Highly moisture permeable hollow fiber membrane and method for producing the same

Abstract

The application relates to the technical field of moisture-permeable membrane materials, and provides a high-moisture-permeable hollow fiber membrane, which comprises a main body, one side of the main body is an inner surface, the other side is an outer surface, the main body has a non-directional winding channel in the main body, the main body comprises a supporting layer and a condensing layer, one side of the supporting layer is the outer surface, one side of the condensing layer is the inner surface, and continuous fibers are transitionally connected between the other side of the supporting layer and the other side of the condensing layer; the supporting layer has an aggregation area for water vapor aggregation, the SEM average pore diameter of the aggregation area is greater than the SEM average pore diameter of the outer surface; the SEM average pore diameter of the outer surface is 0.3-2 mu m; and the SEM average pore diameter of the inner surface is 20-100 nm. The high-moisture-permeable hollow fiber membrane structure provided by the application shows super-high water conversion efficiency and water vapor permeation rate, and also has good tensile strength, so that the service life is long.

Description

Technical Field

[0001] This invention relates to the field of moisture-permeable membrane materials technology, and in particular to a highly moisture-permeable hollow fiber membrane and its preparation method. Background Technology

[0002] Moisture-permeable hollow fiber membranes are mainly used in humidifiers. They generally have good hydrophilicity and selective permeability, separating water vapor in the air from other gas components. Water vapor is transferred from the side with high humidity to the side with low humidity through the membrane.

[0003] Currently, there are many structural types of moisture-permeable hollow fiber membranes on the market. For example, patent CN102481524B, published by Toray Industries, Inc. of Japan on June 18, 2014, provides a water vapor permeable membrane, a hollow yarn membrane, and a hollow yarn membrane assembly. The membrane prepared by this method has adjacent dense layers and support layers. The support layer has finger-like void structures along the thickness direction, and the inner diameter of the finger-like voids in the thickness direction of the membrane is more than 30% of the membrane thickness. The presence of finger-like voids in this membrane allows for a large water vapor permeability, but it results in low tensile strength, thereby reducing the membrane's service life.

[0004] The patent JP2011067812A published by Toray Industries, Inc. of Japan on April 7, 2011, provides a water vapor permeable membrane, a hollow fiber membrane, and a humidifier. The membrane prepared by this patent has adjacent dense layers and support layers. According to the patent specification, the membrane has a large number of pores, and the length of the pores gradually increases from one surface of the membrane to the other. Although such a membrane structure gives it good compressive strength, the water vapor permeability coefficient of the membrane is small, which increases the transit time of water vapor in the membrane and thus reduces the water conversion efficiency of the membrane.

[0005] Therefore, preparing a moisture-permeable hollow fiber membrane with high water conversion efficiency and strong mechanical properties is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] To address the aforementioned problems, this invention aims to provide a highly moisture-permeable hollow fiber membrane and its preparation method. This hollow fiber membrane exhibits high water conversion efficiency and mechanical strength, extending its service life.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A highly permeable hollow fiber membrane includes a main body with an inner surface on one side and an outer surface on the other. The main body has non-directional tortuous pathways. The main body includes a support layer and a condensation layer. One side of the support layer is the outer surface, and one side of the condensation layer is the inner surface. The other side of the support layer and the other side of the condensation layer are connected by continuous fibers. The support layer has a collection region for water vapor accumulation, and the SEM average pore size of the collection region is larger than the SEM average pore size of the outer surface. The SEM average pore size of the outer surface is 0.3-2 μm, and the SEM average pore size of the inner surface is 15-100 nm. Preferably, the SEM average pore size of the outer surface is 0.5-1.5 μm, and the SEM average pore size of the inner surface is 30-70 nm.

[0009] It should be noted that the support layer is the region where water vapor permeates into the hollow fiber membrane and diffuses as gas. The condensation layer is the region where water vapor transforms from gas to liquid. Within the support layer, it extends outwards from the point of maximum SEM average pore size to a point where the SEM average pore size is 0.5 times the maximum SEM average pore size. Figure 5 Marked as A), extending into the condensation layer to a point where the SEM average pore size is 0.5 times the maximum SEM average pore size. Figure 5 Marked as B), the area between A and B is the aggregation zone. "Continuous fiber transition" can be understood as the fibers between the condensation layer and the support layer being "integrated," existing as a continuous whole without additional adhesive bonding. Unless torn by external force, the continuous fibers cannot be separated from each other. Non-directional tortuous pathways refer to irregularly oriented groove structures and / or discretely distributed pore structures, with each non-directional tortuous pathway interconnected. The various surface morphology parameters of the membrane in this application (such as average pore size, average fiber diameter, pore area ratio, and thickness) can be measured by characterizing the membrane structure using a scanning electron microscope (SEM), followed by measurement using computer software (such as Matlab, NIS-Elements, etc.) or manual measurement, and then performing corresponding calculations. During the membrane fabrication process, in the direction perpendicular to the membrane thickness (if the membrane is a flat sheet, this direction is planar; if the membrane is a hollow fiber membrane, this direction is perpendicular to the radius), its various characteristics, such as pore size distribution, are roughly uniform and basically consistent. Therefore, the average pore size of a certain area on the corresponding plane can reflect the overall average pore size of that plane. In actual measurement, the membrane surface can be characterized first using an electron microscope to obtain the corresponding SEM image, and a certain area, such as 1 μm, can be selected. 2 (1μm x 1μm) or 25μm 2(5μm by 5μm), the specific area size depends on the actual situation. Then, use appropriate computer software or manual measurement to determine the diameter of all holes on this area, and then calculate to obtain the average pore diameter of the surface. Of course, those skilled in the art can also obtain the above parameters through other measurement methods. The above measurement methods are for reference only.

[0010] This application features a relatively large SEM average pore size on its outer surface, increasing the amount of water vapor entering the membrane. A large amount of water vapor enters the support layer from the outer surface, initially flowing in a laminar manner within the support layer, resulting in lower flow resistance and increased throughput. The pore size of the support layer initially increases and then decreases. Due to the large SEM average pore size in the aggregation zone, water vapor accumulates there. Simultaneously, during application, the outer surface temperature of the humidifying membrane is relatively high, typically above 90°C. Under this high temperature, the water vapor's movement speed increases. Furthermore, the relatively large SEM average pore size on the outer surface further increases the amount of water vapor entering the membrane. Meanwhile, the inner surface temperature is lower, typically 20-30°C. As the water vapor flows, its temperature gradually decreases, and its flow speed gradually decreases, leading to further accumulation in the aggregation zone. Due to the concentration difference between the accumulation zone and the condensation layer, and the temperature difference between the outer and inner surfaces, water vapor moves towards the condensation layer at a suitable velocity, driven by these concentration and temperature differences. As the temperature decreases and capillary condensation occurs, the water vapor forms liquid water in the condensation layer, which then diffuses towards the inner surface under the influence of the concentration difference. The flow velocity of water vapor varies in each channel. Water vapor molecules in the accumulation zone collide with each other, increasing the flow resistance and reducing the flow velocity. This allows the water vapor to flow towards the condensation layer at a suitable velocity, preventing a large influx of water vapor into the condensation layer and clogging its channels. Clogging would cause a large accumulation of water vapor at the blockage point, resulting in concentration polarization and backflow of water vapor towards the outer surface, thus reducing water conversion efficiency.

