A left-handed polylactic acid piezoelectric film and its preparation method

Abstract

The present invention relates to the field of piezoelectric materials, and more particularly to a method for preparing a L-polylactic acid (PLA) piezoelectric film. The method comprises the following steps: dissolving a certain proportion of L-polylactic acid and vitamin B2 to form a pre-solution; providing a hydroxyapatite solution as a dispersion; adding the dispersion to the pre-solution to form a mixed solution; applying the mixed solution to form a film to be treated on a substrate; and annealing the film to be treated to form a piezoelectric film. The present invention also provides a L-polylactic acid (PLA) piezoelectric film. The L-polylactic acid (PLA) piezoelectric film and its preparation method provided by the present invention address the low piezoelectric coefficient problem of L-polylactic acid (PLA) piezoelectric films in the prior art.

Description

Technical field

[0002] The present invention relates to the technical field of piezoelectric materials, in particular to a left-handed polylactic acid piezoelectric film and a preparation method thereof. [Background Technology]

[0004] Piezoelectric materials are materials that can convert mechanical energy into electrical energy. Among them, piezoelectric polymers, especially polylactic acid piezoelectric polymers, have been widely used in sensors, chips, energy engineering, environmental purification, flaw detection, wearables, etc. due to their strong piezoelectric properties, unique flexibility and high temperature resistance. Traditional polymer piezoelectric materials, such as vinylidene fluoride piezoelectric films, will significantly reduce their piezoelectric properties due to the influence of temperature when the temperature exceeds 100°C. Polylactic acid piezoelectric films have a wider application field than other polymer piezoelectric films due to their high temperature resistance. However, the piezoelectric coefficient of existing left-handed polylactic acid piezoelectric films is often low. Therefore, it is of great significance to seek a method to improve the piezoelectric coefficient of left-handed polylactic acid piezoelectric films. [Summary of the invention]

[0006] In order to solve the problem of low piezoelectric coefficient of left-handed polylactic acid piezoelectric film in the prior art, the present invention provides a left-handed polylactic acid piezoelectric film and a preparation method thereof.

[0007] In order to solve the above technical problems, the present invention provides a method for preparing a left-handed polylactic acid piezoelectric film, which comprises the following steps:

[0008] Dissolving a certain proportion of poly (L-lactic acid) and vitamin B2 to form a pre-solution;

[0009] providing a hydroxyapatite solution as a dispersion;

[0010] adding the dispersion into the pre-solution to form a mixed solution;

[0011] forming a thin film to be treated on a substrate by applying the mixed solution;

[0012] The film to be processed is annealed to form the piezoelectric film.

[0013] Preferably, the mass ratio of poly(L-lactic acid) to vitamin B2 in the pre-solution is in the range of 3-10.

[0014] Preferably, the solvent for dissolving the poly(L-lactic acid) and the vitamin B2 is any one of chloroform, butanone, N,N-dimethylpyrrolidone, and N,N-dimethylamide.

[0015] Preferably, the ratio of poly(L-lactic acid) to vitamin B2 to hydroxyapatite in the mixed solution is 1: (0.01-0.3): (0.01-0.2).

[0016] Preferably, the forming of the pre-solution comprises the following steps: stirring the poly(L-lactic acid) and the vitamin B2 in a solvent at a first stirring speed for a first time, wherein the first stirring speed is 300-400 r / min, and the first time is 2-4 hours.

[0017] Preferably, the forming of the mixed solution specifically includes the following steps: stirring the pre-solution at a second stirring speed while continuously adding the dispersion; after the dispersion is added, stirring at a third stirring speed for a third time and then letting it stand, and the second stirring speed is lower than the third stirring speed.

[0018] Preferably, forming the thin film to be processed on the substrate by applying the mixed solution specifically includes forming a wet film on the substrate by coating, and then drying to form the thin film to be processed.

[0019] Preferably, the annealing treatment specifically includes the following steps: performing annealing treatment on the film to be treated at a temperature of 130-150° C. to obtain the piezoelectric film.

[0020] In order to solve the above technical problems, the present invention also provides a left-handed polylactic acid piezoelectric film, which is prepared using the above-mentioned piezoelectric film preparation method.

[0021] Preferably, the ratio of poly (L-lactic acid) to vitamin B2 to hydroxyapatite in the piezoelectric film is 1: (0.01-0.3): (0.01-0.2).

[0022] Compared with the prior art, the left-handed polylactic acid piezoelectric film and its preparation method provided by the present invention have the following beneficial effects:

[0023] 1. An embodiment of the present invention provides a method for preparing a left-handed polylactic acid piezoelectric film, which includes the following steps: dissolving a certain proportion of left-handed polylactic acid and vitamin B2 to form a pre-solution; providing a hydroxyapatite solution as a dispersion; adding the dispersion to the pre-solution to form a mixed solution; forming the mixed solution into a film to be treated on a substrate; annealing the film to be treated to form a piezoelectric film. Through this preparation method, a left-handed polylactic acid-vitamin B2-hydroxyapatite piezoelectric film is finally obtained. Based on the above method, a stronger hydrogen bond can be formed between the left-handed polylactic acid, vitamin B2, and hydroxyapatite, so that the C=O dipole of the left-handed polylactic acid is highly oriented, and its piezoelectric properties and mechanical strength are further improved. A piezoelectric film with a piezoelectric performance exceeding 18 pc / N can be obtained, which improves the piezoelectric performance of existing piezoelectric films.

