Method for preparing and testing microfiltration composite fiber membrane

Abstract

The invention relates to the field of fiber membrane preparation, in particular to a preparation and test method of a microfiltration composite fiber membrane, which comprises the following steps: preparing a PVA (Polyvinyl Alcohol) solution; accurately and respectively weighing CA and GO, and respectively adding the CA and the GO into the prepared PVA solution to obtain a PVA / CA / GO spinning solution; assembling SVF base cloth on an unwinding mechanism, coating the front end of the base cloth on the surface of a metal mesh curtain above a solution tank, then pouring a spinning solution into the solution tank, and performing electrostatic spinning after adjusting spinning conditions to obtain a composite fiber membrane; the composite fiber membrane is subjected to hot pressing treatment, so that carboxyl on a cross-linking agent citric acid and hydroxyl of a PVA chain are subjected to an esterification reaction, water resistance is improved through structural regulation and control of a PVA polymer, and the microfiltration composite fiber membrane is obtained. According to the invention, the contact area of the cross-linking agent citric acid and PVA is greatly increased, so that the cross-linking effect is more sufficient, and the fiber membrane can maintain a good fiber form after working in water for a long time.

Description

Technical Field

[0001] The invention relates to the field of fiber membrane preparation, and in particular to a preparation and testing method of a microfiltration composite fiber membrane. Background Art

[0002] Polyvinyl alcohol (PVA), as a common organic compound, is widely recognized for its excellent properties such as good film-forming property, antifouling property, long-term heat resistance and acid-base stability. However, the hydrophilic hydroxyl groups within its molecules limit the application of PVA films. Therefore, how to overcome the aforementioned defects is one of the key technical problems to be solved in this field. Summary of the invention

[0003] In view of this, the purpose of the present invention is to propose a method for preparing and testing a microfiltration composite fiber membrane to solve the problem that the hydrophilic hydroxyl groups inside the molecules currently limit the application of PVA membranes.

[0004] Based on the above purpose, the present invention provides a method for preparing and testing a microfiltration composite fiber membrane, comprising:

[0005] S1: preparing 7-10wt% PVA solution;

[0006] S2: Add CA and GO by external addition method: Accurately weigh 10%-20% CA and 0.25-1wt% GO in PVA content, respectively, and add them to the prepared PVA solution, continue stirring for 10-30 minutes, and after CA is completely dissolved, GO is completely dispersed in the PVA solution to obtain PVA / CA / GO spinning solution;

[0007] S3: Assemble the SVF base fabric on the unwinding mechanism, wrap the front end of the base fabric on the surface of the metal mesh curtain above the solution tank, continue to move forward, wind the excess front end of the base fabric on the winding mechanism, adjust the appropriate tension, and then pour the spinning solution into the solution tank, adjust the spinning conditions and perform electrospinning to obtain a composite fiber membrane;

[0008] S4: Hot pressing treatment: The composite fiber membrane is subjected to hot pressing treatment, so that the carboxyl group on the cross-linking agent citric acid reacts with the hydroxyl group on the PVA chain to undergo esterification reaction, and the water resistance is improved by regulating the structure of the PVA polymer to obtain a microfiltration composite fiber membrane.

[0009] Optionally, the preparation of a 7-10wt% PVA solution includes: weighing a predetermined mass of PVA solid powder and a corresponding proportion of deionized water, mixing and adding the mixture into a 1000mL beaker, heating in a water bath at 85-95°C, and mechanically stirring for 2-3h until the PVA is completely dissolved, to obtain a 7-10wt% PVA solution.

[0010] Optionally, the spinning conditions are voltage: 45-80 kV; temperature: 20-25° C.; humidity: 45-60%; spiral speed: 8-12 r / min; winding speed: 0.1-0.5 m / min; receiving distance: 12-18 cm.

[0011] Optionally, after S3, the step further includes: controlling the thickness of the composite fiber membrane to be 40 μm-80 μm by controlling the spinning time.

[0012] Optionally, the temperature of the hot pressing treatment is 140-180°C, and the hot pressing time is 10-30 minutes.

[0013] Based on the same invention, the present invention also provides a method for testing the filtration performance of a microfiltration composite fiber membrane, which is used to test the filtration performance of the above-mentioned microfiltration composite fiber membrane, comprising:

[0014] The microfiltration composite fiber membrane prepared in S4 was placed in a filtration device, and 0.3 μm fluorescent PS microspheres were used as the filter. The composite ultrafiltration membrane was tested under a pressure of 0.025-0.1 MPa. Dead-end filtration was used, and the test water temperature was adjusted to 25.0°C ± 0.5°C, and the pressure was adjusted to 0.150 MPa ± 0.005 MPa. The pre-pressure was performed for 30 minutes, and then the test pressure was gradually reduced to 0.100 MPa to 0.005 MPa. After stabilization for 10 minutes, a certain volume of produced water was collected with a measuring cylinder, and the time was recorded with a stopwatch. Three samples were taken for parallel experiments.

