A green and degradable composite nanofiber membrane and its preparation method and application

Abstract

The present invention provides a green and degradable composite nanofiber membrane and a preparation method thereof. The composite nanofiber membrane is prepared by electrospinning CO2-PU and PLLA, wherein the CO2-PU is prepared from carbon dioxide and 1,6-hexamethylenediamine. The present invention effectively improves the piezoelectric properties of PLLA by adding CO2-PU to PLLA. In addition, the present invention uses carbon dioxide instead of isocyanate for preparation, which is beneficial to the resource utilization of carbon dioxide, reduces the use of highly toxic pollutants, and has the advantage of being green and environmentally friendly. At the same time, the prepared composite nanofiber membrane has a uniform diameter distribution, is degradable, and has the advantages of good thermal stability, and can be applied to piezoelectric sensors.

Description

Technical Field

[0001] The present invention belongs to the field of intelligent polymer materials, and in particular relates to a green and degradable composite nanofiber membrane and a preparation method and application thereof. Background Art

[0002] Piezoelectric materials, including inorganic and organic piezoelectric materials, are materials that convert mechanical energy into electrical energy. They are widely used in actuators, transducers, sensors, and other applications. With the development of smart wearables, flexible piezoelectric materials have become a research hotspot.

[0003] While inorganic piezoelectric materials possess excellent piezoelectric properties and high dielectric constants, they are generally hard and brittle, making them difficult to bend or shape-process into, limiting their application in flexible applications. Organic piezoelectric materials, such as polyvinylidene fluoride (PVDF), possess excellent piezoelectric and flexural properties, allowing for large deformations, and have been extensively studied in recent years. However, the production of PVDF relies on traditional fossil fuels, which is not conducive to sustainable development.

[0004] Polylactic acid (PLLA), an environmentally friendly bio-based polyester, is a biodegradable polymer material of great research value. The presence of a -C=O dipole in its molecular structure also imparts piezoelectric properties to PLLA. However, the piezoelectric properties of current PLLA-based materials are generally low. Therefore, in order to improve piezoelectric properties, it is necessary to develop new PLLA-based composite materials. Summary of the Invention

[0005] Based on the above technical background, the inventors have made great progress and found that the composite nanofiber membrane prepared by adding CO2-PU to PLLA has better piezoelectric properties than PLLA and CO2-PU. At the same time, CO2-PU is prepared from carbon dioxide and 1,6-hexanediamine, and is prepared with carbon dioxide instead of isocyanate, which is not only beneficial to the resource utilization of carbon dioxide, but also can reduce the use of highly toxic pollutants. The preparation process is green, environmentally friendly and pollution-free. In addition, the composite nanofiber membrane has a uniform diameter distribution, good thermal stability and degradability, can be used in piezoelectric sensors, and the prepared piezoelectric sensors have good piezoelectric stability.

[0006] The first aspect of the present invention is to provide a green and degradable composite nanofiber membrane, which is made of CO2-PU and PLLA through electrostatic spinning.

[0007] The second aspect of the present invention is to provide a method for preparing the green degradable composite nanofiber membrane according to the first aspect of the present invention, the preparation method comprising the following steps:

[0008] Step 1: 1,6-hexanediamine is dissolved in a solvent, and CO2 is introduced therein to react to obtain CO2-PU;

[0009] Step 2: dissolving PLLA and the CO2-PU prepared in step 1 in a mixed solvent to obtain a composite spinning solution;

[0010] Step 3: electrospinning the composite spinning solution obtained in step 2 to obtain a composite nanofiber membrane.

