A biodegradable flexible conductive high-hydrophobic composite film and a preparation method and application thereof

Abstract

The application discloses a biodegradable flexible conductive high-hydrophobic sensor substrate and a preparation method and application thereof. A polylactic acid electrostatic spinning solution and a chitosan / polyethylene oxide mixed electrostatic spinning solution are prepared based on safe and non-toxic food-grade materials, and a sandwiched structure flexible substrate is spun by using an electrostatic spinning technology in sequence, a carbon nanotube conductive film is transferred and closely attached to the surface of the polylactic acid layer of the obtained sandwiched structure substrate, and finally, a flexible conductive high-hydrophobic composite substrate is obtained. The hydrophobic-hydrophilic-hydrophobic sandwiched structure is constructed by using the multi-layer electrostatic spinning, and the surface carbon nanotube conductive layer is used to make the substrate have high hydrophobicity, excellent conductivity and flexible stretching characteristics. The preparation method is controllable in process and low in cost, and is further environment-friendly, and the obtained substrate is expected to have a wide application prospect in the fields of food packaging, sensor substrate, intelligent wearing, health monitoring and the like.

Description

Technical Field

[0001] This invention belongs to the field of flexible sensor substrate technology, specifically relating to a biodegradable flexible conductive and highly hydrophobic composite film, its preparation method, and its application. Background Technology

[0002] With the rapid development of flexible electronic technologies such as food traceability systems, wearable electronic devices, health monitoring systems, and electronic skin, consumer demand for flexible sensors is increasing daily. As the supporting carrier and functional integration platform for flexible devices, the sensor substrate needs to possess good flexibility, mechanical strength, and environmental stability. Currently, the industry commonly uses petroleum-based polymers such as polydimethylsiloxane (PDMS), polyimide (PI), and polyethylene (PE) as substrate materials. While these materials possess stable hydrophobicity, their lack of conductivity limits their application in the sensor field. Furthermore, their non-biodegradable nature leads to persistent electronic waste after disposal, causing serious environmental pollution. Therefore, developing biodegradable, highly hydrophobic, and conductive composite flexible substrate materials is crucial for the sustainable development of sensors.

[0003] In recent years, polylactic acid (PLA) has been considered an ideal biodegradable material with broad application prospects due to its excellent biocompatibility, processability, hydrophobicity, and complete biodegradability. Its final products after use are only carbon dioxide and water, which do not pollute the environment. However, as an insulator, PLA cannot meet the basic requirements of sensors for electrical signal transmission, and pure PLA material lacks toughness, making it prone to cracking or breakage under repeated bending. These factors, to some extent, limit the use of PLA.

[0004] To promote the application of PLA in the sensor field, current modification strategies include physicochemical modification and surface coating modification. Barrier substances, antibacterial substances, and plasticizers are added, and the performance of PLA is enhanced through casting or coating processes. However, most PLA-based films currently possess only a single function. For example, biodegradable films lack conductivity and cannot be used to prepare conductive sensor substrates; while sensor substrates with both conductivity and hydrophobicity cannot achieve biodegradability. Therefore, realizing a multifunctional sensor substrate that is biodegradable, conductive, and highly hydrophobic remains a significant challenge. Summary of the Invention

[0005] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0006] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0007] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a biodegradable flexible conductive and highly hydrophobic composite membrane.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: it is obtained by tightly bonding an electrospun film with a three-layer sandwich structure and a carbon nanotube conductive film; The electrospun membrane with the three-layer sandwich structure consists of a polylactic acid spinning layer, a chitosan / polyethylene oxide blend spinning layer, and a polylactic acid spinning layer. As a preferred embodiment of the biodegradable flexible conductive hydrophobic composite membrane of the present invention, the flexible substrate layer of the sandwich structure is a hydrophobic-hydrophilic-hydrophobic sandwich structure, and the thickness ratio of each layer is 0.5~2:0.5~3:0.5~2.