[0015] The pure water permeability is calculated according to formula (1), and the result is the average value of three parallel experiments:

[0016]

[0017] Where:

[0018] P——pure water permeability, in liters per square meter per hour [L / (m2·h)];

[0019] V——pure water permeability, in liters (L);

[0020] S——Effective filtration area of ​​membrane, in square meters (m2);

[0021] t – the time taken to pass through a volume of pure water V, in hours (h).

[0022] Optionally, the testing method further includes:

[0023] Draw the concentration-absorbance standard curve of PS microspheres and derive the linear regression equation;

[0024] The microfiltration composite fiber membrane prepared in S4 was prepared into three membrane samples of the same specifications, washed with distilled water and set aside; then the membrane test device was connected, the test solution was added to the constant temperature liquid storage tank, the membrane test device was operated by dead-end filtration, the test water temperature was adjusted to 25°C ± 0.5°C, the transmembrane pressure difference was gradually adjusted to 0.025-0.10MPa, and the filtrate was collected after the system was stably operated for 10 minutes;

[0025] Using distilled water as a reference, the absorbance of the PS microspheres used was measured by an ultraviolet fluorescence spectrophotometer, and the absorbance (λ) was measured to be the maximum at 389 nm. A 1 cm cuvette was used on a UV-visible spectrophotometer at a wavelength of 389 nm to measure the absorbance values ​​of the test solution before and after filtration, respectively. The absorbance values ​​obtained from the test were calculated through a linear regression equation to calculate the concentration of the PS microsphere solution; the retention rate result was calculated according to formula (2):

[0026]

[0027] Where:

[0028] R——retention rate, %;

[0029] Cp——Concentration of standard substance in the test solution after filtration, in milligrams per liter (mg / L);

[0030] Cf - concentration of standard substance in the test solution before filtration, in milligrams per liter (mg / L).

[0031] The present invention has the following beneficial effects:

[0032] 1. The spinning efficiency of needle-free electrospinning is relatively high. The use of pilot needle-free electrospinning equipment for spinning significantly improves the spinning efficiency.

[0033] 2. PVA material is soluble in water. Compared with organic solvents, this solvent has lower cost and wider sources. In addition, using water as a solvent is in line with the concept of sustainable development.

[0034] 3. GO is dispersed in the spinning solution and is more evenly distributed. The addition of GO makes the fiber thinner and increases the specific surface area of ​​the fiber, which is more conducive to the adsorption and retention of some metal ions and some particulate pollutants in the water, providing a broader space for the use of fiber membranes.

[0035] 4. PVA nanofiber membrane easily swells when in contact with water and is difficult to maintain its fiber shape. Adding the crosslinking agent citric acid to the spinning solution and then spinning it directly into the fiber through electrospinning greatly increases the contact area between the crosslinking agent citric acid and PVA, making the crosslinking effect more complete. The fiber membrane can also maintain a good fiber shape after working in water for a long time.

[0036] 5. The composite fiber membrane can filter at a relatively low pressure, and its pure water flux is higher than 20000L / m2 / h, which reduces energy consumption while maintaining high flux. It also has excellent reusability, and can maintain a relatively high flux and interception rate after repeated use, which greatly improves the reusability and service life of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only for the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0038] Figure 1 :Microfiltration composite microfiltration membrane production structure diagram;

[0039] Figure 2 : SEM image of PVA / CA / GO fiber membrane on the surface of microfiltration composite microfiltration membrane;

[0040] Figure 3 : SEM image of the upper surface of the microfiltration composite microfiltration membrane before the PVA fiber membrane is modified;

[0041] Figure 4 : SEM image of the modified PVA fiber membrane on the upper surface of the microfiltration composite microfiltration membrane after contact with water;

[0042] Figure 5 : Surface SEM image of PS microspheres after filtration by microfiltration composite nanofiber membrane;

[0043] Figure 6 : SEM image of the cross section of spunlace viscose / PVA composite fiber membrane;

[0044] Figure 7 : FT-IR images of nanofiber membrane before and after modification;

[0045] Figure 8 : Test diagram of the reuse performance of microfiltration composite nanofiber membrane. DETAILED DESCRIPTION

[0046] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.

