Preparation method of polyvinyl alcohol-based separation membrane

Abstract

The invention relates to a preparation method of a polyvinyl alcohol-based separation membrane, which comprises the following steps: weighing a certain mass of polyvinyl alcohol 1788 powder, adding the polyvinyl alcohol 1788 powder into deionized water, and stirring until the polyvinyl alcohol 1788 powder is dissolved to obtain a spinning solution; 2 mol / L hydrochloric acid is added into the prepared spinning solution to be stirred to enable the PH to be equal to 1, then a certain mass of SBQ powder is added, stirring continues to be conducted for 2 h to 6 h in a dark place to complete grafting, finally, the PH of the solution is adjusted to be neutral with a 2 mol / L sodium hydroxide solution, and the solution is kept away from the dark place for standby application; the spinning solution prepared in the second step is used for needleless electrostatic spinning, a spunlace viscose / PVA-SBQ nanofiber membrane is obtained, the prepared nanofiber membrane is placed in an ultraviolet curing machine to be subjected to photo-crosslinking, and the polyvinyl alcohol-based separation membrane is prepared. The PVA-SBQ is grafted with an SBQ group to obtain PVA-SBQ, the water resistance of the PVA-SBQ is greatly improved, and the pore structure of the PVA-SBQ is controlled through photo-crosslinking, so that the PVA-SBQ is insoluble in water, but the fibers are allowed to be highly swelled to reduce pores of the PVA-SBQ, and the rejection rate of the PVA-SBQ is higher than that of a traditional PVA electrostatic spinning membrane.

Description

Technical Field

[0001] The present invention relates to a method for preparing a separation membrane, specifically a method for preparing a polyvinyl alcohol-based separation membrane. Background Art

[0002] In the fields of modern materials science and environmental engineering, separation membrane technology has become a key means to achieve various applications such as material separation, purification, and water treatment. With the continuous improvement of requirements for resource utilization efficiency and environmental protection, it is crucial to develop new separation membranes with high separation performance and special properties. For water purification and separation, developing separation membranes that can effectively intercept particles of specific sizes is an important research direction.

[0003] Polyvinyl alcohol (PVA) has become one of the research focuses in the field of membrane materials due to its excellent hydrophilicity, degradability, anti-pollution property, and chemical stability. The PVA material has good film-forming properties and low cost. It uses water as a solvent, which reduces environmental problems during membrane manufacturing. It has been widely used in water treatment and other filtration applications. When PVA contacts water, crosslinking is required to prevent its dissolution, which can be achieved through acetalization or esterification reactions. A dangerous and toxic crosslinking agent, such as glutaraldehyde, is required in the acetalization reaction, while acid catalysis and high temperature (>100 °C) are the rigid conditions for the esterification reaction. Therefore, the existing PVA crosslinking methods are not suitable for large-scale use in membrane materials for separation. The acetalization reaction usually cannot be carried out in an aqueous solution, and anhydrous hydrogen chloride is used as a catalyst. However, in this experiment, by simply adjusting the solution to be acidic, the grafting reaction of SBQ can be completed in an aqueous solution to obtain PVA-SBQ. Photo-crosslinking is an effective and sustainable method that does not require toxic reagents and does not generate toxic substances. For example, polyvinyl alcohol styrylpyridinium salt condensate (PVA-SBQ) is widely used in the printing industry due to its water solubility. Under ultraviolet irradiation, the SBQ on PVA-SBQ can dimerize to form a four-membered ring, crosslinking PVA. Both PVA and SBQ can be dissolved in water as a solvent, and this material is also used in food packaging, wound healing, and drug delivery. A small amount of SBQ grafted onto the PVA molecular chain can obtain excellent photosensitivity without affecting the performance of PVA.