[0011] After slowing down, the water vapor flows towards the condensation layer, where it liquefies into water through capillary condensation and diffuses to the inner surface. The inner surface has a suitable SEM average pore size to ensure that the water diffused to the vicinity of the inner surface is promptly carried away, thereby increasing the water conversion efficiency of the hollow fiber membrane. The support layer near the outer surface has a porous structure with a smaller SEM average pore size compared to the aggregated area, which increases the compressive strength of the outer surface, thereby increasing the mechanical strength of the support layer and ultimately the mechanical strength of the hollow fiber membrane.

[0012] In summary, the hollow fiber membrane prepared in this application has high water conversion efficiency, high mechanical strength, and extended service life.

[0013] Furthermore, the thickness of the aggregation region is 10-60 μm, and the thickness of the aggregation region accounts for 10%-50% of the thickness of the hollow fiber membrane.

[0014] In this application, the thickness of the aggregation zone is 10-60 μm, preferably 25-45 μm, ensuring the aggregation zone occupies a suitable proportion within the hollow fiber membrane. The thickness of the aggregation zone accounts for 10%-50% of the total thickness of the hollow fiber membrane, preferably 20%-35%. This ensures a suitable amount of water vapor accumulates in the aggregation zone, resulting in appropriate water conversion efficiency and mechanical strength for the hollow fiber membrane. If the aggregation zone is too thick, the mechanical strength of the hollow fiber membrane decreases. Furthermore, a higher concentration of water vapor in the aggregation zone can lead to swelling, causing the volume of the aggregation zone to expand and the hollow fiber membrane to deform, thus reducing its water conversion efficiency and mechanical strength. If the aggregation zone is too thin, the concentration difference between the aggregation zone and the inner surface area is smaller, reducing the driving force of water vapor and consequently decreasing the water conversion efficiency of the hollow fiber membrane.

[0015] The thickness of the aggregated zone accounts for 10%-50% of the thickness of the hollow fiber membrane, giving the hollow fiber membrane strong mechanical strength and allowing water vapor to flow at a suitable velocity. If the thickness of the aggregated zone accounts for a large proportion of the thickness of the hollow fiber membrane, the mechanical strength of the hollow fiber membrane will be reduced; if the thickness of the aggregated zone accounts for a small proportion of the thickness of the hollow fiber membrane, the water conversion efficiency of the hollow fiber membrane will be reduced.

[0016] Furthermore, the average SEM pore size of the aggregation region is 0.5-2.5 μm; the average SEM pore size of the aggregation region is 1.2-4.5 times the average SEM pore size of the outer surface.

[0017] In this application, the average SEM pore size of the aggregation region is 0.5-2.5 μm, preferably 0.8-1.7 μm. If the average SEM pore size of the aggregation region is too large, the tensile strength of the aggregation region is reduced, thereby reducing the tensile strength of the hollow fiber membrane. Simultaneously, the amount of water vapor collected in each pore increases, easily leading to excessive water vapor content within the aggregation region. This results in excessively high local water vapor content in the hollow fiber membrane, making it prone to deformation and thus reducing its mechanical strength and water conversion efficiency. If the average SEM pore size of the aggregation region is small, the amount of water vapor collected decreases. The water vapor still flows towards the condensation layer at a higher velocity, easily clogging the condensation layer with smaller pores, leading to concentration polarization and causing water vapor backflow, thus reducing water conversion efficiency.

[0018] The average SEM pore size of the aggregation zone is 1.2-4.5 times that of the average SEM pore size of the outer surface. Preferably, the average SEM pore size of the aggregation zone is 1.5-3 times that of the outer surface. If the average SEM pore size of the aggregation zone is a small multiple of the average SEM pore size of the outer surface, the amount of water vapor accumulating in the aggregation zone is small, and the flow velocity of water vapor in the aggregation zone is low. This reduces the driving force of water vapor, preventing it from flowing out towards the inner surface in time. Concentration polarization easily occurs in the aggregation zone, causing water vapor to flow back towards the outer surface, greatly reducing the water conversion efficiency of the hollow fiber membrane. If the average SEM pore size of the aggregation zone is a large multiple of the average SEM pore size of the outer surface, the amount of water vapor accumulating in the aggregation zone is extremely large, and the driving force of water vapor flowing towards the inner surface is large. A large amount of water vapor flows towards the condensation layer. The condensation layer has a small pore size and cannot transport water vapor to the inner surface in time. This easily causes water vapor to clog the condensation layer, resulting in water vapor backflow and reducing the water conversion efficiency of the hollow fiber membrane.

[0019] Furthermore, the shortest distance from the aggregation area to the outer surface is the first distance, and the shortest distance from the aggregation area to the inner surface is the second distance, wherein the length of the first distance is greater than the length of the second distance.

[0020] It should be noted that the length of the first distance is greater than the length of the second distance. This means the accumulation zone is closer to the inner surface. When the water vapor accumulated in the accumulation zone flows towards the condensation layer at a suitable velocity, and the flow channel has appropriate flow resistance, the water vapor travels a certain distance to the condensation layer, where its velocity decreases to a suitable level, allowing it to flow smoothly towards the condensation layer. There, it condenses into water, which then diffuses to the outer surface at a suitable velocity. If the second distance is longer than the first distance, the distance the water vapor travels from the accumulation zone to the outer surface is too long, resulting in greater fluid resistance. As the flow distance increases, the flow rate of the water vapor decreases, thus reducing the water conversion efficiency of the hollow fiber membrane.

[0021] Furthermore, in the region from the outer surface to the aggregation area, the pore size of the membrane gradually increases towards the aggregation area, and the pore size change gradient near the outer surface is smaller than the pore size change gradient near the aggregation area.

[0022] In this application, there are various structures in the region from the outer surface to the aggregation region, including but not limited to the following structures. For example, in the first type of membrane, the pore size near the outer surface remains essentially constant, while the pore size near the aggregation region increases with a gradient; in the second type of membrane, the pore size gradient near the outer surface is greater than the pore size gradient near the aggregation region; in the third type of membrane, the pore size near the outer surface initially increases with a large gradient, then remains essentially constant, and finally increases with a small gradient; in the fourth type of membrane, the pore size near the outer surface initially increases with a small gradient, then remains essentially constant, and finally increases with a large gradient; in the fifth type of membrane, the pore size increases from the outer surface to the aggregation region... The pore size remains relatively constant in the vicinity of the aggregation zone, but increases abruptly near the aggregation zone. The preferred structure is one where, from the outer surface to the aggregation zone, the membrane pore size gradually increases towards the aggregation zone, and the pore size gradient near the outer surface is smaller than that near the aggregation zone. This can be understood as the membrane pore size increasing abruptly near the aggregation zone, causing water vapor entering the aggregation zone to collide with each other at a relatively high flow rate, generating greater resistance. This causes the water vapor velocity to drop sharply at the moment of collision, which is conducive to the accumulation of water vapor in the aggregation zone, creating a concentration difference. This allows the water vapor to flow towards the condensation layer at a suitable speed, thereby improving the water conversion efficiency of the hollow fiber membrane.

[0023] Furthermore, the length of the first distance is 25-65 μm, and the ratio of the length of the first distance to the length of the second distance is 1.2-4.

