shows that the average diameter of cells is 102.30 mu m, and the cell density is 7.1 multiplied by 105Per cm3The compression modulus is 6.96MPa, the beta crystal form content is 52.2%, the crystallinity is 42.2%, the maximum open-circuit voltage can reach 2.5V, and the maximum short-circuit current can reach 40 nA. After polarization, the maximum open-circuit voltage can reach 3.5V, and the maximum short-circuit current can reach 50nA
Example 7
The embodiment comprises the following steps in parts by weight:
(1) crushing a polyvinylidene fluoride raw material into polyvinylidene fluoride powder with the particle size of 60-250 mu m, and drying for later use;
(2) 100 parts of polyvinylidene fluoride powder for standby in the step (1) and a flow additive of nano SiO20.1 part of the mixture is uniformly mixed, and the product is prepared by a selective laser sintering process to obtain a laser sintering product; wherein, the technological parameters of the selective laser sintering are as follows: preheating temperature is 155 ℃, laser scanning speed is 9600mm/s, laser scanning power is 40W, laser scanning times are 1 time, laser scanning interval is 0.1-0.3 mm, and powder layer spreading thickness is 0.1 mm;
(3) preparing the laser sintering part obtained in the step (2) into a PVDF foam part by adopting a supercritical carbon dioxide kettle pressure foaming method; wherein, the supercritical carbon dioxide kettle pressure foaming method comprises the following process parameters: the pressure in the foaming process is 12MPa, the foaming temperature is 165 ℃, the pressure maintaining time is 30min, and the pressure maintaining temperature is 45 ℃;
(4) polarizing the PVDF foam part obtained in the step (3) to obtain a PVDF piezoelectric foam part; wherein, the polarization technological parameters are as follows: the temperature is 80 ℃, the polarization voltage is 4KV, and the polarization time is 30 min.
The PVDF piezoelectric foam part finally obtained is a test sample with the thickness of 3mm, and through testing, the average diameter of cells is 89.23 mu m, and the cell density is 8.3 multiplied by 105Per cm3The compression modulus is 5.94MPa, the beta crystal form content is 58.9 percent, the crystallinity is 45.9 percent, and the open circuit voltage is the highestThe high voltage can reach 3.8V, and the short-circuit current can reach 52nA at most. After polarization, the maximum open-circuit voltage can reach 4.5V, and the maximum short-circuit current can reach 60 nA.
Example 8
The embodiment comprises the following steps in parts by weight:
(1) crushing a polyvinylidene fluoride raw material into polyvinylidene fluoride powder with the particle size of 60-250 mu m, drying, and selecting BaTiO with the particle size of 500 mu m on the market3Mixing the powder with polyvinylidene fluoride powder uniformly to obtain BaTiO3PVDF mixed powder, in which BaTiO3The addition amount of the powder is 5 wt% of the total;
(2) the BaTiO obtained in the step (1) is treated3100 parts of PVDF mixed powder and flow assistant nano SiO20.1 part of the mixture is uniformly mixed, and the product is prepared by a selective laser sintering process to obtain a laser sintering product; wherein, the technological parameters of the selective laser sintering are as follows: preheating temperature is 155 ℃, laser scanning speed is 9600mm/s, laser scanning power is 40W, laser scanning times are 1 time, laser scanning interval is 0.1-0.3 mm, and powder layer spreading thickness is 0.1 mm;
(3) preparing the laser sintering part obtained in the step (2) by adopting a supercritical carbon dioxide kettle pressure foaming method to obtain BaTiO3PVDF foam parts; wherein, the supercritical carbon dioxide kettle pressure foaming method comprises the following process parameters: the pressure in the foaming process is 16MPa, the foaming temperature is 165 ℃, the pressure maintaining time is 30min, and the pressure maintaining temperature is 45 ℃;
(4) the BaTiO obtained in the step (3)3Polarizing the PVDF foam part to obtain BaTiO3PVDF piezoelectric foam parts; wherein, the polarization technological parameters are as follows: the temperature is 80 ℃, the polarization voltage is 4KV, and the polarization time is 30 min.
Finally obtaining BaTiO3The PVDF piezoelectric foam part is a test sample with the thickness of 3mm, and the test shows that the average diameter of cells is 59.9 mu m, and the cell density is 3.7 multiplied by 106Per cm3The compression modulus is 3.31MPa, the beta crystal form content is 76.5%, the crystallinity is 31.3%, the maximum open-circuit voltage after polarization can reach 12.1V, and the maximum short-circuit current can reach 194 nA.
