High-precision large-flux enhanced polyvinyl chloride hollow fiber membrane as well as preparation method and application thereof

Abstract

The invention discloses a high-precision large-flux enhanced polyvinyl chloride hollow fiber membrane as well as a preparation method and application thereof. The preparation method comprises the following steps: preparing a hollow fiber braided tube from a polymer fiber material by adopting a two-dimensional or three-dimensional braiding technology; the preparation method comprises the following steps: mixing polyvinyl chloride resin, a solvent, a pore-foaming agent and an additive in proportion, stirring at 60-80 DEG C for 4-6 hours to form a homogeneous solution so as to obtain a membrane casting solution, and carrying out vacuum defoaming for 2-4 hours for later use; the outer surface of a hollow fiber braided tube is coated with the membrane casting solution through an annular spinning nozzle, the membrane casting solution partially permeates into gaps of the hollow fiber braided tube, the hollow fiber braided tube passes through the air gaps of 10-30 cm, then the hollow fiber braided tube is immersed in a coagulating bath at the temperature of 20-60 DEG C for phase separation forming, and then a primary enhanced polyvinyl chloride hollow fiber membrane is prepared through hot bath curing at the temperature of 50-70 DEG C; and putting the primary enhanced polyethylene hollow fiber membrane into an extracting agent, and keeping for 12-48 hours to obtain the high-precision large-flux enhanced polyvinyl chloride hollow fiber membrane.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of polymer membrane separation materials. More particularly, it relates to a high-precision large-flux enhanced polyvinyl chloride hollow fiber membrane and a preparation method and application thereof. BACKGROUND

[0002] In the continuous development process of water treatment technology, membrane separation technology has become one of the core technologies in the field of drinking water purification and industrial wastewater treatment due to its high efficiency, energy saving and environmental protection. As a polymer material with huge output, low raw material cost and simple spinning process, polyvinyl chloride (PVC) has great application potential in the preparation of water treatment hollow fiber membranes. Its abundant raw material sources and mature processing technology make it an ideal choice to replace high-priced membrane materials and reduce water treatment costs.

[0003] However, there are many problems to be solved in the practical application of traditional polyvinyl chloride hollow fiber membranes. On the one hand, the pore uniformity of conventional polyvinyl chloride membranes prepared by conventional methods is poor, which limits its interception precision and makes it difficult to effectively remove viruses, colloidal particles and small molecule organic pollutants in water, thus failing to meet the increasingly stringent water quality standards. On the other hand, polyvinyl chloride itself has poor hydrophilicity, which results in low water flux of the membrane, seriously affecting the processing efficiency of the membrane and restricting its popularization and application in large-scale water treatment projects. In addition, the mechanical properties of traditional polyvinyl chloride membranes are insufficient, and under long-term high-pressure operation environment, deformation, damage and other problems easily occur, which greatly shortens the service life of the membrane and increases the operation and maintenance cost.

[0004] To improve the performance of polyvinyl chloride hollow fiber membranes, existing technologies often use methods such as adding inorganic particles and polymer blending for modification (CN115945076A, CN115970519A). However, these methods have defects such as unstable modification effect, easy clogging of membrane pores, and difficulty in achieving synergistic improvement of multiple properties. Some studies attempt to introduce reinforcing materials to improve the mechanical properties of the membrane, such as using non-polyvinyl chloride material braided tubes or fibers for reinforcement (CN110038453B), but due to the poor interfacial compatibility between the reinforcing material and the polyvinyl chloride matrix, the reinforcing material and the membrane matrix easily separate during use. Not only can't effectively enhance the performance of the membrane, but also has a negative impact on the separation performance of the membrane, resulting in a decrease in interception precision and a loss of flux.

