Green and environment-friendly composite nanofiber membrane as well as preparation method and application thereof

Abstract

The invention relates to the technical field of textile engineering, in particular to a green and environment-friendly composite nanofiber membrane and a preparation method and application thereof. Aiming at the problem that a traditional nanofiber composite filter material is not easy to degrade, the preparation method comprises the following steps: S1, preparing a spinning solution; s2, an injector is used for sucking a proper amount of the spinning solution prepared in the step S1, and the injector is fixed to a constant-flow injection pump; s3, preparing a nanofiber collecting device; s4, uniformly spraying the spinning solution in the injector onto a nanofiber collecting device by using a constant-flow injection pump to finish spinning; wherein a solvent of the spinning solution is N, N-dimethylformamide, a solute of the spinning solution comprises polyacrylonitrile and corn protein, and in the spinning solution, the mass fraction interval of the corn protein is 3.3%-4.7%. The composite nanofiber membrane obtained by the preparation method disclosed by the invention can be used as a filtering membrane to be applied to preparation of air filtering products, has excellent filtering efficiency, air permeability and mechanical properties, and is an ideal material in the fields of air filtration, environment purification and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of textile engineering, and particularly relates to a green and environmentally friendly composite nanofiber membrane, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, with the continuous improvement of the industrialization level in China, the quality of the natural environment has declined to some extent. People have great demands for the improvement of the quality of life. Electrospun nanofibers have advantages such as a large specific surface area, a high porosity, good pore connectivity, and controllable thickness, so they have great advantages in air filtration. Controlling the factors affecting the filtration efficiency of nanofibers helps to improve the filtration performance of nanofiber membranes.

[0003] However, nanofiber membranes made of single materials have defects to varying degrees and do not meet the standards of qualified filter materials. Therefore, a solution with good spinnability is usually used as a matrix and compounded with different materials to enhance the filtration performance. Polyacrylonitrile (PAN) is a polymer widely used in the preparation of nanofibers. The nanofiber membrane prepared from it has the characteristics of high porosity, diverse structures, high stability, and easy functionalization and is used as a composite material.

[0004] However, traditional nanofiber composite filter materials are not easily biodegradable and are prone to cause secondary pollution to the environment. Therefore, the preparation of environmentally friendly, efficient, and low-resistance green filter materials is a long-term project. Summary of the Invention

[0005] To solve the above problems, the present invention provides a green and environmentally friendly composite nanofiber membrane, a preparation method thereof, and an application thereof. Using polyacrylonitrile as a matrix and mixing it with a zein solution, the optimal zein dosage is selected through experiments, and a composite nanofiber membrane with good air permeability and moisture permeability, high anti-breaking strength, and extremely high filtration efficiency is obtained.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A preparation method of a green and environmentally friendly composite nanofiber membrane, comprising the following steps:

[0008] S1: Prepare a spinning solution;

[0009] S2: Draw an appropriate amount of the spinning solution prepared in step S1 with a syringe and fix the syringe to a constant-flow injection pump;

[0010] S3: Prepare a nanofiber collection device;

[0011] S4: Use the constant-flow injection pump to uniformly eject the spinning solution in the syringe onto the nanofiber collection device to complete spinning;

[0012] Among them, the solvent of the spinning solution is N,N-dimethylformamide, and the solute includes polyacrylonitrile and zein. In the spinning solution, the mass fraction range of zein is 3.3% to 4.7%.

[0013] Furthermore, the mass fraction of zein is 4%.

[0014] Furthermore, the mass fraction of polyacrylonitrile is 12%.

[0015] Furthermore, in step S4, the rotational speed of the metal roller of the nanofiber collection device is 80 r / min, the distance between the needle of the syringe and the metal roller is 20 cm, and the flow rate of the constant current injection pump is 1.0 mL / h.

[0016] Furthermore, the present invention also provides a green and environmentally friendly composite nanofiber membrane prepared by the above method.

[0017] Furthermore, the present invention also provides the application of the above green and environmentally friendly composite nanofiber membrane in the preparation of air filtration products.

[0018] Preferably, the green and environmentally friendly composite nanofiber membrane is used as a filter membrane in air filtration products.

