A silk fibroin piezoelectric material and its preparation method

Abstract

This invention belongs to the field of biomaterials technology and relates to a silk fibroin piezoelectric material and its preparation method. The preparation method involves dissolving pure silk fibroin in formic acid to obtain a silk fibroin formic acid solution, and then wet spinning the silk fibroin formic acid solution to obtain the silk fibroin piezoelectric material. The wet spinning process is as follows: extrusion through a spinneret → coagulation in a first coagulation bath → coagulation in a second coagulation bath → stretching in a steam bath → winding. The first coagulation bath is water, and its temperature is 20-25°C; the second coagulation bath is water, and its temperature is 30-40°C. The silk fibroin piezoelectric material obtained by this invention exhibits excellent piezoelectric properties.

Description

Technical Field

[0001] This invention belongs to the field of biomaterials technology and relates to a silk fibroin piezoelectric material and its preparation method. Background Technology

[0002] In the healthcare field, continuous physiological signal monitoring is crucial for early disease warning and personalized health management. Wearable devices based on the piezoelectric effect, with their high sensitivity and self-powered characteristics, have broken the dependence of traditional monitoring methods on external power sources and have become a research hotspot. However, commonly used traditional piezoelectric materials such as polyvinylidene fluoride (PVDF) and lead zirconate titanate (PZT), while possessing high piezoelectric properties, suffer from poor biocompatibility and insufficient mechanical flexibility, making it difficult to meet the requirements for long-term comfortable use of wearable devices.

[0003] Silk fibroin, as a natural biomaterial, possesses tunable processability, excellent mechanical properties, non-toxicity, and shear and longitudinal piezoelectricity, enabling it to generate electricity under mechanical stress. This makes it an ideal choice for constructing wearable bio-piezoelectric devices, potentially providing self-powered power for wearable devices. However, the molecular chain distribution of silk fibroin is relatively disordered, with crystalline (β-sheet structure) and amorphous (random structure) regions coexisting. The disorder of the amorphous regions limits the overall piezoelectric performance, resulting in weak intrinsic piezoelectric properties that are difficult to directly meet practical application requirements. Therefore, there is an urgent need to improve its piezoelectric performance.

[0004] Currently, there are two main technical solutions for improving the piezoelectric properties of silk fibroin:

[0005] The first approach involves using composite materials to improve piezoelectric properties. However, adding external components reduces the content of silk fibroin, ultimately affecting the mechanical properties of the silk fibroin material. For example, patent application CN115627589A discloses a biodegradable polymer-modified silk fibroin composite piezoelectric material and its preparation method, which utilizes natural polymers such as silk fibroin to blend with biodegradable synthetic polymers to form a piezoelectric polymer material. Patent application CN115975230A discloses a method for preparing a silk fibroin composite piezoelectric film, which involves spin-coating a composite film by introducing a glycine-chitosan solution into a silk fibroin solution. The glycine-chitosan solution induces the generation of a large number of β-sheet structures in silk fibroin to improve piezoelectric properties.

[0006] The second category involves improving piezoelectric properties from a processing perspective, but the solvents used are toxic or pose environmental risks. For example, Reference 1 (Nano Energy, 2019, 66, 104106.) uses methanol vapor treatment to induce the transformation of the secondary structure of silk fibroin. Methanol is not only volatile but also has a certain degree of toxicity. Reference 2 (Chinese Physics B, 2024, 33, 088707.) uses dry spinning combined with a post-treatment ethanol soaking-stretching process. Formic acid volatilization during dry spinning will cause environmental pollution.

[0007] In addition, specific methods have been employed to improve piezoelectric properties. For example, patent application CN119264502A discloses an ultra-tough piezoelectric material and its preparation method, in which a pre-formed polymer material is simultaneously salted out and stretched in a salting-out solution. The synergistic effect of stretching and salting-out alters the secondary structure within the fiber. Patent application CN114984313A discloses a method to improve the piezoelectric effect of silk fibroin scaffolds, in which a pure silk fibroin scaffold is immersed in a solution of iron oxide nanoparticles, and then the resulting silk fibroin scaffold loaded with iron oxide nanoparticles is treated in an alternating magnetic field. However, the improvement in piezoelectric properties achieved by either method is not significant and is insufficient to meet the practical application requirements for high-performance silk fibroin piezoelectric materials.

