A PES sterilization filter membrane and a preparation method thereof

Abstract

The application relates to a PES bacteria-removing filter membrane and a preparation method thereof. The filter membrane comprises an inlet liquid surface, an outlet liquid surface and a microporous body which is bounded by the inlet liquid surface and the outlet liquid surface, the microporous body is composed of n layers of screening layers, the number n of the screening layers is 100-400, the average pore diameter of the microporous body is 0.3-1 mu m, the microporous body is a symmetrical structure, the symmetrical structure refers to the fact that the variation coefficient C of the fiber width of three continuous regions of the microporous body is less than 0.15. The filter membrane has high flux performance, high bacterial load and high bacteria-removing capacity when filtering a large volume of low-turbidity liquid.

Description

Technical Field

[0001] This application relates to the field of membrane separation technology, and in particular to a PES sterilization filter membrane and its preparation method. Background Technology

[0002] In the production of biological agents, bacterial contamination is unavoidable due to factors such as its presence in raw materials and introduction during production. This contamination can pose a serious threat to the safety of end users (e.g., causing infection, pyrogenic reactions, etc.). Therefore, strict sterilization and / or disinfection treatments are generally performed before the agent is put into use. Existing disinfection methods mainly include high-temperature sterilization, radiation sterilization, and filtration sterilization. Among these, filtration sterilization has become one of the preferred sterilization methods in the life sciences field due to its advantages such as mild conditions, no need to introduce chemical reagents, minimal impact on active ingredients (maintaining the biological activity of proteins, vaccines, etc.), high sterilization efficiency, and ease of scalability.

[0003] Currently, the main membrane materials used for sterilization filtration include PTFE, PVDF, UPE, nylon, and PES. Among them, PES plays a very important role in biopharmaceutical and other fields due to its excellent mechanical properties, heat resistance, alkali resistance, corrosion resistance, gamma ray irradiation resistance, and high flux.

[0004] For example, patent document EP1149624B1 (applied by Parr Corporation) discloses a highly asymmetric sulfone polymer membrane in which the pores on the first surface can be at least about 5 times smaller than the pores on the second surface, and the diameter of the flow channels in the porous support structure gradually increases from the first surface to the second surface. This membrane has an average flow pore size of less than about 0.1 μm, about 0.2 μm, or about 0.3 to about 1.0 μm. The macropore region (the region near the second surface) in the typical V-shaped asymmetric filter membrane disclosed in the above patent has a larger dirt-holding capacity, effectively trapping and accommodating large particulate impurities in the feed liquid, while the micropore region (the region near the first surface) has a smaller pore size, enabling efficient trapping of small particles and bacteria.

[0005] In practical applications such as bacterial isolation, although the aforementioned asymmetric membranes exhibit certain advantages in flux, loading capacity, and retention capacity, their performance still falls short of the actual needs of manufacturing enterprises when processing low-turbidity, relatively clean solutions such as buffer solutions, small-molecule chemical drugs, and eye drops. On the one hand, these solutions contain fewer impurity particles, making them less prone to membrane pore blockage and easier to filter. Therefore, enterprises demand higher flux while ensuring sterilization effectiveness, especially for filtering large volumes of solutions, requiring higher production efficiency. While the aforementioned asymmetric membranes, through their gradient structure design between macropore and micropore regions, balance contaminant carrying capacity and retention accuracy to some extent, their overall flux is still limited by the inherent pore size of the micropore region, making further breakthroughs difficult. On the other hand, the filtration of such low-turbidity, large-volume liquids usually requires extremely high sterilization reliability. For example, even for liquids containing the same concentration of bacteria, the large volume of filtration requires the filter membrane to have a higher bacterial loading capacity. However, even if the filter membrane can achieve extremely high flux, a significant carryover effect will occur under ultra-high flux, posing a risk of bacterial penetration of the membrane layer. Although the aforementioned asymmetric membrane can achieve a high retention capacity, it still has the potential for bacterial leakage under high flux conditions.

[0006] In summary, it is difficult to achieve both high throughput and high retention capacity simultaneously, especially when filtering large volumes of low-turbidity liquids. How to obtain a filter membrane with ultra-high throughput and high retention capacity remains a core challenge in current filter membrane design. Summary of the Invention

[0007] This application provides a PES sterilization filter membrane with excellent bacterial loading capacity. It can exhibit high sterilization performance when filtering large volumes of low-turbidity liquids, while maintaining ultra-high flux performance. This application also provides a method for preparing the filter membrane.