[0005] In recent years, although the industry continues to explore the optimization scheme of polyvinyl chloride membrane, but has not been able to find a kind of both can significantly improve the separation precision and flux of membrane, but also can effectively enhance the mechanical properties and operation stability of the ideal technical path of membrane. Therefore, the development of a kind of can overcome the inherent defects of traditional polyvinyl chloride membrane, through the innovative structure design and process optimization, realize the high precision, large flux and high stability of new type polyvinyl chloride hollow fiber membrane, has important practical significance for promoting the development of water treatment technology, reduce the cost of water treatment. SUMMARY

[0006] Based on the above defects, the first purpose of the present application is to provide a preparation method of high precision and large flux enhanced polyvinyl chloride hollow fiber membrane. The present application adopts the structure of homogeneous reinforced hollow fiber braided tube to prepare high precision and large flux enhanced polyvinyl chloride hollow fiber membrane, and through the structure design and process control of homogeneous reinforced interface combined transition layer, effectively solves the problems of low separation precision and poor mechanical properties of traditional polyvinyl chloride membrane, and provides more efficient and more economical technical solution for water treatment field.

[0007] The second purpose of the present application is to provide a preparation method of the enhanced polyvinyl chloride hollow fiber membrane as described above.

[0008] The third purpose of the present application is to provide an application of the enhanced polyvinyl chloride hollow fiber membrane in preparing membrane separation products.

[0009] In order to achieve the above first purpose, the technical scheme adopted by the present application is as follows:

[0010] The present application discloses a preparation method of large flux enhanced polyvinyl chloride hollow fiber membrane, comprising the following steps:

[0011] The polymer fiber material is prepared into a hollow fiber braided tube by two-dimensional or three-dimensional braiding technology;

[0012] The polyvinyl chloride resin, solvent, pore former and additive are mixed in proportion, stirred at 60-80 DEG C for 4-6h to form a homogeneous solution, and the casting solution is obtained, and vacuum degassing for 2-4h is used for standby;

[0013] The casting solution is coated onto the outer surface of the hollow fiber braided tube by using a ring spinneret, so that the casting solution partially penetrates into the hollow fiber braided tube gap, and after passing through an air gap of 10-30cm (i.e. the air bath length is 10-30cm), it is immersed into a coagulation bath at 20-60 DEG C to separate and form, and then solidified in a hot water bath at 50-70 DEG C to prepare a nascent enhanced polyvinyl chloride hollow fiber membrane;

[0014] The nascent enhanced polyvinyl chloride hollow fiber membrane is placed in an extraction agent for 24-48h to obtain a high precision and large flux enhanced polyvinyl chloride hollow fiber membrane.

[0015] wherein the porogen is selected from one or more of polyethylene glycol, polyvinyl pyrrolidone, polyacrylamide;

[0016] the additive is selected from one or more of sodium chloride, magnesium chloride, calcium carbonate, calcium chloride.

[0017] Further, the casting solution comprises 20-40 wt% of polyvinyl chloride resin, 20-80 wt% of solvent, 5-15 wt% of porogen and 1-5 wt% of additive, by mass fraction.

[0018] Further, the mass ratio of the porogen and the additive is 6-8:4-5.

[0019] Further, the porogen is selected from polyethylene glycol or polyvinyl pyrrolidone, and the additive is selected from a mixed additive of sodium chloride and calcium chloride, and the mass ratio of the porogen and the additive is 6:4.

[0020] Further, the porogen is selected from polyethylene glycol, and the additive is selected from sodium chloride or calcium chloride, and the mass ratio of the porogen and the additive is 2:1.

[0021] Further, the porogen is selected from polyacrylamide, and the additive is selected from sodium chloride or calcium chloride, and the mass ratio of the porogen and the additive is 8:5.

[0022] Further, the air gap is 14-25 cm, preferably 20-25 cm.

[0023] Further, the polymeric fiber material should be selected from a polymeric fiber material that is compatible with polyvinyl chloride, and is selected from polyvinyl chloride fiber, polyacrylonitrile fiber, polyvinyl alcohol fiber, acetate fiber or a mixed fiber thereof.

[0024] Further, the solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, cyclohexanone, tetrahydrofuran; preferably, the solvent is selected from a mixed solvent of N,N-dimethylformamide and N,N-dimethylacetamide, and the mass ratio is 2:1.

[0025] Further, the coagulation bath is selected from one or more of deionized water, ethanol, N,N-dimethylformamide, N,N-dimethylacetamide, and preferably, the coagulation bath is selected from a mixed solution of deionized water and N,N-dimethylformamide, and the mass ratio is 7:3.