[0008] Therefore, there is an urgent need to study a preparation method that can significantly improve the piezoelectric properties of silk fibroin simply by optimizing the process. Summary of the Invention

[0009] The purpose of this invention is to solve the problems existing in the prior art and to provide a silk fibroin piezoelectric material and its preparation method.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A method for preparing a silk fibroin piezoelectric material involves dissolving pure silk fibroin in formic acid to obtain a formic acid solution of silk fibroin, and then performing wet spinning on the formic acid solution of silk fibroin to obtain the silk fibroin piezoelectric material.

[0012] The wet spinning process is as follows: extrusion through a spinneret → coagulation in the first coagulation bath → coagulation in the second coagulation bath → stretching in a steam bath → winding.

[0013] The first coagulation bath is water, and the temperature of the first coagulation bath is 20-25℃;

[0014] The second coagulation bath is water, and the temperature of the second coagulation bath is 30-40℃.

[0015] The silk fibroin fibers of the present invention have excellent piezoelectric properties for the following reasons:

[0016] (1) The piezoelectric properties of silk fibroin fibers are closely related to their crystallinity. The higher the crystallinity, the higher the orderliness of the molecular chains, and the more effectively the polar groups (such as carbonyl and amino groups) on the molecular chains can be arranged to form more dipoles, thereby enhancing the piezoelectric effect.

[0017] Crystallinity is closely related to the β-sheet structure, a common crystalline form in silk fibroin fibers, which requires suitable temperature and time to form. The lower temperature of the first coagulation bath favors the formation of the β-sheet structure; the higher temperature of the second coagulation bath helps break the original random orientation of the silk fibroin molecular chains and rearrange them into a more ordered β-sheet structure. During steam bath stretching, water vapor can penetrate into the internal structure of the silk fibroin, further promoting the crystallization of silk fibroin molecules and the formation of the β-sheet structure.

[0018] (2) The piezoelectric properties of silk fibroin fibers are closely related to the stability of the crystalline regions. The higher the stability of the crystalline regions, the more stable the arrangement of molecular chains within the crystalline regions, the more stable the arrangement of polar groups and the formation of dipoles, and the stronger the piezoelectric effect.

[0019] The lower temperature of the first coagulation bath allows the crystallization process to proceed uniformly, thereby improving the stability of the crystallization region.

[0020] (3) The piezoelectric properties of silk fibroin fibers are closely related to the degree of micro-roughness of the fiber surface. The higher the degree of micro-roughness of the fiber surface, the more conducive it is to increasing the surface polarization field. The micro-roughened fiber surface has more polar groups exposed, which can form more polarization regions under the action of an electric field, thereby enhancing the polarization field of the fiber surface. In addition, the roughened surface can increase the charge density and charge distribution non-uniformity of the fiber surface. This non-uniformity helps to form more local polar regions, thereby improving the polarization ability of the fiber under mechanical stress and enhancing the piezoelectric effect.

[0021] The higher temperature of the second coagulation bath promotes the dual diffusion of formic acid and water. This dual diffusion process facilitates the structural remodeling and reorganization of silk fibroin, thus contributing to the formation of micro-roughness on the fiber surface. During the dual diffusion process, due to the uneven diffusion of the solvent, micro-irregular structures, i.e., micro-roughness, may form on the fiber surface.

[0022] (4) The piezoelectric properties of silk fibroin fibers are closely related to the number of micro-defects on the fiber surface. The fewer the micro-defects, the more favorable it is to obtain a uniform polarity distribution, so that the polarization can be more effectively conducted to the polarized dipole, thereby enhancing the piezoelectric output performance of the fiber and thus enhancing the piezoelectric effect.

[0023] During steam bath stretching, the steam helps to eliminate internal stress and reduce microscopic defects.

[0024] (5) The piezoelectric properties of silk fibroin fibers are closely related to their orientation. The higher the orientation, the more ordered the molecular chains are arranged, the more consistent the orientation of the polar groups, and the easier it is for the formed dipoles to be polarized under mechanical stress, resulting in a stronger piezoelectric effect.