[0004] Electrospinning technology is a commonly used method for preparing nanofibers and submicron fibers. Its main principle is that conductive polymer droplets are subjected to electrostatic force, gravity and other forces in a high-voltage electrostatic field, and are continuously accelerated, stretched, and the diameter is reduced. At the same time, with the volatilization of the solvent, they are finally solidified into nanofibers or submicron fibers and received by the receiving device. Compared with other fibers, electrospun nanofibers have the advantages of small diameter, large specific surface area, high porosity, etc., and the production process is simple and controllable, the material source is wide, and the price is low. Therefore, nanofibers have broad prospects in water treatment. At present, there have been extensive studies on applying polymer electrospun materials to ultrafiltration membranes, nanofiltration membranes, reverse osmosis and other fields. Needleless electrospinning technology can significantly improve production efficiency, and its productivity is 3-250 times higher than that of needle-based electrospinning systems, because it forms jet streams directly on the free liquid surface, avoiding the problem of the number of needles being limited in traditional needle-based electrospinning. In addition, needleless electrospinning does not require the use of needles, which reduces maintenance problems caused by needle blockage and reduces production costs. Summary of the Invention

[0005] Now, in order to solve the above technical problems, the present invention proposes a preparation method of a polyvinyl alcohol-based separation membrane. The technical problems to be solved by the present invention are realized by the following technical solutions:

[0006] A preparation method of a polyvinyl alcohol-based separation membrane, the method comprising the following steps:

[0007] The first step: Weigh a certain mass of polyvinyl alcohol 1788 powder, add it to deionized water, and stir with a magnetic stirrer at room temperature until the polyvinyl alcohol is completely dissolved to obtain a homogeneous and stable spinning solution with a mass fraction of 10%;

[0008] The second step: Add 2mol / L hydrochloric acid to the prepared spinning solution and stir to make its pH = 1. Then add a certain mass of SQB powder and continue to stir in the dark for 2h to 6h to complete grafting. Finally, adjust its pH to neutral with 2mol / L sodium hydroxide solution and keep it in the dark for standby;

[0009] The third step: Use the spinning solution prepared in the second step for needleless electrospinning to obtain a hydroentangled viscose / PVA-SBQ nanofiber membrane;

[0010] The fourth step: Place the prepared nanofiber membrane in an ultraviolet curing machine for photocrosslinking to prepare a polyvinyl alcohol-based separation membrane, wherein the photocrosslinking time is between 30s and 15min.

[0011] The mass of SQB added in the second step is between 0.5% and 1%.

[0012] In the third step, the electrospinning process parameters are set as follows: the receiving distance is 25 cm, the reciprocating rate is 50 mm·s-1, the temperature is 18°C to 20°C, and the humidity is 20% to 30%; the applied voltage is 30 kV to 55 kV, and the electrospun viscose is received for 3 min to 30 min.

[0013] In the fourth step, the crosslinking process parameters are set as follows: the power is between 0 - 2382 mW / cm2, the energy is 0 - 12828 mj / cm2 every 3 seconds, the temperature is 39°C to 55°C, the power is above 300 W, and the crosslinking time is 30 s - 15 min.

[0014] The beneficial effects of the present invention are as follows: First, although the original PVA membrane material has good hydrophilicity, excellent mechanical strength, chemical stability, and biocompatibility, it dissolves immediately in water and has extremely poor water resistance, making it inapplicable to the water treatment field. In the present invention, it is grafted with SBQ groups to obtain PVA-SBQ, which greatly improves its water resistance, provides a new idea for the application of PVA membranes in the water treatment field, and is electrospun onto electrospun viscose and compounded with it through needleless electrospinning technology, improving its mechanical properties to a certain extent. By controlling its pore structure through photocrosslinking, it does not dissolve in water but allows the fibers to swell highly to reduce its pores, achieving a higher rejection rate than traditional PVA electrospun membranes.

[0015] Second, the present invention uses needleless electrospinning to prepare a composite separation membrane, which can achieve high-efficiency large-scale production. When treating the feed liquid, the feed end first contacts a material with excellent hydrophilicity, uniform fiber distribution, good pore connectivity, and high porosity, and then enters the electrospun viscose layer. The high hydrophilicity of this nanofiber layer ensures high filtration accuracy, greatly improves the membrane flux and rejection effect, solves problems such as pollution blockage by large particles and impurities, enhances the durability of the membrane, and can operate under a low pressure of 0.05 MPa, greatly extending the service life of the membrane.