[0009] As a preferred embodiment of the biodegradable flexible conductive and highly hydrophobic composite membrane of the present invention, wherein the mass ratio of chitosan to polyethylene oxide in the chitosan / polyethylene oxide mixed layer is 5~9:1~5.

[0010] Another objective of this invention is to provide a method for preparing a biodegradable flexible conductive and highly hydrophobic composite membrane.

[0011] To solve the above-mentioned technical problems, the present invention provides the following technical solution: including, Polylactic acid is dissolved in a mixed solvent of N,N-dimethylformamide and dichloromethane to obtain a PLA spinning solution with a mass concentration of 5~20wt%. Chitosan is dissolved in acetic acid solution and stirred until dissolved. Glycerin is then added, and the solution is obtained after the chitosan is completely dissolved. Polyethylene oxide was added to ultrapure water and magnetically stirred until dissolved to obtain a PEO solution; The CS solution and PEO solution are stirred until they are evenly mixed to obtain a CS-PEO blend spinning solution with a CS to PEO mass ratio of 5~9:1~5. PLA spinning solution and CS-PEO blended spinning solution were respectively filled into syringes and connected to the syringe pump of the electrospinning machine for electrospinning. First, an outer PLA spinning layer is spun, then a middle CS-PEO blend spinning layer is spun, and finally an inner PLA spinning layer is spun to form a three-layer sandwich electrospun film. The three-layer sandwich electrospun membrane was dried in a vacuum drying oven, and a carbon nanotube film was attached to the surface of the dried electrospun membrane to obtain a flexible conductive and highly hydrophobic composite membrane.

[0012] In a preferred embodiment of the preparation method of the biodegradable flexible conductive and hydrophobic composite membrane of the present invention, the amount of glycerol added is 20-40 wt% of chitosan.

[0013] As a preferred embodiment of the preparation method of the biodegradable flexible conductive and highly hydrophobic composite membrane of the present invention, the electrospinning flow rate is 0.1~2 ml / min, the distance between the needle and the collecting plate is 10~20 cm, the receiving roller speed is 20~300 r / min, and the translation speed is 20~70 cm / min.

[0014] In a preferred embodiment of the preparation method of the biodegradable flexible conductive and highly hydrophobic composite membrane of the present invention, the positive voltage during the electrospinning process is 10~21kV, the negative voltage is 1~3kV, and the ambient humidity is 30~75%.

[0015] In a preferred embodiment of the preparation method of the biodegradable flexible conductive and highly hydrophobic composite film of the present invention, the drying temperature of the drying treatment is 40~60℃ and the drying time is 6~12h.

[0016] Another objective of this invention is to provide a biodegradable flexible conductive and highly hydrophobic composite film as a sensor substrate for the preparation of food sensors and smart wearables.

[0017] Another object of the present invention is to provide a biodegradable flexible conductive and highly hydrophobic composite film for use as a food packaging material.

[0018] Beneficial effects of this invention: 1. This invention utilizes a three-layer sandwich structure combined with carbon nanotubes to give the substrate both high hydrophobicity (contact angle of 138°) and conductivity (resistance of 10 ohms). 2 -10 3 With its excellent flexibility (Ω), it solves the problem of traditional substrates having single functions or difficulty in achieving synergistic performance.

[0019] 2. The structure prepared by this invention has strong stability. The glycerol in the middle CS-PEO blended spinning layer can enhance the toughness of the substrate, the outer PLA layer provides structural support, and the carbon nanotube film and the spinning film are tightly bonded at the interface. After repeated stretching and bending, the performance degradation is small and the stability is excellent.

[0020] 3. This invention uses electrospinning technology to prepare the sandwich structure, with well-defined parameters (such as spinning voltage, flow rate, humidity, etc.), making it easy to control the microstructure of the membrane; the vacuum filtration method is used to composite carbon nanotube films, which is simple to operate and has good repeatability.