[0019] The present invention has the following beneficial effects:

[0020] 1. The solvent of the green and environmentally friendly composite nanofiber membrane of the present invention is N,N-dimethylformamide, and the solute polyacrylonitrile and zein are prepared by electrospinning technology. Among them, the mass fraction of zein is 3.3% to 4.7%. Especially when the mass fraction is 4%, it shows excellent filtration performance. It has a uniform fiber distribution, a moderate fiber diameter, a high porosity, and can achieve a filtration efficiency of up to 99.44%, while maintaining a low resistance pressure drop (128.87 Pa), and is suitable for applications in environmental protection products such as air filtration.

[0021] 2. Using zein as one of the main components, which belongs to renewable resources and is more environmentally friendly compared with traditional chemical materials. The solvent selected in its preparation process is N,N-dimethylformamide, which ensures the stability of the solution and the quality of fiber forming, and reduces the use and emission of harmful substances.

[0022] 3. The green and environmentally friendly composite nanofiber membrane of the present invention shows good mechanical properties, with both high breaking strength and appropriate elongation rate, ensuring the service life and durability of the membrane, and is especially suitable for the working conditions required for long-term operation in air filters.

[0023] 4. Excellent air permeability and hydrophobicity. The air permeability of the PAN / zein composite nanofiber membrane of the present invention ranges from 112.06 mm / s to 129.4 mm / s, and the initial water contact angle is between 102.35° and 110.7°. It has a low flow resistance to air and can prevent blockage caused by moisture accumulation at the same time.

[0024] 5. It can be used as an air filtration membrane in various scenarios in the environmental protection field, including industrial waste gas filtration, air purification equipment, and personal protective masks, etc., providing an efficient, environmentally friendly and durable solution BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The attached drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0026] Figure 1 It is the SEM image of the composite nanofiber membrane of the present invention;

[0027] Figure 2 It is the infrared spectrum diagram of the nanofiber membrane of the present invention;

[0028] Figure 3 It is the relationship diagram between the air permeability and the mass fraction of zein of the present invention;

[0029] Figure 4 It is the relationship diagram between the water contact angle at 1 s and the mass fraction of zein of the present invention;

[0030] Figure 5 It is the schematic diagram of the water contact angle at 1 s of the composite nanofiber membrane of the present invention;

[0031] Figure 6 It is the relationship diagram between the mass fraction of zein and the water vapor transmission rate of the present invention;

[0032] Figure 7 It is the relationship diagram between the breaking strength and elongation at break of the composite nanofiber membrane of the present invention;

[0033] Figure 8 It is the relationship diagram between the mass fraction of zein and the resistance pressure drop of the present invention;

[0034] Figure 9 It is the relationship diagram between the mass fraction of zein and the filtration efficiency of the present invention;

[0035] Figure 10 It is the relationship diagram between the mass fraction of zein and the quality factor of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0036] To enable those of ordinary skill in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0037] Example 1:

[0038] In this example, polyacrylonitrile (PAN) with a mass fraction of 12% and zein with mass fractions of 2.7%, 3.3%, 4.0%, 4.7%, 5.3%, 6.0%, and 6.7% were mixed to prepare a PAN / zein spinning solution for preparing a green and environmentally friendly composite nanofiber membrane (hereinafter referred to as the PAN / zein composite nanofiber membrane).

[0039] 1 Preparation of solutions

[0040] 1.1 Materials and instruments

[0041] The materials and instruments used in this experiment are shown in Table 1.

[0042] Table 1 Materials and instruments used in this experiment

[0043]

[0044] Instruments: FA1004B electronic balance, weighing paper, rubber dropper, spatula, glass bottle, beaker, magnetic stirrer, magnetic stirring rotor.

[0045] 1.2 Preparation of solutions

[0046] Prepare 30 g of PAN / zein solutions with different concentrations, pure PAN solution, and pure zein solution. The amounts of PAN, zein, and N,N-dimethylformamide used to prepare the solutions are shown in Table 2 below:

[0047] Table 2 Contents of drugs used in the solutions

[0048]

[0049] Prepare a pure zein membrane. The zein is 6.0 g, with a mass fraction of 20%. The solvent used is an ethanol aqueous solution with a ratio of anhydrous ethanol / water of 6 / 4, where the anhydrous ethanol is 14.4 g and the water is 9.6 g.