[0024] 2. The mass ratio of L-polylactic acid and vitamin B2 in the pre-solution of the embodiment of the present invention is in the range of 3-10; the L-polylactic acid: vitamin B2: hydroxyapatite in the mixed solution is 1: (0.01-0.3): (0.01-0.2). The specific limitation of the raw materials improves the piezoelectric properties of the L-polylactic acid-vitamin B2-hydroxyapatite piezoelectric film, thereby enabling the L-polylactic acid-vitamin B2-hydroxyapatite piezoelectric film to have a wider range of practical applications.

[0025] 3. The solvent for dissolving poly (L-lactic acid) and vitamin B2 is any one of chloroform, butanone, N,N-dimethylpyrrolidone, and N,N-dimethylamide. Organic solvents are easy to dissolve poly (L-lactic acid) and are easy to volatilize.

[0026] 4. The pretreatment of the embodiment of the present invention includes the following steps: forming a pre-solution includes the following steps: stirring L-polylactic acid and vitamin B2 in a solvent at a first stirring speed for a first time, the first stirring speed is 300-400r / min, and the first time is 2-4 hours. The pretreatment makes the mixing of L-polylactic acid and vitamin B2 more complete.

[0027] 5. The stirring and degassing process of the embodiment of the present invention includes the following steps: forming a mixed solution specifically includes the following steps: stirring the pre-solution at a second stirring speed while continuously adding the dispersion liquid; after the dispersion liquid is added, stirring at a third stirring speed for a third time and then standing, the second stirring speed is lower than the third stirring speed, and the hydroxyapatite is more fully dispersed in the pre-solution by stirring the mixed solution.

[0028] 6. In the embodiment of the present invention, the mixed solution is formed on the substrate to form a thin film to be treated, specifically comprising forming a wet film on the substrate by coating, and then drying to form the thin film to be treated. The uniformity of the wet film is ensured by scraping, making the surface of the wet film smoother. At the same time, scraping can also prevent the appearance of air bubbles in the wet film, further improving the flatness of the piezoelectric film, and making the thickness and flatness of the piezoelectric film better.

[0029] 7. The annealing process in the embodiment of the present invention specifically includes the following steps: annealing the film to be treated at a temperature of 130-150°C to obtain a piezoelectric film. The annealing process promotes the crystallization of the L-polylactic acid, improving the piezoelectric properties of the film. Annealing also enhances the mechanical properties of the L-polylactic acid piezoelectric film, allowing the material to withstand greater deformation, indirectly enhancing its piezoelectric properties. Furthermore, the films produced by this preparation method have a wide range of thicknesses and are suitable for a wide range of applications.

[0030] 8. The embodiment of the present invention further provides a left-handed polylactic acid piezoelectric film, which has the same beneficial effects as the above-mentioned piezoelectric film and will not be described in detail here.

Brief Description of the Drawings

[0032] Figure 1 This is a flow chart of the method for preparing a left-handed polylactic acid piezoelectric film provided by the first embodiment of the present invention.

[0033] Figure 2 This is a specific flow chart of forming a mixed solution in the method for preparing a left-handed polylactic acid piezoelectric film provided by the first embodiment of the present invention.

[0034] Figure 3 30° C. is a response voltage diagram of the left-handed polylactic acid piezoelectric film in the second embodiment of the present invention.

[0035] Figure 4 3 is a response voltage diagram of the left-handed polylactic acid piezoelectric film at 60° C. in the second embodiment of the present invention.

[0036] Figure 5 3 is a response voltage diagram of the left-handed polylactic acid piezoelectric film at 90° C. in the second embodiment of the present invention.

[0037] Figure 6 1 is a response voltage diagram of the left-handed polylactic acid piezoelectric film at 120° C. in the second embodiment of the present invention. [Specific implementation method]

[0039] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and implementation examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0040] In the embodiments provided herein, it should be understood that "B corresponding to A" means that B is associated with A and B can be determined based on A. However, it should also be understood that determining B based on A does not mean determining B based solely on A; B can also be determined based on A and / or other information.

[0041] It should be understood that references to "one embodiment" or "an embodiment" throughout this specification mean that specific features, structures, or characteristics associated with the embodiment are included in at least one embodiment of the present invention. Therefore, the phrases "in one embodiment" or "in an embodiment" appearing throughout this specification do not necessarily refer to the same embodiment. Furthermore, these specific features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. Those skilled in the art should also be aware that the embodiments described in this specification are all optional embodiments, and the actions and modules involved are not necessarily required for the present invention.