[0025] The lower temperature of the first coagulation bath facilitates the formation of hydrogen bonds between molecular chains, thereby influencing the arrangement and orientation of silk fibroin molecular chains. This results in a more ordered arrangement and higher degree of orientation of silk fibroin molecular chains during the subsequent stretching and orientation process.

[0026] As a preferred technical solution:

[0027] The preparation method of the silk fibroin piezoelectric material described above involves the following steps: dissolving degummed silk fibers in a calcium chloride formic acid solution to form a membrane, and then removing the calcium chloride from the membrane to obtain pure silk fibroin.

[0028] In the preparation method of the silk fibroin piezoelectric material described above, the concentration of the formic acid solution for silk fibroin is 20-25 wt%. The concentration of the formic acid solution for silk fibroin is closely related to the crystallization behavior during wet spinning. A higher initial concentration promotes the formation of a tighter molecular network in the coagulation bath of the spinning solution, providing a structural basis for subsequent crystallization. When wet spinning begins, the difference in the interfacial environment between water and fiber drives water to gradually penetrate into the fiber, while formic acid partially permeates out. Due to the different diffusion rates of water and formic acid, a concentration gradient is formed. This gradient acts as a crystallization driving force, causing the molecular chains of the original amorphous regions to rearrange and become more ordered, thereby enhancing crystallinity. In this process, the synergistic effect of diffusion rate and concentration gradient precisely controls the uniformity and efficiency of crystallization: excessively rapid diffusion may lead to uneven crystallization, while an appropriate concentration gradient ensures a smooth and sufficient crystallization process. Therefore, the initial concentration of the silk fibroin solution indirectly regulates the quality and efficiency of crystallization during wet spinning by influencing diffusion behavior and the formation of the concentration gradient.

[0029] In the preparation method of the silk fibroin piezoelectric material described above, the extrusion speed of the spinneret is 1-1.5 mL / min, the ambient temperature is 24±5℃, and the ambient relative humidity is 35±5%.

[0030] In the preparation method of the silk fibroin piezoelectric material described above, the length of the first coagulation bath is 25-30 cm.

[0031] In the preparation method of the silk fibroin piezoelectric material described above, the length of the second coagulation bath is 30-40 cm.

[0032] The method for preparing a silk fibroin piezoelectric material as described above involves a steam bath stretching ratio of 2.5-3, which enables the silk fibroin molecular chains to be oriented in an orderly manner along the stretching direction. Simultaneously, it induces partial orientation of the silk fibroin molecular chains and the formation of β-sheet structures, thereby constructing long-range ordered crystal regions.

[0033] The preparation method of the silk fibroin piezoelectric material described above involves a winding speed of 2-3 m / min.

[0034] The present invention also provides a silk fibroin piezoelectric material, which is prepared by the preparation method of a silk fibroin piezoelectric material as described in any of the preceding claims.

[0035] As a preferred technical solution:

[0036] The silk fibroin piezoelectric material described above has a piezoelectric output of 25-30V, a dry-state tensile strength of 220-240MPa, and a dry-state elongation at break of 1.5-2.5%.

[0037] Beneficial effects:

[0038] (1) This invention, through an innovative wet spinning process, precisely controls the coagulation bath temperature and steam bath stretching, significantly improving the crystallinity, crystallization region stability, and surface micro-roughness of silk fibroin fibers, reducing micro-defects and improving orientation, achieving orderly arrangement of polar groups in molecular chains, forming more stable dipoles, greatly enhancing the piezoelectric effect of the material, and breaking through the bottleneck of weak intrinsic piezoelectric properties of silk fibroin.

[0039] (2) By flexibly controlling key parameters such as coagulation bath temperature and stretching ratio, this invention can achieve precise adjustment of the performance of silk fibroin piezoelectric materials, meet the differentiated requirements of piezoelectric performance in different application scenarios, and greatly expand the application range of silk fibroin materials.