[0050] Solution preparation process: Clean and dry the glass bottle. Place a beaker on the electronic balance and press the tare key. When the screen shows 0, start weighing. First, weigh the corresponding mass of the solvent, and suck out the excess solvent with a dropper. After weighing the solvent, place a weighing paper on the electronic balance and tare again. When the screen shows 0, start weighing the corresponding solute. Replace the weighing paper after each weighing, and scoop out the excess medicine with a spatula. Pour the weighed solvent into the glass bottle, then pour the weighed solute into the glass bottle. Put in a magnetic stirring rotor, attach the corresponding label, and place the glass bottle on a magnetic stirrer at room temperature for stirring. Stir the pure corn protein solution for 2 - 3 h, and stir the pure PAN solution and PAN / corn protein solution for 8 - 12 h. After stirring evenly, there are a few bubbles in the solution. Let it stand for 1 - 2 h to eliminate the bubbles.

[0051] Preparation of 2 nanofiber membranes

[0052] 2.1 Materials and instruments

[0053] Materials: Pure PAN solution with 12% PAN mass fraction, PAN / corn protein solutions with 12% PAN mass fraction and 2.7%, 3.3%, 4.0%, 4.7%, 5.3%, 6.0%, 6.7% corn protein mass fraction, and pure corn protein solution with 20% corn protein mass fraction.

[0054] Instruments: QX1 electrostatic spinning oriented nanofiber collection device (manufactured by Donghua University), LSP01 - 3A injection pump (Baoding Longer Precision Pump Co., Ltd.), DE - 100 high - voltage DC power supply (Dalian Dingtong Technology Development Co., Ltd.), 10 mL syringe, 18G needle, aluminum foil, non - woven fabric.

[0055] 2.2 Preparation process of nanofiber membranes

[0056] First, turn on the air conditioner to control the ambient temperature at 20 - 24 °C and the ambient humidity at 50% - 60%. Conduct experimental preparations under suitable ambient temperature and humidity conditions. Use a 10 mL syringe to draw an appropriate amount of the prepared and well - stirred spinning solution, attach the needle to the syringe, and fix the syringe on a constant - flow injection pump. Cut an appropriate length of aluminum foil paper, wrap and fix it on the metal roller of the electrospun oriented nanofiber collection device. Set the rotation speed of the metal roller of the electrospun oriented nanofiber collection device at 80 r / min, adjust the distance between the needle and the metal collection roller to 20 cm, adjust the flow rate of the injection pump to 1.0 mL / h, clamp the high - voltage DC power supply clip on the needle, click the run button on the electrospun oriented nanofiber collection device to make the metal roller rotate, then click the start button of the injection pump to push the syringe until a solution appears at the needle part. At the same time, turn on the high - voltage DC power supply and adjust the voltage to 16.45 kV. Subsequently, it can be observed that the hemispherical droplet becomes slender, forming a jet stream, and the jet stream forms a Taylor cone that finally covers the aluminum foil wrapped around the metal roller of the electrospun oriented nanofiber collection device. The uniform rotation of the metal roller makes the nanofibers falling on the aluminum foil paper evenly covered, and finally a nanofiber membrane is formed and covers the aluminum foil paper. It is also necessary to prepare nanofiber membranes on non - woven fabrics for performance testing. First, wrap and fix the aluminum foil paper on the metal roller, then wrap the non - woven fabric on the aluminum foil paper and repeat the above operations. The spinning time is controlled at 1 h. After spinning, peel it off and dry it in a shady place for subsequent performance testing. In this example, pure PAN nanofiber membranes without zein, PAN / zein composite nanofiber membranes with zein mass fractions of 2.7%, 3.3%, 4.0%, 4.7%, 5.3%, 6.0%, 6.7%, and a pure zein membrane with a mass fraction of 20% were prepared.

[0057] Label the pure PAN nanofiber membrane as sample No. 1, label the PAN / zein composite nanofiber membranes with zein mass fractions of 2.7%, 3.3%, 4.0%, 4.7%, 5.3%, 6.0%, 6.7% as samples No. 2, 3, 4, 5, 6, 7, 8, and label the zein nanofiber membrane with a mass fraction of 20% as sample No. 9. Since the molecular weight of zein is in the range of 25000 - 45000, which is relatively small, the film - forming property of sample No. 9 is very poor, and the obtained fibers are powdery and cannot be tested for filtration performance, air permeability, etc. Therefore, in this example, only the infrared spectrum of sample No. 9 was tested, and other properties were not tested.