[0047] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0048] like Figure 1 As shown, a preparation and testing method of a microfiltration composite fiber membrane comprises:

[0049] S1: Prepare 7-10wt% PVA solution: weigh a predetermined mass of PVA solid powder and a corresponding proportion of deionized water, add the mixture into a 1000mL beaker, heat in a water bath at 85-95°C, and mechanically stir for 2-3h until the PVA is completely dissolved to obtain a 7-10wt% PVA solution.

[0050] S2: Add crosslinking agent citric acid (CA) and nanoparticle graphene oxide (GO) by external addition method: Accurately weigh 10%-20% CA and 0.25-1wt% GO in PVA content, add them to the prepared PVA solution, and continue stirring for 10-30 minutes. After CA is completely dissolved and GO is completely dispersed in the PVA solution, turn off the heating device and stirring device to obtain PVA / CA / GO spinning solution. Under normal temperature conditions (20-25℃), stand for 12-24 hours for degassing until the bubbles in the solution disappear completely.

[0051] S3: Assemble the spunlace viscose fiber membrane (SVF) base fabric on the unwinding mechanism, wrap the front end of the base fabric on the surface of the metal mesh curtain above the solution tank, continue to move forward, and wind the excess front end of the base fabric on the winding mechanism, and adjust the appropriate tension. Then pour the spinning solution into the solution tank, adjust the appropriate spinning conditions for electrostatic spinning to obtain a composite fiber membrane. Figure 6This is a SEM image of the cross section of the spunlace viscose / PVA composite fiber membrane. The spinning conditions are voltage: 45-80kV; temperature: 20-25℃; humidity: 45-60%; spiral speed: 8-12r / min; winding speed: 0.1-0.5m / min; receiving distance: 12-18cm. The thickness of the composite fiber membrane is controlled to 40μm-80μm by controlling the spinning time, and the influence of different thickness composite membranes on its flux and retention rate is explored.

[0052] S4: Hot pressing treatment: The composite fiber membrane is hot pressed at a high temperature of 140-180°C to allow the carboxyl group on the cross-linking agent citric acid to undergo an esterification reaction with the hydroxyl group on the PVA chain. The water resistance is improved by regulating the structure of the PVA polymer to obtain a microfiltration composite fiber membrane. Figure 7 This is the infrared spectrum of the composite fiber membrane. The cross-linked fiber membrane has a characteristic absorption peak of carbonyl at 1718cm-1; the asymmetric stretching vibration characteristic absorption peak of COC appears at 1088cm-1, indicating the existence of ester structure. The stretching vibration of CH bond appears at 2940cm-1, indicating that citric acid is bonded to polyvinyl alcohol. Figure 2 This is the SEM image of the PVA / CA / GO fiber membrane on the surface of the microfiltration composite microfiltration membrane. The hot pressing time is 10-30min.

[0053] The present invention also provides a method for testing the filtration performance of a microfiltration composite fiber membrane, which is used to test the filtration performance of the microfiltration composite fiber membrane, comprising:

[0054] The microfiltration composite fiber membrane prepared in S4 was placed in a filtration device, and 0.3μm fluorescent PS microspheres were used as the filter material. The composite ultrafiltration membrane was tested for filtration at a pressure of 0.025-0.1MPa. According to the national standard GB / T32360-2015 ultrafiltration membrane test method, pure water flux and PS microsphere filtration tests were performed. Dead-end filtration was used, the test water temperature was adjusted to 25.0℃±0.5℃, the pressure was adjusted to 0.150MPa±0.005MPa, the pre-pressure was 30min, and then the test pressure was gradually reduced to 0.100MPa±0.005MPa. After stabilization for 10min, a certain volume of produced water was collected with a measuring cylinder, and the time used was recorded with a stopwatch, and 3 samples were taken for parallel experiments. Figure 5 This is the surface SEM image of PS microspheres after being filtered by microfiltration composite nanofiber membrane.

[0055] The pure water permeability is calculated according to formula (1), and the result is the average value of three parallel experiments:

[0056]

[0057] Where:

[0058] P——pure water permeability, in liters per square meter per hour [L / (m2·h)];

[0059] V——pure water permeability, in liters (L);

[0060] S——Effective filtration area of ​​membrane, in square meters (m2);

[0061] t – the time taken to pass through a volume of pure water V, in hours (h).

[0062] The test method also includes:

[0063] Draw the concentration-absorbance standard curve of PS microspheres and derive the linear regression equation;

[0064] Specifically, 0.2 g of fluorescent PS microspheres with a solid content of 5% was accurately weighed, water was added to dissolve it, and the solution was transferred into a 100 mL volumetric flask. Deionized water was added to the scale line, shaken, and ultrasonicated for 30 min to prepare a PS microsphere solution with a mass concentration of 100 mg / L as the test solution.