[0040] (3) This invention does not require the addition of external reinforcing materials or toxic solvents. It achieves the improvement of the piezoelectric properties of silk fibroin by simply optimizing the combination of process parameters. Compared with traditional methods, this preparation process is simple, mild, and highly repeatable, which is conducive to large-scale production and reducing production costs. Moreover, the volatilization of formic acid in the wet spinning process is low, resulting in low environmental risk. It is in line with the concept of green and sustainable development and is of great significance to promoting the development of environmentally friendly piezoelectric materials. Detailed Implementation

[0041] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0042] The following are the test methods for the relevant performance indicators in each embodiment and comparative example:

[0043] Piezoelectric output: A 2cm×1cm silk fibroin piezoelectric material was used as the piezoelectric layer, and aluminum electrodes were used as the positive and negative electrodes. The material was encapsulated with polyimide tape to obtain a silk fibroin-based piezoelectric energy harvester (SF-PENGs). The piezoelectric output could be read by connecting it in series with an oscilloscope and an electrometer. The ambient temperature during the test was 20±3℃ and the relative humidity was 40±5%.

[0044] Dry fracture strength: Tested using an electronic universal testing machine. Test parameters: clamp distance 4cm, tensile rate 1mm / min, ambient temperature 23±5℃, and relative humidity 40±5%.

[0045] Elongation at break in dry state: Tested using an electronic universal testing machine. Test parameters: clamp distance 4cm, tensile rate 1mm / min, ambient temperature 23±5℃, and relative humidity 40±5%.

[0046] Example 1

[0047] A method for preparing a silk fibroin piezoelectric material, the specific steps of which are as follows:

[0048] (1) Preparation of raw materials;

[0049] silkworm cocoons;

[0050] Sodium carbonate aqueous solution: The concentration of sodium carbonate is 0.05 wt%;

[0051] Water: Deionized water;

[0052] Formic acid solution of calcium chloride: calcium chloride concentration is 2 wt%;

[0053] Formic acid;

[0054] (2) Preparation of degummed filaments;

[0055] After manually peeling the clean silkworm cocoons into thin layers, they are boiled in a sodium carbonate solution to remove sericin. Then they are taken out and washed clean with water. The above degumming-washing steps are repeated twice to finally obtain degummed silk.

[0056] (3) Preparation of pure silk fibroin;

[0057] After drying the degummed filaments at 5°C for 12 hours, they were placed in a formic acid solution of calcium chloride and stirred continuously with a magnetic stirrer for 4 hours until completely dissolved. After dissolution, the solution was filtered to obtain a mixed solution of silk fibroin, formic acid, and calcium chloride. The mixed solution was evenly spread on a hot plate and dried for 6 hours to form a film. The film was then peeled off and immersed in water to remove calcium chloride. Finally, it was dried at room temperature to obtain pure silk fibroin.

[0058] (4) Preparation of silk fibroin piezoelectric materials;

[0059] Pure silk fibroin was dissolved in formic acid to prepare a 23wt% silk fibroin formic acid solution. The solution was then wet-spun to obtain a silk fibroin piezoelectric material. The wet-spinning process was as follows: spinneret extrusion → first coagulation bath coagulation → second coagulation bath coagulation → steam bath stretching → winding. During spinneret extrusion, the extrusion speed was 1.25 mL / min, the ambient temperature was 25℃, and the relative humidity was 38%. The first coagulation bath was 25 cm long, contained water, and had a temperature of 20℃. The second coagulation bath was 30 cm long, contained water, and had a temperature of 30℃. The steam bath stretching ratio was 2.5. The winding speed was 2.5 m / min.

[0060] The final silk fibroin piezoelectric material has a piezoelectric output of 30V, a dry breaking strength of 235MPa, and a dry breaking elongation of 2%.

[0061] Comparative Example 1

[0062] A method for preparing a silk fibroin piezoelectric material is basically the same as that in Example 1, except that the temperature of the first coagulation bath is the same as that of the second coagulation bath, both being 30°C.

[0063] The final silk fibroin piezoelectric material has a piezoelectric output of 18.2V, a dry breaking strength of 180.6MPa, and a dry breaking elongation of 1.1%.