[0011] The third aspect of the present invention is to provide an application of the green degradable composite nanofiber membrane according to the first aspect of the present invention or the green degradable composite nanofiber membrane prepared by the preparation method described in the second aspect of the present invention, which can be used in piezoelectric sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Shown are scanning electron microscope photos of the products obtained in Examples 1 to 6 and the comparative example;

[0013] Figure 2 Scanning electron microscope photographs of Example 3 and Examples 7 to 11 are shown;

[0014] Figure 3 Shown are the XRD diffraction patterns of the products obtained in Examples 1 to 6 and the comparative example;

[0015] Figure 4 The infrared spectrum test graphs of the products obtained in Examples 1 to 6 and the comparative example are shown;

[0016] Figure 5 TG graphs of PLLA and CO2-PU prepared in the comparative example and the composite nanofiber membrane prepared in Example 3 are shown;

[0017] Figure 6 The piezoelectric performance test diagrams of the products obtained in Examples 1 to 6 and the comparative example are shown;

[0018] Figure 7 The piezoelectric performance test diagrams of the products obtained in Example 3 and Examples 7 to 11 are shown;

[0019] Figure 8 Showing water contact angle test photos of the composite nanofiber membranes prepared in Examples 1 to 6, and the PLLA and CO2-PU fiber membranes prepared in the comparative example;

[0020] Figure 9 A photo showing the stability test of the piezoelectric sensor;

[0021] Figure 10 Photos showing the application test of piezoelectric sensors. DETAILED DESCRIPTION

[0022] The present invention will be described in detail below, and the characteristics and advantages of the present invention will become clearer and more distinct with the following description.

[0023] The first aspect of the present invention is to provide a green and degradable composite nanofiber membrane, which is made by electrostatic spinning of CO2-PU (PU is polyurea) and PLLA (polylactic acid).

[0024] The present inventors have found that the piezoelectric properties of the composite nanofiber membrane prepared from PLLA and CO2-PU are significantly improved, and are higher than the piezoelectric properties of PLLA or CO2-PU.

[0025] The mass ratio of the CO2-PU to the PLLA is (0.02-0.6):1, preferably (0.05-0.5):1, and more preferably (0.07-0.4):1.

[0026] Experiments have shown that as the amount of CO2-PU added increases, the piezoelectric properties of the composite nanofiber membrane gradually improve, but if the amount added is too much, the piezoelectric properties gradually decrease, which is not conducive to the improvement of the piezoelectric properties.

[0027] The CO2-PU of the present invention is prepared from carbon dioxide and 1,6-hexanediamine, and the molar ratio of carbon dioxide to 1,6-hexanediamine is (5-11):1, preferably (6-10):1, and more preferably (7-9):1.

[0028] In the field of piezoelectric materials, the polyurea used in existing technologies requires the reaction of phosgene or isocyanate with diamine during its preparation. Phosgene is highly toxic, and isocyanate is also toxic and carcinogenic. CO2 is a major greenhouse gas and a vital carbon resource. Using CO2 as a raw material instead of highly toxic phosgene or isocyanate to prepare polyurea not only reduces the use of highly toxic pollutants but also facilitates the resource utilization of CO2, offering raw material advantages and significant social and environmental benefits.

[0029] The green and degradable composite nanofiber membrane of the present invention has a water contact angle of 123-135° and good hydrophobicity.

[0030] The fiber diameter of the composite nanofiber membrane is 100-500nm, the thermal degradation temperature is 300-340°C, the piezoelectric performance is good, and the piezoelectric sensor made from the composite nanofiber membrane has good piezoelectric stability.

[0031] The present invention firstly synthesizes CO2-PU using CO2 and hexamethylenediamine as raw materials, and then utilizes electrostatic spinning technology to compound CO2-PU and L-polylactic acid (PLLA) to prepare CO2-PU / PLLA composite nanofiber membrane.

[0032] The second aspect of the present invention is to provide a method for preparing the green degradable composite nanofiber membrane according to the first aspect of the present invention, the preparation method comprising the following steps:

[0033] Step 1: 1,6-hexanediamine is dissolved in a solvent, and CO2 is introduced therein to react to obtain CO2-PU;

[0034] Step 2: dissolving PLLA and the CO2-PU prepared in step 1 in a mixed solvent to obtain a composite spinning solution;

[0035] Step 3: electrospinning the composite spinning solution obtained in step 2 to obtain a composite nanofiber membrane.