[0016] Third, compared with other chemical crosslinking methods of PVA membranes, the present invention can maintain a relatively high porosity without using dangerous and toxic crosslinking agents and high-power and high-energy-consuming high-temperature treatment technologies. This method can make the nanofiber membrane applicable to the water treatment field in only 60 s, and a high-flux and high-rejection separation membrane material can be obtained after 600 s of complete crosslinking. The method is simple, efficient, energy-saving, and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be further described below in conjunction with the drawings and embodiments.

[0018] Figure 1 It is a test result diagram of the embodiment in the present invention;

[0019] Figure 2 It is a SEM diagram of PVA-SBQ nanofibers in the present invention;

[0020] Figure 3 This is the SEM image of the PVA-SBQ nanofibers after wet state drying following photocrosslinking in the present invention;

[0021] Figure 4 This is the analysis diagram of the mechanical properties of the polyvinyl alcohol-based separation membrane in the present invention;

[0022] Figure 5 This is the pore size distribution diagram of the polyvinyl alcohol-based separation membrane in the present invention. Detailed implementation manners

[0023] In order to enable those skilled in the art to better understand the technical solution of the present invention, the following will combine the accompanying drawings in the embodiments to more clearly and completely elaborate on the present invention. Of course, the described embodiments are only a part of the present invention rather than all of it. Based on this embodiment, other embodiments obtained by those skilled in the art without creative efforts are within the protection scope of the present invention.

[0024] As Figures 1 to 5 shown, a preparation method of a polyvinyl alcohol-based separation membrane includes the following steps:

[0025] The first step: Weigh a certain mass of polyvinyl alcohol 1788 powder, add it to deionized water, and stir it with a magnetic stirrer at room temperature until the polyvinyl alcohol is completely dissolved to obtain a uniform and stable spinning solution with a mass fraction of 10%;

[0026] The second step: Add 2 mol / L hydrochloric acid to the prepared spinning solution and stir to make its pH = 1. Subsequently, add a certain mass of SBQ powder and continue to stir in the dark for 2 h to 6 h to complete grafting. Finally, adjust its pH to neutral with 2 mol / L sodium hydroxide solution and keep it in the dark for standby;

[0027] The third step: Use the spinning solution prepared in the second step for needleless electrospinning to obtain a hydroentangled viscose / PVA-SBQ nanofiber membrane;

[0028] The fourth step: Place the prepared nanofiber membrane in an ultraviolet curing machine for photocrosslinking to prepare a polyvinyl alcohol-based separation membrane, where the photocrosslinking time is between 30 s and 15 min.

[0029] PVA-SBQ is a photosensitive polymer material, and its ultraviolet cross-linking principle is mainly based on the photochemical reaction of the styrylpyridinium salt (SBQ) group. Under ultraviolet light irradiation, the SBQ group undergoes a photodimerization reaction to form covalent bonds, thereby establishing a three-dimensional network structure between PVA molecules. This cross-linking not only enhances the mechanical properties and stability of the material but also improves its chemical and thermal stability. By controlling the dose and time of ultraviolet light irradiation, the degree of cross-linking can be adjusted to optimize the pore size distribution and filtration performance of the membrane.

[0030] The mass of SBQ added in the second step is between 0.01% and 1%.

[0031] In the third step, the electrospinning process parameters are set as follows: the receiving distance is 25 cm, the reciprocating rate is 50 mm·s -1 , the temperature is 18°C to 20°C, and the humidity is 20% to 30%; the applied voltage is 30 kV to 55 kV, and it is received by spunlace viscose for 3 min to 30 min.

[0032] In the fourth step, the cross-linking process parameters are set as follows: the power is between 0 - 2382 mW / cm 2 and the energy is between 0 - 12828 mj / cm 2 every 3 seconds, the temperature is 39°C to 55°C, and the power is above 300 W.