[0064] Comparing Comparative Example 1 with Example 1, it can be found that Comparative Example 1 has lower piezoelectric output and dry breaking strength. The reason is that the first coagulation bath temperature used in Comparative Example 1 is higher. On the one hand, it inhibits the crystallization process of silk fibroin, resulting in a reduction in the fiber crystallization area and a weakening of the piezoelectric effect. On the other hand, inappropriate temperature can cause stress release or unevenness inside the fiber, destroying the stability of the crystallization area and affecting the consistency of the fiber's mechanical properties, leading to a decrease in dry breaking strength. In addition, higher temperature may increase the activity of molecular chain movement, making the fiber soft and easily deformable, making it difficult to maintain a stable polarity distribution, further weakening the piezoelectric performance.

[0065] Comparative Example 2

[0066] A method for preparing a silk fibroin piezoelectric material is basically the same as that in Example 1, except that the temperature of the second coagulation bath is the same as that of the first coagulation bath, which is 20°C.

[0067] The final silk fibroin piezoelectric material has a piezoelectric output of 20.5V, a dry breaking strength of 190.6MPa, and a dry breaking elongation of 1.3%.

[0068] Comparing Comparative Example 2 with Example 1, it can be found that Comparative Example 2 has lower piezoelectric output and dry-state breaking strength. The reasons are as follows: both the first and second coagulation baths are set at 20°C, which fails to effectively promote the initial coagulation and crystal structure formation of silk fibroin; the temperature change during spinning is too mild, which cannot provide enough heat energy to cause protein molecules to rearrange, making it difficult to form ordered crystals or polarized regions, thus affecting the piezoelectric output; at the same time, it fails to promote the full orientation of protein chains, resulting in defects such as pores and cracks inside the fiber, which reduces mechanical strength.

[0069] Comparative Example 3

[0070] A method for preparing a silk fibroin piezoelectric material is basically the same as that in Example 1, except that: in step (4), the stretching is done in a water bath at a temperature of 35°C and the stretching ratio is 2.5.

[0071] The final silk fibroin piezoelectric material has a piezoelectric output of 24V, a dry breaking strength of 200.83MPa, and a dry breaking elongation of 1.5%.

[0072] Comparing Comparative Example 3 with Example 1, it can be found that Comparative Example 3 has lower piezoelectric output and mechanical properties. The reason is that steam bath stretching can promote the orderly arrangement of protein chains under high temperature environment, improve crystallinity and orientation, thereby significantly improving piezoelectric and mechanical properties; while water bath stretching alone cannot fully stimulate the crystal reorganization of protein chains, resulting in limited performance improvement.

[0073] Example 2

[0074] A method for preparing a silk fibroin piezoelectric material, the specific steps of which are as follows:

[0075] (1) Preparation of raw materials;

[0076] silkworm cocoons;

[0077] Sodium carbonate aqueous solution: The concentration of sodium carbonate is 0.05 wt%;

[0078] Water: Deionized water;

[0079] Formic acid solution of calcium chloride: calcium chloride concentration is 2 wt%;

[0080] Formic acid;

[0081] (2) Preparation of degummed filaments;

[0082] After manually peeling the clean silkworm cocoons into thin layers, they are boiled in a sodium carbonate solution to remove sericin. Then they are taken out and washed clean with water. The above degumming-washing steps are repeated twice to finally obtain degummed silk.

[0083] (3) Preparation of pure silk fibroin;

[0084] After drying the degummed filaments at 5°C for 12 hours, they were placed in a formic acid solution of calcium chloride and stirred continuously with a magnetic stirrer for 4 hours until completely dissolved. After dissolution, the solution was filtered to obtain a mixed solution of silk fibroin, formic acid, and calcium chloride. The mixed solution was evenly spread on a hot plate and dried for 6 hours to form a film. The film was then peeled off and immersed in water to remove calcium chloride. Finally, it was dried at room temperature to obtain pure silk fibroin.