[0036] This step is described and explained in detail below.

[0037] Step 1: 1,6-hexanediamine is dissolved in a solvent, and CO2 is introduced therein to react to obtain CO2-PU.

[0038] The solvent is selected from one or more of N-methylpyrrolidone, N,N-dimethylformamide and tetrahydrofuran, preferably one or two of N-methylpyrrolidone and N,N-dimethylformamide.

[0039] After 1,6-hexanediamine is dissolved in the solvent, its molar concentration is 2 to 3 mmol / mL, preferably 2.3 to 2.7 mmol / mL.

[0040] The amount of carbon dioxide introduced is 3 to 7 MPa, preferably 4 to 6 MPa, and more preferably 5 MPa.

[0041] The reaction is preferably carried out in a batch reactor at a reaction temperature of 150 to 220°C, preferably 160 to 200°C, and more preferably 170 to 190°C.

[0042] The reaction time is 5 to 15 hours, preferably 7 to 12 hours, and more preferably 9 to 11 hours.

[0043] The reaction is carried out under stirring at a stirring speed of 500 to 1000 r / min, preferably 700 to 900 r / min.

[0044] After the reaction is completed, the product is washed and dried. The washing agent is preferably one or more of water, ethanol, acetone, methanol and N,N-dimethylformamide, preferably one or two of water and ethanol.

[0045] The drying temperature is 60 to 90° C., preferably 70 to 80° C., and the drying time is 10 to 15 hours, preferably 12 to 13 hours.

[0046] Step 2: PLLA and the CO2-PU prepared in step 1 are dissolved in a mixed solvent to obtain a composite spinning solution.

[0047] The mass ratio of the CO2-PU to the PLLA is (0.02-0.6):1, preferably (0.05-0.5):1, and more preferably (0.07-0.4):1.

[0048] The mixed solvent is obtained by mixing dichloromethane and hexafluoroisopropanol, wherein the volume ratio of dichloromethane to hexafluoroisopropanol is (4-10):3, and preferably the volume ratio is (6-7):3. Dichloromethane and hexafluoroisopropanol are commonly used solvents for electrospinning. PLLA has good solubility in dichloromethane, and CO2-PU has good solubility in hexafluoroisopropanol. Therefore, the dichloromethane and hexafluoroisopropanol mixed solvent is selected to completely dissolve PLLA and CO2-PU, thereby obtaining a uniform composite spinning solution.

[0049] The dissolution is carried out under stirring at a temperature of 25 to 40° C., preferably 30° C., which is conducive to the smooth dissolution of CO2-PU and PLLA.

[0050] The mass concentration of the composite spinning solution is 0.7 to 1.2 g / mL, preferably 0.8 to 1.1 g / mL, and more preferably 0.85 to 1.05 g / mL.

[0051] The mass concentration of the composite spinning solution will affect the progress of electrospinning and the diameter distribution of the obtained fibers. The composite spinning solution in the above mass concentration range is not only conducive to the spinning process, but also the diameter of the obtained composite nanofibers is uniform.

[0052] Step 3: electrospinning the composite spinning solution obtained in step 2 to obtain a composite nanofiber membrane.

[0053] In the present invention, the electrospinning voltage is 15 to 25 kV, preferably 17 to 23 kV, and more preferably 18 to 21 kV.

[0054] The electrospinning speed is 1 to 3 mL / h, preferably 1.5 to 2.5 mL / h, and more preferably 1.8 to 2.2 mL / h.

[0055] The electrostatic spinning distance is 5 to 20 cm, preferably 7 to 15 cm, and more preferably 9 to 12 cm.

[0056] The electrospinning time is 1 to 4 hours, preferably 1.5 to 3 hours, and more preferably 1.8 to 2.5 hours.