[0065] Pipette 0.1mL, 0.25mL, 0.5mL, 1mL, 2mL, and 3mL of the prepared PS microsphere solution into 100mL volumetric flasks, add deionized water to the scale line, shake well, and prepare PS microsphere standard solutions with mass concentrations of 1mg / L, 2.5mg / L, 5mg / L, 10mg / L, 20mg / L, and 30mg / L, respectively;

[0066] Using deionized water as a reference, the absorbance values ​​of the prepared solutions were measured at a wavelength of 389 nm using a 1 cm cuvette on a UV-visible spectrophotometer. With the PS microsphere concentration as the abscissa and the absorbance value as the ordinate, a concentration-absorbance standard curve of the PS microspheres was plotted, and a linear regression equation was obtained.

[0067] The microfiltration composite fiber membrane prepared in S4 was prepared into three membrane samples of the same specifications, washed with distilled water and set aside; then the membrane test device was connected, the test solution was added to the constant temperature liquid storage tank, the membrane test device was operated by dead-end filtration, the test water temperature was adjusted to 25°C ± 0.5°C, the transmembrane pressure difference was gradually adjusted to 0.025-0.10MPa, and the filtrate was collected after the system was stably operated for 10 minutes;

[0068] Using distilled water as a reference, the absorbance of the PS microspheres used was measured by an ultraviolet fluorescence spectrophotometer, and the absorbance (λ) was measured to be the maximum at 389 nm. A 1 cm cuvette was used on a UV-visible spectrophotometer at a wavelength of 389 nm to measure the absorbance values ​​of the test solution before and after filtration, respectively. The absorbance values ​​obtained from the test were calculated through a linear regression equation to calculate the concentration of the PS microsphere solution; the retention rate result was calculated according to formula (2):

[0069]

[0070] Where:

[0071] R——retention rate, %;

[0072] Cp——Concentration of standard substance in the test solution after filtration, in milligrams per liter (mg / L);

[0073] Cf - concentration of standard substance in the test solution before filtration, in milligrams per liter (mg / L).

[0074] Example 1

[0075] 1. Prepare a 9 wt% PVA solution: Accurately weigh 90 g of PVA solid powder and 910 g of deionized water, mix and add into a 1000 mL beaker, heat in a water bath at 90°C, and mechanically stir for 2-3 h until the PVA is completely dissolved to obtain a 9 wt% PVA solution.

[0076] 2. Add CA and GO by external addition method: Accurately weigh CA (about 9g) accounting for 10% of PVA content and GO (about 5g) accounting for 0.5wt%, respectively, and add them to the prepared PVA solution, and continue stirring for 15min. Add them to the prepared PVA solution respectively, and continue stirring for 10-30min. After CA is completely dissolved and GO is completely dispersed in the PVA solution, turn off the heating device and the stirring device to obtain PVA / CA / GO spinning solution. After CA is completely dissolved, turn off the heating device and the stirring device to obtain PVA / CA / GO spinning solution. Under normal temperature conditions (20-25℃), let it stand for 12h for degassing until the bubbles in the solution disappear completely.

[0077] 3. Assemble the spunlace viscose base fabric on the unwinding mechanism, wrap the front end of the base fabric on the surface of the metal mesh curtain above the solution tank, continue to move forward, and wind the excess front end of the base fabric on the winding mechanism to adjust the appropriate tension. Then pour the spinning solution into the solution tank, adjust the appropriate spinning conditions for electrostatic spinning to obtain the composite fiber membrane. The spinning conditions are voltage: 45kV; temperature: 20-25℃; humidity: 45-60%; spiral speed: 8-12r / min; winding speed: 0.1m / min; receiving distance: 12-18cm. By controlling the spinning time, the thickness of the composite fiber membrane is controlled to 40μm, and the influence of composite membranes of different thicknesses on its flux and retention rate is explored.

[0078] 4. Hot pressing treatment: Under high temperature conditions of 130°C, the carboxyl groups on the cross-linking agent react with the hydroxyl groups on the PVA chain to undergo an esterification reaction, and the water resistance is improved by regulating the structure of the PVA polymer. The composite fiber membrane spun in step 3 is hot pressed to obtain a microfiltration composite fiber membrane, and the hot pressing time is 10 minutes.

[0079] 5. Place the composite fiber membrane prepared in step 4 in a filtration device, use 0.3 μm fluorescent PS microspheres as the filter, and perform a filtration test at a pressure of 0.05 MPa according to the filtration performance test method.

[0080] Example 2

[0081] 1. Prepare a 9 wt% PVA solution: Accurately weigh 90 g of PVA solid powder and 910 g of deionized water, mix and add into a 1000 mL beaker, heat in a water bath at 90°C, and mechanically stir for 2-3 h until the PVA is completely dissolved to obtain a 9 wt% PVA solution.