[0085] (4) Preparation of silk fibroin piezoelectric materials;

[0086] Pure silk fibroin was dissolved in formic acid to prepare a 25wt% silk fibroin formic acid solution. The solution was then wet-spun to obtain a silk fibroin piezoelectric material. The wet-spinning process was as follows: spinneret extrusion → first coagulation bath coagulation → second coagulation bath coagulation → steam bath stretching → winding. During spinneret extrusion, the extrusion speed was 1 mL / min, the ambient temperature was 24℃, and the relative humidity was 35%. The first coagulation bath was 26 cm long, contained water, and had a temperature of 24℃. The second coagulation bath was 37 cm long, contained water, and had a temperature of 32℃. The steam bath stretching ratio was 3. The winding speed was 3 m / min.

[0087] The final silk fibroin piezoelectric material has a piezoelectric output of 25V, a dry breaking strength of 220MPa, and a dry breaking elongation of 1.5%.

[0088] Example 3

[0089] A method for preparing a silk fibroin piezoelectric material, the specific steps of which are as follows:

[0090] (1) Preparation of raw materials;

[0091] silkworm cocoons;

[0092] Sodium carbonate aqueous solution: The concentration of sodium carbonate is 0.05 wt%;

[0093] Water: Deionized water;

[0094] Formic acid solution of calcium chloride: calcium chloride concentration is 2 wt%;

[0095] Formic acid;

[0096] (2) Preparation of degummed filaments;

[0097] After manually peeling the clean silkworm cocoons into thin layers, they are boiled in a sodium carbonate solution to remove sericin. Then they are taken out and washed clean with water. The above degumming-washing steps are repeated twice to finally obtain degummed silk.

[0098] (3) Preparation of pure silk fibroin;

[0099] After drying the degummed filaments at 5°C for 12 hours, they were placed in a formic acid solution of calcium chloride and stirred continuously with a magnetic stirrer for 4 hours until completely dissolved. After dissolution, the solution was filtered to obtain a mixed solution of silk fibroin, formic acid, and calcium chloride. The mixed solution was evenly spread on a hot plate and dried for 6 hours to form a film. The film was then peeled off and immersed in water to remove calcium chloride. Finally, it was dried at room temperature to obtain pure silk fibroin.

[0100] (4) Preparation of silk fibroin piezoelectric materials;

[0101] Pure silk fibroin was dissolved in formic acid to prepare a 22wt% silk fibroin formic acid solution. The solution was then wet-spun to obtain a silk fibroin piezoelectric material. The wet-spinning process was as follows: spinneret extrusion → first coagulation bath coagulation → second coagulation bath coagulation → steam bath stretching → winding. During spinneret extrusion, the extrusion speed was 1.4 mL / min, the ambient temperature was 28℃, and the relative humidity was 30%. The length of the first coagulation bath was 28 cm, the first coagulation bath was water, and the temperature of the first coagulation bath was 22℃. The length of the second coagulation bath was 40 cm, the second coagulation bath was water, and the temperature of the second coagulation bath was 40℃. The stretching ratio of the steam bath stretching was 2.8. The winding speed was 2.6 m / min.

[0102] The final silk fibroin piezoelectric material has a piezoelectric output of 28V, a dry breaking strength of 235 MPa, and a dry breaking elongation of 2.5%.

[0103] Example 4

[0104] A method for preparing a silk fibroin piezoelectric material, the specific steps of which are as follows:

[0105] (1) Preparation of raw materials;

[0106] silkworm cocoons;

[0107] Sodium carbonate aqueous solution: The concentration of sodium carbonate is 0.05 wt%;

[0108] Water: Deionized water;

[0109] Formic acid solution of calcium chloride: calcium chloride concentration is 2 wt%;

[0110] Formic acid;

[0111] (2) Preparation of degummed filaments;

[0112] After manually peeling the clean silkworm cocoons into thin layers, they are boiled in a sodium carbonate solution to remove sericin. Then they are taken out and washed clean with water. The above degumming-washing steps are repeated twice to finally obtain degummed silk.

[0113] (3) Preparation of pure silk fibroin;

[0114] After drying the degummed filaments at 5°C for 12 hours, they were placed in a formic acid solution of calcium chloride and stirred continuously with a magnetic stirrer for 4 hours until completely dissolved. After dissolution, the solution was filtered to obtain a mixed solution of silk fibroin, formic acid, and calcium chloride. The mixed solution was evenly spread on a hot plate and dried for 6 hours to form a film. The film was then peeled off and immersed in water to remove calcium chloride. Finally, it was dried at room temperature to obtain pure silk fibroin.