[0042] In various embodiments of the present invention, it should be understood that the size of the serial numbers of the above-mentioned processes does not necessarily mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0043] The flow charts and block diagrams in the accompanying drawings of the present invention illustrate the possible implementation architecture, functions and operations of the systems, methods and computer program products according to various embodiments of the present application. In this regard, each box in the flow chart or block diagram can represent a module, program segment or a part of code, and the module, program segment or a part of code contains one or more executable instructions for realizing the specified logical function. It should also be noted that in some alternative implementation schemes, the functions marked in the box can also occur in a different order than those marked in the accompanying drawings. For example, two boxes represented in succession can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, which is determined based on the functions involved. It should be noted that each box in the block diagram and / or flow chart, and the combination of the boxes in the block diagram and / or flow chart can be implemented by a dedicated hardware-based system that performs the specified function or operation, or can be implemented by a combination of dedicated hardware and computer instructions.

[0044] See also Figure 1 The first embodiment of the present invention provides a method for preparing a left-handed polylactic acid piezoelectric film, which comprises the following steps:

[0045] Step S1, dissolving a certain proportion of poly (L-lactic acid) and vitamin B2 to form a pre-solution;

[0046] Step S2, providing a hydroxyapatite solution as a dispersion liquid;

[0047] Step S3, adding the dispersion liquid to the pre-solution to form a mixed solution;

[0048] Step S4, forming a thin film to be processed on the substrate by applying the mixed solution;

[0049] Step S5: performing annealing treatment on the film to be processed to form a piezoelectric film.

[0050] Understandably, by this preparation method, a left-handed polylactic acid-vitamin B2-hydroxyapatite piezoelectric film is finally obtained. Based on the above method, a stronger hydrogen bond can be formed between left-handed polylactic acid, vitamin B2 and hydroxyapatite, so that the C=O dipole of left-handed polylactic acid is highly oriented, further promoting the crystallization of left-handed polylactic acid, and ensuring that the left-handed polylactic acid piezoelectric film has good high temperature resistance, its piezoelectric properties and mechanical strength are further improved. In addition, the simultaneous dissolution of hydroxyapatite, left-handed polylactic acid and vitamin B2 will cause the problem of excessive solution viscosity. Therefore, by dissolving hydroxyapatite alone to prepare a dispersion, the problem of excessive simultaneous dissolution solution viscosity is solved.

[0051] In the above-mentioned step S1, the mass ratio of left-handed polylactic acid and vitamin B2 in the pre-solution ranges from 3 to 10. Alternatively, the mass ratio of left-handed polylactic acid and vitamin B2 can also range from 3 to 5, 3 to 6.66, 3 to 8, 4 to 9 or 6.66 to 10. Specifically, the mass ratio of left-handed polylactic acid and vitamin B2 can also be 3, 5, 6.66, 8, 9 or 10. It is understandable that the hydroxyl groups and oxygen-containing functional groups on the surface of vitamin B2 hydrogen bond with the ester carbonyl groups in polylactic acid, promote the ester carbonyl C=O dipole orientation, and thus improve its piezoelectric properties.

[0052] Furthermore, in step S1, a solvent is selected to dissolve the poly(L-lactic acid) and vitamin B2. The solvent is an organic solvent, and the solvent is any one of chloroform, butanone, N,N-dimethylpyrrolidone, and N,N-dimethylamide. Specifically, the solvent is chloroform. As can be understood, chloroform is easy to dissolve the poly(L-lactic acid) and is easily volatile.

[0053] Preferably, in the above-mentioned step S1, the left-handed polylactic acid and vitamin B2 are first mixed and then a solvent is added to dissolve them, and the pre-solution is pretreated simultaneously during the dissolution. Pre-mixing can make the left-handed polylactic acid and vitamin B2 more uniform, which is convenient for the subsequent dissolution. The pre-treatment comprises the following steps: the left-handed polylactic acid and vitamin B2 are dissolved in chloroform and ultrasonically cleaned using an ultrasonic cleaning device. After completing the ultrasonic cleaning, the left-handed polylactic acid and vitamin B2 are stirred for a first time at a first stirring speed. It is understandable that ultrasonic cleaning causes the insoluble impurities in the pre-solution to settle, and after ultrasonic cleaning, the dirt is filtered and separated, thereby achieving the removal of impurities in the pre-solution. At the same time, ultrasonic cleaning has a fast cleaning speed and a good cleaning effect. Wherein, the first stirring speed is 300-500r / min, and the first stirring time is 2-4 hours. Preferably, the first stirring speed is 400r / min, and the stirring time is 3 hours. By stirring, the left-handed polylactic acid and vitamin B2 are more evenly dispersed in the solvent chloroform.

[0054] In step S2, hydroxyapatite is dissolved in an organic solvent to form a dispersion. Optionally, the organic solvent is any one of chloroform, butanone, N,N-dimethylpyrrolidone, and N,N-dimethylamide. Preferably, the organic solvent is chloroform. Furthermore, the dissolved dispersion can be subjected to a crushing treatment. The crushing treatment specifically involves treating the dispersion with an ultrasonic crusher for 20-30 minutes. It is understood that the crushing treatment allows the hydroxyapatite to be more evenly dispersed in the chloroform.

