CN114276632B

CN114276632B - PVDF material with three-dimensional size, high reduction degree and high beta crystal content as well as preparation method and application of PVDF material

Info

Publication number: CN114276632B
Application number: CN202111608836.6A
Authority: CN
Inventors: 张楚虹; 贺丽蓉; 韩铖; 王琪
Original assignee: Sichuan University
Current assignee: Sichuan University
Priority date: 2021-12-27
Filing date: 2021-12-27
Publication date: 2022-10-04
Anticipated expiration: 2041-12-27
Also published as: CN114276632A

Abstract

The invention discloses a PVDF material with three-dimensional size, high reduction degree and high beta crystal content, a preparation method and application thereof, wherein the preparation method comprises the following steps: (1) PVDF and riboflavin are dissolved in a solvent according to the mass ratio of 0.05-0.2; (2) refrigerating and preserving the mixed solution to obtain mixed ink; (3) And (3) placing the mixed ink into a DIW 3D printer for printing and molding, then placing the mixed ink into water for solvent exchange, and then performing freeze drying to obtain the ink. The raw materials used by the method are wide in source and low in cost, the beta crystal form-PVDF with high three-dimensional size and high reduction degree and high purity is obtained, the beta crystal content is 95%, the three-dimensional structure forming is controllable, the piezoelectric conversion performance of the piezoelectric device is improved, and the product manufactured by the method can be used as a piezoelectric mechanical energy collecting device, a piezoelectric sensor, a piezoelectric driver and the like and is used in the fields of new energy, pressure sensing, artificial intelligence and the like.

Description

PVDF material with three-dimensional size, high reduction degree and high beta crystal content as well as preparation method and application of PVDF material

Technical Field

The invention belongs to the technical field of 3D printing material modification, and particularly relates to a PVDF material with three-dimensional size, high reduction degree and high beta crystal content, and a preparation method and application thereof.

Background

3D printing has become the leading technology for manufacturing complex architecture. Due to the designability and simplicity of 3D printing technology, it has gradually been integrated into various fields including electronics, intelligent robots, sensors, and the like.

Among existing 3D printing technologies, such as Direct Ink Writing (DIW), fused deposition modeling, stereolithography, etc., in terms of material development, DIW is one of the most common additive manufacturing methods to create complex three-dimensional shapes by forming inks with controlled rheological properties. The geometry is built layer by layer using a computer controlled motion to fill a dispenser with ink having shear thinning properties. To date, DIW has been successfully printed with various materials, such as metals, polymers, ceramics. In the DIW technique, ink control is a difficult problem due to its special rheological properties.

PVDF is currently the most common commercial piezoelectric polymer. These polymers are stable at room temperature, easy to process, chemically inert, biocompatible, and have higher piezoelectric conversion efficiency than other piezoelectric polymers. These properties make PVDF have great potential in the field of flexible electronics.

The properties of PVDF are directly influenced by its structure, mainly depending on its crystalline form. PVDF exists in five crystal forms, the most common of which is alpha and beta phases, and the F atom and the H atom of alpha-PVDF are alternately arranged on two sides, the dipole moments are opposite in direction, and no electric activity exists. The F atoms in the beta-PVDF are concentrated on one side of a carbon chain, the dipoles are perpendicular to the main chain and have the same direction, and the crystal form is the crystal form with the highest electrical activity of the PVDF. However, the thermodynamically most stable conformation is the alpha phase. Therefore, increasing the beta phase content is a key issue in utilizing PVDF as a piezoelectric material. Many techniques have been shown to increase the proportion of the beta phase in PVDF by inducing dipole alignment, such as stretching, high electric field polarization, thermal annealing.

The high-pressure and high-speed shearing action generated by DIW 3D printing on the extruded filaments promotes the arrangement of PVDF dipoles and induces a beta phase; secondly, the printing process is carried out at room temperature, so that the beta phase is effectively prevented from being converted to the non-piezoelectric phase (alpha) at high temperature, and the stability of the piezoelectric phase is facilitated. However, the current DIW 3D printing high-crystal PVDF technology has the following problems: (1) PVDF inks tend to be difficult to maintain in shape after extrusion; (2) After printing and molding, under the condition of drying at room temperature, the solvent is volatilized to cause the warping deformation and shrinkage of the workpiece, and the molding quality is poor; (3) The current DIW 3D printing process can only obtain a PVDF film, and cannot construct a three-dimensional structure.