[0033] The preparation of the polyvinyl alcohol-based separation membrane using the above method includes the following examples:

[0034] Example 1:

[0035] 1. Prepare a hydrophilic polyvinyl alcohol nanofiber layer using needleless electrospinning technology: Accurately weigh 60 g of polyvinyl alcohol (PVA) powder, dissolve it in 540 ml of deionized water, and stir it with a magnetic stirrer at room temperature until the polyvinyl alcohol is completely dissolved to obtain a homogeneous and stable spinning solution with a mass fraction of 10%. Use a 2 mol / L HCl solution to adjust the pH to 1. Then add 1% of SBQ by mass, and continue to stir at room temperature for 4 h, and then adjust it to neutral with a 2 mol / L NaOH solution. Use the above spinning solution for needleless electrospinning. Set the electrospinning process parameters as follows: the distance between the spinneret and the receiving plate is 25 cm, the reciprocating rate is 50 mm·s-1, the applied voltage is 55 kV, and it is received by spunlace viscose for 3 - 30 min to obtain a spunlace viscose / PVA-SBQ composite nanofiber membrane.

[0036] 2. Place the above composite nanofiber membrane in an ultraviolet curing machine for photocrosslinking: Cut the nanofiber membrane into a square with a size of 4×4 cm, and place it in the ultraviolet curing machine. Set the process parameters of the ultraviolet curing machine as follows: the power is between 2382 mW / cm2, and the energy is 12828 mj / cm every 3 seconds2 The temperature is 39 °C, the power is 300 W, and the time is 1 min. Among them, each side is cross-linked for 30 s. The finally prepared polyvinyl alcohol-based separation membrane is named M1.

[0037] Example 2:

[0038] 1. Prepare a hydrophilic polyvinyl alcohol nanofiber layer by using needleless electrospinning technology: Accurately weigh 60 g of polyvinyl alcohol (PVA) powder, dissolve it in 540 ml of deionized water, and stir it with a magnetic stirrer at room temperature until the polyvinyl alcohol is completely dissolved to obtain a uniform and stable spinning solution with a mass fraction of 10%. Use a 2 mol / L HCl solution to adjust the pH to 1. Then add 0.5% by mass of SQB, continue to stir at room temperature for 4 h - 8 h, and then adjust it to neutral with a 2 mol / L NaOH solution. Use the above spinning solution for needleless electrospinning. Set the electrospinning process parameters as follows: the distance between the spinneret and the receiving plate is 25 cm, the reciprocating rate is 50 mm·s-1, the applied voltage is 55 kV, and receive it through spunlace viscose for 3 - 30 min to obtain a spunlace viscose / PVA-SBQ composite nanofiber membrane.

[0039] 2. Place the above composite nanofiber membrane in an ultraviolet curing machine for photocrosslinking: Cut the nanofiber membrane into a square with a size of 4×4 cm, and place it in the ultraviolet curing machine. Set the process parameters of the ultraviolet curing machine as follows: the power is between 2382 mW / cm2, and the energy is 12828 mj / cm every 3 seconds 2 The temperature is 39 °C, the power is 300 W, and the time is 1 min. Among them, each side is cross-linked for 30 s. The finally prepared polyvinyl alcohol-based separation membrane is named M2.

[0040] Example 3:

[0041] 1. Prepare a hydrophilic polyvinyl alcohol nanofiber layer by using needleless electrospinning technology: Accurately weigh 60 g of polyvinyl alcohol (PVA) powder, dissolve it in 540 ml of deionized water, and stir it with a magnetic stirrer at room temperature until the polyvinyl alcohol is completely dissolved to obtain a uniform and stable spinning solution with a mass fraction of 10%. Use 2 - 5 ml of 2 mol / L HCl solution to adjust the pH to 1. Then add 0.5% by mass of SQB, continue to stir at room temperature for 4 h - 8 h, and then adjust it to neutral with a 2 mol / L NaOH solution. Use the above spinning solution for needleless electrospinning. Set the electrospinning process parameters as follows: the distance between the spinneret and the receiving plate is 25 cm, the reciprocating rate is 50 mm·s-1, the applied voltage is 55 kV, and receive it through spunlace viscose for 3 - 15 min to obtain a spunlace viscose / PVA-SBQ composite nanofiber membrane.