[0055] In step S3, the ratio of poly(L-lactic acid) to vitamin B2 to hydroxyapatite in the mixed solution is 1:(0.01-0.3):(0.01-0.2). Specifically, the ratio of poly(L-lactic acid) to vitamin B2 to hydroxyapatite can also be 1:0.01:0.01, 1:0.15:0.05, 1:0.15:0.15, 1:0.03:0.2, 1:0.3:0.05, or 1:0.3:0.2. Preferably, the ratio of poly(L-lactic acid) to vitamin B2 to hydroxyapatite is 1:0.15:0.15. Understandably, the amount of vitamin B2 added is not less than the amount of hydroxyapatite added. Adding a large amount of reactant later will cause uneven dispersion. Therefore, the above method chooses to add the dispersion prepared by dissolving hydroxyapatite to the pre-solution formed by dissolving L-polylactic acid and vitamin B2, making the dispersion of the reactants in the solution more uniform, further improving the piezoelectric performance of the film product. At the same time, the optimal mixing ratio obtained through experimental comparison can make the prepared piezoelectric material solution have a higher piezoelectric material coefficient after crystallization, thereby making the piezoelectric film have a wider range of practical applications.

[0056] Preferably, combined Figure 1 and Figure 2 In the above step S3, adding the dispersion liquid to the pre-solution to form a mixed solution specifically includes the following steps:

[0057] S31, stirring the pre-solution at a second stirring speed while continuously adding the dispersion liquid;

[0058] S32, after the dispersion is added, stirring is performed at a third stirring speed for a third time and then allowed to stand.

[0059] In step S31, the second stirring speed is 200-300 r / min. Preferably, the second stirring speed is 250 r / min. It is understood that the pre-solution is stirred at the second stirring speed for a second time, which is determined by the amount of the dispersion. When the dispersion is added, stirring at the second stirring speed is completed. By stirring the pre-solution at the second stirring speed and continuously adding the dispersion to the pre-solution, the phenomenon of agglomeration and uneven dispersion caused by the addition of hydroxyapatite and vitamin B2 is effectively prevented.

[0060] In step S32, the third stirring speed is 300-400 r / min, and the stirring time is 2-4 hours. Preferably, the third stirring speed is 400 r / min, and the stirring time is 3 hours. By stirring the pre-solution at the third stirring speed, the hydroxyapatite is more fully dispersed in the pre-solution.

[0061] Preferably, the solution is allowed to stand for 1-2 hours after stirring, preferably, the standing time is 1 hour. By standing the solution after the third stirring under a certain pressure, the foam generated by the mixed solution under stirring can be removed, thereby achieving degassing of the mixed solution, so that the piezoelectric material solution has a uniform texture when crystallizing into a piezoelectric material, without cavities caused by bubbles, and the piezoelectric coefficient is increased.

[0062] It should be noted that the second stirring speed is lower than the third stirring speed. If the second stirring speed is too high, the dispersion liquid will splash when the dispersion liquid is added, resulting in waste of the dispersion liquid. The third stirring speed is used to stir the mixed solution after the dispersion liquid is added. The purpose of stirring is to mix the dispersion liquid and the pre-solution more evenly. That is, if the third stirring speed is too slow, the dispersion liquid and the pre-solution will mix unevenly, while if it is too fast, the amount of bubbles in the mixed solution will increase, affecting the piezoelectric performance of the piezoelectric film.

[0063] Optionally, in step S4, the mixed solution is applied to form a thin film to be treated on a substrate by coating, forming a wet film on the substrate, and then drying to form a thin film to be treated. The substrate includes any one of ITO (indium tin oxide) glass, silicon wafer, copper foil, and aluminum plate. The coating method includes any one of spin coating, spray coating, and full coating. Specifically, the coating method is blade coating, and the substrate is a flexible copper foil. Furthermore, the specific steps of coating are to adjust the scale of the scraper to 330μm-440μm; slowly and evenly drip the prepared left-handed polylactic acid-vitamin B2-hydroxyapatite mixed solution onto the blade edge, and after dripping a sufficient amount of the mixed solution, the scraper is scraped at a scraping speed of 10-30mm / s to form a left-handed polylactic acid wet film of uniform thickness on the flexible copper foil. It can be understood that the scraping speed can also be 10-25mm / s, 10-20mm / s, 15-25mm / s, or 20-25mm / s. Preferably, the scraping speed is 20 mm / s. By controlling the scraping speed, the mixed solution is distributed more evenly on the flexible copper foil. In addition, the prepared mixed solution is slowly and evenly dripped onto the blade edge to ensure the uniformity of the wet film while preventing air bubbles from forming in the wet film, thereby improving the flatness of the wet film.

[0064] Furthermore, in the above step S4, the drying process includes the following specific steps: vacuum drying the wet film formed on the flexible copper foil and the flexible copper foil to form a dry film; taking out the dry film and drying it with hot air to form a dried film.

[0065] It is understood that the vacuum drying temperature is 25-35°C and the vacuum drying time is 5-10 minutes. The vacuum drying time is short, does not affect the transparency of the film, and also improves the drying efficiency. The hot air drying temperature is 70-90°C and the drying time is 60-110 minutes.