Disclosure of Invention

Aiming at the prior art, the invention provides a PVDF material with three-dimensional size, high reduction degree and high beta crystal content, a preparation method and application thereof, and aims to solve the problems that the shape of a PVDF ink extruded by the existing printing method is difficult to maintain, a workpiece is easy to warp, deform and shrink, the molding quality is poor, a three-dimensional structure cannot be constructed and the like.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows: the printing method of the PVDF material with the three-dimensional size, the high reduction degree and the high beta crystal content comprises the following steps:

(1) Dissolving PVDF and riboflavin in a solvent according to a mass ratio of 0.05-0.2;

(2) Refrigerating and preserving the mixed solution to obtain mixed ink;

(3) And (3) placing the mixed ink into a DIW 3D printer for printing and molding, then placing the mixed ink into water for solvent exchange for 11-13 h, and then carrying out freeze drying to obtain the ink.

According to the invention, by means of the riboflavin modified PVDF material, strong dipole-dipole and hydrogen bond interaction exists between polar groups such as hydroxyl and amino of the riboflavin and a-CF bond of the PVDF, so that the high beta crystal content of the PVDF can be effectively induced, and the high beta crystal content PVDF-based functional device can be obtained by DIW 3D printing. In the regulation and control of the ink, the interaction also effectively improves the rheological property of the ink, promotes the polymer to increase the viscosity and quickly recovers the macroscopic elastic modulus after extruding a needle, and the shape is kept after molding.

In addition, the post-treatment modes of solvent exchange and freeze drying are adopted, so that the problems of warping deformation and shrinkage of PVDF are effectively solved, and the structure of a printed part is controllable; on the other hand, solvent exchange may lose some of the riboflavin, but does not affect the β -crystal content of the PVDF and the final piezoelectric properties of the printed article.

On the basis of the technical scheme, the invention can be further improved as follows.

Further, the mass ratio of PVDF to riboflavin in the mixed solution was 0.08.

Further, the solvent is N, N dimethylformamide or a mixture of N, N dimethylformamide and acetone.

Further, the cold storage was performed at 0 ℃ overnight.

Furthermore, the printing temperature of the printing forming is 20-30 ℃, the diameter of the printing nozzle is 0.6-0.8 mm, and the printing speed is 5-15 mm/s.

Furthermore, the freeze drying temperature is-40 to-50 ℃, the pressure is-5 Pa, and the time is 24 hours.

The invention also provides the PVDF material which is prepared by the printing method and has three-dimensional size, high reduction degree and high beta crystal content.

The invention also provides application of the PVDF material with three-dimensional size, high reduction degree and high beta crystal content in preparation of a piezoelectric device.

The piezoelectric device includes a mechanical energy collecting device, a sensor, a driver, and the like.

The beneficial effects of the invention are:

1. according to the invention, strong dipole-dipole and hydrogen bond interaction exists between polar groups such as hydroxyl and amino of riboflavin and-CF bond of PVDF, so that beta crystal in PVDF material can be effectively induced to form, and DIW 3D printing is realized to obtain a PVDF-based functional device with high beta crystal content.

2. 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 riboflavin is used as a green modifier, is environment-friendly and can be recycled.

3. The ink used for printing has excellent rheological property, and the dimensional stability of a workpiece is greatly improved.

4. The beta-crystal form-PVDF (beta crystal content 95%) with high three-dimensional size and high reduction degree and high purity is obtained, and the piezoelectric conversion performance of the piezoelectric device is greatly improved.

5. The three-dimensional structure of the beta-crystal form-PVDF with high three-dimensional size, high reduction degree and high purity, which is obtained by the invention, can be molded controllably, and the designability of the structure of a workpiece is greatly improved.

6. The beta crystal form-PVDF with high three-dimensional size, high reduction degree and high purity, which is obtained by the invention, is well suitable for DIW 3D printing intelligent manufacturing technology, and products manufactured by the method can be used as piezoelectric mechanical energy collecting devices, piezoelectric sensors, piezoelectric drivers and the like, and are used in the fields of new energy, pressure sensing, artificial intelligence and the like.

Drawings

FIGS. 1 and 2 are rheological tests of pure PVDF with riboflavin-added PVDF;

FIG. 3 is a DSC measurement of pure PVDF with riboflavin-added PVDF;

FIG. 4 is a DIW 3D infrared test of pure PVDF printed and riboflavin added PVDF;

FIG. 5 is a graphical representation of a shaped sample of PVDF/VB2 without and with post-treatment;

FIG. 6 is a functional representation of the capacitance of a DIW 3D printed riboflavin-added PVDF device;

fig. 7 is a piezoelectric voltage test of the PVDF piezoelectric device with riboflavin added by FDM 3D printing.

Detailed Description

The following examples are provided to illustrate specific embodiments of the present invention.