[0021] 4. The PLA, CS, PEO and carbon nanotubes used in this invention are all common materials with wide availability, low cost and excellent biocompatibility, making them suitable for applications in multiple fields. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1 This is a schematic diagram of the structure of the flexible conductive and highly hydrophobic sensor substrate prepared according to the present invention.

[0023] Figure 2 This is a water contact angle test diagram of the flexible conductive and highly hydrophobic composite membrane prepared in Example 1 of the present invention.

[0024] Figure 3 The resistance test diagram is shown for the flexible conductive and highly hydrophobic composite film prepared in Example 1 of this invention.

[0025] Figure 4 This is a bending schematic diagram of the flexible conductive and highly hydrophobic composite film prepared in Example 1 of the present invention.

[0026] Figure 5 This is a scanning electron microscope image of the flexible conductive and highly hydrophobic sensor substrate prepared in Example 1 of the present invention.

[0027] Figure 6 This is a comparison of the tensile properties of the electrospun films prepared by Comparative Examples 1 to 3 of the present invention.

[0028] Figure 7 This is a comparison of the tensile properties of different spun films in Examples 1 to 5 of the present invention.

[0029] Figure 8 These are scanning electron microscope images of the flexible conductive and highly hydrophobic composite films prepared in Comparative Examples 4 and 5 of this invention.

[0030] Figure 9 This is Comparative Example 5 of the present invention, showing the spinning effect of the middle layer of the spinning membrane after adjusting the spinning positive voltage parameters and flow rate.

[0031] Figure 10 This is a comparison diagram of the electrospun films prepared in Example 1 and Comparative Example 6 after a contact angle of 60 s.

[0032] Figure 11 This is a comparison of the tensile properties of the electrospun films prepared in Comparative Example 7 and Comparative Example 8. Detailed Implementation

[0033] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0034] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0035] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0036] Unless otherwise specified, all raw materials used in this invention are commercially available in the field. Example 1

[0037] This embodiment provides a method for preparing a biodegradable flexible conductive and highly hydrophobic composite film, specifically: Polylactic acid (PLA) powder was dissolved in a mixed solvent of N,N-dimethylformamide (DMF) and dichloromethane (DCM) in a volume ratio of 7:3 and stirred until completely dissolved to obtain a polylactic acid spinning solution with a mass concentration of 10 wt%. Chitosan (CS) was dissolved in a 1% acetic acid solution. After stirring until dissolved, 30 wt% of glycerol was added. After the chitosan was completely dissolved, a 3 wt% chitosan solution was obtained. 3g of polyethylene oxide (PEO) was added to 100g of ultrapure water and magnetically stirred for 10 hours until dissolved to obtain a PEO solution. Take 70 ml of CS solution and 30 ml of PEO solution and stir until they are evenly mixed to form a CS-PEO blend spinning solution with a CS to PEO mass ratio of 7:3. Polylactic acid spinning solution and CS-PEO blend spinning solution were respectively filled into syringes and connected to the syringe pump of the electrospinning machine. The electrospinning parameters were set as follows: The flow rate was 0.2 ml / min, the distance between the needle and the collecting plate was 16 cm, the receiving roller rotation speed was 50 r / min, and the translation speed was 45 cm / min. First, an outer PLA spinning layer is spun, then a middle CS-PEO blend spinning layer is spun, and finally an inner PLA spinning layer is spun to form a three-layer sandwich electrospun film with a thickness ratio of 1:1.5:1. The electrospun membrane with a three-layer sandwich structure was placed in a vacuum drying oven and dried at 45°C for 12 hours to remove residual DMF and DCM solvents. Carbon nanotubes and sodium dodecylbenzenesulfonate were added to ultrapure water at a mass ratio of 1:3. The mixture was sonicated for 30 minutes and magnetically stirred to obtain a uniformly dispersed carbon nanotube solution with a concentration of 1 mg / mL. The solution was then used to prepare a carbon nanotube film by vacuum filtration. The film was then bonded to the dried electrospun membrane surface with conductive silver paste to obtain the flexible conductive and highly hydrophobic composite membrane of this embodiment.