[0066] Furthermore, in step S5 above, the annealing treatment includes the following specific steps: placing the dried film together with the substrate at an annealing temperature for 45-60 minutes. Optionally, the annealing temperature is 130-150°C. The annealing temperature may also be 130-145°C, 135-140°C, 135-150°C, or 140-150°C. Specifically, the annealing temperature is 130°C, 135°C, 140°C, 145°C, or 150°C. It can be understood that the ester carbonyl group C=O in L-polylactic acid is fixed relative to the main chain and cannot rotate. The crystallized L-polylactic acid crystals have excellent piezoelectric properties. The crystallinity of L-polylactic acid is improved by annealing, so that the prepared L-polylactic acid piezoelectric film has good piezoelectric properties. Specifically, compared with L-polylactic acid that has not been annealed, the crystallinity of L-polylactic acid that has been annealed is increased by 20-35%, and the final crystallinity of the L-polylactic acid piezoelectric film is in the range of 30%-40%. In addition, annealing will enhance the mechanical properties of the L-polylactic acid piezoelectric film, allowing the material to withstand greater deformation, indirectly enhancing its piezoelectric properties. The advantage of L-polylactic acid over other polymer piezoelectric materials is that the processing technology is simple. Only annealing operation is required to obtain a piezoelectric material with excellent piezoelectric properties. In addition, the piezoelectric film after annealing can have excellent high-temperature resistance. The high-temperature resistance makes the application scenarios of L-polylactic acid piezoelectric film more extensive. By annealing at an annealing temperature of 130-150° C., the crystallization of L-polylactic acid in the L-polylactic acid-vitamin B2-hydroxyapatite piezoelectric film is promoted, thereby further improving the piezoelectric properties of the film.

[0067] The piezoelectric film thickness can also be 5 μm to 20 μm, 5 μm to 45 μm, 20 μm to 30 μm, 30 μm to 40 μm, or 20 μm to 50 μm. Specifically, the piezoelectric film thickness is 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 45 μm, or 50 μm. The film prepared by the preparation method of this embodiment has a wide range of film thicknesses and a wide range of application scenarios.

[0068] In order to solve the above technical problems, the second embodiment of the present invention further provides a left-handed polylactic acid piezoelectric film, which is prepared using the piezoelectric film preparation method as described above.

[0069] Specifically, the piezoelectric film of this embodiment is prepared by dissolving L-polylactic acid and vitamin B2 in an organic solvent and pre-treating the solution to form a pre-solution. A hydroxyapatite solution is then used as a dispersion. The dispersion is then added to the pre-solution and stirred to form a mixed solution. The mixed solution is then coated on a substrate, which is then dried to form a pre-treated film. The pre-treated film is then annealed to form the piezoelectric film.

[0070] In the piezoelectric film product of this embodiment, the ratio of L-polylactic acid: vitamin B2: hydroxyapatite is 1: (0.01-0.3): (0.01-0.2). Specifically, the ratio of L-polylactic acid: vitamin B2: hydroxyapatite can also be 1: 0.01: 0.01, 1: 0.15: 0.05, 1: 0.15: 0.15, 1: 0.03: 0.2, 1: 0.3: 0.05 or 1: 0.3: 0.2. In this embodiment, in order to better reflect the effect of the amount of the components added to the reactants on the response voltage of the L-polylactic acid piezoelectric film, the present invention further provides the following experimental groups and comparative groups for experimental group 1:

[0071] Experimental Group 1: A pre-solution was prepared by dissolving a predetermined ratio of poly(L-lactic acid) and vitamin B2 to form a pre-solution. A hydroxyapatite solution was then provided as a dispersion. The dispersion was added to the pre-solution and stirred to degas to form a mixed solution. The mixed solution had a ratio of poly(L-lactic acid) to vitamin B2 to hydroxyapatite of 1:0.15:0.15. The mixed solution was then applied to a substrate, which was then dried and annealed to form a thin film to be tested.

[0072] Experimental Group 2: The difference between it and the above experimental group 1 is: L-polylactic acid: vitamin B2: hydroxyapatite = 1:0.15:0.05

[0073] Experimental Group 3: The difference between it and the above experimental group 1 is: L-polylactic acid: vitamin B2: hydroxyapatite = 1:0.15:0.10

[0074] Experimental Group 4: The difference between it and the above experimental group 1 is: L-polylactic acid: vitamin B2: hydroxyapatite = 1:0.15:0.20

[0075] Experimental Group 5: The difference between Experimental Group 5 and Experimental Group 1 is that the mass fraction of vitamin B2 is 15%, and the mass fraction of hydroxyapatite is 0%.

[0076] Experimental Group 6: The difference between it and the above-mentioned Experimental Group 5 is that the mass fraction of vitamin B2 is specifically 5%.

[0077] Experimental Group 7: The difference between it and the above-mentioned Experimental Group 5 is that the mass fraction of vitamin B2 is specifically 10%.

[0078] Experimental Group 8: The difference between it and the above-mentioned Experimental Group 5 is that the mass fraction of vitamin B2 is specifically 20%.