[0058] 3 Performance study of the PAN / zein composite nanofiber membranes in this example

[0059] The instruments used for performance research are shown in Table 3.

[0060] Table 3 Instruments and production units used

[0061]

[0062] 3.1 Microscopic Morphology Analysis

[0063] The equipment scans and bombards the sample in a grid pattern with a focused electron beam under vacuum conditions, enabling the interaction between electrons and the sample to observe and analyze the surface or fracture morphology of the sample. As shown Figure 1 as Figure 1 Figure 12 is a scanning electron microscope image of PAN / zein composite nanofibers at 10,000 times magnification. It can be seen from the figure that there are grooves along the longitudinal direction of the fibers in the PAN / zein composite nanofilm. And with the increase in the zein content, the fiber diameter increases to varying degrees, and there is an adhesion phenomenon between the fibers. Overall, the fiber distribution is relatively uniform, indicating that the solutes in the PAN / zein solution are completely dissolved and have good film-forming properties under the action of the electric field force. The change in diameter is related to the zein content. The increase in the zein content increases the viscosity of the PAN / zein solution, making it more difficult for the electric field force to overcome the surface tension between the solutions during electrospinning, thus increasing the fiber diameter

[0064] Based on the images obtained from the scanning electron microscope, the Image J software was used to measure the diameters of the fibers in the PAN / zein composite nanofiber membranes with different mass fractions. Each group had 50 data points, and the office tools were used to process the data, calculate the average diameter and diameter standard deviation of the nanofibers, and the results are shown in Table 4 below

[0065] Table 4 Average Diameter and Diameter Standard Deviation of PAN / Zein Composite Nanofibers

[0066]

[0067] It can be seen that the diameter of pure PAN nanofibers is relatively small, at 222.9 nm. After adding zein, the diameter of the PAN / zein composite nanofibers increases significantly, ranging from 400 to 634 nm, and the average diameter generally shows an increasing trend with the increase in the zein mass fraction. This is because as the zein mass increases, the viscosity of the PAN / zein solution continuously increases. During the electrospinning process, the jet is subject to greater viscous resistance and smaller stretching force, resulting in an increase in fiber diameter. According to the diameter standard deviation, the larger the standard deviation, the greater the dispersion of the diameter. With the increase in the zein mass, the diameter standard deviation of the PAN / zein composite nanofibers shows an increasing trend, indicating that as the zein increases, the grooves on the longitudinal surface of the fibers continuously increase, affecting the dispersion of the fiber diameter. However, the difference in the diameter standard deviation of the PAN / zein composite nanofibers with different mass fractions is not significant, and the fiber distribution is uniform

[0068] 3.2 Infrared Spectroscopy Analysis

[0069] First, use scissors to cut the sample to the appropriate size. Then, peel the sample from the aluminum foil and fold it into a shape of moderate thickness. Set the instrument parameters and different background processing methods. Place the sample and secure it. Click "Acquire Sample," enter a title, and confirm. The instrument will begin scanning. After the scan is complete, remove the sample and collect the background spectrum. The software automatically deducts the background information after collecting the background spectrum. After the acquisition is complete, save the data in both SPA and CSV formats. Test the samples one by one. After completion, shut down the software, computer, infrared host, and regulated power supply.

[0070] Reference Figure 2 Infrared spectra of pure PAN film, pure zein film and PAN / zein films with different concentrations.

[0071] It can be clearly observed that the pure PAN film has a -1 、2246.5cm -1 、1428cm -1 and 1706.1cm -1 The characteristic peaks of the pure zein film are represented by methylene (-CH2 stretching vibration peak), cyano (C≡N stretching vibration peak), methylene (-CH2 bending vibration peak) and carbonyl (C=O stretching vibration peak). The more obvious characteristic peak on the pure zein film is at 3288.5cm -1 and 1644.6cm -1 、1266.1cm -1 At. They represent the stretching vibration peaks of OH in amide II band, C=O in amide I band, and CN in amide III band respectively. In the infrared spectra of PAN / zein composite nanofiber membranes with different mass fractions, it can be found that the -CH2 stretching vibration peak, C≡N stretching vibration peak and -CH2 bending vibration peak of pure PAN membrane still exist. It can also be found that the stretching vibration peaks of OH in amide II band, C=O in amide I band and CN in amide III band of pure zein membrane exist. However, the stretching vibration peak at 1706.1cm on pure PAN membrane is -1 The C=O stretching vibration peak of the pure PAN membrane disappears. A careful observation of the infrared spectrum shows that the stretching vibration peak intensity of C=O in the amide I band on PAN / zein is significantly enhanced, and increases with the increase of the zein mass fraction, indicating that the characteristic group C=O on the pure PAN membrane shifts to the low-frequency direction, thereby causing the stretching vibration peak of C=O in the amide I band on the PAN / zein composite nanofiber membrane to shift to the low-frequency direction. -1 The intensity of the characteristic peak of carbonyl group increases.