[0038] Figure 1 This is a schematic diagram of the flexible conductive and highly hydrophobic composite film prepared in this embodiment. It is composited with carbon nanotubes through a three-layer sandwich structure design. The electrospun film of the three-layer sandwich structure consists of a polylactic acid (PLA) spinning layer, a chitosan / polyethylene oxide (PEO) blend spinning layer, and another PLA spinning layer, with a thickness ratio of 1:1.5:1. This substrate also possesses high hydrophobicity (e.g., ...). Figure 2 As shown, its contact angle is 138°) conductivity (such as Figure 3 As shown, the resistance is 122.2Ω) and it has excellent flexibility (such as... Figure 4 As shown in the figure, it solves the problem of traditional substrates having single functions or difficulty in coordinating performance.

[0039] Figure 5 The image shows a scanning electron microscope (SEM) image of the flexible conductive and highly hydrophobic composite membrane prepared in this embodiment. As can be seen from the image, the flexible conductive and highly hydrophobic composite membrane has a tight and uniform spinning structure, with fibers that are interwoven and stacked, uniform in shape and thickness, and without any unevenness in the size of the liquid droplets. The fibers exhibit a uniform and disordered network structure. Example 2

[0040] The difference between this embodiment and Example 1 is that the volume ratio of chitosan solution and PEO solution is adjusted to 60ml:40ml to form a chitosan-PEO blend spinning solution with a mass ratio of CS to PEO of 6:4. The remaining steps and processes are the same as in Example 1, resulting in the flexible conductive and highly hydrophobic composite film of this embodiment. Example 3

[0041] The difference between this embodiment and Example 1 is that the volume ratio of chitosan solution and PEO solution is adjusted to 50ml:50ml to form a chitosan-PEO blend spinning solution with a mass ratio of CS to PEO of 5:5. The remaining steps and processes are the same as in Example 1, resulting in the flexible conductive and highly hydrophobic composite film of this embodiment. Example 4

[0042] The difference between this embodiment and Example 1 is that the volume ratio of chitosan solution and PEO solution is adjusted to 80ml:20ml to form a chitosan-PEO blend spinning solution with a CS to PEO mass ratio of 8:2. The remaining steps and processes are the same as in Example 1, resulting in the flexible conductive and highly hydrophobic composite film of this embodiment. Example 5

[0043] The difference between this embodiment and Example 1 is that the volume ratio of chitosan solution and PEO solution is adjusted to 90ml:10ml to form a chitosan-PEO blend spinning solution with a CS to PEO mass ratio of 9:1. The remaining steps are the same as in Example 1, resulting in the flexible conductive and highly hydrophobic composite membrane of this embodiment. Comparative Example 1

[0044] This comparative example prepared an electrospun membrane based solely on CS and PEO, specifically: 1) Prepare CS solution and PEO solution according to the method in Example 1. Take 70 ml of CS solution and 30 ml of PEO solution and stir evenly to obtain the blended spinning solution.

[0045] 2) The blending spinning solution is loaded into a syringe and connected to the syringe pump of the electrospinning machine. The electrospinning parameters are set as follows: The flow rate was 0.2 ml / min, the distance between the needle and the collecting plate was 16 cm, the receiving roller rotation speed was 50 r / min, and the translation speed was 45 cm / min. 3) After spinning, the film was dried at 45°C under vacuum for 6 hours to remove residual solvent, thus obtaining the electrospun film (CS / PEO) of this comparative example. Comparative Example 2