[0024] This application features a suitable first distance, with a length of 25-65 μm, preferably 30-45 μm. This ensures a suitable amount of water vapor is collected in the aggregation zone. If the first distance is long, the path for water vapor to enter the aggregation zone is longer, reducing the amount of water vapor collected within the zone and thus reducing the driving force for water vapor diffusion to the inner surface. If the first distance is short, the amount of water vapor collected in the aggregation zone is large, which can easily lead to swelling, causing the volume of the aggregation zone to expand and the hollow fiber membrane to deform.

[0025] The ratio of the length of the first distance to the length of the second distance is 1.2-4, preferably 1.8-3.2. This allows water vapor in the accumulation zone to diffuse towards the inner surface at a suitable rate. If the ratio of the length of the first distance to the length of the second distance is large, the rate of water vapor diffusion towards the inner surface decreases; if the ratio is small, the amount of water vapor accumulated in the accumulation zone is large, which cannot diffuse to the condensation layer in time, easily causing concentration polarization, resulting in water vapor backflow and reducing the water conversion efficiency of the humidification membrane.

[0026] Furthermore, the closest distance from the aggregation zone to the condensation layer is called the third distance, the length of which is 8-30 μm, and the ratio of this distance to the thickness of the hollow fiber membrane is 6%-35%.

[0027] It should be noted that in this application, there is a suitable third distance between the aggregation zone and the condensation layer to ensure that the water vapor in the aggregation zone diffuses to the condensation layer at an appropriate rate, avoiding a decrease in the water vapor diffusion rate or blockage of the pores in the condensation layer. Water vapor diffuses outward from the aggregation zone at a relatively high rate. If the third distance between the aggregation zone and the condensation layer is short, the water vapor will still diffuse to the condensation layer at a high speed, easily causing blockage of the water vapor in the condensation layer and resulting in water vapor backflow. If the third distance between the aggregation zone and the condensation layer is long, the water vapor diffusion rate to the condensation layer is low, thus reducing the diffusion rate of water vapor in the condensation layer and consequently reducing the water conversion efficiency of the hollow fiber membrane.

[0028] Furthermore, the area of ​​the support layer near the outer surface has sheet-like fibers and nodes forming a honeycomb porous structure, with adjacent nodes connected by sheet-like fibers, and each node connected to 3-7 sheet-like fibers.

[0029] It should be noted that sheet fibers are fibers of a certain width and length that connect adjacent nodes. A node is formed by multiple interconnected porous structures on the cross-section of the hollow fiber membrane. Each node connects 3-7 sheet fibers, which can be understood as each node connecting 3-7 porous structures. These 3-7 porous structures support each other, making the structure more stable. When the outer surface is subjected to significant pressure, the pressure on the node is distributed to each sheet fiber connected to the node, resulting in a more uniform pressure distribution across the hollow fiber membrane, preventing excessive local stress, and increasing the compressive strength of the hollow fiber membrane. Preferably, each node connects 3 sheet fibers, i.e., each node connects 3 porous structures. These 3 porous structures support each other, forming a standard honeycomb structure. When subjected to external pressure, the force on the honeycomb structure is mostly axial, keeping the internal average stress and deformation relatively small compared to the honeycomb structure itself, thus maximizing the deformation resistance of the area near the outer surface.

[0030] Furthermore, in the honeycomb porous structure, each pore is formed by an average of 3-10 nodes and sheet-like fibers surrounding adjacent nodes; the average particle size of the nodes is 100-200 nm.

[0031] In this application, each hole in the honeycomb porous structure has an average of 3-10 nodes. Multiple nodes divide the hole wall into a structure composed of multiple sheet-like fibers connected together, that is, each hole is composed of a polygonal structure. When the honeycomb porous structure is subjected to pressure, the pressure on the hole wall is distributed to each side of the polygon, which can effectively prevent the hole from collapsing.

[0032] The average particle size of the nodes is 100-200 nm, ensuring that the nodes have a suitable size so that the structure has appropriate SEM average pore size and mechanical strength. If the average particle size of the nodes is large, it will reduce the SEM average pore size of the honeycomb porous structure, which will easily reduce the water vapor throughput and thus reduce the water conversion efficiency of the hollow fiber membrane. If the average particle size of the nodes is small, it will reduce the SEM average pore size of the honeycomb porous structure, resulting in a decrease in the compressive strength of the honeycomb porous structure and thus a decrease in the mechanical strength of the hollow fiber membrane.

[0033] Furthermore, the average thickness of the sheet fibers is 40-80 nm, and the average length of the sheet fibers between two adjacent nodes is 100-300 nm.

[0034] In this application, the sheet fibers have a suitable average thickness of 40-80 nm, which gives the sheet fibers sufficient mechanical strength and the honeycomb porous structure a suitable average SEM pore size. If the average thickness of the sheet fibers is too thick, the average SEM pore size of the honeycomb porous structure will be reduced, thereby reducing the water conversion efficiency of the hollow fiber membrane; if the average thickness of the sheet fibers is too thin, the thinner sheet fibers are more prone to breakage or deformation when the hollow fiber membrane is subjected to greater pressure.

[0035] The average length of the sheet fibers between two adjacent nodes is 100-300 nm, which gives the honeycomb porous structure a suitable average pore size according to SEM. Simultaneously, the number of nodes and sheet fibers constituting each pore structure is appropriate. If the average length of the sheet fibers between two adjacent nodes is large, it tends to result in larger pore sizes, increasing the amount of water vapor passing through and accumulating in the aggregation region, easily leading to concentration polarization and reducing the water conversion efficiency of the hollow fiber membrane. Conversely, if the average length of the sheet fibers between two adjacent nodes is small, it tends to increase the number of nodes forming individual pores, increasing the number of sides of the polygon in each pore. As the number of pore sides increases, the stability of the honeycomb porous structure decreases, thereby reducing the mechanical strength of the hollow fiber membrane.

[0036] Furthermore, the support layer near the condensation layer also has strip-shaped fibers forming a sponge-like porous structure, the average diameter of which is 20-200 nm.

[0037] In this application, the strip fibers form a sponge-like porous structure, and the average diameter of the strip fibers is 20-200 nm. If the average diameter of the strip fibers is large, the porosity of the support layer near the condensation layer will decrease, thereby affecting the diffusion rate of water vapor in the hollow fiber membrane. If the average diameter of the strip fibers is small, the pore area ratio of the support layer near the condensation layer will increase, thereby reducing its mechanical strength. When subjected to greater pressure, the hollow fiber membrane is prone to deformation.

[0038] The average diameter of the strip-shaped fibers in the support layer near the condensation layer of this application is 20-200 nm, which can provide a certain degree of support and protection for the support layer, making the pore structure formed by the hollow fiber membrane more stable, less prone to collapse, and having good pressure resistance, so that the hollow fiber membrane as a whole has good tensile strength; at the same time, it makes the pore distribution of the hollow fiber membrane uniform and has a suitable porosity, so that the hollow fiber membrane has a high water conversion efficiency.

[0039] Furthermore, the pore area ratio of the outer surface is 8%-30%; the pore area ratio of the inner surface is 3%-12%; the first water contact angle of the outer surface is 65-90°, and the first water contact angle of the outer surface is 5-25° larger than the first water contact angle of the inner surface.