[0072] 3.3 Breathability analysis

[0073] First, cut ten square samples of 15 cm×15 cm from the specimen. Set the experimental parameter of pressure to 100 Pa. Place the uniform part of the specimen on the nozzle of the instrument, clamp the specimen after avoiding the wrinkled and edge positions, and start the instrument. Test each different mass fraction once, and take the average value of the air permeability obtained.

[0074] From Figure 3 It can be seen that the air permeability of pure PAN nanofibers is 88.3 mm / s, and the air permeability of PAN / zein composite nanofiber membranes is in the range of 112.06 mm / s to 129.4 mm / s, indicating that the air permeability of PAN / zein composite nanofiber membranes is significantly greater than that of pure PAN nanofibers. This is mainly because the diameter of pure PAN nanofibers is smaller, and the standard deviation of the diameter is also relatively small. The fiber diameter distribution is relatively uniform, the pore size of the fiber membrane is small, and the air permeability of the fiber membrane is the worst. On the other hand, the diameter of PAN / zein composite nanofibers shows an increasing trend, resulting in an increasing trend in its air permeability. From the previous scanning electron microscope results, it can be seen that the fibers in the PAN / zein composite nanofiber membrane are evenly distributed. When the mass fraction of zein is 4.7%, the air permeability of the composite nanofiber membrane is the best. At this time, the fiber diameter is larger and the standard deviation of the diameter is smaller, indicating that the fiber diameters do not differ much. The larger fiber diameter makes the pore size in the composite nanofiber membrane larger and the porosity also larger, thus making the air permeability performance of the composite nanofiber membrane the best; when the mass fraction of zein is greater than 4.7%, the air permeability of the composite nanofiber membrane decreases slightly. This is mainly because there is adhesion between the nanofibers in samples 6#, 7#, and 8#, and the difference in nanofiber diameters is relatively large, resulting in a decrease in the porosity of the fiber membrane and a decrease in air permeability.

[0075] 3.4 Analysis of wetting performance

[0076] From Figure 4 It can be known that the initial water contact angle of the pure PAN nanofiber membrane is 106.11°, and the initial water contact angle of the PAN / zein composite nanofiber membrane is in the range of 102.35° to 110.7°. The water contact angles are all greater than 90°, and the surface of the composite nanofiber membrane is hydrophobic. And the water contact angle is relatively stable before 25 s. This is because both polyacrylonitrile and zein are hydrophobic. The addition of zein enhances the hydrophobicity of the PAN / zein composite nanofibers. And with the increase in the mass fraction of zein, the diameter of the PAN / zein composite nanofibers increases, and the roughness of the fiber surface increases. Therefore, the water contact angle of the PAN / zein composite nanofiber membrane also shows an increasing trend with the increase in the mass fraction of zein, showing strong hydrophobic properties and poor wetting performance. It is beneficial for the application of PAN / zein composite nanofiber membranes in air filtration and is not easily affected by water vapor.

[0077] 3.5 Analysis of moisture permeability

[0078] Cut three specimens with a diameter of 70 mm from PAN / zein composite nanofiber membranes with different mass fractions. Open the equipment and set the experimental parameters: temperature 38 °C, relative humidity 90%, and experimental time 1 h. Then use a Y802k type rapid eight-basket oven to dry the silica gel for color change. Set the parameters as temperature 100 °C. After the temperature rises to the specified temperature, dry for 40 min. After drying, put an appropriate amount of silica gel for color change into the moisture permeability cup. Place the side of the non-woven fabric with the fiber membrane facing up on the moisture permeability cup, put on the washer and compression ring, tighten the nut, and seal the side with tape to prevent moisture from entering from the side and causing errors. After covering the lid of the moisture permeability cup, weigh it. After weighing, put the sample into the sample chamber that has reached the specified experimental conditions and conduct moisture permeability treatment for 1 h. After the treatment, weigh the specimen, calculate the mass change of the moisture permeability cup before and after moisture permeability, and thus calculate the moisture permeability.