[0079] Comparative group 1: The difference between it and the experimental group 1 is: L-polylactic acid: vitamin B2: hydroxyapatite = 1:0:0

[0080] Comparative group 2: The difference between it and the above-mentioned experimental group 5 is that the mass fraction of vitamin B2 is specifically 0%.

[0081] Table 1. Comparison of the response voltage test results of the films obtained in experimental groups 1-8 and comparative groups 1-2

[0082]

[0083] Based on the contents in Table 1, by comparing experimental groups 1-8 and comparative groups 1-2, it can be seen that vitamin B2 is added in this embodiment, and vitamin B2 forms hydrogen bonds with left-handed polylactic acid. The hydrogen bonding effect improves the degree of C=O dipole orientation, thereby affecting the crystallinity of left-handed polylactic acid, so that the film response voltage is improved. This embodiment controls the proportion of hydroxyapatite added to avoid excessive hydroxyapatite addition and causing agglomeration, thereby affecting the piezoelectric properties of left-handed polylactic acid. At the same time, the addition of hydroxyapatite strengthens the hydrogen bonding effect formed between vitamin B2 and left-handed polylactic acid. The crystallinity of left-handed polylactic acid is further improved, thereby improving the response voltage of the piezoelectric film.

[0084] In this embodiment, in order to better demonstrate the superiority of the piezoelectric film prepared by the above-mentioned piezoelectric film preparation method in improving the piezoelectric coefficient, the present invention further provides the following experimental groups and comparative groups for Experimental Group 2:

[0085] Experimental Group 9: A certain ratio of poly (L-lactic acid) and vitamin B2 was dissolved in chloroform and ultrasonically cleaned using an ultrasonic cleaning device. After ultrasonic cleaning, the solution was stirred at a first stirring speed of 400 r / min to form a pre-solution. The mass ratio of poly (L-lactic acid) to vitamin B2 was 6.66.

[0086] Hydroxyapatite is provided and dissolved in chloroform, and the dispersion is disrupted for 30 minutes using an ultrasonic disruptor to form a dispersion.

[0087] The pre-solution was stirred at a second stirring speed of 250 r / min, while the dispersion was continuously and quantitatively added. After the dispersion was added, the mixture was stirred for a third stirring time of 3 hours. After stirring, the mixture was allowed to stand and degas for 1 hour to form a mixed solution. The mixed solution had a ratio of poly (L-lactic acid): vitamin B2: hydroxyapatite of 1:0.15:0.15.

[0088] The mixed solution was applied to a flexible copper foil by knife coating at a speed of 20 mm / s. The wet film formed on the flexible copper foil and the flexible copper foil were vacuum dried to form a dry film. The dry film was removed and hot air dried to form a dried thin film. The vacuum drying temperature was 25-35°C for 6 minutes. The hot air drying temperature was 70-90°C for 90 minutes.

[0089] The dried film was placed in an annealing temperature of 140° C. for 45 minutes to form a piezoelectric film to be tested. The thickness of the formed piezoelectric film was 10 μm.

[0090] Experimental group 10: The difference between the experimental group 10 and the experimental group 9 is that the mass ratio of poly (L-lactic acid) to vitamin B2 is 1.25.

[0091] Experimental Group 11: The difference between Experimental Group 1 and Experimental Group 1 is that the mass ratio of poly(L-lactic acid) to vitamin B2 is 2.

[0092] Experimental Group 12: The difference between Experimental Group 1 and Experimental Group 1 is that the mass ratio of poly(L-lactic acid) to vitamin B2 is 8.

[0093] Experimental group 13: The difference between it and the above-mentioned experimental group 1 is that the mass ratio of poly (L-lactic acid) to vitamin B2 is 10.

[0094] Experimental group 14: The difference between it and the above-mentioned experimental group 1 is that: poly-L-lactic acid: vitamin B2: hydroxyapatite = 1:0.01:0.05.

[0095] Experimental group 15: The difference between it and the above-mentioned experimental group 1 is that: poly (L-lactic acid): vitamin B2: hydroxyapatite = 1:0.0.15:0.05.

[0096] Experimental Group 16: The difference between it and the above-mentioned Experimental Group 1 is that: poly-L-lactic acid: vitamin B2: hydroxyapatite = 1:0.15:0.2.

[0097] Experimental Group 17: The difference between Experimental Group 1 and Experimental Group 1 is that the first stirring speed is 300 r / min.

[0098] Experimental Group 18: The difference between Experimental Group 1 and Experimental Group 1 is that the second stirring speed is 300 r / min.

[0099] Experimental Group 19: The difference between it and the above-mentioned Experimental Group 1 is that the substrate is a silicon wafer.

[0100] Experimental Group 20: The difference between it and Experimental Group 1 is that the scraping speed is 10 mm / s

[0101] Experimental Group 21: The difference between it and the above-mentioned Experimental Group 1 is that the drying treatment is natural drying at room temperature and pressure.

[0102] Experimental Group 22: The difference between Experimental Group 22 and Experimental Group 1 is that the annealing time is 130 minutes.