[0046] This comparative example prepared an electrospun film based solely on PLA, specifically: 1) A polylactic acid spinning solution with a mass concentration of 10 wt% was prepared according to the method in Example 1; 2) The polylactic acid spinning solution is loaded into a syringe and connected to the syringe pump of the electrospinning machine. The electrospinning parameters are set as follows: The flow rate was 0.2 ml / min, the distance between the needle and the collecting plate was 16 cm, the receiving roller speed was 200 r / min, and the translation speed was 45 cm / min. 3) After spinning, the film is dried under vacuum at 45°C for 12 hours to remove residual solvent, thus obtaining the electrospun film (PLA) of this comparative example. Comparative Example 3

[0047] This comparative example provides an electrospun film based on CS and PVA, specifically: 1) Chitosan is dissolved in a 1% acetic acid solution. After stirring until dissolved, 30% (by weight of chitosan) of glycerol is added. Once the chitosan is completely dissolved, a chitosan solution with a concentration of 3% (w%) is obtained. 10g of PVA was added to 100g of ultrapure water and magnetically stirred for 10 hours until dissolved, yielding a PVA solution with a concentration of 10% (w%). Take 70 ml of CS solution and 30 ml of PVA solution and stir until they are evenly mixed to form a CS-PVA blend spinning solution with a CS to PVA mass ratio of 7:3.

[0048] 2) Fill the CS-PVA blend spinning solution into syringes, connect them to the syringe pump of the electrospinning machine, and set the electrospinning parameters as follows: The flow rate was 0.3 ml / min, the distance between the needle and the collecting plate was 16 cm, the receiving roller speed was 60 r / min, the translation speed was 45 cm / min, the positive voltage was 17 kV, the negative voltage was -1.52 kV, the ambient temperature was 25℃, and the ambient humidity was 50%.

[0049] After spinning, the film was dried under vacuum at 45°C for 6 hours to remove residual solvent, thus obtaining the electrospun film (CS / PVA) of this comparative example.

[0050] Figure 6 A comparison of the tensile properties of the electrospun films obtained in Comparative Examples 1 to 3 shows that the spun film obtained in Comparative Example 3 is too hard, brittle, and prone to cracking, making it unsuitable for forming a flexible film with PLA. Figure 9 As shown, even after adjusting the spinning positive voltage parameters and flow rate, the spinning of the middle layer of the spinning membrane failed, and it formed liquid droplets, failing to form a film on the PLA membrane and unable to be evenly distributed on the roller collector; while Comparative Example 1 could form a soft and unbreakable film with PLA, indicating that the co-spinning of CS and PEO can better achieve the formation of a flexible substrate.

[0051] The contact angles and resistances of different spinning films from Examples 1 to 5 and Comparative Examples 1 and 2 are compared, and the results are shown in Table 1.

[0052] Table 1 Figure 7 This section compares the tensile properties of the electrospun films prepared in Examples 1-5, with proportions corresponding to spun films of different CS and PEO ratios in Examples 1-5. Figure 7As shown in Table 1, when the mass ratio of CS to PEO is 7:3, the composite membrane exhibits the best overall performance, with superior hydrophobicity, conductivity, and tensile stability. This is because the flexibility and structural support of the intermediate fiber are balanced under this ratio, resulting in a tighter interfacial bond with the outer PLA and carbon nanotube films, which synergistically enhances the multifunctional properties of the composite membrane. Comparative Example 4

[0053] The difference between this comparative example and Example 1 is that the concentration of polylactic acid spinning solution in step 1) is adjusted to 8 wt%, while the remaining steps are the same as in Example 1, to obtain the flexible conductive and highly hydrophobic composite film of this comparative example. Comparative Example 5

[0054] The difference between this comparative example and Example 1 is that the concentration of polylactic acid spinning solution in step 1) is adjusted to 12wt%, while the remaining steps are the same as in Example 1, to obtain the flexible conductive and highly hydrophobic composite film of this comparative example.