[0057] The receiving roll has a rotation speed of 50 to 4000 r / min, preferably 70 to 3500 r / min, and more preferably 100 to 3000 r / min.

[0058] Experiments have shown that the rotation speed of the receiving roller has a great influence on the piezoelectric properties of the prepared composite nanofiber membrane. As the rotation speed of the receiving roller increases, the piezoelectric properties of the composite nanofiber membrane decreases. When the rotation speed of the receiving roller is within the above range, the piezoelectric properties of the composite nanofiber membrane are good, and the fiber diameter is evenly distributed.

[0059] The third aspect of the present invention is to provide an application of the green degradable composite nanofiber membrane according to the first aspect of the present invention or the green degradable composite nanofiber membrane prepared by the preparation method described in the second aspect of the present invention, which can be used in piezoelectric sensors.

[0060] The beneficial effects of the present invention are:

[0061] (1) The raw materials of the composite nanofiber membrane of the present invention are widely available and low in toxicity. The preparation process is safe and does not produce toxic substances. This not only reduces the use of highly toxic pollutants but also facilitates the resource utilization of carbon dioxide.

[0062] (2) The composite nanofiber membrane of the present invention has uniform fiber diameter distribution, good piezoelectric properties, is biodegradable, and is environmentally friendly, and can be used in piezoelectric sensors;

[0063] (3) The composite fiber membrane of the present invention has a large water contact angle and good hydrophobicity, and also has the advantage of good thermal stability;

[0064] (4) The piezoelectric sensor made of the composite fiber membrane of the present invention has good piezoelectric stability.

[0065] Example

[0066] The present invention is further described below through specific examples. These examples are only intended to illustrate the present invention and are not intended to limit the scope of the present invention.

[0067] Example 1

[0068] 5 mmol of HMDA (1,6-hexanediamine) and 2 mL of NMP (N-methylpyrrolidone) were added to a batch reactor. The reactor was sealed and purged with CO2 to displace the air in the reactor and the solvent. Then, 5 MPa of CO2 was added. The reactor was placed in a 180°C furnace with a magnetic stirrer set at 800 rpm for 10 hours. After the reaction, the reactor was cooled to room temperature, the unreacted CO2 was released, and the solid product was collected. The product was washed several times with deionized water and ethanol to obtain a white solid, CO2-PU. This solid was dried in a vacuum oven at 80°C for 12 hours and then ground into a powder.

[0069] 0.8 g of PLLA and 0.07 g of CO2-PU (8 wt%) were placed in a 25 mL stoppered flask and dissolved in 10 mL of a mixed solvent of DCM (dichloromethane) and HFIP (hexafluoroisopropanol) at 30 °C with stirring. DCM :V HFIP =7:3) to obtain CO2-PU / PLLA composite spinning solution.

[0070] A high-voltage electrospinning machine (TL-Pro-BM, Shenzhen Tongli Micro-Nano Technology Co., Ltd.) was used with aluminum foil as the substrate, the receiving roller speed was 300 r / min, the spinning voltage was 20 kV, the spinning speed was 2 mL / h, the spinning distance was 10 cm, and the spinning time was 2 h. The above composite spinning solution was spun to prepare CO2-PU / PLLA composite nanofiber membrane, which was named PLLA-8.

[0071] Example 2

[0072] A nanofiber membrane was prepared in a manner similar to Example 1, except that 0.8 g of PLLA and 0.11 g of CO2-PU (12 wt%) were placed in a 25 mL stoppered Erlenmeyer flask. This resulted in a CO2-PU / PLLA composite nanofiber membrane, designated PLLA-12.

[0073] Example 3

[0074] A nanofiber membrane was prepared in a manner similar to Example 1, except that 0.8 g of PLLA and 0.15 g of CO2-PU (16 wt%) were placed in a 25 mL stoppered Erlenmeyer flask. This resulted in a CO2-PU / PLLA composite nanofiber membrane, designated PLLA-16.