[0103] Experimental Group 23: The difference between Experimental Group 23 and Experimental Group 1 is that the annealing time is 150 minutes.

[0104] Experimental Group 24: The difference between Experimental Group 24 and Experimental Group 1 is that the annealing temperature is 130°C.

[0105] Experimental Group 25: The difference between Experimental Group 25 and Experimental Group 1 is that the annealing temperature is 150°C.

[0106] Comparative Group 3: A mixture of polylactic acid and vitamin B2 was dissolved in chloroform, and polylactic acid powder and vitamin B2 powder were added and stirred. Then the chloroform solution was added to make a mixed solution. The mixed solution was placed on a stirrer at a speed of 250r / min. After 6 hours, the speed was adjusted to 200r / min, and the stirred mixed solution was vacuum dried. The sample was then placed in a hot drying oven at 90°C and dried for 1 hour, and then taken out for use. The fourth step is annealing. The dried sample was placed in a 150°C oven again and taken out after 4 hours to obtain the piezoelectric film sample to be tested.

[0107] Comparative Group 3: The difference between it and the experimental group 1 is that the annealing time is 50 minutes.

[0108] Comparative Group 4: The difference between it and the experimental group 1 is that the annealing time is 180 minutes.

[0109] Comparative Group 5: The difference between it and the experimental group 1 is that the annealing temperature is 100°C.

[0110] Comparative Group 6: The difference between it and the experimental group 1 is that the annealing temperature is 160°C.

[0111] Comparative Group 7: The difference between it and the experimental group 1 is that the thickness of the piezoelectric film is 5 microns.

[0112] Table 2. Comparison of the piezoelectric coefficient test results of the films obtained from experimental groups 9-25 and comparative groups 3-7

[0113]

[0114] Based on the contents in Table 2, it can be seen from the experimental data of the above experimental groups 9-25 and comparative groups 3-7 that the piezoelectric film provided by the present invention, compared with the piezoelectric film made of only L-polylactic acid or L-polylactic acid-vitamin B2 as raw materials, the hydroxyapatite added by the present invention strengthens the hydrogen bonding between vitamin B2 and L-polylactic acid. At the same time, by controlling the amount of hydroxyapatite added, the piezoelectric coefficient of the piezoelectric film exceeds 18 pc / N, specifically in the range of 18-22 pc / N, thereby significantly improving the piezoelectric coefficient.

[0115] Please continue reading Figures 3 to 6 , Figures 3 to 6 This is the effect of temperature on the response voltage of the left-handed polylactic acid piezoelectric film prepared in this embodiment. It can be seen that by testing the left-handed polylactic acid piezoelectric film at 30°C, 60°C, 90°C and 120°C, the amplitude of the response voltage can be maintained at 0.4mV, that is, the piezoelectric properties of the left-handed polylactic acid piezoelectric film will not be affected under certain temperature changes. Compared with conventional polymer piezoelectric films, the left-handed polylactic acid piezoelectric film has better high temperature resistance. At the same time, the left-handed polylactic acid piezoelectric film will not be affected by its piezoelectric properties at 30-120°C, making the application range of the left-handed polylactic acid piezoelectric film wider, such as piezoelectric devices used in power grids and 5G communication equipment.

[0116] Compared with the prior art, the left-handed polylactic acid piezoelectric film and its preparation method provided by the present invention have the following beneficial effects:

[0117] 1. An embodiment of the present invention provides a method for preparing a left-handed polylactic acid piezoelectric film, which includes the following steps: dissolving a certain proportion of left-handed polylactic acid and vitamin B2 to form a pre-solution; providing a hydroxyapatite solution as a dispersion; adding the dispersion to the pre-solution to form a mixed solution; forming the mixed solution into a film to be treated on a substrate; annealing the film to be treated to form a piezoelectric film. Through this preparation method, a left-handed polylactic acid-vitamin B2-hydroxyapatite piezoelectric film is finally obtained. Based on the above method, a stronger hydrogen bond can be formed between the left-handed polylactic acid, vitamin B2, and hydroxyapatite, so that the C=O dipole of the left-handed polylactic acid is highly oriented, and its piezoelectric properties and mechanical strength are further improved. A piezoelectric film with a piezoelectric performance exceeding 18 pc / N can be obtained, which improves the piezoelectric performance of existing piezoelectric films.

[0118] 2. The mass ratio of L-polylactic acid and vitamin B2 in the pre-solution of the embodiment of the present invention is in the range of 3-10; the L-polylactic acid: vitamin B2: hydroxyapatite in the mixed solution is 1: (0.01-0.3): (0.01-0.2). The specific limitation of the raw materials improves the piezoelectric properties of the L-polylactic acid-vitamin B2-hydroxyapatite piezoelectric film, thereby enabling the L-polylactic acid-vitamin B2-hydroxyapatite piezoelectric film to have a wider range of practical applications.

[0119] 3. The solvent for dissolving poly (L-lactic acid) and vitamin B2 is any one of chloroform, butanone, N,N-dimethylpyrrolidone, and N,N-dimethylamide. Organic solvents are easy to dissolve poly (L-lactic acid) and are easy to volatilize.