[0040] In this application, the outer surface has a suitable pore area ratio, allowing for an appropriate amount of water vapor to enter the membrane instantaneously, thus ensuring a suitable permeation rate and ultimately resulting in a high water conversion efficiency for the hollow fiber membrane. If the pore area ratio of the outer surface is large, the amount of water vapor entering the membrane instantaneously increases, and the accumulation zone cannot collect all the water vapor, potentially leading to blockage or backflow of some water vapor, reducing water conversion efficiency and increasing gas ingress. Conversely, if the pore area ratio of the outer surface is small, the permeability of water vapor through the hollow fiber membrane decreases, thereby reducing the water conversion efficiency of the hollow fiber membrane.

[0041] This application features a suitable internal surface porosity, which effectively removes water near the inner surface from the membrane, preventing water from accumulating in the condensation layer, blocking the pores, and reducing the water conversion efficiency of the hollow fiber membrane. Simultaneously, the condensed water in the condensation layer effectively reduces the gas throughput. If the internal surface porosity is too large, the mechanical strength of the inner surface decreases, making it prone to collapse under pressure, thus increasing gas throughput. Conversely, if the internal surface porosity is too small, water in the condensation layer cannot diffuse to the outside of the membrane in time, leading to water accumulation within the condensation layer, clogging it, and reducing the water conversion efficiency of the hollow fiber membrane.

[0042] It should be noted that the inner surface of this application has a suitable first water contact angle, allowing water inside the hollow fiber membrane to flow to the inner surface at a suitable flow rate, and preventing water accumulation on the inner surface, thereby increasing the humidification effect of the membrane. When the first water contact angle of the inner surface is small, the hydrophilicity of the inner surface is large, causing water to accumulate in the area near the inner surface of the membrane, thus reducing the rate of water diffusion; when the first water contact angle of the inner surface is too large, the hydrophilicity near the inner surface area is small, resulting in a decrease in the water flow velocity in the flow channel near the inner surface area, thus reducing the rate of water diffusion. The outer surface of this application has a suitable first water contact angle, increasing the amount of water vapor entering the outer surface, while effectively preventing water vapor from accumulating in the outer surface area, which helps to improve the water conversion efficiency of the hollow fiber membrane. When the water contact angle of the outer surface is too large, the hydrophobicity near the outer surface area is large, reducing the amount of water vapor entering the outer surface area; when the water contact angle of the outer surface is small, the hydrophilicity near the outer surface area is large, which is not conducive to the diffusion of water vapor to the inner surface, thus reducing the amount of water vapor passing through. One method is to first tear the hollow fiber membrane into several layers, and then use a contact angle tester to test the corresponding parameters. Alternatively, those skilled in the art can obtain the above parameters through other measurement methods. The above measurement methods are for reference only.

[0043] Furthermore, the roughness Ra of the inner surface is 5-20 μm, and the roughness of the outer surface is 5-20 μm greater than that of the inner surface.

[0044] It should be noted that the surface roughness of a solid reflects its surface area; the rougher the surface, the larger the surface area, and the greater the amount of water vapor absorbed. The outer surface of this application has a relatively large roughness, resulting in a larger surface area and a greater contact area with water vapor, thus increasing the amount of water vapor absorbed. With a suitable pore size on the outer surface, the water vapor flux is further increased on top of the already large flux. Furthermore, the roughness of the outer surface is 5-20 μm greater than that of the inner surface, ensuring that the inner surface has a suitable roughness and a suitable surface area, resulting in a suitable diffusion rate of condensate from the inner surface to the outside of the membrane.

[0045] The hollow fiber membrane was roughened using a roughness tester, and the results showed that the inner and outer surfaces had suitable roughness.

[0046] Furthermore, the hollow fiber membrane has a thickness of 75-145 μm, a porosity of 40%-75%, a water conversion efficiency of 45%-70%, a water vapor permeation rate of 0.5-2.5 g / min, a tensile strength of 4-9 MPa, and an elongation at break of 40%-130%.

[0047] When the thickness of the hollow fiber membrane is too small, its mechanical strength is reduced, making it prone to deformation under pressure. When the thickness of the hollow fiber membrane is too large, the time for water vapor to permeate through the membrane is increased, resulting in excessive time costs. The hollow fiber membrane provided in this application has a thickness of 75-145 μm, ensuring that the hollow fiber membrane has high mechanical strength, high water conversion efficiency, and a fast water vapor permeation rate, resulting in lower time costs.

[0048] The tensile strength and elongation at break are important indicators for evaluating the mechanical strength of hollow fiber membranes. Under certain conditions, the greater the tensile strength of a hollow fiber membrane, the better its mechanical strength. Tensile strength refers to the membrane's ability to withstand parallel tensile forces. During testing under certain conditions, the membrane sample is subjected to a tensile load until it breaks. Based on the maximum tensile load at failure and the change in the membrane sample's dimensions (length), the tensile strength and elongation at break can be calculated. Both tensile strength and elongation at break can be measured using a universal tensile testing machine. The filter membrane of this invention has a tensile strength of 4-9 MPa and an elongation at break of 40-130%, indicating that the hollow fiber membrane of this application has high tensile strength and elongation at break, as well as good pressure resistance. Its mechanical properties are good, its industrial application value is high, and it fully meets market demands.

[0049] The hollow fiber membrane provided in this application has a water vapor permeation rate of 0.5-2.5 g / min and a water conversion efficiency of 45-70%, ensuring a high water conversion efficiency and enabling the hollow fiber membrane to have a good humidification effect.

[0050] The method for preparing the high moisture permeability hollow fiber membrane described in any one of the above methods includes the following steps:

[0051] S1: Prepare casting solution and core solution; the casting solution comprises the following components by weight: 18-25 parts of polysulfone polymer, 5-20 parts of hydrophilic additive, 55-80 parts of first organic solvent and 1-5 parts of sulfonated polyethersulfone; the core solution comprises a second organic solvent and a non-solvent, wherein the non-solvent is water and its content is 45%-80%.

[0052] S2: Spinning: The film-forming solution is sprayed from the annular part of the double-tube nozzle, and the core solution is sprayed from the center to form a molded product with an inner surface and an outer surface.

[0053] S3: The molded product is placed in a phase separation liquid for preliminary phase separation to form a film. The phase separation liquid includes a third organic solvent and water, and the water content is 30%-45%. The preliminary phase separation time is 20-60 seconds.

[0054] S4: Immerse the biofilm in pure water to perform complete phase separation. The complete phase separation time is 40-80 seconds.

[0055] S5: Rewind and dry.

[0056] Furthermore, before the initial phase separation of the molded article, the molded article undergoes pre-phase separation in an air section, where the humidity of the air section is 80%-100% and the residence time of the membrane fibers is 1-5 seconds.

[0057] Furthermore, the hydrophilic additive is at least one of polyethylene glycol, polyvinylpyrrolidone, polyethyleneimine, and polyvinyl alcohol; the first organic solvent, the second organic solvent, and the third organic solvent are all at least one of dimethyl sulfoxide, dimethylformamide, N-ethylpyrrolidone, dimethylacetamide, and N-methylpyrrolidone; and the polysulfone polymer is at least one of polyethersulfone, polysulfone, and polyarylsulfone.