[0026] Further, the extractant is selected from one or more of deionized water, ethanol, toluene, acetone, butanol, and preferably, the extractant is ethanol.

[0027] Further, a pretreatment operation is further included before the coating of the casting solution, and the following exemplary operation is provided to remove stains on the surface of the hollow fiber braided tube, and the specific steps are as follows: the hollow fiber braided tube is cleaned by ultrasonic cleaning in a 5wt% NaOH solution for 10-30min, and then the cleaned hollow fiber braided tube is placed in a 50-80℃ air drying oven for drying for 15-30min for standby.

[0028] To achieve the above-mentioned second object, the application adopts the following technical solutions:

[0029] The application discloses a high-precision large-flux enhanced polyvinyl chloride hollow fiber membrane, which is prepared by the preparation method.

[0030] Further, the thickness of the polyvinyl chloride separation membrane layer is 30-200μm, the outer diameter of the hollow fiber braided tube is 1.0-2.0mm, and the thickness of the interfacial bonding transition layer is 10-50nm.

[0031] The average pore size of the enhanced polyvinyl chloride hollow fiber membrane is 30-150nm, and the pore size in the whole area has little difference (within <±6nm), the contact angle is 40-75°, and the interfacial bonding strength is 4-8Mpa.

[0032] The pure water flux of the enhanced polyvinyl chloride hollow fiber membrane is ≥1200L·m -2 ·h -1 bar, the porosity is ≥55%, the bovine serum protein rejection rate is >99.9%, and the methylene blue dye rejection rate is >99%.

[0033] To achieve the above-mentioned third object, the application adopts the following technical solutions:

[0034] The application discloses an application of the enhanced polyvinyl chloride hollow fiber membrane in the preparation of a membrane separation product.

[0035] The application has the following beneficial effects:

[0036] 1、The application creatively adopts the homogeneous enhancement composite principle, uniformly coats the film-forming polymer on the outer surface of the hollow fiber braided tube, enhances the bonding force between the separation layer and the support layer through the good compatibility of the two, improves the stability of the service of the separation membrane material, and prolongs the service life.

[0037] 2, The preparation method of the application has the characteristics of high separation precision, large pure water flux, stable mechanical property, and the reinforced polyvinyl chloride hollow fiber membrane is easy to clean and can be reused. Through testing, the pure water flux of the reinforced polyvinyl chloride hollow fiber membrane is ≥1200L·m -2 ·h -1 bar, porosity ≥55%, bovine serum protein rejection rate >99.9%, methylene blue dye rejection rate >99%.

[0038] 3, The raw materials used in the preparation method of the application are cheap and easy to obtain, and have been completely localized. It is a simple preparation process and membrane preparation method, which is conducive to large-scale industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The cross-sectional electron micrograph of the reinforced polyvinyl chloride hollow fiber membrane prepared in Example 1 of the application.

[0040] Figure 2 The cross-sectional electron micrograph of the reinforced polyvinyl chloride hollow fiber membrane prepared in Example 2 of the application. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical scheme and advantages of the embodiments of the application clearer, the technical scheme of the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the application.

[0042] Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in this paper can be purchased or prepared by existing methods.

[0043] Example 1

[0044] This example provides a preparation method of high-precision large-flux reinforced polyvinyl chloride hollow fiber membrane, the steps are as follows:

[0045] S1, select polyvinyl chloride fiber with good compatibility with polyvinyl chloride and polyacrylonitrile fiber, and prepare a mixed fiber hollow fiber braided tube with an outer diameter of 1.8mm by using two-dimensional braiding technology, and pretreat it. The mixed fiber hollow fiber braided tube is cleaned with a 5wt% NaOH solution for 15min, and then the cleaned mixed fiber hollow fiber braided tube is placed in a 60℃ air drying oven for 10min to remove surface stains and dry.