[0055] Figure 8 The images show scanning electron microscope (SEM) images of the flexible conductive and highly hydrophobic composite membranes prepared in Comparative Examples 4 and 5. As can be seen from the images, the composite membrane obtained by adjusting the PLA concentration has an insufficiently dense and uniform spinning structure, and its morphology is not uniform. There are obvious inconsistencies in thickness and droplet size. The fibers exhibit a disordered network structure, which is significantly different from Example 1. Comparative Example 6

[0056] This comparative example provides an electrospun film with PLA as the core, specifically: A polylactic acid spinning solution with a mass concentration of 10 wt% was prepared according to the method in Example 1; CS solution and PEO solution were prepared according to the method in Example 1. 70 ml of CS solution and 30 ml of PEO solution were stirred evenly to obtain the blended spinning solution.

[0057] 2) The polylactic acid spinning solution and the CS-PEO blend spinning solution are respectively filled into syringes and connected to the syringe pump of the electrospinning machine. The electrospinning parameters are set as follows: The flow rate was 0.2 ml / min, the distance between the needle and the collecting plate was 16 cm, the receiving roller speed was 50 r / min, the translation speed was 45 cm / min, the positive voltage was 17 kV, the negative voltage was -1.52 kV, the ambient temperature was 25℃, and the ambient humidity was 50%. First, a CS-PEO blended spinning layer is spun, then a PLA spinning layer is spun, and finally a CS-PEO blended spinning layer is spun to form a three-layer sandwich electrospun film. 3) After spinning, the film was dried at 45°C under vacuum for 6 hours to remove residual solvent, thus obtaining the electrospun film (CS / PEO-PLA-CS / PEO) of this comparative example.

[0058] Figure 10 This is a comparison diagram of the electrospun films prepared in Example 1 and Comparative Example 6 after a contact angle of 60 s. Figure 10 A and Figure 10 B represents the change in contact angle of Example 1 after 60 seconds, which is unchanged. Figure 10 C and Figure 10 D represents the change in contact angle of Comparative Example 6 after 60 seconds, which changed from 125.3° to 90.3°. It can be seen that the hydrophobic effect of Example 1 is significantly higher than that of Comparative Example 6. Comparative Example 7

[0059] The difference between this comparative example and Example 1 is that the thickness ratio of the electrospun film with the three-layer sandwich structure is adjusted to 1:0.5:1. The remaining steps and processes are the same as in Example 1, resulting in the flexible conductive and highly hydrophobic composite film of this example. Comparative Example 8

[0060] The difference between this comparative example and Example 1 is that the thickness ratio of the electrospun film with the three-layer sandwich structure is adjusted to 1:2.5:1. The remaining steps and processes are the same as in Example 1, resulting in the flexible conductive and highly hydrophobic composite film of this example.

[0061] Figure 11 To compare the tensile properties of electrospun films with different thickness ratios obtained in Comparative Examples 7 and 8, the figure shows electrospun films with different thickness ratios. It can be seen that the intermediate layer of the electrospun film obtained in Comparative Example 7 is relatively thin, and it is brittle and has poor flexibility during stretching, making it prone to cracking. The intermediate layer of the electrospun film obtained in Comparative Example 8 is relatively thick, and the intermediate interlayer is too hard, making it unable to form good flexibility with the soft outer layer. This indicates that a thickness ratio of 1:1.5:1 can better achieve the construction of a flexible substrate.

[0062] In summary, the PLA-CS / PEO-PLA sandwich structure designed in this invention utilizes a CS / PEO blended spinning core layer to improve brittleness, while the flexible PEO segments buffer stress, and CS induces crack deflection. These two elements synergistically enhance the PLA's resistance to bending fracture, cleverly achieving functional integration and complementary advantages. Specifically, the outermost layers are pure polylactic acid, primarily providing mechanical support, high hydrophobic protection (contact angle up to 138°), and a biodegradable main framework; the middle layer is a chitosan / polyethylene oxide blend functional layer. With a carbon nanotube filtration membrane attached to one side, this four-layer structure, through a synergistic effect, ultimately enables the substrate to simultaneously possess biodegradability, flexibility, hydrophobicity, and conductivity.