[0079] As Figure 5 shown, the moisture permeability of the pure PAN nanofiber membrane is 3113.8 g / m 2 ·d. The moisture permeability of the PAN / zein composite nanofiber membrane is in the range of 3110.09 - 3458.96 g / m 2 ·d, and the highest moisture permeability reaches 3458.96 g / m 2 ·d. The moisture permeability of the composite nanofiber membrane is generally greater than that of pure PAN. With the increase of the zein mass fraction, the moisture permeability of the composite nanofiber membrane shows a decreasing trend. It can be seen from the water contact angle analysis that the surface of the PAN / zein composite nanofiber membrane is hydrophobic. Also, since the increase of the zein mass fraction will increase the surface grooves of the composite nanofiber membrane and increase the roughness of the fiber surface, the roughness of the solid surface will enhance its hydrophobic property. Therefore, the higher the water contact angle, the rougher the fiber surface, and the weaker the ability of the composite nanofiber itself to adsorb and desorb water molecules, and the worse the moisture permeability performance of the PAN / zein composite nanofiber membrane. Also, because with the increase of the zein mass fraction, the fiber diameter in the PAN / zein composite nanofiber membrane becomes larger, and the diameter and water contact angle are inversely proportional to the capillary adsorption ability of water molecules, thus reducing the moisture permeability of the PAN / zein composite nanofiber membrane and decreasing the moisture permeability performance.

[0080] 3.6 Analysis of tensile and elongation properties

[0081] First, cut several samples of 5mm×25mm from the non-woven fabric. Use tweezers to peel off the fiber membrane from the non-woven fabric. Turn on the instrument and set the experimental parameters: clamping distance 20mm; tensile speed 20mm / min; elongation range; strength range and other parameters. Then clamp both ends of the specimen on the upper and lower clamps respectively. After completion, start the measurement. Each group of specimens is measured ten times. After obtaining the results, save the data.

[0082] As Figure 6 shown, it can be seen that the PAN / zein composite nanofiber membrane has relatively high breaking strength and elongation at break. Its breaking strength is 4.33 - 10.43MPa, and the elongation at break is 68.6% - 99.91%. When the mass fraction of zein is 4.0%, the breaking strength of the composite nanofiber membrane is the largest, which is 10.43MPa, but its elongation is 68.60%. This is because its diameter is the thinnest, the standard deviation of the diameter is also smaller, the fiber diameter distribution is relatively uniform, and the breaking strength of the fiber membrane is large while the elongation is small. When the mass fraction of zein is 6.0%, the breaking strength of the composite nanofiber membrane is the smallest, which is 4.33MPa, and the elongation at break is the largest, which is 99.91%. This is because as the fiber diameter increases, the standard deviation of the diameter is also the largest, and the dispersion degree of the fiber diameter distribution is too large, resulting in an increase in the non-simultaneity of fiber breakage in the composite nanofiber membrane, thus reducing the breaking strength of the fiber membrane and increasing the elongation at break.

[0083] 3.7 Filtration performance analysis

[0084] Before the test, prepare an appropriate amount of sodium chloride solution with a mass fraction of 2% and add it to the container. Turn on the screw air compressor to make it communicate with the pressure vessel, so that the pressure in the pressure vessel reaches 0.7 - 0.8MPa. Turn on the freeze dryer and open the connection valve between the compressed air precision instrument and the TSI-8130A instrument. Then turn on the TSI-8130A instrument for preheating. After the preheating is completed, set the experimental parameters. Set the air flow rate to 30L / min and the sodium chloride particle diameter to 0.26μm. Place the sample on the disc, clamp it and then conduct the test. Record the data according to the results of the instrument and conduct subsequent sorting and analysis.