[0046] S2, mixing polyvinyl chloride, N,N-dimethylformamide and N,N-dimethylacetamide mixed solvent, polyethylene glycol and mixed additives of sodium chloride and calcium chloride, wherein polyvinyl chloride accounts for 26wt%, N,N-dimethylformamide and N,N-dimethylacetamide mixed solvent accounts for 64wt%, the mass ratio of N,N-dimethylformamide and N,N-dimethylacetamide is 2:1, polyethylene glycol accounts for 6wt%, and the mixed additive of sodium chloride and calcium chloride accounts for 4wt%, the mass ratio of sodium chloride and calcium chloride is 3:1, stirring at 70℃ for 4h to form a homogeneous solution, obtaining a casting solution, vacuum degassing for 4h for standby.

[0047] S3, after pressurizing the reaction kettle, the casting solution obtained in step S2 is coated onto the outer surface of the hollow fiber braid tube treated in S1 through an annular spinneret, so that the casting solution partially penetrates into the interstices of the hollow fiber braid tube, after passing through an air gap of 14cm, it is immersed in a water bath at 30℃, and then separated and formed, and then solidified in a hot water bath at 50℃ to prepare a nascent reinforced polyvinyl chloride hollow fiber membrane.

[0048] S4, the nascent reinforced polyvinyl chloride hollow fiber membrane is placed in ethanol for 24h to obtain a high-precision large-flux reinforced polyvinyl chloride hollow fiber membrane. The reinforced polyvinyl chloride hollow fiber membrane comprises a polyvinyl chloride separation membrane layer with uniform pore size on the outer side, a hollow fiber braid tube for reinforcement on the inner side, and an interfacial bonding transition layer between the polyvinyl chloride separation membrane layer and the hollow fiber braid tube.

[0049] The cross-sectional morphology of the prepared high-precision large-flux reinforced polyvinyl chloride hollow fiber membrane is scanned by electron microscopy, and the results are as shown in Figure 1 The thickness of the polyvinyl chloride separation membrane layer is 180μm, the thickness of the interfacial bonding transition layer is 25nm, the pure water flux of the controllable pore size large-flux reinforced polyvinyl chloride hollow fiber membrane is 1350L·m -2 ·h -1 bar, the porosity is 60%, the interfacial bonding strength is 5.5Mpa, the average pore size is 65±3nm, the contact angle is 70°, the bovine serum albumin rejection rate is 99.9%, and the methylene blue dye rejection rate is 99.3%.

[0050] Comparative Example 1

[0051] A single polyacrylonitrile fiber braid tube (not mixed with polyvinyl chloride fibers) is used, and the other steps are the same as in Example 1. The results show that the thickness of the interfacial bonding transition layer is only 5nm, and the interfacial bonding strength is 3.2MPa, which is significantly lower than that of Example 1, indicating that mixed fibers can enhance the interfacial bonding performance, and other data are not much different from those of Example 1.

[0052] Example 2

[0053] The example provides a preparation method of high-precision large-flux enhanced polyvinyl chloride hollow fiber membrane, and the steps are as follows:

[0054] S1, select polyacrylonitrile fiber with good compatibility with polyvinyl chloride, prepare polyacrylonitrile fiber hollow fiber braided tube with an outer diameter of 1.8 mm by adopting two-dimensional braiding technology, and pretreat it. The hollow fiber braided tube is cleaned by ultrasonic cleaning in a 5wt% NaOH solution for 12 min, and then the cleaned hollow fiber braided tube is placed in a 60℃ air drying oven for drying for 15 min to remove surface stains and dry.

[0055] S2, mix polyvinyl chloride, N,N-dimethylformamide and N,N-dimethylacetamide mixed solvent, polyethylene glycol and sodium chloride, wherein polyvinyl chloride accounts for 22wt%, N,N-dimethylformamide and N,N-dimethylacetamide mixed solvent accounts for 66wt%, the mass ratio of N,N-dimethylformamide and N,N-dimethylacetamide is 2:1, polyethylene glycol accounts for 8wt%, and sodium chloride accounts for 4wt%, form a homogeneous solution by stirring at 65℃ for 4h to obtain a casting solution, and vacuum degassing for 3h for standby.