[0008] In a first aspect, this application provides a PES sterilization filter membrane, including an inlet surface, an outlet surface, and a microporous body bounded by the inlet surface and the outlet surface. The microporous body is composed of a network fiber structure, and the pores of the network fiber structure constitute filter pores within the microporous body. The filter pores are interconnected to form a tortuous path, and the tortuous path connects the inlet surface and the outlet surface. The microporous body is composed of n sieve layers, where the number of sieve layers n is between 100 and 400, and n is obtained by the following formula: Where H is the thickness of the microporous body, in μm. The average pore size of the microporous body is expressed in μm. The average fiber width of the microporous body is expressed in μm, wherein the average pore diameter is... X1, X2, and X3 are the arithmetic mean of X1, X2, and X3. The cross-section of the microporous body is divided into three continuous regions of equal thickness along the thickness direction, and the microstructure of these three continuous regions is characterized. The average pore diameters X1, X2, and X3 of each region are measured, and the average fiber width is... The arithmetic mean of the average fiber widths D1, D2, and D3 of the three consecutive regions; The average pore size of the microporous body The thickness is 0.3-1 μm; The microporous body has a symmetrical structure, which means that the coefficient of variation C of the fiber width in the three continuous regions of the microporous body is less than 0.15.

[0009] As mentioned above, the specific problem this application aims to solve is the contradiction between retention capacity and flux when filtering large-volume, low-turbidity liquids with high bacterial loads. This is because, when the microbial contamination level of the liquid is the same, a larger filtration volume means a higher bacterial load on the filter membrane, while higher retention capacity often means lower bacterial load and lower flux. When filtering such liquids, due to the relatively low amount of impurities, the degree of membrane fouling is not severe during filtration, and the flux decline is not significant. Therefore, membrane fouling is no longer the primary factor limiting flux; the filtration process is more limited by the permeation resistance of the filter membrane itself. More importantly, filtering large-volume liquids places more stringent requirements on the bacterial load capacity of the filter membrane (i.e., the total amount of bacteria that can be retained per unit area of ​​the filter membrane). For example, the internationally accepted guidance document PDA TR26 and the internationally accepted standard document ASTM F838-20 for the bacterial retention performance of membrane filters for liquid filtration both require a challenge level of not less than 10 for the sterilizing membrane. 7 cfu / cm 2 The defective Pseudomonas aeruginosa (ATCC 19146) can be used to obtain sterile filtrate. However, when the microbial contamination level of the feed solution is similar, the concentration of microorganisms in the feed solution is similar. When the feed solution volume is large, it will pose a higher challenge to the filter membrane in terms of microbial load, which naturally puts forward higher requirements for the bacterial loading capacity of the filter membrane.

[0010] However, the inventors of this application discovered in their research that for filtering large-volume, low-turbidity liquids, conventional V-type asymmetric membranes exhibit a phenomenon of "decreasing retention with increasing filtration volume." This may be because the aforementioned liquids contain relatively few impurities, and the main retained substances are small microorganisms such as bacteria. The retention function is highly dependent on the small pore area, which has a relatively small thickness, while the large pore area only provides mechanical support (the pre-filtration function of the large pore area is relatively limited). Initially, bacteria are mainly retained in the small pore area. However, due to the limited contaminant-holding capacity of the small pore area, as the filtration volume increases, this area gradually becomes filled and blocked by bacteria, preferentially blocking the smaller pores in that area. Once the smaller pores are blocked, the flow path of the liquid changes, flowing out through the remaining larger pores within the small pore area. Since these larger pores already have a weaker retention capacity for bacteria, they become "leakage channels" for bacteria under high load conditions, causing the overall retention capacity of the filter membrane to decrease significantly with increasing filtration volume (LRV decay). This is an inherent weakness of V-type asymmetric membranes under this specific operating condition. Although increasing the thickness of the pore area or decreasing the pore size of the pore area can alleviate the above phenomenon to some extent, this will increase the permeation resistance of the filter membrane itself, leading to a further reduction in flux (not only does the initial flux decrease, but the flux decay also accelerates due to the reduced dirt-holding space in the pore area after the pore size is reduced, and the flux at the process endpoint also decreases).