[0075] Example 4

[0076] A nanofiber membrane was prepared in a manner similar to Example 1, except that 0.8 g of PLLA and 0.20 g of CO2-PU (20 wt%) were placed in a 25 mL stoppered Erlenmeyer flask to prepare a CO2-PU / PLLA composite nanofiber membrane, designated PLLA-20.

[0077] Example 5

[0078] A nanofiber membrane was prepared in a manner similar to Example 1, except that 0.8 g of PLLA and 0.25 g of CO2-PU (24 wt%) were placed in a 25 mL stoppered Erlenmeyer flask. This produced a CO2-PU / PLLA composite nanofiber membrane, designated PLLA-24.

[0079] Example 6

[0080] A nanofiber membrane was prepared in a manner similar to Example 1, except that 0.8 g of PLLA and 0.31 g of CO2-PU (28 wt%) were placed in a 25 mL stoppered Erlenmeyer flask. This produced a CO2-PU / PLLA composite nanofiber membrane, designated PLLA-28.

[0081] Example 7

[0082] The nanofiber membrane was prepared in a manner similar to Example 3, except that the receiving roller rotated at a speed of 100 r / min.

[0083] Example 8

[0084] The nanofiber membrane was prepared in a manner similar to Example 3, except that the receiving roller rotated at 600 r / min.

[0085] Example 9

[0086] The nanofiber membrane was prepared in a manner similar to Example 3, except that the receiving roller rotated at a speed of 1000 r / min.

[0087] Example 10

[0088] The nanofiber membrane was prepared in a manner similar to Example 3, except that the receiving roller rotated at a speed of 2000 r / min.

[0089] Example 11

[0090] The nanofiber membrane was prepared in a manner similar to Example 3, except that the receiving roller rotated at a speed of 3000 r / min.

[0091] Comparative Example

[0092] Comparative Example 1

[0093] The nanofiber membrane was prepared in a manner similar to Example 1, except that no CO2-PU was added.

[0094] Comparative Example 2

[0095] The nanofiber membrane was prepared in a manner similar to Example 1, except that PLLA was not added.

[0096] Experimental example

[0097] Experimental Example 1 SEM test

[0098] The products obtained in Examples 1 to 11 and the comparative examples were tested by scanning electron microscopy using a field emission scanning electron microscope (SEM, JSM-7500F, JEOL Ltd.). The test results of the products obtained in Comparative Examples 1 to 2 and Examples 1 to 6 are as follows: Figure 1 a, 1b, 1c, 1d, 1e, 1f, 1g and 1h, the test results of Example 3 and Examples 7 to 11 are as shown in Figure 2 As shown in a, 2b, 2c, 2d, 2e and 2f.

[0099] from Figure 1 and Figure 2 It can be seen that the diameter of the composite nanofibers prepared in Examples 1 to 11 of the present invention is smaller than that of the PLLA fibers, ranging from 100 to 500 nm, and has a uniform diameter distribution.

[0100] Experimental Example 2 XRD test

[0101] The products obtained in Examples 1 to 6 and the comparative example were tested by X-ray diffractometer (XRD, D8 DISCOVER, Bruker, Germany). Figure 3 shown.

[0102] from Figure 3 It can be seen that the spectra of the products obtained in Examples 1 to 6 have no obvious characteristic peaks, indicating that the obtained composite nanofiber membranes are not crystallized.

[0103] Experimental Example 3 FT-IR test

[0104] The products obtained in Examples 1 to 6 and the comparative example were tested by infrared spectroscopy using a Fourier transform infrared spectrometer (FT-IR, Thermo Nicolet iS10, Thermo Fisher Scientific). The test results are shown in FIG. Figure 4 shown.

[0105] from Figure 4 It can be seen that the characteristic peaks attributable to PLLA in the products prepared in Examples 1 to 6 did not shift, while the characteristic peaks attributable to CO2-PU red-shifted, indicating that there is a synergistic effect between PLLA and CO2-PU.