[0056] S3, after pressurizing the reaction kettle, the casting solution obtained in step S2 is coated onto the outer surface of the hollow fiber braided tube treated in S1 through an annular spinneret, so that the casting solution partially penetrates into the gap of the hollow fiber braided tube. After passing through a 16cm air gap, it is immersed in a 40℃ water bath, separated and formed, and then solidified in a 60℃ hot water bath to prepare a nascent enhanced polyvinyl chloride hollow fiber membrane.

[0057] S4, the nascent enhanced polyvinyl chloride hollow fiber membrane is placed in ethanol for 24h to obtain a high-precision large-flux enhanced polyvinyl chloride hollow fiber membrane. The enhanced polyvinyl chloride hollow fiber membrane comprises a polyvinyl chloride separation membrane layer with uniform pore size on the outside, a hollow fiber braided tube for reinforcement on the inside, and an interfacial bonding transition layer between the polyvinyl chloride separation membrane layer and the hollow fiber braided tube.

[0058] The cross-sectional morphology of the prepared high-precision large-flux enhanced polyvinyl chloride hollow fiber membrane is scanned by electron microscope, and the results are as follows Figure 2 . The thickness of the polyvinyl chloride separation membrane layer is 150μm, the thickness of the interfacial bonding transition layer is 20nm, the pure water flux of the controllable pore size large-flux enhanced polyvinyl chloride hollow fiber membrane is 1680L·m -2 ·h -1 bar, the porosity is 63%, the interfacial bonding strength is 5.2Mpa, the average pore size is 60±2nm, the contact angle is 68°; the bovine serum albumin rejection rate is 99.9%; the methylene blue dye rejection rate is 99.5%.

[0059] Comparative example 2

[0060] The air gap is shortened to 10 cm, and other steps are the same as in Example 2. The results show that the pure water flux is 865 L·m-2·h-1·bar-1, the interfacial bonding strength is 3.8 MPa, and the methylene blue rejection rate is 97.8%, all of which are lower than those of Example 2, indicating that the air gap of 16 cm can improve the comprehensive performance, and other data are not much different from those of Example 2. -2 ·h - 1 The air gap is shortened to 10 cm, and other steps are the same as in Example 2. The results show that the pure water flux is 865 L·m-2·h-1·bar-1, the interfacial bonding strength is 3.8 MPa, and the methylene blue rejection rate is 97.8%, all of which are lower than those of Example 2, indicating that the air gap of 16 cm can improve the comprehensive performance, and other data are not much different from those of Example 2.

[0061] Example 3

[0062] The present example provides a preparation method of a high-precision large-flux reinforced polyvinyl chloride hollow fiber membrane, and the steps are as follows:

[0063] S1, select polyvinyl chloride fibers with good compatibility with polyvinyl chloride, and prepare polyvinyl chloride hollow fiber braided tubes with an outer diameter of 1.5 mm using two-dimensional braiding technology, and pretreat the polyvinyl chloride hollow fiber braided tubes. The polyvinyl chloride hollow fiber braided tubes are cleaned with an ultrasonic cleaner with a 5wt% NaOH solution for 20 minutes. Then, the cleaned polyvinyl chloride hollow fiber braided tubes are placed in a 60℃ air drying oven for 20 minutes to remove surface stains and dry.

[0064] S2, mix polyvinyl chloride, N,N-dimethylacetamide, polyvinylpyrrolidone, and a mixed additive of sodium chloride and calcium chloride, wherein polyvinyl chloride accounts for 30wt%, N,N-dimethylacetamide accounts for 60wt%, polyvinylpyrrolidone accounts for 6wt%, and the mixed additive of sodium chloride and calcium chloride accounts for 4wt%, and the mass ratio of sodium chloride to calcium chloride is 3:1. Stir at 70℃ for 4h to form a homogeneous solution to obtain a casting solution, and vacuum degassing for 3h for standby.

[0065] S3, after pressurizing the reaction kettle, the casting solution obtained in step S2 is coated onto the outer surface of the hollow fiber braided tube treated in step S1 through an annular spinneret, so that the casting solution partially penetrates into the gap of the hollow fiber braided tube. After passing through an air gap of 20 cm, immerse in a 20℃ coagulation bath for phase separation and molding, and then solidify in a 50℃ hot water bath to prepare a nascent reinforced polyvinyl chloride hollow fiber membrane.