[0082] 2. Add CA and GO by external addition method: Accurately weigh CA (13.5g, which accounts for 15% of PVA content) and GO (0.5wt%, which is about 5g), and add them to the prepared PVA solution, and continue stirring for 15 minutes. Add them to the prepared PVA solution separately, and continue stirring for 10-30 minutes. After CA is completely dissolved and GO is completely dispersed in the PVA solution, turn off the heating device and the stirring device to obtain PVA / CA / GO spinning solution. After CA is completely dissolved, turn off the heating device and the stirring device to obtain PVA / CA / GO spinning solution. Under normal temperature conditions (20-25℃), let it stand for 12 hours for degassing until the bubbles in the solution disappear completely.

[0083] 3. Assemble the spunlace viscose base fabric on the unwinding mechanism, wrap the front end of the base fabric on the surface of the metal mesh curtain above the solution tank, continue to move forward, and wind the extra front end of the base fabric on the winding mechanism to adjust the appropriate tension. Then pour the spinning solution into the solution tank, adjust the appropriate spinning conditions for electrostatic spinning to obtain the composite fiber membrane. The spinning conditions are voltage: 45kV; temperature: 20-25℃; humidity: 45-60%; spiral speed: 8-12r / min; winding speed: 0.1m / min; receiving distance: 12-18cm. By controlling the spinning time, the thickness of the composite fiber membrane is controlled to 80μm, and the influence of composite membranes of different thicknesses on its flux and retention rate is explored.

[0084] 4. Hot pressing treatment: Under high temperature conditions of 130°C, the carboxyl groups on the cross-linking agent react with the hydroxyl groups on the PVA chain to undergo an esterification reaction, and the water resistance is improved by regulating the structure of the PVA polymer. The composite fiber membrane spun in step 3 is hot pressed to obtain a microfiltration composite fiber membrane, and the hot pressing time is 10 minutes.

[0085] 5. Place the composite fiber membrane prepared in step 4 in a filtration device, use 0.3 μm fluorescent PS microspheres as the filter, and perform a filtration test at a pressure of 0.1 MPa according to the filtration performance test method.

[0086] Example 3

[0087] 1. Prepare a 9 wt% PVA solution: Accurately weigh 90 g of PVA solid powder and 910 g of deionized water, mix and add into a 1000 mL beaker, heat in a water bath at 90°C, and mechanically stir for 2-3 h until the PVA is completely dissolved to obtain a 9 wt% PVA solution.

[0088] 2. Add CA and GO by external addition method: Accurately weigh CA (13.5g, which accounts for 15% of PVA content) and GO (0.5wt%, which is about 5g), and add them to the prepared PVA solution, and continue stirring for 15 minutes. Add them to the prepared PVA solution separately, and continue stirring for 10-30 minutes. After CA is completely dissolved and GO is completely dispersed in the PVA solution, turn off the heating device and the stirring device to obtain PVA / CA / GO spinning solution. After CA is completely dissolved, turn off the heating device and the stirring device to obtain PVA / CA / GO spinning solution. Under normal temperature conditions (20-25℃), let it stand for 12 hours for degassing until the bubbles in the solution disappear completely.

[0089] 3. Assemble the spunlace viscose base fabric on the unwinding mechanism, wrap the front end of the base fabric on the surface of the metal mesh curtain above the solution tank, continue to move forward, and wind the extra front end of the base fabric on the winding mechanism to adjust the appropriate tension. Then pour the spinning solution into the solution tank, adjust the appropriate spinning conditions for electrostatic spinning to obtain the composite fiber membrane. The spinning conditions are voltage: 60kV; temperature: 20-25℃; humidity: 45-60%; spiral speed: 8-12r / min; winding speed: 0.1m / min; receiving distance: 12-18cm. By controlling the spinning time, the thickness of the composite fiber membrane is controlled to 60μm, and the influence of composite membranes of different thicknesses on its flux and retention rate is explored.

[0090] 4. Hot pressing treatment: Under high temperature conditions of 130°C, the carboxyl groups on the cross-linking agent react with the hydroxyl groups on the PVA chain to undergo an esterification reaction, and the water resistance is improved by regulating the structure of the PVA polymer. The composite fiber membrane spun in step 3 is hot pressed to obtain a microfiltration composite fiber membrane, and the hot pressing time is 15 minutes.

[0091] 5. Place the composite fiber membrane prepared in step 4 in a filtration device, use 0.3 μm fluorescent PS microspheres as the filter, and perform a filtration test at a pressure of 0.05 MPa according to the filtration performance test method.