Example 9
The embodiment comprises the following steps in parts by weight:
(1) crushing a polyvinylidene fluoride raw material into polyvinylidene fluoride powder with the particle size of 60-250 mu m, drying, and selecting BaTiO with the particle size of 500 mu m on the market3Mixing the powder with polyvinylidene fluoride powder uniformly to obtain BaTiO3PVDF mixed powder, in which BaTiO3The addition amount of the powder is 10 wt% of the total;
(2) the BaTiO obtained in the step (1) is treated3100 parts of PVDF mixed powder and flow assistant nano SiO20.1 part of the mixture is uniformly mixed, and the product is prepared by a selective laser sintering process to obtain a laser sintering product; wherein, the technological parameters of the selective laser sintering are as follows: preheating temperature is 155 ℃, laser scanning speed is 9600mm/s, laser scanning power is 40W, laser scanning times are 1 time, laser scanning interval is 0.1-0.3 mm, and powder layer spreading thickness is 0.1 mm;
(3) preparing the laser sintering part obtained in the step (2) by adopting a supercritical carbon dioxide kettle pressure foaming method to obtain BaTiO3PVDF foam parts; wherein, the supercritical carbon dioxide kettle pressure foaming method comprises the following process parameters: the pressure in the foaming process is 16MPa, the foaming temperature is 165 ℃, the pressure maintaining time is 30min, and the pressure maintaining temperature is 45 ℃;
(4) polarizing the PVDF foam part obtained in the step (3) to obtain BaTiO3PVDF piezoelectric foam parts; wherein, the polarization technological parameters are as follows: the temperature is 80 ℃, the polarization voltage is 4KV, and the polarization time is 30 min.
Finally obtaining BaTiO3The PVDF piezoelectric foam part is a test sample with the thickness of 3mm, and the test shows that the average diameter of cells is 50.5 mu m, and the cell density is 8.6 multiplied by 106Per cm3The compression modulus is 2.67MPa, the beta crystal form content is 80.5%, the crystallinity is 36.1%, the maximum open-circuit voltage after polarization can reach 13.6V, and the maximum short-circuit current can reach 228 nA.
Example 10
The embodiment comprises the following steps in parts by weight:
(1) crushing a polyvinylidene fluoride raw material into polyvinylidene fluoride powder with the particle size of 60-250 mu m, drying, and selecting the polyvinylidene fluoride powder in the marketSelling BaTiO of 500 mu m particle size3Mixing the powder with polyvinylidene fluoride powder uniformly to obtain BaTiO3PVDF mixed powder, in which BaTiO3The addition amount of the powder is 15 wt% of the total;
(2) the BaTiO obtained in the step (1) is treated3100 parts of PVDF mixed powder and flow assistant nano SiO20.1 part of the mixture is uniformly mixed, and the product is prepared by a selective laser sintering process to obtain a laser sintering product; wherein, the technological parameters of the selective laser sintering are as follows: preheating temperature is 155 ℃, laser scanning speed is 9600mm/s, laser scanning power is 40W, laser scanning times are 1 time, laser scanning interval is 0.1-0.3 mm, and powder layer spreading thickness is 0.1 mm;
(3) preparing the laser sintering part obtained in the step (2) by adopting a supercritical carbon dioxide kettle pressure foaming method to obtain BaTiO3PVDF foam parts; wherein, the supercritical carbon dioxide kettle pressure foaming method comprises the following process parameters: the pressure in the foaming process is 16MPa, the foaming temperature is 165 ℃, the pressure maintaining time is 30min, and the pressure maintaining temperature is 45 ℃;
(4) polarizing the PVDF foam part obtained in the step (3) to obtain BaTiO3PVDF piezoelectric foam parts; wherein, the polarization technological parameters are as follows: the temperature is 80 ℃, the polarization voltage is 4KV, and the polarization time is 30 min.
Finally obtaining BaTiO3The PVDF piezoelectric foam part is a test sample with the thickness of 3mm, and the test shows that the average diameter of cells is 39.3 mu m, and the cell density is 1 multiplied by 107Per cm3The compression modulus is 3.25MPa, the beta crystal form content is 79.8%, the crystallinity is 33.1%, the maximum open-circuit voltage after polarization can reach 14.8V, and the maximum short-circuit current can reach 254 nA.