[0066] S4, place the nascent reinforced polyvinyl chloride hollow fiber membrane in a butanol extractant and keep it for 24h to obtain a high-precision large-flux reinforced polyvinyl chloride hollow fiber membrane. The reinforced polyvinyl chloride hollow fiber membrane comprises a polyvinyl chloride separation membrane layer with uniform pore size on the outer side, a hollow fiber braided tube for reinforcement on the inner side, and an interfacial bonding transition layer between the polyvinyl chloride separation membrane layer and the hollow fiber braided tube.

[0067] The thickness of the polyvinyl chloride separation membrane layer is 120 μm, the thickness of the interface bonding transition layer is 30 nm, the pure water flux of the controllable aperture large flux enhanced polyvinyl chloride hollow fiber membrane is 1870 L·m -2 ·h -1 bar, the porosity is 65%, the interface bonding strength is 7.5 MPa, the average pore size is 55±2 nm, the contact angle is 65°, the bovine serum albumin rejection rate is 99.9%, and the methylene blue dye rejection rate is 99.6%.

[0068] Comparative Example 3

[0069] The additive is only anhydrous sodium chloride, and the other steps are the same as in Example 3. The pure water flux thereof is 1520 L·m -2 ·h -1 bar, the interface bonding strength is 6.7 MPa, which verifies that the composite additive in Example 3 has the effect of enhancing the membrane performance, and the other data are not much different from those in Example 3.

[0070] Example 4

[0071] The example provides a preparation method of a high-precision large-flux enhanced polyvinyl chloride hollow fiber membrane, and the steps are as follows:

[0072] S1, select polyvinyl alcohol fibers with good compatibility with polyvinyl chloride, prepare a polyvinyl alcohol hollow fiber braided tube with an outer diameter of 1.5 mm by using two-dimensional braiding technology, and pretreat the polyvinyl alcohol hollow fiber braided tube. The hollow fiber braided tube is cleaned with an ultrasonic cleaner with a 5wt% NaOH solution for 18 minutes. Then, the cleaned hollow fiber braided tube is placed in a 60°C air drying oven for 20 minutes to remove surface stains and dry.

[0073] S2, mix polyvinyl chloride, N,N-dimethylformamide, polyacrylamide and calcium carbonate, wherein polyvinyl chloride accounts for 32wt%, N,N-dimethylformamide accounts for 55wt%, polyacrylamide accounts for 8wt%, and calcium carbonate accounts for 5wt%, stir at 80°C for 4h to form a homogeneous solution, obtain a casting solution, and vacuum degassing for 3h for standby.

[0074] S3, after pressurizing the reaction kettle, the casting solution obtained in step S2 is coated onto the outer surface of the hollow fiber braided tube treated in step S1 through an annular spinneret, so that the casting solution partially penetrates into the gap of the hollow fiber braided tube. After passing through a 25cm air gap, immerse in a 40°C water bath, separate and form, and then prepare a nascent enhanced polyvinyl chloride hollow fiber membrane by solidifying in a 60°C hot water bath.

[0075] S4, the nascent reinforced polyvinyl chloride hollow fiber membrane is put into an acetone extractant for 24 hours to obtain a high-precision large-flux reinforced polyvinyl chloride hollow fiber membrane. The reinforced polyvinyl chloride hollow fiber membrane comprises a polyvinyl chloride separation membrane layer with uniform pore size on the outer side, a hollow fiber braided tube for reinforcement on the inner side, and an interfacial bonding transition layer between the polyvinyl chloride separation membrane layer and the hollow fiber braided tube.

[0076] The thickness of the polyvinyl chloride separation membrane layer is 90 μm, the thickness of the interfacial bonding transition layer is 37 nm, and the pure water flux of the controllable-pore-size large-flux reinforced polyvinyl chloride hollow fiber membrane is 2120 L·m -2 ·h -1 bar, the porosity is 68%, the interfacial bonding strength is 7 MPa, the average pore size is 50±3 nm, the contact angle is 60°, the bovine serum albumin rejection rate is 99.9%, and the methylene blue dye rejection rate is 99.8%.