[0058] In the above method, a casting solution and a core solution are prepared. The casting solution includes a polysulfone polymer, a hydrophilic additive, a first organic solvent, and sulfonated polyethersulfone. The hydrophilic additive is at least one of polyethylene glycol, polyvinylpyrrolidone, polyethyleneimine, and polyvinyl alcohol to increase the hydrophilicity of the casting solution. Adding a small amount of sulfonated polyethersulfone to the casting solution can further increase the hydrophilicity of the membrane. However, if the content of sulfonated polyethersulfone is too high, it will reduce the mechanical strength and brittleness during the film formation process, thereby reducing the tensile strength of the hollow fiber membrane. Furthermore, since sulfonated polyethersulfone is a water-soluble substance, according to the principle of like dissolves like, sulfonated polyethersulfone gradually migrates towards the core solution, resulting in a higher content of sulfonic acid groups on the inner surface than on the outer surface. The content of sulfonic acid groups gradually decreases from the inner surface to the outer surface, leading to a gradual decrease in hydrophilicity from the inner surface to the outer surface.

[0059] The core liquid includes a second organic solvent and a high content of non-solvent (water). The water content in the core liquid is 45%-80%. When the casting liquid and the core liquid are extruded from the spinning nozzle at the same time, the temperature of the spinning nozzle and the casting liquid are the same to avoid the casting liquid temperature being affected by the excessively high temperature of the spinning nozzle. The temperature of the casting liquid is higher than that of the core liquid, which accelerates the phase separation on the inner surface. At the same time, the increase in the non-solvent content of the core liquid causes it to separate rapidly near the inner surface area, further accelerating the phase separation. This results in a smaller SEM average pore size and pore area ratio of the pores formed on the inner surface. The rate at which the core liquid enters the membrane gradually decreases, and the content of the core liquid entering the membrane gradually increases, causing the pore size to gradually increase and forming aggregation zones. The molded article is placed in a phase-separating solution for preliminary phase separation. Higher water content in the solution results in faster phase separation on the outer surface, leading to smaller pore sizes on the outer surface. The phase-separating solution in this application has a suitable water content, resulting in suitable pore sizes on the outer surface. The phase-separating solution flows into the interior of the molded article through these pores. Based on the appropriate water content and separation time, a suitable pore structure is achieved near the outer surface, resulting in a pre-phase-separated molded article. The pre-phase-separated molded article is then placed in pure water for complete phase separation. Water penetrates from the outer surface along the thickness direction of the molded article towards the inner surface, ensuring complete phase separation and facilitating the full leaching of the first organic solvent. Finally, the article is washed in water and then dried to obtain a hollow fiber membrane.

[0060] Preferably, the molded article with inner and outer surfaces is placed in a high-humidity airflow with a suitable phase separation rate, which is conducive to the formation of a suitable porous structure near the outer surface area and the outer surface. At the same time, water vapor condenses onto the surface of the membrane liquid, and the polymer in the solution condenses on the surface of the water droplet under the action of hydrophilic balance, forming a polymer layer (that is, stabilizing the water droplet and slowing down the growth rate of the water droplet), promoting the formation of a honeycomb porous structure.

[0061] Preferably, stretching the formed membrane at a stretching rate of 3-12 m / min for 1-5 times can effectively prevent the shrinkage of pores formed by phase separation, thus playing a shaping role. Furthermore, at a suitable stretching rate, the pore size within the same layer is more uniform. An appropriate stretching ratio can effectively avoid fiber breakage due to excessive stretching or poor stretching effect due to insufficient stretching. Finally, the membrane is washed in water, then wound up and dried to obtain the hollow fiber membrane.

[0062] The present application provides the following beneficial effects: the hollow fiber membrane exhibits high water conversion efficiency and mechanical strength, extending its service life. The preparation method provided by this invention allows for the convenient, rapid, and effective preparation of the aforementioned hollow fiber membrane. Attached Figure Description

[0063] The accompanying drawings, which are provided to further illustrate this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application.

[0064] Figure 1 The image shows a scanning electron microscope (SEM) image of the inner surface of the hollow fiber membrane prepared in Example 4, with a magnification of 10000×.

[0065] Figure 2 The image shown is a scanning electron microscope (SEM) image of the outer surface of the hollow fiber membrane prepared in Example 4, with a magnification of 10000×.

[0066] Figure 3 The image shows a scanning electron microscope (SEM) image of the cross-section of the hollow fiber membrane prepared in Example 4, near the inner surface, with a magnification of 10000×.

[0067] Figure 4 The image shown is a scanning electron microscope (SEM) image of the cross-section of the hollow fiber membrane prepared in Example 4, near the outer surface, with a magnification of 10000×.

[0068] Figure 5 The image shows a scanning electron microscope (SEM) image of the cross-section of the hollow fiber membrane prepared in Example 4, with a magnification of 1000×.

[0069] Figure 6 The image shown is a scanning electron microscope (SEM) image of the inner surface of the hollow fiber membrane prepared in Example 7, with a magnification of 5000×.

[0070] Figure 7 The image shown is a scanning electron microscope (SEM) image of the outer surface of the hollow fiber membrane prepared in Example 7, with a magnification of 2000×.

[0071] Figure 8 The image shown is a scanning electron microscope (SEM) image of the cross-section of the hollow fiber membrane prepared in Example 7, near the inner surface, with a magnification of 5000×.

[0072] Figure 9 The image shown is a scanning electron microscope (SEM) image of the cross-section of the hollow fiber membrane prepared in Example 7, near the outer surface, with a magnification of 5000×.

[0073] Figure 10 The image shown is a scanning electron microscope (SEM) image of the cross-section of the hollow fiber membrane prepared in Example 7, with a magnification of 700×. Detailed Implementation

[0074] To more clearly illustrate the overall concept of this application, detailed descriptions are provided below using examples. Unless otherwise specified, the raw materials and equipment used in the preparation of the hollow fiber membranes in the following examples are commercially available. Specifically, a Hitachi S-5500 scanning electron microscope was used to characterize the structural morphology of the filter membrane.

[0075] Example 1

[0076] S1: Preparation of casting solution and core solution;

[0077] The casting solution comprises the following components by weight: 21 parts polyethersulfone polymer, 15 parts polyethylene glycol, 65 parts dimethylformamide, and 1.5 parts sulfonated polyethersulfone.

[0078] The core fluid comprises N-methylpyrrolidone and a non-solvent, wherein the non-solvent is water and its content is 79%;

[0079] S2: Spinning: The film-forming solution is sprayed from the annular part of the double-tube nozzle, and the core solution is sprayed from the center to form a molded product with an inner surface and an outer surface.

[0080] S3: Pre-phase separation, the molded product passes through an air section with a humidity of 88% and a membrane fiber residence time of 4.5s;

[0081] S4: The molded product is placed in a phase separation liquid for preliminary phase separation to form a film. The phase separation liquid includes dimethylacetamide and water, and the water content is 32%. The preliminary phase separation time is 55s.

[0082] S5: Immerse the biofilm in pure water for complete phase separation. The complete phase separation time is 75 seconds.

[0083] S6: The formed film is stretched 2.5 times at a stretching rate of 7.5 m / min, then wound up and dried.

[0084] Example 2

[0085] S1: Preparation of casting solution and core solution;

[0086] The casting solution comprises the following components by weight: 22 parts polyarylsulfone, 12 parts polyethyleneimine, 70 parts N-ethylpyrrolidone, and 3 parts sulfonated polyethersulfone.