Example 11
The embodiment comprises the following steps in parts by weight:
(1) crushing a polyvinylidene fluoride raw material into polyvinylidene fluoride powder with the particle size of 60-250 mu m, drying, and selecting BaTiO with the particle size of 500 mu m on the market3Mixing the powder with polyvinylidene fluoride powder uniformly to obtain BaTiO3PVDF mixed powder, in which BaTiO3The addition amount of the powder is 20 wt% of the total;
(2) the BaTiO obtained in the step (1) is treated3100 parts of PVDF mixed powder and flow assistant nano SiO20.1 part of the mixture is uniformly mixed, and the product is prepared by a selective laser sintering process to obtain a laser sintering product; wherein, the technological parameters of the selective laser sintering are as follows: preheating temperature is 155 ℃, laser scanning speed is 9600mm/s, laser scanning power is 40W, laser scanning times are 1 time, laser scanning interval is 0.1-0.3 mm, and powder layer spreading thickness is 0.1 mm;
(3) preparing the laser sintering part obtained in the step (2) by adopting a supercritical carbon dioxide kettle pressure foaming method to obtain BaTiO3PVDF foam parts; wherein, the supercritical carbon dioxide kettle pressure foaming method comprises the following process parameters: the pressure in the foaming process is 16MPa, the foaming temperature is 165 ℃, the pressure maintaining time is 30min, and the pressure maintaining temperature is 45 ℃;
(4) polarizing the PVDF foam part obtained in the step (3) to obtain BaTiO3PVDF piezoelectric foam parts; wherein, the polarization technological parameters are as follows: the temperature is 80 ℃, the polarization voltage is 4KV, and the polarization time is 30 min.
Finally obtaining BaTiO3The PVDF piezoelectric foam part is a test sample with the thickness of 3mm, and the test shows that the average diameter of cells is 31.6 mu m, and the cell density is 1.2 multiplied by 107Per cm3The compression modulus is 1.44MPa, the beta crystal form content is 80.6%, the crystallinity is 43.6%, the maximum open-circuit voltage after polarization can reach 20.9V, and the maximum short-circuit current can reach 262 nA.
Example 12
The embodiment comprises the following steps in parts by weight:
(1) crushing a polyvinylidene fluoride raw material into polyvinylidene fluoride powder with the particle size of 60-250 mu m, and drying for later use;
(2) uniformly mixing 100 parts of the polyvinylidene fluoride powder prepared in the step (1) and 0.5 part of a flow assistant talcum powder, and performing a selective laser sintering process to obtain a laser sintered product; wherein, the technological parameters of the selective laser sintering are as follows: preheating temperature is 160 ℃, laser scanning speed is 9600mm/s, laser scanning power is 40W, laser scanning times are 2 times, laser scanning interval is 0.1-0.3 mm, and powder layer spreading thickness is 0.3 mm;
(3) preparing the laser sintering part obtained in the step (2) into a PVDF foam part by adopting a supercritical carbon dioxide kettle pressure foaming method; wherein, the supercritical carbon dioxide kettle pressure foaming method comprises the following process parameters: the pressure in the foaming process is 16MPa, the foaming temperature is 170 ℃, the pressure maintaining time is 60min, and the pressure maintaining temperature is 45 ℃;
(4) polarizing the PVDF foam part obtained in the step (3) to obtain a PVDF piezoelectric foam part; wherein, the polarization technological parameters are as follows: the temperature is 100 ℃, the polarization voltage is 4KV, and the polarization time is 60 min.
Example 13
The embodiment comprises the following steps in parts by weight:
(1) crushing a polyvinylidene fluoride raw material into polyvinylidene fluoride powder with the particle size of 60-250 mu m, and drying for later use;
(2) uniformly mixing 100 parts of the polyvinylidene fluoride powder prepared in the step (1) and 0.5 part of a flow assistant talcum powder, and performing a selective laser sintering process to obtain a laser sintered product; wherein, the technological parameters of the selective laser sintering are as follows: preheating temperature is 150 ℃, and laser scanning speed is 8000mm/s
The laser scanning power is 10W, the laser scanning times are 1 time, the laser scanning interval is 0.1-0.3 mm, and the powder layer spreading thickness is 0.2 mm;
(3) preparing the laser sintering part obtained in the step (2) into a PVDF foam part by adopting a supercritical carbon dioxide kettle pressure foaming method; wherein, the supercritical carbon dioxide kettle pressure foaming method comprises the following process parameters: the pressure in the foaming process is 7MPa, the foaming temperature is 150 ℃, the pressure maintaining time is 30min, and the pressure maintaining temperature is 35 ℃;
(4) polarizing the PVDF foam part obtained in the step (3) to obtain a PVDF piezoelectric foam part; wherein, the polarization technological parameters are as follows: the temperature is 80 ℃, the polarization voltage is 3KV, and the polarization time is 40 min.