[0077] Comparative Example 4

[0078] In Comparative Example 4, the additive calcium carbonate is replaced by sodium chloride, the air gap is reduced to 8 cm, and the other steps are the same as in Example 4. The pure water flux is 1780 L·m -2 ·h -1 bar, the contact angle is 75°, the methylene blue rejection is 99.0%, and the advantages of the calcium carbonate additive and the 25 cm air gap in Example 4 in improving the flux and hydrophilicity are highlighted, and the other data are not much different from those in Example 4.

[0079] Example 5

[0080] The present example provides a method for preparing a high-precision large-flux reinforced polyvinyl chloride hollow fiber membrane, comprising the following steps:

[0081] S1, polyvinyl chloride fibers and polyvinyl alcohol fibers with good compatibility with polyvinyl chloride are selected, a two-dimensional braiding technique is used to prepare a mixed fiber hollow fiber braided tube with an outer diameter of 1.2 mm, and the mixed fiber hollow fiber braided tube is pretreated. The mixed fiber hollow fiber braided tube is washed with a 5 wt% NaOH solution for 15 minutes under ultrasonic waves, and then the cleaned mixed fiber hollow fiber braided tube is dried in a 60°C air-drying oven for 20 minutes to remove surface stains and dry the mixed fiber hollow fiber braided tube.

[0082] S2, mixing polyvinyl chloride, N, N-dimethylformamide and N, N-dimethylacetamide mixed solvent, polyethylene glycol and calcium carbonate, wherein the polyvinyl chloride accounts for 21wt%, the N, N-dimethylformamide and N, N-dimethylacetamide mixed solvent accounts for 67wt%, the mass ratio of N, N-dimethylformamide and N, N-dimethylacetamide is 2:1, the polyethylene glycol accounts for 8wt%, and the calcium carbonate accounts for 4wt%, stirring at 80℃ for 4h to form a homogeneous solution to obtain a casting solution, and vacuum degassing for 3h for standby.

[0083] S3, after pressurizing the reaction kettle, the casting solution obtained in step S2 is coated onto the outer surface of the hollow fiber braided tube treated in S1 through an annular spinneret, so that the casting solution partially penetrates into the interstices of the hollow fiber braided tube, after passing through an air gap of 20cm, it is immersed in a water bath at 50℃, phase separation molding, and then solidification in a hot water bath at 70℃ to prepare a nascent reinforced polyvinyl chloride hollow fiber membrane.

[0084] S4, the nascent reinforced polyvinyl chloride hollow fiber membrane is placed in an ethanol extractant for 30h to obtain a high-precision large-flux reinforced polyvinyl chloride hollow fiber membrane. The reinforced polyvinyl chloride hollow fiber membrane comprises a polyvinyl chloride separation membrane layer with uniform pore size on the outside, a hollow fiber braided tube for reinforcement on the inside, and an interfacial bonding transition layer between the polyvinyl chloride separation membrane layer and the hollow fiber braided tube.

[0085] The thickness of the polyvinyl chloride separation membrane layer is 60μm, the thickness of the interfacial bonding transition layer is 28nm, the pure water flux of the controllable pore size large-flux reinforced polyvinyl chloride hollow fiber membrane is 2630L·m -2 ·h -1 bar, porosity 70%, interfacial bonding strength 7.2MPa, average pore size 55±4nm, contact angle 49°; bovine serum albumin rejection rate 99.9%; methylene blue dye rejection rate 99.2%.

[0086] Comparative Example 5

[0087] The extraction time is shortened to 20h, and the other steps are the same as in Example 5. Its pure water flux is 2100L·m -2 ·h -1 bar, porosity 62%, interfacial bonding strength 5.8MPa, which shows the key role of the extraction time of 30h in Example 5 in the permeation performance and structural stability of the reinforced membrane, and the other data are not much different from those in Example 5.

[0088] Obviously, the above embodiments of the present application are merely exemplary and are not intended to limit the embodiments of the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art, and it is impossible to enumerate all the embodiments here. Any obvious changes or variations derived from the technical solutions of the present application are still within the protection scope of the present application.