[0011] The inventors of this application have discovered that the above-mentioned problems can be effectively improved by using a roughly symmetrical membrane structure (i.e., the coefficient of variation of fiber width C in the three continuous regions of the pore body is <0.15), combined with a specific pore size (0.3-1μm) and a sufficient number of sieve layers (n=100-400). The filter membrane consists of hundreds of sieve layers along its entire thickness, and the feed liquid is sieved once each time it flows through a sieve layer. Although the retention capacity of a single-layer sieve is very low (because the average pore size of a single-layer sieve is larger than the size of bacteria, making it difficult to efficiently retain bacteria through size sieving), the symmetrical membrane has a network of fiber structures and a three-dimensional interconnected filtration pore network formed by the fiber structures. These filtration pores are not completely aligned in the thickness direction (i.e., the direction of liquid flow), but are stacked in an alternating manner (for example, some of the upper filtration pores may be connected to the lower filtration pores, while the rest correspond to the lower fiber structure). Through mechanisms such as inertial impaction and bacterial deposition in the groove structure, bacteria can be retained at the stacked junctions of the filtration pores and in the network of fiber structures on the pore walls. Therefore, after hundreds of continuous sievings, the cumulative retention probability is significantly improved, and the entire membrane can still reliably meet the sterilization requirements.

[0012] More importantly, the retention behavior differs significantly from conventional V-shaped asymmetric membranes. Because a single sieve layer retains only a very small amount of bacteria, as filtration continues, the retained bacteria are not concentrated in a single thin layer, but rather distributed and deposited roughly evenly over a larger area of ​​the membrane. Retention is achieved through the staggered stacking of pores. While the small pores in the sieve layer have a higher retention potential, the medium and large pore structures also possess a certain retention capacity. Bacteria are also relatively evenly distributed and deposited within the sieve layer. Therefore, as bacteria gradually deposit on the pore walls, the effective pore size of the entire membrane also gradually decreases—and this reduced pore size further enhances the retention capacity of each layer. Furthermore, since there are at least 100 sieve layers, redundant sieve layer structures exist downstream of the filter membrane to prevent bacterial leakage. This creates a positive feedback loop: continuous filtration → uniform bacterial deposition → gradual reduction in overall pore size → increased single-layer retention capacity → more reliable retention. In other words, contrary to the trend of "the more you filter, the worse the retention becomes" of V-type asymmetric membranes, the symmetric multilayer membrane of this application shows the result of "the more you filter, the better the retention becomes" when filtering large volumes of low-turbidity liquids.

[0013] It must be pointed out that the aforementioned effects of the filter membrane in this application are not universally applicable to most operating conditions. The inventors of this application discovered during testing that when this symmetrical membrane is used to filter high-turbidity liquids (containing a large number of impurity particles of different sizes, such as the complex TSB culture medium), the performance is the opposite: because the symmetrical membrane has similar pore sizes throughout, impurities of different sizes are concentrated and trapped near the inlet surface, quickly forming a filter cake layer and causing blockage. Its loading capacity is far lower than that of the V-type asymmetric membrane with staged retention capabilities. Therefore, the solution in this application is specifically designed for the specific operating condition of "low turbidity and large volume," and is not superior to asymmetric membranes in all scenarios.

[0014] In terms of flux, the symmetrical membrane in this application has a large filtration pore size (average pore size of 0.3-1 μm) and the number of sieve layers is not excessively redundant, not exceeding 400 layers. Therefore, the filtration resistance of the membrane itself is greatly reduced. Combined with the low-pollution characteristics of the low-turbidity feed liquid, high flux performance is achieved.

[0015] It should be noted that achieving the above-mentioned effects requires a coordinated relationship between the pore size and the number of sieve layers in the symmetrical membrane: If the pore size is too large, the retention probability of a single sieve layer will be too low, especially under high bacterial load conditions, where even hundreds of sieve layers cannot guarantee the overall membrane's retention reliability; if the pore size is too small, the flux advantage will be lost, and an excessively small pore size will increase the single-layer retention, disrupting the uniformly distributed retention pattern, and may even lead to concentrated retention and clogging, as seen in conventional symmetrical membranes. Too few sieve layers result in insufficient cumulative retention, while too many result in an excessively thick membrane, increased resistance, and also affect the filtration flux.

[0016] It should be noted that the "torsional pathway" in this application refers to a network of fibers with irregularly oriented groove structures and / or discretely distributed pore structures, and these structures are interconnected to form a tortuous pathway, so that the feed liquid can penetrate the filter membrane through the interconnected pathways. Bacteria and other impurities in the feed liquid are trapped in the inlet surface of the filter membrane or in the tortuous pathway inside, thereby achieving the effect of filtration and sterilization.