[0087] The core fluid comprises N-ethylpyrrolidone and a non-solvent, wherein the non-solvent is water and its content is 54%.

[0088] S2: Spinning: The film-forming solution is sprayed from the annular part of the double-tube nozzle, and the core solution is sprayed from the center to form a molded product with an inner surface and an outer surface.

[0089] S3: Pre-phase separation, the molded product passes through an air section with a humidity of 81% and a membrane fiber residence time of 2 seconds;

[0090] S4: The molded product is placed in a phase separation liquid for initial phase separation to form a film. The phase separation liquid includes dimethyl sulfoxide and water, and the water content is 41%. The initial phase separation time is 45s.

[0091] S5: Immerse the biofilm in pure water for complete phase separation. The complete phase separation time is 50 seconds.

[0092] S6: The formed film is stretched three times at a stretching rate of 10.5 m / min, then wound up and dried.

[0093] Example 3

[0094] S1: Preparation of casting solution and core solution;

[0095] The casting solution comprises the following components by weight: 19.5 parts polysulfone, 6 parts polyethyleneimine, 58 parts dimethylformamide, and 4.5 parts sulfonated polyethersulfone.

[0096] The core fluid comprises dimethylacetamide and a non-solvent, wherein the non-solvent is water and its content is 72%;

[0097] S2: Spinning: The film-forming solution is sprayed from the annular part of the double-tube nozzle, and the core solution is sprayed from the center to form a molded product with an inner surface and an outer surface.

[0098] S3: Pre-phase separation, the molded product passes through an air section with a humidity of 84% and a membrane fiber residence time of 3 seconds;

[0099] S4: The molded product is placed in a phase separation liquid for initial phase separation to form a film. The phase separation liquid includes dimethylacetamide and water, and the water content is 37%. The initial phase separation time is 35s.

[0100] S5: Immerse the biofilm in pure water for complete phase separation. The complete phase separation time is 60s.

[0101] S6: The formed film is stretched by 1.5 times at a stretching rate of 8m / min, then wound up and dried.

[0102] Example 4

[0103] S1: Preparation of casting solution and core solution;

[0104] The casting solution comprises the following components by weight: 20 parts polysulfone, 8 parts polyvinyl alcohol, 78 parts N-ethylpyrrolidone, and 2 parts sulfonated polyethersulfone.

[0105] The core fluid includes N-ethylpyrrolidone and a non-solvent, wherein the non-solvent is water and its content is 63%;

[0106] S2: Spinning: The film-forming solution is sprayed from the annular part of the double-tube nozzle, and the core solution is sprayed from the center to form a molded product with an inner surface and an outer surface.

[0107] S3: Pre-phase separation, the molded product passes through an air section with a humidity of 98% and a membrane fiber residence time of 3.5s;

[0108] S4: The molded product is placed in a phase separation liquid for initial phase separation to form a film. The phase separation liquid includes dimethylacetamide and water, and the water content is 43%. The initial phase separation time is 50s.

[0109] S5: Immerse the biofilm in pure water for complete phase separation. The complete phase separation time is 55s.

[0110] S6: The formed film is stretched twice at a stretching rate of 9.5 m / min, then wound up and dried.

[0111] Example 5

[0112] S1: Preparation of casting solution and core solution;

[0113] The casting solution comprises the following components by weight: 18 parts polyethersulfone, 9 parts polyvinylpyrrolidone, 63 parts dimethylformamide, and 1.6 parts sulfonated polyethersulfone.

[0114] The core fluid includes dimethylformamide and a non-solvent, wherein the non-solvent is water and its content is 75%.

[0115] S2: Spinning: The film-forming solution is sprayed from the annular part of the double-tube nozzle, and the core solution is sprayed from the center to form a molded product with an inner surface and an outer surface.

[0116] S3: Pre-phase separation, the molded product passes through an air section with a humidity of 95% and a membrane fiber residence time of 2.5s;

[0117] S4: The molded product is placed in a phase separation liquid for initial phase separation to form a film. The phase separation liquid includes N-methylpyrrolidone and water, and the water content is 40%. The initial phase separation time is 30s.

[0118] S5: Immerse the biofilm in pure water to perform complete phase separation. The complete phase separation time is 70 seconds.

[0119] S6: The formed film is stretched by 1 time at a stretching rate of 7m / min, then wound up and dried.

[0120] Example 6

[0121] S1: Preparation of casting solution and core solution;

[0122] The casting solution comprises the following components by weight: 23 parts polyarylsulfone, 10 parts polyethylene glycol, 57 parts dimethyl sulfoxide, and 2.4 parts sulfonated polyethersulfone.

[0123] The core fluid comprises dimethylacetamide and a non-solvent, wherein the non-solvent is water and its content is 57%.

[0124] S2: Spinning: The film-forming solution is sprayed from the annular part of the double-tube nozzle, and the core solution is sprayed from the center to form a molded product with an inner surface and an outer surface.

[0125] S3: Pre-phase separation, the molded product passes through an air section with a humidity of 83% and a membrane fiber residence time of 4s;

[0126] S4: The molded product is placed in a phase separation liquid for initial phase separation to form a film. The phase separation liquid includes dimethylacetamide and water, and the water content is 36%. The initial phase separation time is 40 seconds.

[0127] S5: Immerse the biofilm in pure water for complete phase separation. The complete phase separation time is 45 seconds.

[0128] S6: The formed film is stretched 3.5 times at a stretching rate of 4 m / min, then wound up and dried.

[0129] Example 7

[0130] S1: Preparation of casting solution and core solution;

[0131] The casting solution comprises the following components in parts by weight: 24 parts polysulfone, 13 parts polyethyleneimine, 68 parts N-methylpyrrolidone, and 2.7 parts sulfonated polyethersulfone.

[0132] The core fluid includes N-methylpyrrolidone and a non-solvent, wherein the non-solvent is water and its content is 66%;

[0133] S2: Spinning: The film-forming solution is sprayed from the annular part of the double-tube nozzle, and the core solution is sprayed from the center to form a molded product with an inner surface and an outer surface.

[0134] S3: Pre-phase separation, the molded product passes through an air section with a humidity of 87% and a membrane fiber residence time of 1.5s;

[0135] S4: The molded product is placed in a phase separation liquid for initial phase separation to form a film. The phase separation liquid includes N-ethylpyrrolidone and water, and the water content is 39%. The initial phase separation time is 25s.

[0136] S5: Immerse the biofilm in pure water for complete phase separation. The complete phase separation time is 65 seconds.

[0137] S6: The formed film is stretched 4 times at a stretching rate of 11m / min, then wound up and dried.

[0138] Example 8

[0139] S1: Preparation of casting solution and core solution;

[0140] The casting solution comprises the following components by weight: 19 parts polyethersulfone, 11 parts polyethylene glycol, 74 parts dimethylacetamide, and 3.2 parts sulfonated polyethersulfone.

[0141] The core fluid comprises dimethylacetamide and a non-solvent, wherein the non-solvent is water and its content is 48%.

[0142] S2: Spinning: The film-forming solution is sprayed from the annular part of the double-tube nozzle, and the core solution is sprayed from the center to form a molded product with an inner surface and an outer surface.