Claims

1. A method for preparing a high-precision large-flux enhanced polyvinyl chloride hollow fiber membrane, characterized in that, The method comprises the following steps: Preparation of hollow fiber braided tube by using two-dimensional or three-dimensional braiding technology; Mixing polyvinyl chloride resin, solvent, pore-forming agent and additive in proportion, stirring at 60-80℃ for 4-6h to form a homogeneous solution, obtaining casting solution, vacuum degassing for 2-4h for standby; Coating the casting solution to the outer surface of the hollow fiber braided tube by using annular spinneret, allowing the casting solution to partially penetrate into the hollow fiber braided tube gap, after passing through 10-30cm air gap, immersing into 20-60℃ coagulation bath for phase separation forming, then curing in 50-70℃ hot water bath to prepare nascent reinforced polyvinyl chloride hollow fiber membrane; Placing the nascent reinforced polyvinyl chloride hollow fiber membrane into the extraction agent, keeping for 24-48h to obtain high-precision large-flux reinforced polyvinyl chloride hollow fiber membrane; The pore-forming agent is selected from one or more of polyethylene glycol, polyvinylpyrrolidone and polyacrylamide; The additive is selected from one or more of sodium chloride, magnesium chloride, calcium carbonate and calcium chloride.

2. The production method according to claim 1, characterized by, The casting solution comprises 20-40wt% polyvinyl chloride resin, 20-80wt% solvent, 5-15wt% pore-forming agent and 1-5wt% additive.

3. The production method according to claim 2, characterized by, The mass ratio of the pore-forming agent to the additive is 6-8:4-5; Preferably, the pore-forming agent is selected from polyethylene glycol or polyvinylpyrrolidone, the additive is selected from mixed additive of sodium chloride and calcium chloride, and the mass ratio of the pore-forming agent to the additive is 6:4; Preferably, the pore-forming agent is selected from polyethylene glycol, the additive is selected from sodium chloride or calcium chloride, and the mass ratio of the pore-forming agent to the additive is 2:1; Preferably, the pore-forming agent is selected from polyacrylamide, the additive is selected from sodium chloride or calcium chloride, and the mass ratio of the pore-forming agent to the additive is 8:

5.

4. The method of claim 1, wherein, The polymer fiber material is selected from polyvinyl chloride fiber, polyacrylonitrile fiber, polyvinyl alcohol fiber, acetate fiber or mixed fiber thereof.

5. The preparation method according to claim 1, characterized in that, The solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, cyclohexanone and tetrahydrofuran.

6. The method of claim 1, wherein, The coagulation bath is selected from one or more of deionized water, ethanol, N,N-dimethylformamide and N,N-dimethylacetamide.

7. The preparation method according to claim 1, characterized in that, The extraction agent is selected from one or more of deionized water, ethanol, toluene, acetone and butanol.

8. A high precision, high flux, enhanced polyvinylchloride hollow fiber membrane, characterized in that, The reinforced polyvinyl chloride hollow fiber membrane prepared by the preparation method of any one of claims 1-7 comprises a polyvinyl chloride separation membrane layer with uniform pore size on the outer side, a hollow fiber braided tube for reinforcement on the inner side and an interfacial bonding transition layer between the polyvinyl chloride separation membrane layer and the hollow fiber braided tube.

9. The reinforced polyvinyl chloride hollow fiber membrane according to claim 8, characterized in that, The thickness of the polyvinyl chloride separation membrane layer is 30-200μm, the outer diameter of the hollow fiber braided tube is 1.0-2.0mm, and the thickness of the interfacial bonding transition layer is 10-50nm; The average pore size of the reinforced polyvinyl chloride hollow fiber membrane is 30-150nm, the contact angle is 40-75°, and the interfacial bonding strength is 4-8Mpa; The pure water flux of the enhanced polyvinyl chloride hollow fiber membrane is ≥1200 L·m -2 ·h -1 bar, porosity ≥ 55%, bovine serum protein rejection > 99.9%, methylene blue dye rejection > 99%.

10. Use of the reinforced polyvinyl chloride hollow fiber membrane of claim 8 or 9 in the preparation of membrane separation products.

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