[0092] Example 4

[0093] 1. Prepare a 9 wt% PVA solution: Accurately weigh 90 g of PVA solid powder and 910 g of deionized water, mix and add into a 1000 mL beaker, heat in a water bath at 90°C, and mechanically stir for 2-3 h until the PVA is completely dissolved to obtain a 9 wt% PVA solution.

[0094] 2. Add CA and GO by external addition method: Accurately weigh CA (13.5g, which accounts for 15% of PVA content) and GO (0.5wt%, which is about 5g), and add them to the prepared PVA solution, and continue stirring for 15 minutes. Add them to the prepared PVA solution separately, and continue stirring for 10-30 minutes. After CA is completely dissolved and GO is completely dispersed in the PVA solution, turn off the heating device and the stirring device to obtain PVA / CA / GO spinning solution. After CA is completely dissolved, turn off the heating device and the stirring device to obtain PVA / CA / GO spinning solution. Under normal temperature conditions (20-25℃), let it stand for 12 hours for degassing until the bubbles in the solution disappear completely.

[0095] 3. Assemble the spunlace viscose base fabric on the unwinding mechanism, wrap the front end of the base fabric on the surface of the metal mesh curtain above the solution tank, continue to move forward, and wind the extra front end of the base fabric on the winding mechanism to adjust the appropriate tension. Then pour the spinning solution into the solution tank, adjust the appropriate spinning conditions for electrostatic spinning to obtain the composite fiber membrane. The spinning conditions are voltage: 60kV; temperature: 20-25℃; humidity: 45-60%; spiral speed: 8-12r / min; winding speed: 0.1m / min; receiving distance: 12-18cm. By controlling the spinning time, the thickness of the composite fiber membrane is controlled to 60μm, and the influence of composite membranes of different thicknesses on its flux and retention rate is explored.

[0096] 4. Hot pressing treatment: Under high temperature conditions of 180°C, the carboxyl groups on the cross-linking agent react with the hydroxyl groups on the PVA chain to undergo an esterification reaction, and the water resistance is improved by regulating the structure of the PVA polymer. The composite fiber membrane spun in step 3 is hot pressed to obtain a microfiltration composite fiber membrane, and the hot pressing time is 10 minutes.

[0097] 5. Place the composite fiber membrane prepared in step 4 in a filtration device, use 0.3 μm fluorescent PS microspheres as the filter, and perform a filtration test at a pressure of 0.05 MPa according to the filtration performance test method.

[0098] Example 5

[0099] 1. Prepare a 9 wt% PVA solution: Accurately weigh 90 g of PVA solid powder and 910 g of deionized water, mix and add into a 1000 mL beaker, heat in a water bath at 90°C, and mechanically stir for 2-3 h until the PVA is completely dissolved to obtain a 9 wt% PVA solution.

[0100] 2. Add CA and GO by external addition method: Accurately weigh CA (13.5g, which accounts for 15% of PVA content) and GO (0.5wt%, which is about 5g), and add them to the prepared PVA solution, and continue stirring for 15 minutes. Add them to the prepared PVA solution separately, and continue stirring for 10-30 minutes. After CA is completely dissolved and GO is completely dispersed in the PVA solution, turn off the heating device and the stirring device to obtain PVA / CA / GO spinning solution. After CA is completely dissolved, turn off the heating device and the stirring device to obtain PVA / CA / GO spinning solution. Under normal temperature conditions (20-25℃), let it stand for 12 hours for degassing until the bubbles in the solution disappear completely.

[0101] 3. Assemble the spunlace viscose base fabric on the unwinding mechanism, wrap the front end of the base fabric on the surface of the metal mesh curtain above the solution tank, continue to move forward, wind the extra front end of the base fabric on the winding mechanism, and adjust the appropriate tension. Then pour the spinning solution into the solution tank, adjust the appropriate spinning conditions for electrostatic spinning to obtain the composite fiber membrane. The spinning conditions are voltage: 60kV; temperature: 20-25℃; humidity: 45-60%; spiral speed: 10r / min; winding speed: 0.1m / min; receiving distance: 12-18cm. By controlling the spinning time, the thickness of the composite fiber membrane is controlled to 60μm, and the influence of composite membranes of different thicknesses on its flux and retention rate is explored.

[0102] 4. Hot pressing treatment: Under high temperature conditions of 150°C, the carboxyl groups on the cross-linking agent react with the hydroxyl groups on the PVA chain to undergo an esterification reaction, and the water resistance is improved by regulating the structure of the PVA polymer. The composite fiber membrane spun in step 3 is hot pressed to obtain a microfiltration composite fiber membrane, and the hot pressing time is 15 minutes.