[0106] Experimental Example 4 TG Test

[0107] The thermal stability of the PLLA and CO2-PU nanofiber membranes prepared in the comparative example and the nanofiber membrane prepared in Example 3 was tested using a thermogravimetric analyzer (TG, 209F1, NETZSCH, Germany) at a heating rate of 10°C / min. Figure 5 a, 5b and 5c.

[0108] from Figure 5As can be seen from the results, the degradation temperature of the composite nanofiber membrane prepared in Example 3 is higher than 300°C, indicating that the addition of CO2-PU to PLLA can maintain good thermal stability of the nanofiber membrane. It can also be seen that the degradation temperature of Example 3 is lower than that of PLLA and CO2-PU, indicating that the addition of CO2-PU to PLLA can improve the degradability of the composite nanofiber membrane to a certain extent.

[0109] Experimental Example 5 Piezoelectric Performance Test

[0110] The piezoelectric performance of the products obtained in Examples 1 to 11 and the comparative example was tested. The specific test process was as follows: aluminum foil was used as electrodes on both sides of the composite nanofiber membrane, and then two copper strips were drawn from the electrodes and connected to the wires. The device was packaged with transparent tape to make a piezoelectric sensor. A linear motor was used as a device to apply a constant force. The sensor was continuously struck at a rate of 1 time / s, and an electrometer (6514 type, Keithley Instruments, USA) was used to collect the electrical signal output by the sensor. The test results of Examples 1 to 6 and the comparative example are shown in Figure 2. Figure 6 As shown, the test results of Example 3 and Examples 7 to 11 are as follows Figure 7 shown.

[0111] from Figure 6 As can be seen from the results, the piezoelectric properties of the composite nanofiber membranes prepared in Examples 1 to 6 are significantly better than those of PLLA or CO2-PU, indicating that adding CO2-PU to PLLA can produce composite nanofiber membranes with excellent piezoelectric properties. It can also be seen that as the amount of CO2-PU added gradually increases, the piezoelectric properties of the composite nanofiber membranes first increase and then decrease, reaching the optimal piezoelectric performance when the CO2-PU addition is 16%.

[0112] from Figure 7 It can be seen that with the increase of the receiving roller rotation speed, the piezoelectric performance of the composite nanofiber membranes prepared in Example 3 and Examples 7 to 11 decreases. When the receiving roller rotation speed is 100 r / min, the piezoelectric performance of the composite nanofiber membrane is optimal.

[0113] Experimental Example 6 Contact Angle Test

[0114] The hydrophilicity of the composite nanofiber membranes prepared in Examples 1 to 6 and the PLLA and CO2-PU fiber membranes prepared in the comparative example was tested using an optical contact angle meter (OCA20, Dataphysics Instrument Co., Ltd., Germany). The test results are as follows: Figure 8 shown.

[0115] from Figure 8 It can be seen that CO2-PU has good hydrophilicity and PLLA has poor hydrophilicity. The water contact angle of the composite nanofiber membranes prepared in Examples 1 to 6 is 123 to 135°, and the hydrophobicity is good.

[0116] Experimental Example 7: Stability Test of Piezoelectric Sensor

[0117] The stability test of the composite nanofiber membrane prepared in Example 3 was conducted. The specific test process was as follows: aluminum foil was used as electrodes on both sides of the composite nanofiber membrane. Two copper strips were then drawn from the electrodes and connected to the wires. The device was encapsulated with transparent tape to form a piezoelectric sensor. A linear motor was used as a device to apply a constant force. The sensor was continuously struck 20,000 times at a rate of 1 time / s. The electrical signal output by the sensor was collected using an electrometer (Model 6514, Keithley Instruments, USA). The test results are shown in Figure 2. Figure 9 shown.

[0118] from Figure 9 It can be seen from the figure that the piezoelectric sensor made of the composite nanofiber membrane of the present invention has good piezoelectric stability.