Comparative example 1
The comparative example comprises the following steps in parts by weight:
(1) crushing a polyvinylidene fluoride raw material into polyvinylidene fluoride powder with the particle size of 60-250 mu m, and drying for later use;
(2) 100 parts of polyvinylidene fluoride powder for later use in the step (1) and a flow aid (nano SiO)2)0.1 part of the mixture is uniformly mixed, and the product is prepared by a selective laser sintering process to obtain a laser sintering product; wherein, the technological parameters of the selective laser sintering are as follows: preheating temperature 155 ℃, laser scanning speed 9600mm/s, laser scanning power 40W, laser scanning times of 1 time, laser scanning interval of 0.1mm and powder layer thickness of 0.1 mm;
(3) preparing the laser sintering part obtained in the step (2) into a PVDF foam part by adopting a supercritical carbon dioxide kettle pressure foaming method; wherein, the supercritical carbon dioxide kettle pressure foaming method comprises the following process parameters: the pressure in the foaming process is 6MPa, the foaming temperature is 165 ℃, the pressure maintaining time is 30min, and the pressure maintaining temperature is 45 ℃;
at the moment the pressure is less than CO2Reaching the supercritical state, and being incapable of preparing PVDF piezoelectric foam.
Comparative example 2
The comparative example comprises the following steps in parts by weight:
(1) crushing a polyvinylidene fluoride raw material into polyvinylidene fluoride powder with the particle size of 60-250 mu m, and drying for later use;
(2) 100 parts of polyvinylidene fluoride powder for later use in the step (1) and a flow aid (nano SiO)2)0.1 part of the mixture is uniformly mixed, and the product is prepared by a selective laser sintering process to obtain a laser sintering product; wherein, the technological parameters of the selective laser sintering are as follows: preheating temperature 155 ℃, laser scanning speed 9600mm/s, laser scanning power 40W, laser scanning times of 1 time, laser scanning interval of 0.1mm and powder layer thickness of 0.1 mm;
(3) preparing the laser sintering part obtained in the step (2) into a PVDF foam part by adopting a supercritical carbon dioxide kettle pressure foaming method; wherein, the supercritical carbon dioxide kettle pressure foaming method comprises the following process parameters: the pressure in the foaming process is 18MPa, the foaming temperature is 165 ℃, the pressure maintaining time is 30min, and the pressure maintaining temperature is 45 ℃;
at this time, the kettle pressure foaming equipment is unstable, temperature rise treatment is difficult to perform, and danger is easy to occur.
Comparative example 3
The comparative example comprises the following steps in parts by weight:
(1) crushing a polyvinylidene fluoride raw material into polyvinylidene fluoride powder with the particle size of 60-250 mu m, and drying for later use;
(2) 100 parts of polyvinylidene fluoride powder for later use in the step (1) and a flow aid (nano SiO)2)0.1 part of the mixture is uniformly mixed, and the product is prepared by a selective laser sintering process to obtain a laser sintering product; wherein, the technological parameters of the selective laser sintering are as follows: preheating temperature 155 ℃, laser scanning speed 9600mm/s, laser scanning power 40W, laser scanning times of 1 time, laser scanning interval of 0.1mm and powder layer thickness of 0.1 mm;
(3) preparing the laser sintering part obtained in the step (2) into a PVDF foam part by adopting a supercritical carbon dioxide kettle pressure foaming method; wherein, the supercritical carbon dioxide kettle pressure foaming method comprises the following process parameters: the pressure in the foaming process is 16MPa, the foaming temperature is 145 ℃, the pressure maintaining time is 30min, and the pressure maintaining temperature is 45 ℃;
(4) polarizing the PVDF foam part obtained in the step (3) to obtain a PVDF piezoelectric foam part; wherein, the polarization technological parameters are as follows: the temperature is 80 ℃, the polarization voltage is 4KV, and the polarization time is 30 min.