[0085] Refer to Figure 7 and Figure 8, the filtration efficiency of the pure PAN nanofiber membrane is 95.75%, and the resistance pressure drop is 94.38 Pa; the filtration efficiency of the PAN / zein composite nanofiber membrane is between 92.75% and 99.44%, and the resistance pressure drop is between 83.3 Pa and 137.1 Pa. With the increase of the zein mass fraction, both the filtration efficiency and the resistance pressure drop show a trend of increasing first and then decreasing. The nanofiber membrane mainly blocks and filters fine particulate matter through physical barrier, electrostatic adsorption, diffusion, inertial collision, etc. The factors affecting the filtration performance of the nanofiber membrane mainly include fiber diameter, active groups contained in the fiber membrane, etc. It can be seen from the SEM images of the fiber membrane that the diameter of the pure PAN nanofibers is smaller, and the pore size of the fiber membrane is smaller under the same thickness condition. It mainly filters particulate matter through physical barrier and inertial collision; the active groups such as amide bonds contained in zein can effectively adsorb particulate matter. Therefore, when the zein mass fraction is 4.0%, due to the smaller fiber diameter of the fiber membrane and the presence of more active groups in the fiber membrane, its maximum filtration efficiency is 99.44%; when the content of zein continues to increase, due to the larger fiber diameter and larger pore size in the fiber membrane, the filtration efficiency of the fiber membrane decreases again; when the zein mass fraction is 6.7%, the filtration efficiency of the composite nanofiber membrane is only 92.75%.

[0086] The resistance pressure drop is a factor affecting the energy consumption of the filtration performance of the composite nanofiber membrane. High-quality filter materials need to have the performance of high efficiency and low resistance. Also, because the resistance pressure drop and the filtration efficiency almost rise and fall simultaneously, a quality factor needs to be introduced to measure the filtration performance of the pure PAN and PAN / zein composite nanofiber membranes. The larger the quality factor, the better the filtration performance of the composite nanofiber membrane, as Figure 9 shown.

[0087] Referring to Figure 9 and Figure 10 , the quality factor of the pure PAN nanofiber membrane is 0.03346 Pa -1 , the quality factor of the PAN / zein composite nanofiber membrane is 0.03032 - 0.04023 Pa -1 , with the increase of the zein content, the quality factor of the PAN / zein composite nanofiber membrane shows a trend of increasing first and then decreasing, which is consistent with the change trend of the filtration efficiency and the resistance pressure drop. Among them, the quality factor of the PAN / zein composite nanofiber membrane with a zein mass fraction of 4.0% is the highest, which is 0.04013 Pa -1 , its filtration efficiency is 99.44%, and the resistance pressure drop is 128.87 Pa, belonging to a high-efficiency and low-resistance composite nanofiber membrane filter membrane. When the zein mass fraction is 4.7%, the quality factor of the PAN / zein composite nanofiber membrane is 0.03891 Pa -1, its filtration efficiency is 99.19%, and the resistance pressure drop is 123.76 Pa, which also belongs to the category of high-efficiency and low-resistance composite nanofiber filtration membranes.

[0088] 3.8 Summary

[0089] Analyze and summarize the experimental results of the microscopic morphology, infrared spectral characteristics, air permeability and moisture permeability, mechanical strength and elongation, filtration performance, and water contact angle of pure PAN and PAN / zein composite nanofiber membranes.

[0090] (1) Microstructural analysis: The diameter of pure PAN nanofibers is relatively small, being 222.9 nm. The diameter of PAN / zein composite nanofibers is larger (400 - 634 nm), and as the mass fraction of zein increases, the average fiber diameter generally shows an increasing trend. Moreover, as the zein content increases, the roughness of the fiber surface increases, and there is an adhesion phenomenon between the fibers.

[0091] (2) Infrared characteristic analysis: Characteristic groups of pure PAN membranes and pure zein can be found on the PAN / zein composite nanofiber membranes. The characteristic group C=O on the pure PAN membrane shifts towards the low-frequency direction to the stretching vibration peak of C=O in the amide I band on the pure zein membrane, thereby increasing the characteristic peak intensity of the carbonyl group at 1644.6 cm -1 on the PAN / zein composite nanofiber membranes. It proves that PAN and zein are fully mixed.

[0092] (3) Air permeability analysis: The air permeability of pure PAN nanofibers is 88.3 mm / s, and the air permeability of PAN / zein composite nanofiber membranes is in the range of 112.06 mm / s - 129.4 mm / s. The air permeability of PAN / zein composite nanofiber membranes is significantly greater than that of pure PAN nanofibers, mainly because the diameter of the composite nanofibers increases and the diameter standard deviation increases, increasing the porosity of the composite nanofiber membranes, thereby increasing the air permeability.