[0143] S3: Pre-phase separation, the molded product passes through an air section with a humidity of 89% and a membrane fiber residence time of 5s;

[0144] S4: The molded product is placed in a phase separation liquid for initial phase separation to form a film. The phase separation liquid includes N-methylpyrrolidone and water, and the water content is 33%. The initial phase separation time is 60s.

[0145] S5: Immerse the biofilm in pure water to perform complete phase separation. The complete phase separation time is 80 seconds.

[0146] S6: The formed film is stretched 4.5 times at a stretching rate of 5 m / min, then wound up and dried.

[0147] Comparative Example 1

[0148] S1: Preparation of casting solution and core solution;

[0149] The casting solution comprises the following components by weight: 22 parts polysulfone, 12 parts polyethyleneimine, 70 parts dimethylacetamide, and 4 parts sulfonated polyethersulfone.

[0150] The core fluid includes dimethylacetamide and a non-solvent, wherein the non-solvent is water and its content is 20%;

[0151] S2: Spinning: The film-forming solution is sprayed from the annular part of the double-tube nozzle, and the core solution is sprayed from the center to form a molded product with an inner surface and an outer surface.

[0152] S3: Pre-phase separation, the molded product passes through an air section with a humidity of 81% and a membrane fiber residence time of 2 seconds;

[0153] S4: The molded product is placed in a phase separation liquid for initial phase separation to form a film. The phase separation liquid includes dimethylformamide and water, and the water content is 35%. The initial phase separation time is 45 seconds.

[0154] S5: Immerse the biofilm in pure water for complete phase separation. The complete phase separation time is 50 seconds.

[0155] S6: The formed film is stretched three times at a stretching rate of 10.5 m / min, then wound up and dried.

[0156] Compared with Example 2, Comparative Example 1 reduced the content of non-solvents in the core liquid, so that there were no aggregation areas in the hollow fiber membrane, that is, there were no areas in the internal structure of the membrane with an average pore size larger than the outer surface, while the inner surface had a larger pore size structure, which greatly reduced the water vapor throughput of the hollow fiber membrane, thereby reducing the water conversion efficiency of the hollow fiber membrane.

[0157] Performance Experiment

[0158] Structural characterization

[0159] The hollow fiber membranes obtained in each embodiment and comparative example were characterized by longitudinal section, inner surface, and outer surface morphology. Measurements were also performed on the thickness of each layer in the main body, the average pore size using SEM, and the fiber size, as well as the porosity and thickness of the hollow fiber membrane. The measurement data are shown in Tables 1-6, and the morphology characterization results for Examples 1-8 are shown in [Table missing]. Figures 1-10 .

[0160] Table 1 Characterization of the outer surface structure of hollow fiber membranes in each example

[0161]

[0162] According to the data in Table 1, the outer surfaces of Examples 1-8 have suitable average pore size and pore area. In particular, the membrane structure of Example 2 has a larger average pore size and pore area on the outer surface, which increases the water vapor permeation. The membrane structure of Example 3 has a smaller first water contact angle on the outer surface, which increases the hydrophilicity of the outer surface and thus increases the water vapor permeation.

[0163] Table 2 Characterization of the inner surface structure of hollow fiber membranes in each example

[0164]

[0165]

[0166] According to the data in Table 2, the hollow fiber membrane structures prepared in Examples 1-8 have suitable average pore size and pore area on their inner surfaces. Among them, the membrane structure of Comparative Example 1 has a larger average pore size and pore area ratio on its inner surface, so there is no condensation layer in the hollow fiber membrane prepared in Comparative Example 1, which reduces the water conversion efficiency of the hollow fiber membrane.

[0167] Table 3 Characterization of each example membrane structure

[0168]

[0169]

[0170] According to the data in Table 3, the hollow fiber membrane structures prepared in Examples 1-8 have aggregated regions with suitable average pore size and thickness. However, in Comparative Example 1, the absence of aggregated regions with larger average pore sizes leads to the formation of small-diameter pores inside the hollow fiber membrane, thus reducing the water conversion efficiency of the hollow fiber membrane.

[0171] Table 4 Characterization of each example membrane structure

[0172]

[0173] According to the data in Table 4, the hollow fiber membrane structures of Examples 1-8 have suitable sizes for the first distance, the second distance, the third distance, and the average diameter of the strip fibers. As can be seen from the above, since there is no clustered region with a large average pore size in the hollow fiber membrane structure prepared in Comparative Example 1, there is no first distance, second distance, third distance, or strip fibers in the hollow fiber membrane structure of Comparative Example 1.

[0174] Table 5. Characterization of the honeycomb porous structure of hollow fibers in each example.

[0175]

[0176] According to the data in Table 5, the hollow fiber membrane structures of Examples 4 and 5 have a honeycomb porous structure, which increases the tensile strength and internal and external burst pressure of the hollow fiber membranes of Examples 4 and 5.

[0177] Performance testing

[0178] The tensile strength and elongation of the hollow fiber membranes obtained in each example were tested using a tensile testing machine.

[0179] The water conversion efficiency of the hollow fiber membranes obtained in each example was tested.

[0180] A homemade hollow fiber component was used, with humid air entering through the wet in end and dry air through the dry in end. Digital display thermometers and hygrometers were used to monitor the humidification effect at both the dry out and wet out ends. Different humidification data were obtained by varying the gas flow rates at the dry in and wet in ends. Different humidification data were also obtained by adding a one-way pressure relief valve at the dry out end to increase the pressure of the dry flow.

[0181] Calculation results: Where: D—density of dry gas or wet vapor, unit (g / m³) 3 K1, K2—constants; T—temperature at the dry-in end, dry-out end, wet-in end, or wet-out end of the hollow fiber membrane, in °C; T1—temperature constant, in °C. —Humidity of the dry in end, dry out end, wet in end, or wetout end of the hollow fiber membrane, in %RH.

[0182] V = Q * H Where: V—volume of dry or moist gas, unit (m³) 3 Q—volume flow rate of dry or wet gas, in units of (m³ / s). 3 / h), H—gas flow rate time, in hours.

[0183] m = ρ * v where m—water content at the dry out end or wet in end of the hollow fiber membrane, in g; ρ—density of dry gas or wet vapor, in g / m³. 3 v—volume of dry or moist gas, unit (m³) 3 ).

[0184] In the formula, ω is the water conversion efficiency, m1 is the water content at the dry out end of the hollow fiber membrane (in g), and m2 is the water content at the wet in end of the hollow fiber membrane (in g).

[0185] The air permeability of the hollow fiber membranes obtained in each example was tested using a gas flow meter.

[0186] The internal burst pressure of the hollow fiber membranes obtained in each example was tested.

[0187] Experimental conditions: (1) Hollow fiber membranes were immersed in pure water at 80℃ for 1-2 minutes to obtain fully wetted hollow fiber membranes; (2) The effective length of the hollow fiber membranes was 11-12 cm.

[0188] A self-made hollow fiber component is constructed. The component has a pressure relief port that allows air to circulate with the outside of the hollow fiber membrane tube. A moistened hollow fiber membrane is placed inside the hollow fiber membrane component, and compressed air at a certain pressure is introduced into the tube of the hollow fiber membrane. The pressure inside the tube of the hollow fiber membrane is greater than the pressure outside the tube. When the hollow fiber membrane bursts, the relevant pressure data is recorded.

[0189] External burst pressure was tested on the hollow fiber membranes obtained in each example.