At the moment, the foaming temperature is too low, the laser sintering part is only partially foamed, most parts of the laser sintering part are not foamed, the mould is difficult to be completely filled after foaming, and the dimensional precision is reduced.
Comparative example 4
The comparative example comprises the following steps in parts by weight:
(1) crushing a polyvinylidene fluoride raw material into polyvinylidene fluoride powder with the particle size of 60-250 mu m, and drying for later use;
(2) 100 parts of polyvinylidene fluoride powder for later use in the step (1) and a flow aid (nano SiO)2)0.1 part of the mixture is uniformly mixed, and the product is prepared by a selective laser sintering process to obtain a laser sintering product; wherein, the technological parameters of the selective laser sintering are as follows: preheating temperature 155 ℃, laser scanning speed 9600mm/s, laser scanning power 40W, laser scanning times of 1 time, laser scanning interval of 0.1mm and powder layer thickness of 0.1 mm;
(3) preparing the laser sintering part obtained in the step (2) into a PVDF foam part by adopting a supercritical carbon dioxide kettle pressure foaming method; wherein, the supercritical carbon dioxide kettle pressure foaming method comprises the following process parameters: the pressure in the foaming process is 16MPa, the foaming temperature is 175 ℃, the pressure maintaining time is 30min, and the pressure maintaining temperature is 45 ℃;
at this point, the foaming temperature is already higher than the melting point of PVDF, and the part is completely melted.

Claims (8)

1. A method for preparing a PVDF-based piezoelectric foam part based on selective laser sintering is characterized by comprising the following steps in parts by weight:
(1) preparing polyvinylidene fluoride powder suitable for selective laser sintering or polyvinylidene fluoride/inorganic filler mixed powder;
(2) uniformly mixing 100 parts of polyvinylidene fluoride powder or polyvinylidene fluoride/inorganic filler mixed powder prepared in the step (1) with 0.1-0.5 part of a flow aid, and performing a selective laser sintering process to obtain a finished product, namely a laser sintered product; wherein, the technological parameters of the selective laser sintering are as follows: preheating temperature is 150-160 ℃, laser scanning speed is 8000-9600 mm/s, laser scanning power is 10-40W, laser scanning times are 1-2 times, laser scanning distance is 0.1-0.3 mm, and powder spreading layer thickness is 0.1-0.3 mm;
(3) preparing the laser sintering part obtained in the step (2) into a PVDF-based foam part by adopting a supercritical carbon dioxide kettle pressure foaming method; wherein, the supercritical carbon dioxide kettle pressure foaming method comprises the following process parameters: the pressure in the foaming process is 7-16 MPa, the foaming temperature is 150-170 ℃, the pressure maintaining time is 30-60 min, and the pressure maintaining temperature is 35-45 ℃;
(4) and (4) polarizing the PVDF-based foamed part obtained in the step (3) at the temperature of 80-100 ℃ to obtain the PVDF-based piezoelectric foamed part.
2. The method of claim 1, further comprising: the inorganic filler in the step (1) mainly comprises BaTiO3At least one of PZT, ZnO and boron nitride.
3. The method of claim 2, further comprising: in the step (1), the inorganic filler is BaTiO3And the addition amount of the inorganic filler is 3-20 wt% of the total amount.
4. The method of claim 1, further comprising: in the step (2), the flow aid is nano silicon dioxide or talcum powder.
5. The method of claim 1, further comprising: and (3) controlling the thickness of the solid structure of the laser sintering part in the step (2) to be 2-2.5 mm.
6. The method of claim 1, further comprising: in the step (3), the pressure in the foaming process is 10-16 MPa, and the foaming temperature is 160-170 ℃.
7. The method of claim 1, further comprising: the supercritical carbon dioxide kettle pressure foaming method in the step (3) has the following process parameters: the pressure in the foaming process is 7-16 MPa, the foaming temperature is 150-170 ℃, the pressure maintaining time is 30-45 min, and the pressure maintaining temperature is 35-45 ℃.
8. The method of claim 7, further comprising: the supercritical carbon dioxide kettle pressure foaming method in the step (3) has the following process parameters: the pressure in the foaming process is 10-16 MPa, the foaming temperature is 160-167 ℃, the pressure maintaining time is 30-45 min, and the pressure maintaining temperature is 35-45 ℃.
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