Example 1

A preparation method of PVDF material with three-dimensional size, high reduction degree and high beta crystal content comprises the following steps:

(1) Uniformly dispersing 625g of riboflavin in 17ml of N, N-Dimethylformamide (DMF) solvent, then pouring 5g of PVDF powder into the solvent, placing the mixture into a double-planet dispersing machine, and stirring the mixture for 10min at the rotating speed of 2000rpm to obtain a mixed solution;

(2) Storing the mixed solution at 0 ℃ overnight to obtain mixed ink;

(3) And (2) putting the mixed ink into a DIW 3D printer, extruding and molding the mixed ink through a printing needle head according to a preset model, wherein the printing temperature range is 25 ℃, the diameter of a printing nozzle is 0.6mm, the printing speed is 10mm/s, then putting the mixed ink into water for solvent exchange for 12 hours, and then carrying out freeze drying for 24 hours at-45 ℃ and-5 Pa to obtain the ink.

Example 2

A preparation method of a PVDF material with three-dimensional size, high reduction degree and high beta crystal content comprises the following steps:

(1) Uniformly dispersing 1000g of riboflavin in 10ml of N, N-Dimethylformamide (DMF) and 7ml of Acetone (AR) solvent, pouring 5g of PVDF powder, placing the PVDF powder into a double-planet dispersing machine, and stirring at the rotating speed of 2000rpm for 10min to obtain a mixed solution;

(2) Storing the mixed solution at 0 ℃ overnight to obtain mixed ink;

(3) And (2) putting the mixed ink into a DIW 3D printer, extruding and molding the mixed ink through a printing needle head according to a preset model, wherein the printing temperature range is 20 ℃, the diameter of a printing nozzle is 0.6mm, the printing speed is 5mm/s, then putting the mixed ink into water for solvent exchange for 11 hours, and then freeze-drying the mixed ink at-40 ℃ and-5 Pa for 24 hours to obtain the ink.

Example 3

(1) Uniformly dispersing 250g of riboflavin in 17ml of N, N-Dimethylformamide (DMF) solvent, then pouring 5g of PVDF powder, keeping the temperature at 60 ℃, and stirring at the rotating speed of 520r/min for 6 hours to obtain a mixed solution;

(2) Storing the mixed solution at 0 ℃ overnight to obtain mixed ink;

(3) And (2) putting the mixed ink into a DIW 3D printer, performing extrusion molding through a printing needle head according to a preset model, wherein the used printing temperature range is 30 ℃, the diameter of a printing nozzle is 0.8mm, the printing speed is 15mm/s, then putting the mixed ink into water for solvent exchange for 13h, and then performing freeze drying for 24h at-50 ℃ and-5 Pa to obtain the ink.

Example 4

(1) Uniformly dispersing 500g of riboflavin in 10ml of N, N-Dimethylformamide (DMF) and 7ml of Acetone (AR) solvent, then pouring 5g of PVDF powder, keeping the temperature at 60 ℃, and stirring for 6 hours at the rotating speed of 520r/min to obtain a mixed solution;

(2) Storing the mixed solution at 0 ℃ overnight to obtain mixed ink;

(3) And (2) putting the mixed ink into a DIW 3D printer, extruding and molding the mixed ink through a printing needle head according to a preset model, wherein the printing temperature range is 25 ℃, the diameter of a printing nozzle is 0.7mm, the printing speed is 10mm/s, then putting the mixed ink into water for solvent exchange for 12 hours, and then carrying out freeze drying for 24 hours at-45 ℃ and-5 Pa to obtain the ink.

In examples 1 to 4, the model of the double planetary disperser was AR-100 (Thinky). The DIW 3D printer adopts a professional desktop DIW desktop printer, and the model is Allevi 3 (Alleviinc).

Comparative example 1

The molded sample was dried in a fume hood at room temperature, and the rest of the procedure was the same as in example 1.

Comparative example 2

The molded sample was dried in a fume hood at room temperature, and the rest of the procedure was the same as in example 2.

Comparative example 3

The molded sample was dried in a fume hood at room temperature, and the rest of the procedure was the same as in example 3.

Comparative example 4

The molded sample was dried in a fume hood at room temperature, and the rest of the procedure was the same as in example 4.

Experimental example 1

Rheological characterization of the ink formulated in example 1: performing rheological analysis by using a rotational rheometer (TA) to determine the viscosity (eta), the yield stress (tau) and the elastic modulus (G') of the sample; performing thermal analysis by Differential Scanning Calorimetry (DSC), and measuring the melting point (Tm) and the crystallinity (χ c) (the mass of the sample is about 7mg, the temperature range is 30-200 ℃, the heating rate is 10 ℃/min, and the sample is in a nitrogen atmosphere); the crystal structure of PVDF (Nicolet is50, thermo Fisher, USA) was identified by infrared spectroscopy (FT-IR) with a resolution of 4cm ^-1 Analysis by adopting ATR mode is 4000-400 cm ^-1 Representative bands within the range, and the phase content was calculated quantitatively.