[0115] (4) Preparation of silk fibroin piezoelectric materials;

[0116] Pure silk fibroin was dissolved in formic acid to prepare a 24wt% silk fibroin formic acid solution. Silk fibroin piezoelectric materials were then produced by wet spinning. The wet spinning process was as follows: spinneret extrusion → first coagulation bath coagulation → second coagulation bath coagulation → steam bath stretching → winding. During spinneret extrusion, the extrusion speed was 1.3 mL / min, the ambient temperature was 29℃, and the relative humidity was 36%. The length of the first coagulation bath was 27 cm, the first coagulation bath was water, and the temperature of the first coagulation bath was 25℃. The length of the second coagulation bath was 38 cm, the second coagulation bath was water, and the temperature of the second coagulation bath was 38℃. The stretching ratio of the steam bath stretching was 2.6. The winding speed was 2.8 m / min.

[0117] The final silk fibroin piezoelectric material has a piezoelectric output of 26V, a dry breaking strength of 240MPa, and a dry breaking elongation of 1.9%.

[0118] Example 5

[0119] A method for preparing a silk fibroin piezoelectric material, the specific steps of which are as follows:

[0120] (1) Preparation of raw materials;

[0121] silkworm cocoons;

[0122] Sodium carbonate aqueous solution: The concentration of sodium carbonate is 0.05 wt%;

[0123] Water: Deionized water;

[0124] Formic acid solution of calcium chloride: calcium chloride concentration is 2 wt%;

[0125] Formic acid;

[0126] (2) Preparation of degummed filaments;

[0127] After manually peeling the clean silkworm cocoons into thin layers, they are boiled in a sodium carbonate solution to remove sericin. Then they are taken out and washed clean with water. The above degumming-washing steps are repeated twice to finally obtain degummed silk.

[0128] (3) Preparation of pure silk fibroin;

[0129] After drying the degummed filaments at 5°C for 12 hours, they were placed in a formic acid solution of calcium chloride and stirred continuously with a magnetic stirrer for 4 hours until completely dissolved. After dissolution, the solution was filtered to obtain a mixed solution of silk fibroin, formic acid, and calcium chloride. The mixed solution was evenly spread on a hot plate and dried for 6 hours to form a film. The film was then peeled off and immersed in water to remove calcium chloride. Finally, it was dried at room temperature to obtain pure silk fibroin.

[0130] (4) Preparation of silk fibroin piezoelectric materials;

[0131] Pure silk fibroin was dissolved in formic acid to prepare a 23wt% silk fibroin formic acid solution. The solution was then wet-spun to obtain a silk fibroin piezoelectric material. The wet-spinning process was as follows: spinneret extrusion → first coagulation bath coagulation → second coagulation bath coagulation → steam bath stretching → winding. During spinneret extrusion, the extrusion speed was 1.2 mL / min, the ambient temperature was 20℃, and the relative humidity was 32%. The first coagulation bath was 30 cm long, contained water, and had a temperature of 23℃. The second coagulation bath was 32 cm long, contained water, and had a temperature of 36℃. The steam bath stretching ratio was 2.9. The winding speed was 2 m / min.

[0132] The final silk fibroin piezoelectric material has a piezoelectric output of 27V, a dry breaking strength of 225MPa, and a dry breaking elongation of 1.8%.

[0133] Example 6

[0134] A method for preparing a silk fibroin piezoelectric material, the specific steps of which are as follows:

[0135] (1) Preparation of raw materials;

[0136] silkworm cocoons;

[0137] Sodium carbonate aqueous solution: The concentration of sodium carbonate is 0.05 wt%;

[0138] Water: Deionized water;

[0139] Formic acid solution of calcium chloride: calcium chloride concentration is 2 wt%;

[0140] Formic acid;

[0141] (2) Preparation of degummed filaments;

[0142] After manually peeling the clean silkworm cocoons into thin layers, they are boiled in a sodium carbonate solution to remove sericin. Then they are taken out and washed clean with water. The above degumming-washing steps are repeated twice to finally obtain degummed silk.