[0120] 4. The pretreatment of the embodiment of the present invention includes the following steps: forming a pre-solution includes the following steps: stirring L-polylactic acid and vitamin B2 in a solvent at a first stirring speed for a first time, the first stirring speed is 300-400r / min, and the first time is 2-4 hours. The pretreatment makes the mixing of L-polylactic acid and vitamin B2 more complete.

[0121] 5. The stirring and degassing process of the embodiment of the present invention includes the following steps: forming a mixed solution specifically includes the following steps: stirring the pre-solution at a second stirring speed while continuously adding the dispersion liquid; after the dispersion liquid is added, stirring at a third stirring speed for a third time and then standing, the second stirring speed is lower than the third stirring speed, and the hydroxyapatite is more fully dispersed in the pre-solution by stirring the mixed solution.

[0122] 6. In the embodiment of the present invention, the mixed solution is formed on the substrate to form a thin film to be treated, specifically comprising forming a wet film on the substrate by coating, and then drying to form the thin film to be treated. The uniformity of the wet film is ensured by scraping, making the surface of the wet film smoother. At the same time, scraping can also prevent the appearance of air bubbles in the wet film, further improving the flatness of the piezoelectric film, and making the thickness and flatness of the piezoelectric film better.

[0123] 7. The annealing process in the embodiment of the present invention specifically includes the following steps: annealing the film to be treated at a temperature of 130-150°C to obtain a piezoelectric film. The annealing process promotes the crystallization of the L-polylactic acid, improving the piezoelectric properties of the film. Annealing also enhances the mechanical properties of the L-polylactic acid piezoelectric film, allowing the material to withstand greater deformation, indirectly enhancing its piezoelectric properties. Furthermore, the films produced by this preparation method have a wide range of thicknesses and are suitable for a wide range of applications.

[0124] 8. The embodiment of the present invention further provides a left-handed polylactic acid piezoelectric film, which has the same beneficial effects as the above-mentioned piezoelectric film and will not be described in detail here.

[0125] The above is a detailed introduction to a left-handed polylactic acid piezoelectric film and a preparation method thereof disclosed in an embodiment of the present invention. Specific examples are used in this article to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; at the same time, for general technical personnel in this field, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention. Any modifications, equivalent replacements and improvements made within the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a left-handed polylactic acid piezoelectric film, characterized in that: It includes the following steps: Dissolving a certain proportion of poly (L-lactic acid) and vitamin B2 to form a pre-solution; providing a hydroxyapatite solution as a dispersion; adding the dispersion into the pre-solution to form a mixed solution; The mixed solution contains poly (L-lactic acid): vitamin B2: hydroxyapatite = 1: (0.01-0.3): (0.01-0.2); forming a thin film to be treated on a substrate by applying the mixed solution; The film to be processed is annealed to form the piezoelectric film.

2. The method for preparing the left-handed polylactic acid piezoelectric film according to claim 1, wherein: The mass ratio of poly(L-lactic acid) to vitamin B2 in the pre-solution is in the range of 3-10.

3. The method for preparing the left-handed polylactic acid piezoelectric film according to claim 1, wherein: The solvent for dissolving the poly(L-lactic acid) and the vitamin B2 is any one of chloroform, butanone, N,N-dimethylpyrrolidone and N,N-dimethylamide.

4. The method for preparing a left-handed polylactic acid piezoelectric film according to claim 1, wherein: The ratio of poly(L-lactic acid) to vitamin B2 to hydroxyapatite in the mixed solution is 1:0.15:0.

15.

5. The method for preparing the left-handed polylactic acid piezoelectric film according to claim 1, wherein: The forming of the pre-solution comprises the following steps: stirring the poly(L-lactic acid) and the vitamin B2 in a solvent at a first stirring speed for a first time, wherein the first stirring speed is 300-400 r / min and the first time is 2-4 hours.

6. The method for preparing a left-handed polylactic acid piezoelectric film according to claim 1, wherein: The forming of the mixed solution specifically includes the following steps: stirring the pre-solution at a second stirring speed while continuously adding the dispersion; after the dispersion is added, stirring at a third stirring speed for a third time and then letting it stand, wherein the second stirring speed is lower than the third stirring speed.

7. The method for preparing a left-handed polylactic acid piezoelectric film according to claim 1, wherein: The step of applying the mixed solution to form a thin film to be processed on a substrate specifically includes forming a wet film on the substrate by coating, and then drying to form the thin film to be processed.

8. The method for preparing a left-handed polylactic acid piezoelectric film according to claim 1, wherein: The film to be processed is annealed at a temperature of 130-150° C. to obtain the piezoelectric film.

9. A left-handed polylactic acid piezoelectric film, characterized in that: The piezoelectric film is prepared by the method for preparing the left-handed polylactic acid piezoelectric film according to any one of claims 1 to 8.

10. The method for preparing a piezoelectric film according to claim 9, wherein: The piezoelectric film has a ratio of poly (L-lactic acid) to vitamin B2 to hydroxyapatite of 1: (0.01-0.3): (0.01-0.2).

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