[0190] Experimental conditions: (1) Hollow fiber membranes were immersed in pure water at 80℃ for 1-2 minutes to obtain fully wetted hollow fiber membranes; (2) The effective length of the hollow fiber membranes was 11-12 cm.

[0191] A self-made hollow fiber miniature component was constructed. The air inside the hollow fiber membrane tube circulates with the atmosphere. A moistened hollow fiber membrane was placed inside the hollow fiber membrane miniature component, and compressed air at a certain pressure was introduced into the hollow fiber membrane miniature component. The pressure outside the hollow fiber membrane tube was greater than the pressure inside the membrane tube. When the hollow fiber membrane deformed, the relevant pressure data was recorded.

[0192] Table 6 Hollow Fiber Membrane Performance Tests

[0193]

[0194] According to the data in Table 6, the hollow fiber membranes prepared in Examples 1-8 all exhibit high water conversion efficiency, water vapor permeation rate, tensile strength, and internal and external burst pressure, as well as suitable elongation at break. Among them, Example 3 shows high water conversion efficiency, while Examples 4 and 5, due to their honeycomb porous structure, also demonstrate good tensile strength and internal and external burst pressure. In contrast, the hollow fiber membrane prepared in Comparative Example 1 has lower water conversion efficiency, water vapor permeation rate, tensile strength, and internal and external burst pressure.

[0195] The above description is merely an embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of this application should be included within the scope of the claims of this application.

Claims

1. A high moisture permeable hollow fiber membrane comprising a body having an inner surface on one side and an outer surface on the other side, the body having non- oriented tortuous passages therein, characterized in that, The main body includes a support layer and a condensation layer. One side of the support layer is an outer surface, and one side of the condensation layer is an inner surface. The other side of the support layer and the other side of the condensation layer are connected by continuous fibers. The support layer has a gathering region for water vapor accumulation, and the average SEM pore size of the gathering region is larger than the average SEM pore size of the outer surface. The average SEM pore size of the outer surface is 0.3-2 μm; the average SEM pore size of the inner surface is 15-100 nm. The thickness of the aggregation region is 10-60 μm; The shortest distance from the aggregation area to the outer surface is the first distance, and the shortest distance from the aggregation area to the inner surface is the second distance. The length of the first distance is greater than the length of the second distance. The shortest distance from the aggregation region to the condensation layer is called the third distance, and the length of the third distance is 8-30 μm. The support layer near the condensation layer also has strip-shaped fibers forming a sponge-like porous structure, and the average diameter of the strip-shaped fibers is 20-200 nm; The aggregation area is the region between A and B. Within the support layer, A extends outward from the point of maximum SEM average pore size to a point where the SEM average pore size is 0.5 times the maximum SEM average pore size, and B extends into the condensation layer to a point where the SEM average pore size is 0.5 times the maximum SEM average pore size.

2. The high moisture-permeable hollow fiber membrane according to claim 1, characterized by The thickness of the aggregation region accounts for 10%-50% of the thickness of the hollow fiber membrane.

3. The high moisture permeability hollow fiber membrane according to claim 1, characterized in that, The average SEM pore size of the aggregation region is 0.5-2.5 μm; the average SEM pore size of the aggregation region is 1.2-4.5 times that of the average SEM pore size of the outer surface.

4. The high moisture permeability hollow fiber membrane according to claim 1, characterized in that, In the region from the outer surface to the aggregation area, the pore size of the membrane gradually increases towards the aggregation area, and the pore size change gradient near the outer surface is smaller than the pore size change gradient near the aggregation area.

5. The high moisture permeability hollow fiber membrane according to claim 1, characterized in that, The length of the first distance is 25-65 μm, and the ratio of the length of the first distance to the length of the second distance is 1.2-4.

6. The high moisture permeability hollow fiber membrane according to claim 1, characterized in that, The ratio of the length of the third distance to the thickness of the hollow fiber membrane is 6%-35%.

7. The high moisture permeability hollow fiber membrane according to claim 1, characterized in that, The area of ​​the support layer near the outer surface has sheet-like fibers and nodes forming a honeycomb porous structure. Adjacent nodes are connected by sheet-like fibers, and each node is connected by 3-7 sheet-like fibers.

8. The high moisture permeability hollow fiber membrane according to claim 7, characterized in that, Each pore in the honeycomb porous structure is formed by an average of 3-10 nodes and sheet-like fibers surrounding two adjacent nodes; the average particle size of the nodes is 100-200 nm.

9. The high moisture permeability hollow fiber membrane according to claim 7, characterized in that, The average thickness of the sheet fibers is 40-80 nm, and the average length of the sheet fibers between two adjacent nodes is 100-300 nm.

10. The high moisture permeability hollow fiber membrane according to claim 1, characterized in that, The porosity of the outer surface is 8%-30%; the porosity of the inner surface is 3%-12%. The first water contact angle of the outer surface is 65-90°, and the first water contact angle of the outer surface is 5-25° larger than the first water contact angle of the inner surface.

11. The high moisture permeability hollow fiber membrane according to claim 1, characterized in that, The roughness Ra of the inner surface is 5-20 μm, and the roughness of the outer surface is 5-20 μm greater than that of the inner surface.

12. The high moisture permeability hollow fiber membrane according to claim 1, characterized in that, The hollow fiber membrane has a thickness of 75-145 μm, a porosity of 40%-75%, a water conversion efficiency of 45%-70%, a water vapor permeation rate of 0.5-2.5 g / min, a tensile strength of 4-9 MPa, and an elongation at break of 40%-130%.

13. The method for preparing the high moisture permeability hollow fiber membrane according to any one of claims 1-12, characterized in that: S1: Preparation of casting solution and core solution; The casting solution comprises the following components by weight: 18-25 parts of polysulfone polymer, 5-20 parts of hydrophilic additive, 55-80 parts of first organic solvent, and 1-5 parts of sulfonated polyethersulfone. The core fluid includes a second organic solvent and a non-solvent, wherein the non-solvent is water and its content is 45%-80%; S2: Spinning: The film-forming solution is sprayed from the annular part of the double-tube nozzle, and the core solution is sprayed from the center to form a molded product with an inner surface and an outer surface. S3: The molded product is placed in a phase separation liquid for preliminary phase separation to form a film. The phase separation liquid includes a third organic solvent and water, and the water content is 30%-45%. The preliminary phase separation time is 20-60 seconds. S4: Immerse the biofilm in pure water to perform complete phase separation. The complete phase separation time is 40-80 seconds. S5: Rewind and dry.

14. The method for preparing the high moisture permeability hollow fiber membrane according to claim 13, characterized in that: Before the initial phase separation of the molded article, the molded article undergoes pre-phase separation in an air section with a humidity of 80%-100% and a membrane fiber residence time of 1-5 seconds.

15. The method for preparing the high moisture permeability hollow fiber membrane according to claim 13, characterized in that: The hydrophilic additive is at least one of polyethylene glycol, polyvinylpyrrolidone, polyethyleneimine, and polyvinyl alcohol; The first organic solvent, the second organic solvent, and the third organic solvent are all at least one of dimethyl sulfoxide, dimethylformamide, N-ethylpyrrolidone, dimethylacetamide, and N-methylpyrrolidone; The polysulfone polymer is at least one of polyethersulfone, polysulfone, and polyarylsulfone.

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