[0143] (3) Preparation of pure silk fibroin;

[0144] After drying the degummed filaments at 5°C for 12 hours, they were placed in a formic acid solution of calcium chloride and stirred continuously with a magnetic stirrer for 4 hours until completely dissolved. After dissolution, the solution was filtered to obtain a mixed solution of silk fibroin, formic acid, and calcium chloride. The mixed solution was evenly spread on a hot plate and dried for 6 hours to form a film. The film was then peeled off and immersed in water to remove calcium chloride. Finally, it was dried at room temperature to obtain pure silk fibroin.

[0145] (4) Preparation of silk fibroin piezoelectric materials;

[0146] Pure silk fibroin was dissolved in formic acid to prepare a 24wt% silk fibroin formic acid solution. The solution was then wet-spun to obtain a silk fibroin piezoelectric material. The wet-spinning process was as follows: spinneret extrusion → first coagulation bath coagulation → second coagulation bath coagulation → steam bath stretching → winding. During spinneret extrusion, the extrusion speed was 1.5 mL / min, the ambient temperature was 19℃, and the relative humidity was 40%. The length of the first coagulation bath was 27 cm, the first coagulation bath was water, and the temperature of the first coagulation bath was 21℃. The length of the second coagulation bath was 35 cm, the second coagulation bath was water, and the temperature of the second coagulation bath was 35℃. The stretching ratio of the steam bath stretching was 2.7. The winding speed was 2.4 m / min.

[0147] The final silk fibroin piezoelectric material has a piezoelectric output of 29V, a dry breaking strength of 238MPa, and a dry breaking elongation of 2.3%.

Claims

1. A method for preparing a silk fibroin piezoelectric material, characterized in that, Pure silk fibroin is dissolved in formic acid to obtain a formic acid solution of silk fibroin. The formic acid solution of silk fibroin is then wet-spun to obtain a silk fibroin piezoelectric material. The wet spinning process is as follows: extrusion through a spinneret → coagulation in the first coagulation bath → coagulation in the second coagulation bath → stretching in a steam bath → winding. The first coagulation bath is water, and the temperature of the first coagulation bath is 20-25℃; The second coagulation bath is water, and the temperature of the second coagulation bath is 30-40℃; The piezoelectric output of silk fibroin piezoelectric materials is 25-30V.

2. The method for preparing a silk fibroin piezoelectric material according to claim 1, characterized in that, The preparation process of pure silk fibroin is as follows: after dissolving degummed silk in a formic acid solution of calcium chloride, a membrane is formed, and then the calcium chloride in the membrane is removed to obtain pure silk fibroin.

3. The method for preparing a silk fibroin piezoelectric material according to claim 1, characterized in that, The concentration of the formic acid solution for silk fibroin is 20-25 wt%.

4. The method for preparing a silk fibroin piezoelectric material according to claim 1, characterized in that, When the spinneret is extruded, the extrusion speed is 1-1.5 mL / min, the ambient temperature is 24±5℃, and the ambient relative humidity is 35±5%.

5. The method for preparing a silk fibroin piezoelectric material according to claim 1, characterized in that, The length of the first coagulation bath is 25-30cm.

6. The method for preparing a silk fibroin piezoelectric material according to claim 1, characterized in that, The length of the second coagulation bath is 30-40cm.

7. The method for preparing a silk fibroin piezoelectric material according to claim 1, characterized in that, The stretching ratio for steam bath stretching is 2.5-3.

8. The method for preparing a silk fibroin piezoelectric material according to claim 1, characterized in that, The winding speed is 2-3 m / min.

9. A silk fibroin piezoelectric material, characterized in that, It is prepared by the method of any one of claims 1-8 for the preparation of a silk fibroin piezoelectric material.

10. A silk fibroin piezoelectric material according to claim 9, characterized in that, The piezoelectric output of silk fibroin piezoelectric materials is 25-30V, the dry breaking strength is 220-240MPa, and the dry breaking elongation is 1.5-2.5%.