[0119] Experimental Example 8 Application Test of Piezoelectric Sensor

[0120] The composite nanofiber membrane prepared in Example 3 was subjected to application tests. The specific test process was as follows: aluminum foil was used as electrodes on both sides of the composite nanofiber membrane. Two copper strips were then drawn from the electrodes and connected to the wires. The device was encapsulated with transparent tape to form a piezoelectric sensor. The piezoelectric sensor was fixed to different parts of the human body to monitor the physiological parameters and dynamic conditions of the human body. The electrical signal output by the sensor was collected using an electrometer (Model 6514, Keithley Instruments, USA). Arterial pulsation, swallowing, bending of the wrist, elbow, and knee joints, and walking were monitored respectively. The test results were as follows: Figure 10 As shown in a, 10b, 10c, 10d, 10e, and 10f.

[0121] from Figure 10 As can be seen from a, 10b, 10c, 10d, 10e, and 10f, the piezoelectric sensor made of the composite nanofiber membrane of the present invention can accurately monitor human vital signs and movement status such as arterial pulsation, swallowing, bending of the wrist, elbow, and knee joints, and walking in real time.

[0122] The present invention has been described in detail above with reference to specific embodiments and exemplary examples. However, these descriptions should not be construed as limiting the present invention. Those skilled in the art will appreciate that various equivalent substitutions, modifications, or improvements may be made to the technical solutions and implementations of the present invention without departing from the spirit and scope of the present invention, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A green and degradable composite nanofiber membrane, characterized in that: The composite nanofiber membrane is made of CO2-PU and PLLA by electrospinning. The mass ratio of CO2-PU and PLLA is (0.02-0.6):1, The CO2-PU is prepared from carbon dioxide and 1,6-hexanediamine, and the molar ratio of carbon dioxide to 1,6-hexanediamine is (5-11):

1. 1,6-Hexanediamine is dissolved in a solvent, and CO2 is introduced into the solvent for reaction. The amount of carbon dioxide introduced is 3-7 MPa, the reaction temperature is 150-220°C, and the reaction time is 5-15 hours.

2. The composite nanofiber membrane according to claim 1, characterized in that The green degradable composite nanofiber membrane has a water contact angle of 123-135 degrees, a fiber diameter of 100-500 nm, and a thermal degradation temperature of 300-340°C.

3. A method for preparing a green and degradable composite nanofiber membrane, characterized in that: The preparation method comprises the following steps:

1. Step 1: 1,6-hexanediamine is dissolved in a solvent, and CO2 is introduced therein to react to obtain CO2-PU, wherein the molar ratio of carbon dioxide to 1,6-hexanediamine is (5-11):1; 2. Step 2: PLLA and the CO2-PU obtained in step 1 are dissolved in a mixed solvent, wherein the mass ratio of the CO2-PU to the PLLA is (0.02-0.6):1, to obtain a composite spinning solution; Step 3: electrospinning the composite spinning solution obtained in step 2, wherein the electrospinning voltage is 15-25 kV, the electrospinning speed is 1-3 mL / h, the electrospinning distance is 5-20 cm, the electrospinning time is 1-4 h, and the receiving roller speed is 50-4000 r / min to obtain a composite nanofiber membrane. In step 1, The amount of carbon dioxide introduced is 3-7 MPa; The reaction temperature is 150-220°C, and the reaction time is 5-15h.

4. The preparation method according to claim 3, characterized in that In step 2, The mixed solvent is obtained by mixing dichloromethane and hexafluoroisopropanol, and the volume ratio of dichloromethane to hexafluoroisopropanol is (4-10):

3.

5. The preparation method according to claim 3, characterized in that In step 2, The mass concentration of the composite spinning solution is 0.7-1.2 g / mL.

6. Use of the green degradable composite nanofiber membrane according to claim 1 or 2 or the green degradable composite nanofiber membrane prepared by the preparation method according to any one of claims 3 to 5, in a piezoelectric sensor.

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