[0042] 2. Place the above composite nanofiber membrane in an ultraviolet curing machine for photocrosslinking: Cut the nanofiber membrane into squares with a size of 4×4 cm and place them in the ultraviolet curing machine. Set the process parameters of the ultraviolet curing machine as follows: the power is 2382 mW / cm 2 between, the energy is 12828 mj / cm every 3 seconds 2 , the temperature is 39 °C, the power is 300 W, and the time is 10 min. Crosslink each side for 300 s. The finally prepared polyvinyl alcohol-based separation membrane is named M3.

[0043] Example 4:

[0044] 1. Prepare a hydrophilic polyvinyl alcohol nanofiber layer using needleless electrospinning technology: Accurately weigh 60 g of polyvinyl alcohol (PVA) powder, dissolve it in 540 ml of deionized water, and stir it with a magnetic stirrer at room temperature until the polyvinyl alcohol is completely dissolved to obtain a homogeneous and stable spinning solution with a mass fraction of 10%. Use a 2 mol / L HCl solution to adjust the pH to 1. Then add 1% SBQ by mass fraction and continue to stir at room temperature for 4 h, and then adjust it to neutral with a 2 mol / L NaOH solution. Use the above spinning solution for needleless electrospinning. Set the electrospinning process parameters as follows: the distance between the spinneret and the receiving plate is 25 cm, the reciprocating rate is 50 mm·s-1, the applied voltage is 55 kV, and receive it by hydroentangled viscose for 20 - 30 min to obtain a hydroentangled viscose / PVA-SBQ composite nanofiber membrane.

[0045] 2. Place the above composite nanofiber membrane in an ultraviolet curing machine for photocrosslinking: Cut the nanofiber membrane into squares with a size of 4×4 cm and place them in the ultraviolet curing machine. Set the process parameters of the ultraviolet curing machine as follows: the power is 2382 mW / cm 2 between, the energy is 12828 mj / cm every 3 seconds 2 , the temperature is 39 °C, the power is 300 W, and the time is 10 min. Crosslink each side for 300 s. The finally prepared polyvinyl alcohol-based separation membrane is named M4.

[0046] Filtration performance test

[0047] Take a titanium dioxide dispersion with a size of 10 - 25 nm as a reference object. Weigh 0.1 g of titanium dioxide particles into a volumetric flask, add 3% sodium dodecylbenzenesulfonate, make up the volume to 1 L, put in a rotor and stir on a magnetic stirrer for 24 h to obtain a homogeneous solution with a mass fraction of 1%. Then filter it using a dead-end filtration device. Use an ultraviolet spectrophotometer to measure the absorbance of the solution before and after filtration, and calculate the pure water flux of the composite fiber according to formula (1), and calculate the filtration effect of the composite fiber on the filtrate according to formula (2):

[0048]

[0049] In the formula:

[0050] P is the pure water permeation rate, with the unit of liters per square meter per hour [L / (m 2 ·h)];

[0051] V is the pure water permeation volume, with the unit of liters (L);

[0052] S is the effective filtration area of the membrane, with the unit of square meters (m 2 );

[0053] t is the time taken for the pure water with a permeation volume of V to pass through, with the unit of hours (h).

[0054]

[0055] In the formula:

[0056] Q is the filtration efficiency;

[0057] V 0 is the absorbance value at the maximum absorption wavelength of the reactant before filtration;

[0058] V 1 is the absorbance value at the maximum absorption wavelength of the reactant after filtration.