[0063] This invention addresses the technical bottleneck of existing sensor substrates in achieving a balance between biocompatibility, high hydrophobicity, flexibility, and conductivity by proposing an innovative composite preparation strategy based on multilayer electrospinning and carbon nanotube transfer bonding.

[0064] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A biodegradable, flexible, conductive, and highly hydrophobic composite membrane, characterized in that: It is obtained by tightly bonding an electrospun membrane with a three-layer sandwich structure and a carbon nanotube conductive film. The electrospun membrane with the three-layer sandwich structure is composed of a polylactic acid spinning layer, a chitosan / polyethylene oxide blend spinning layer, and a polylactic acid spinning layer, with a thickness ratio of 0.5~2:0.5~3:0.5~2 for each layer. The polylactic acid (PLA) spinning layer is obtained by electrospinning PLA spinning solution, wherein the concentration of PLA in the PLA spinning solution is 5-20 wt%.

2. The biodegradable flexible conductive and highly hydrophobic composite membrane as described in claim 1, characterized in that: The three-layer sandwich structure is a hydrophobic-hydrophilic-hydrophobic sandwich structure.

3. The biodegradable flexible conductive and highly hydrophobic composite membrane as described in claim 1, characterized in that: The mass ratio of chitosan to polyethylene oxide in the chitosan / polyethylene oxide hybrid layer is 5~9:1~5.

4. The method for preparing the biodegradable flexible conductive and highly hydrophobic composite membrane according to any one of claims 1 to 3, characterized in that: include, Polylactic acid is dissolved in a mixed solvent of N,N-dimethylformamide and dichloromethane to obtain a PLA spinning solution with a mass concentration of 5~20wt%. Chitosan is dissolved in acetic acid solution and stirred until dissolved. Glycerin is then added, and the solution is obtained after the chitosan is completely dissolved. Polyethylene oxide is added to ultrapure water and magnetically stirred until dissolved to obtain a PEO solution; The CS solution and PEO solution are stirred until they are evenly mixed to obtain a CS-PEO blend spinning solution with a CS to PEO mass ratio of 5~9:1~5. PLA spinning solution and CS-PEO blended spinning solution were respectively filled into syringes and connected to the syringe pump of the electrospinning machine for electrospinning. First, an outer PLA spinning layer is spun, then a middle CS-PEO blend spinning layer is spun, and finally an inner PLA spinning layer is spun to form a three-layer sandwich electrospun film. The three-layer sandwich electrospun membrane was dried in a vacuum drying oven, and a carbon nanotube film was attached to the surface of the dried electrospun membrane to obtain a flexible conductive and highly hydrophobic composite membrane.

5. The method for preparing the biodegradable flexible conductive and highly hydrophobic composite membrane as described in claim 4, characterized in that: The amount of glycerol added is 20-40 wt% of chitosan.

6. The method for preparing the biodegradable flexible conductive and highly hydrophobic composite membrane as described in claim 4, characterized in that: The electrospinning flow rate is 0.1~2 ml / min, the distance between the needle and the collecting plate is 10~20 cm, the receiving roller speed is 20~300 r / min, and the translation speed is 20~70 cm / min.

7. The method for preparing the biodegradable flexible conductive and highly hydrophobic composite membrane as described in claim 6, characterized in that: The positive voltage during the electrospinning process is 10~21kV, the negative voltage is 1~3kV, and the ambient humidity is 30%~75%.

8. The method for preparing the biodegradable flexible conductive and highly hydrophobic composite membrane as described in claim 4, characterized in that: The drying temperature for the drying process is 40~60℃, and the drying time is 6~12h.

9. The application of the biodegradable flexible conductive and highly hydrophobic composite film as described in any one of claims 1 to 3 as a sensor substrate in the preparation of food sensors and smart wearables.

10. The application of the biodegradable flexible conductive and highly hydrophobic composite film as described in any one of claims 1 to 3 as a food packaging material.

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