[0103] 5. Place the composite fiber membrane prepared in step 4 in a filtration device, use 0.3 μm fluorescent PS microspheres as the filter, and perform a filtration test at a pressure of 0.1 MPa according to the filtration performance test method.

[0104] Example 6

[0105] 1. Prepare a 9 wt% PVA solution: Accurately weigh 90 g of PVA solid powder and 910 g of deionized water, mix and add into a 1000 mL beaker, heat in a water bath at 90°C, and mechanically stir for 2-3 h until the PVA is completely dissolved to obtain a 9 wt% PVA solution.

[0106] 2. Add CA and GO by external addition method: Accurately weigh CA (13.5g, which accounts for 15% of PVA content) and GO (0.5wt%, which is about 5g), and add them to the prepared PVA solution, and continue stirring for 15 minutes. Add them to the prepared PVA solution separately, and continue stirring for 10-30 minutes. After CA is completely dissolved and GO is completely dispersed in the PVA solution, turn off the heating device and the stirring device to obtain PVA / CA / GO spinning solution. After CA is completely dissolved, turn off the heating device and the stirring device to obtain PVA / CA / GO spinning solution. Under normal temperature conditions (20-25℃), let it stand for 12 hours for degassing until the bubbles in the solution disappear completely.

[0107] 3. Assemble the spunlace viscose base fabric on the unwinding mechanism, wrap the front end of the base fabric on the surface of the metal mesh curtain above the solution tank, continue to move forward, wind the extra front end of the base fabric on the winding mechanism, and adjust the appropriate tension. Then pour the spinning solution into the solution tank, adjust the appropriate spinning conditions for electrostatic spinning to obtain the composite fiber membrane. The spinning conditions are voltage: 60kV; temperature: 20-25℃; humidity: 45-60%; spiral speed: 10r / min; winding speed: 0.1m / min; receiving distance: 12-18cm. By controlling the spinning time, the thickness of the composite fiber membrane is controlled to 80μm, and the influence of composite membranes of different thicknesses on its flux and retention rate is explored.

[0108] 4. Hot pressing treatment: Under high temperature conditions of 150°C, the carboxyl groups on the cross-linking agent react with the hydroxyl groups on the PVA chain to undergo an esterification reaction, and the water resistance is improved by regulating the structure of the PVA polymer. The composite fiber membrane spun in step 3 is hot pressed to obtain a microfiltration composite fiber membrane, and the hot pressing time is 15 minutes.

[0109] 5. Place the composite fiber membrane prepared in step 4 in a filtration device, use 0.3 μm fluorescent PS microspheres as the filter, and perform a filtration test at a pressure of 0.05 MPa according to the filtration performance test method.

[0110] Table 1: Composite nanofiber membrane filtration performance test table

[0111]

[0112] Due to the adoption of the above technical solution, the present invention has the following advantages and effects:

[0113] 1. The spinning efficiency of needle-free electrospinning is relatively high. The use of pilot needle-free electrospinning equipment for spinning significantly improves the spinning efficiency.

[0114] 2. PVA material is soluble in water. Compared with organic solvents, this solvent has lower cost and wider sources. In addition, using water as a solvent is in line with the concept of sustainable development.

[0115] 3. GO is dispersed in the spinning solution and is more evenly distributed. The addition of GO makes the fiber thinner and increases the specific surface area of ​​the fiber, which is more conducive to the adsorption and retention of some metal ions and some particulate pollutants in the water, providing a broader space for the use of fiber membranes.

[0116] 4. If Figure 2 , Figure 3 , Figure 4As shown in the figure, PVA nanofiber membrane easily swells when it comes into contact with water and it is difficult to maintain the fiber morphology. The cross-linking agent citric acid is added to the spinning solution and then directly spun into the fiber through electrospinning, which greatly increases the contact area between the cross-linking agent citric acid and PVA, making the cross-linking effect more complete. The fiber membrane can also maintain a good fiber morphology after working in water for a long time.

[0117] 5. If Figure 8 As shown in the figure, the composite fiber membrane can filter at a relatively low pressure, and its pure water flux is higher than 20000L / m2 / h, which reduces energy consumption while maintaining high flux. It also has excellent reusability, and can maintain a relatively high flux and retention rate after repeated use, greatly improving the reusability and service life of the material.

[0118] It should be understood by those skilled in the art that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention (including the claims) is limited to these examples. Under the concept of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the above aspects of the present invention, which are not provided in detail for the sake of simplicity.