FIG. 1 and FIG. 2, FIG. 3, FIG. 4, FIG. 5 are graphs of TA, DSC, FTIR test results and molded samples, the TA results showing that the viscosity of the modified PVDF increases with the addition of riboflavin, and the fluidity of the PVDF increases significantly with the addition of riboflavin with increasing shear; the yield stress and elastic modulus of PVDF added with riboflavin are increased. The DSC results show that DSC pure PVDF has a crystallinity χ c of 68.95%, while at a riboflavin content of 2wt%, the crystallinity χ c is around 74.69%, increasing by about 5.74%; FTIR results show that the beta phase content of pure PVDF without a modifier is 72.44% after DIW 3D printing, while the beta phase content of PVDF modified by riboflavin can reach 95.34%, thus proving that the DIW 3D printing and molding of PVDF with high beta crystal content can be realized under the combined action of the shear force of DIW printing and the riboflavin modification. The molded samples showed shrinkage and deformation of the samples when dried at room temperature; after post-treatment with solvent exchange and freeze-drying, the sample retained the size and shape of the printed pattern intact.

Experimental example 2

The part obtained by DIW 3D printing of the riboflavin-modified PVDF of example 1 was impacted by a linear motor, and the alternating current generated by piezoelectric transformation was converted into direct current by a bridge rectifier, then a 1uf50V capacitor was charged, and the capacitor was charged to more than 4V 400s after rectification (see FIG. 6). Therefore, the DIW 3D printing technology can be used for preparing a self-polarized high-beta crystal form-PVDF energy harvesting piezoelectric device, and has excellent piezoelectric conversion performance.

Experimental example 3

Characterization of piezoelectric properties

Piezoelectric performance testing was performed using a linear motor and Labview system, i.e., the DIW 3D printed unmodified pure PVDF, example 1 riboflavin modified PVDF, was fitted with electrodes on both sides, and the linear motor applied a force to it, which was converted into a visible electrical signal by conducting a charge to an electrometer (Keithley 6514) via a wire connection.

As a result, as shown in fig. 7, after DIW 3D printing, the open circuit voltage of pure PVDF was 2.90V, and the open circuit voltage of riboflavin-modified PVDF could reach 17.8V, which is increased by 6.14 times. Therefore, the invention can realize DIW 3D printing and forming of PVDF with high beta crystal content by riboflavin modification, and the piezoelectric conversion performance is greatly improved.

Experimental example 4

The piezoelectric conversion performance of the existing DIW 3D printed PVDF-based piezoelectric device of the document and the modified PVDF-based piezoelectric device prepared in example 1 of the present invention were compared, and the results are shown in table 1 below:

table 1 comparison table of piezoelectric conversion performance of modified DIW piezoelectric device of the present invention with literature

PVDF/IL, PVDF/BTO and PVDF/GP are ionic liquids respectively, barium titanate and graphene are used as beta-crystal inducers to be compounded with a PVDF matrix to be used as a product for DIW printing, and PVDF/VB2 is the PVDF modified by riboflavin.

While the present invention has been described in detail with reference to the embodiments, it should not be construed as limited to the scope of the patent. Various modifications and alterations that may occur to those skilled in the art without the benefit of this disclosure are intended to be covered by this patent.

Claims

1. A preparation method of a PVDF material with three-dimensional size, high reduction degree and high beta crystal content is characterized by comprising the following steps:

(1) PVDF and riboflavin are co-dissolved in a solvent according to the mass ratio of 0.05-0.2;

(2) Refrigerating and preserving the mixed solution to obtain mixed ink;

2. The production method according to claim 1, characterized in that: the mass ratio of PVDF to riboflavin in the mixed solution is 0.08.

3. The method of claim 1, wherein: the solvent is N, N dimethylformamide or a mixture of N, N dimethylformamide and acetone.

4. The method of claim 1, wherein: the cold storage is storage at 0 ℃ overnight.

5. The production method according to claim 1, characterized in that: the printing temperature of the printing forming is 20-30 ℃, the diameter of the printing nozzle is 0.6-0.8 mm, and the printing speed is 5-15 mm/s.

6. The method of claim 1, wherein: the freeze drying temperature is-40 to-50 ℃, the pressure is-5 Pa, and the time is 24 hours.

7. The PVDF material which is prepared by the preparation method of any one of claims 1-6 and has high three-dimensional size, high reduction degree and high beta crystal content.

8. Use of the PVDF material of claim 7 having both a three-dimensional high degree of reduction and a high beta crystal content in the preparation of a piezoelectric device.