[0093] (4) Moisture permeability analysis: The moisture permeability of the pure PAN nanofiber membrane is 3113.8 g / m 2 ·d, and the moisture permeability of PAN / zein composite nanofiber membranes is in the range of 3110.09 - 3458.96 g / m 2 ·d. The moisture permeability of the composite nanofiber membranes is generally greater than that of pure PAN.

[0094] (5) Mechanical tensile properties analysis: It can be seen that the PAN / zein composite nanofiber membrane has relatively high tensile strength and elongation at break. Its tensile strength is 4.33 - 10.43 MPa, and the elongation at break is 68.6% - 99.91%. When the mass fraction of zein is 4.0%, the tensile strength of the composite nanofiber membrane is the highest at 10.43 MPa, but its elongation is relatively small, at 68.60%.

[0095] (6) Filtration performance analysis: The filtration efficiency of the pure PAN nanofiber membrane is 95.75%, and the resistance pressure drop is 94.38 Pa; the filtration efficiency of the PAN / zein composite nanofiber membrane is between 92.75% and 99.44%, and the resistance pressure drop is between 83.3 Pa and 137.1 Pa. With the increase of the mass fraction of zein, the filtration efficiency, resistance pressure drop, and quality factor as a whole show a trend of first increasing and then decreasing. When the mass fraction of zein is 4.0%, the quality factor of the PAN / zein composite nanofiber membrane is the highest, at 0.04013 Pa -1 , its filtration efficiency is 99.44%, and the resistance pressure drop is 128.87 Pa, belonging to a high-efficiency and low-resistance composite nanofiber membrane filter.

[0096] (7) Water contact angle analysis: The initial water contact angle of the pure PAN nanofiber membrane is 106.11°. The initial water contact angle of the PAN / zein composite nanofiber membrane is between 102.35° and 110.7°. The water contact angles are all greater than 90°. The surfaces of both the pure PAN and the composite PAN / zein nanofiber membranes show hydrophobicity.

[0097] In summary, in this example, the PAN / zein composite nanofiber membrane with a zein mass fraction of 4.0% has good performance, small diameter and uniform distribution. There are active groups on the surface of the fiber membrane, which can filter particulate matter through adsorption. It also has good air permeability and moisture permeability, the highest tensile strength, a filtration efficiency as high as 99.44%, a resistance pressure drop of only 128.87 Pa, and the highest quality factor of 0.04023 Pa -1 .

[0098] Example Two:

[0099] This example provides a green and environmentally friendly composite nanofiber membrane prepared by the preparation method in Example One.

[0100] Example Three:

[0101] This example provides the application of the green and environmentally friendly composite nanofiber membrane in Example Two in the preparation of air filtration products. Among them, the green and environmentally friendly composite nanofiber membrane is used as a filter membrane in air filtration products.

[0102] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and what is described in the above embodiments and the specification is only to illustrate the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A preparation method of a green and environmentally friendly composite nanofiber membrane, characterized in that, It includes the following steps: S1: Prepare a spinning solution; S2: Use a syringe to suck an appropriate amount of the spinning solution prepared in step S1, and fix the syringe to a constant flow injection pump; S3: Prepare a nanofiber collection device; S4: Use the constant flow injection pump to uniformly eject the spinning solution in the syringe onto the nanofiber collection device to complete spinning; Among them, the solvent of the spinning solution is N,N-dimethylformamide, and the solute includes polyacrylonitrile and zein; in the spinning solution, the mass fraction range of the zein is 3.3% to 4.7%.

2. The preparation method of the green and environment-friendly composite nanofiber membrane according to claim 1, characterized in that, The mass fraction of the zein is 4%.

3. The preparation method of the green and environment-friendly composite nanofiber membrane according to claim 2, wherein, The mass fraction of the polyacrylonitrile is 12%.

4. The preparation method of the green environmental protection composite nanofiber membrane according to claim 1, characterized in that In step S4, the rotation speed of the metal roller of the nanofiber collection device is 80 r / min, the distance between the needle of the syringe and the metal roller is 20 cm, and the flow rate of the constant flow injection pump is 1.0 mL / h.

5. A green and environmentally friendly composite nanofiber membrane prepared by the preparation method according to any one of claims 1-4.

6. Use of the green and environmentally friendly composite nanofiber membrane according to claim 5 in the preparation of air filtration products.

7. The application according to claim 6, wherein The green and environmentally friendly composite nanofiber membrane is used as a filter membrane in air filtration products.

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