[0119] The present invention is intended to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a microfiltration composite fiber membrane, characterized in that: include: S1: preparing 7-10wt% PVA solution; S2: Add CA and GO by external addition method: Accurately weigh 10%-20% CA and 0.25-1wt% GO in PVA content, respectively, and add them to the prepared PVA solution, continue stirring for 10-30 minutes, and after CA is completely dissolved, GO is completely dispersed in the PVA solution to obtain PVA / CA / GO spinning solution; S3: Assemble the SVF base fabric on the unwinding mechanism, wrap the front end of the base fabric on the surface of the metal mesh curtain above the solution tank, continue to move forward, wind the excess front end of the base fabric on the winding mechanism, adjust the appropriate tension, and then pour the spinning solution into the solution tank, adjust the spinning conditions and perform electrospinning to obtain a composite fiber membrane; S4: Hot pressing treatment: The composite fiber membrane is subjected to hot pressing treatment, so that the carboxyl group on the cross-linking agent citric acid reacts with the hydroxyl group on the PVA chain to undergo esterification reaction, and the water resistance is improved by regulating the structure of the PVA polymer to obtain a microfiltration composite fiber membrane.

2. The method for preparing a microfiltration composite fiber membrane according to claim 1, characterized in that: The preparation of the 7-10wt% PVA solution includes: weighing a predetermined mass of PVA solid powder and a corresponding proportion of deionized water, adding the mixture into a 1000mL beaker, heating in a water bath at 85-95°C, and mechanically stirring for 2-3h until the PVA is completely dissolved, thereby obtaining a 7-10wt% PVA solution.

3. The method for preparing a microfiltration composite fiber membrane according to claim 1, characterized in that: The spinning conditions are voltage: 45-80 kV; temperature: 20-25° C.; Humidity: 45-60%; spiral speed: 8-12r / min; winding speed: 0.1-0.5m / min; receiving distance: 12-18cm.

4. The method for preparing a microfiltration composite fiber membrane according to claim 1, characterized in that: The step S3 further includes: controlling the thickness of the composite fiber membrane to be 40 μm-80 μm by controlling the spinning time.

5. The method for preparing a microfiltration composite fiber membrane according to claim 1, characterized in that: The temperature of the hot pressing treatment is 140-180° C., and the hot pressing time is 10-30 minutes.

6. A method for testing the filtration performance of a microfiltration composite fiber membrane, characterized in that: Used to test the filtration performance of the microfiltration composite fiber membrane according to claim 1, comprising: The microfiltration composite fiber membrane prepared in S4 was placed in a filtration device, and 0.3 μm fluorescent PS microspheres were used as the filter. The composite ultrafiltration membrane was tested under a pressure of 0.025-0.1 MPa. Dead-end filtration was used, and the test water temperature was adjusted to 25.0°C ± 0.5°C, and the pressure was adjusted to 0.150 MPa ± 0.005 MPa. The pre-pressure was performed for 30 minutes, and then the test pressure was gradually reduced to 0.100 MPa to 0.005 MPa. After stabilization for 10 minutes, a certain volume of produced water was collected with a measuring cylinder, and the time was recorded with a stopwatch. Three samples were taken for parallel experiments. The pure water permeability is calculated according to formula (1), and the result is the average value of three parallel experiments: Where: P——pure water permeability, in liters per square meter per hour [L / (m2·h)]; V——pure water permeability, in liters (L); S——Effective filtration area of ​​membrane, in square meters (m2); t – the time taken to pass through a volume of pure water V, in hours (h).

7. The method for testing the filtration performance of a microfiltration composite fiber membrane according to claim 6, characterized in that: The test method also includes: Draw the concentration-absorbance standard curve of PS microspheres and derive the linear regression equation; The microfiltration composite fiber membrane prepared in S4 was prepared into three membrane samples of the same specifications, washed with distilled water and set aside; then the membrane test device was connected, the test solution was added to the constant temperature liquid storage tank, the membrane test device was operated by dead-end filtration, the test water temperature was adjusted to 25°C ± 0.5°C, the transmembrane pressure difference was gradually adjusted to 0.025-0.10MPa, and the filtrate was collected after the system was stably operated for 10 minutes; Using distilled water as a reference, the absorbance of the PS microspheres used was measured by an ultraviolet fluorescence spectrophotometer, and the absorbance (λ) was measured to be the maximum at 389 nm. A 1 cm cuvette was used on a UV-visible spectrophotometer at a wavelength of 389 nm to measure the absorbance values ​​of the test solution before and after filtration, respectively. The absorbance values ​​obtained from the test were calculated through a linear regression equation to calculate the concentration of the PS microsphere solution; the retention rate result was calculated according to formula (2): Where: R——retention rate, %; Cp is the concentration of the standard substance in the test solution after filtration, in milligrams per liter (mg / L); Cf is the concentration of the standard substance in the test solution before filtration, in milligrams per liter (mg / L).

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