[0059] From Figure 2 it can be obtained that the fiber diameter is concentrated in the range of 200 - 350 nm. PVA itself dissolves in water and cannot be used for water treatment, so its fiber morphology after contacting water cannot be characterized. However, after grafting SBQ and photo-crosslinking, such as Figure 3 , it still maintains the fiber morphology when contacting water. This is because under ultraviolet light induction, PVA - SBQ undergoes a photodimerization reaction to form a macromolecular network structure. This network structure may limit the contact between the hydrophilic groups of PVA and water molecules, thereby improving the water resistance of the overall material. However, the fibers highly swell, the fiber diameter increases, and the diameter distribution range becomes wider. It makes the pore radius move within a smaller range to intercept particles smaller than the normal nanofiber membrane size. Its pore size distribution diagram is as shown in Figure 4 . In addition, the introduction of SBQ may affect the arrangement and crystallization behavior of PVA molecular chains. Since the hydrophilicity of PVA depends on the hydrogen bonds formed between the hydroxyl groups (-OH) on its molecular chains and water molecules, the presence of SBQ may interfere with the formation of these hydrogen bonds and reduce the hydrophilicity of the material to a certain extent. The introduction of SBQ and ultraviolet light induction improve the water resistance of the material to a certain extent, enabling PVA to be insoluble in water. As the crosslinking time increases, it can be preliminarily judged that crosslinking may be complete at 600 seconds of photo-crosslinking. From Figure 4 it can be obtained that the hydroentangled viscose plays a mechanical support role. The test results of the composite fibers in Examples 1 - 4 are as shown in Figure 1As shown. From the table, it can be seen that compared with Comparative Example 1, for M5 and M6, the introduction of SBQ and photo-crosslinking enable the membrane to be used in the field of water treatment. By comparing Example 1 and Example 2, it can be obtained that a relatively low content of SBQ can achieve a good crosslinking effect. By comparing Example 1 and Example 3, it can be obtained that in Example 1, due to the short photo-crosslinking time, its flux effect is poor, and the best crosslinking effect can be achieved after ten minutes of photo-crosslinking, obtaining a nanofiber membrane material with high flux and high rejection rate. By comparing Example 3 and Example 4, it can be obtained that the membrane thickness has a crucial impact on the flux. The membrane thickness is controlled by controlling the electrospinning time. Generally speaking, a thinner membrane has a higher porosity and better flux. From the results of the control group, it can be obtained that the hydroentangled viscose has no effect on the water flux and does not play a role in retaining titanium dioxide. Combining with the mechanical property diagram, it can be known that the hydroentangled viscose only plays a role in supporting and enhancing the mechanical properties.

[0060] The above shows and describes 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. What is described in the above embodiments and the specification is only 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 protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a polyvinyl alcohol-based separation membrane, characterized in that: The method comprises the following steps: Step 1: Weigh a certain mass of polyvinyl alcohol 1788 powder, add it into deionized water, and stir it with a magnetic stirrer at room temperature until the polyvinyl alcohol is completely dissolved to obtain a uniform and stable spinning solution with a mass fraction of 10%; Step 2: Add 2 mol / L hydrochloric acid to the prepared spinning solution and stir to make its pH = 1, then add a certain amount of SBQ powder and continue to stir in the dark for 2h to 6h to complete the grafting, and finally adjust its pH to neutral with 2 mol / L sodium hydroxide solution and keep it in the dark for later use; Step 3: The spinning solution prepared in the second step is used for needle-free electrospinning to obtain a spunlace viscose / PVA-SBQ nanofiber membrane; Step 4: Place the prepared nanofiber membrane in a UV curing machine for photo-crosslinking to prepare a polyvinyl alcohol-based separation membrane, wherein the photo-crosslinking time is between 30s-15min.

2. The method for preparing a polyvinyl alcohol-based separation membrane according to claim 1, characterized in that: The mass of SBQ added in the second step is between 0.5% and 1%.

3. The method for preparing a polyvinyl alcohol-based separation membrane according to claim 1, characterized in that: In the third step, the electrospinning process parameters were set as follows: receiving distance 25 cm, reciprocating speed 50 mm·s-1, temperature 18°C ​​to 20°C, humidity 20% to 30%; applied voltage 30 kV to 55 kV, and receiving by hydroentanglement viscose for 3 min to 30 min.

4. The method for preparing a polyvinyl alcohol-based separation membrane according to claim 1, characterized in that: In the fourth step, the cross-linking process parameters are set as follows: power 0-2382mW / cm 2 The energy is between 0-12828mj / cm 2 Every 3 seconds, the temperature is 39℃ to 55℃, the power is above 300W, and the cross-linking is 30s-15min.

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