[0017] In this application, the coefficient of variation C of the fiber width in the three continuous regions of the microporous body is less than 0.15, which means that the fiber width of the filter membrane in this application is not much different in the thickness direction. Since PES filter membranes are often prepared by phase separation method, the formation of fiber entity and pore structure in the membrane preparation process is synchronous. This indicates that the structure of each region of the filter membrane in this application is relatively consistent (both the pore size and fiber size are relatively similar), that is, the filter membrane in this application is a basically symmetrical membrane.

[0018] Unless otherwise specified, the numerical ranges in this application include endpoint values.

[0019] In this application, the average pore size of the microporous body Average fiber width of the microporous body The coefficient of variation (C) of the fiber width in the three continuous regions of the microporous body is measured as follows: The cross-section of the PES filter membrane is characterized using a scanning electron microscope or other microscopic observation equipment (enough to encompass the entire cross-section). Along the thickness direction of the microporous body, its cross-section is divided into three continuous regions of equal thickness, denoted as region D1, region D2, and region D3. Feature points are selected in the aforementioned electron microscope images. Appropriate magnifications are selected for each of the three regions (enough to clearly show the pore edges and fiber edges), finally obtaining three high-magnification electron microscope images. The average pore size and fiber width in the three high-magnification electron microscope images are measured respectively. Taking region D1 as an example: Import the high-magnification electron microscope image of region D1 into Nano Measure software. Randomly select a filter aperture and draw four intersecting line segments on it. The intersection of these four line segments is the approximate geometric center of the filter aperture. The start and end points of the line segments are the intersection points with the edge of the filter aperture. The included angle between any two adjacent line segments is approximately 45°, so that the filter aperture is approximately divided equally by the four line segments. Measure the lengths of the four line segments and denote them as L1, L2, L3, and L4, respectively. Calculate the average value of L1, L2, L3, and L4. This average This is the radial dimension of the filter pore. Measure the radial dimensions of at least 50 filter pores randomly in the same manner (measure all filter pores within a certain field of view if possible), and then calculate the average radial dimension of these at least 50 filter pores. This average value is the average pore diameter X1 of region D1. Following this method, measure the average pore diameters X2 and X3 of regions D2 and D3. The arithmetic mean of X1, X2, and X3 is the average pore diameter of the microporous body. .

[0020] Import the high-magnification electron microscope image of region D1 into Nano Measure software. Randomly select fibers and measure their width. Repeat this process to randomly measure the width of 50 fibers. Calculate the average width of these 50 fibers, which is the average fiber width D1 of region D1. Similarly, measure the average fiber widths D2 and D3 of regions D2 and D3. The arithmetic mean of D1, D2, and D3 is the average fiber width of the microporous matrix. .

[0021] Based on the data measured above, using the formula The coefficient of variation C of the fiber width in the three continuous regions of the microporous body can be obtained.

[0022] It should be noted that when measuring the pore size of the filter, a large number of fibers are broken in the cross-sectional electron microscope image due to sample preparation. The broken fibers cannot be combined to form a complete pore structure. Therefore, in this application, the filter pore with a complete outline is mainly measured.

[0023] Optionally, the number n of the sieve layers is related to the average pore size of the microporous body. The ratio is 190-600μm -1 .

[0024] It is understandable that the relationship between the number of sieve layers and the aperture in the above scheme is achieved through n / The ratio is further limited to 190-600 μm. In this symmetrical multilayer system, increasing the pore size leads to a decrease in the retention probability of a single sieve layer, requiring a higher number of sieve layers to compensate. Conversely, decreasing the pore size increases the retention capacity of the sieve layers, which can be used in conjunction with a reduced number of sieve layers to avoid excessive filtration resistance. (The last part, "n / ", appears to be an incomplete sentence or a fragment and is left untranslated.) Maintaining a flexible adjustment within the 190-600μm range ensures the reliability of the overall membrane's retention capacity and guarantees good flux performance. If the ratio is too low, it means the number of sieve layers is insufficient to match the increase in pore size, increasing the risk of bacterial leakage; if the ratio is too high, it means the membrane is too thick, weakening flux performance.

[0025] Optionally, the average fiber solidity of the sieve layer is 25%-55%.

[0026] By adopting the above technical solution, as mentioned earlier, the staggered stacking of membrane pores and fiber structures in the thickness direction is an important factor affecting the retention capacity of the filter membrane. The average fiber solid ratio of the sieve layer is controlled at 25%-55%. The fiber solid ratio refers to the area ratio of fiber solids in each sieve layer, which directly affects the retention and dirt-holding capacity of each sieve layer. The smaller the average fiber solid ratio, the smaller the fiber area ratio and the larger the pore area ratio, the larger the dirt-holding space, but the worse the retention capacity of each sieve layer.

[0027] This application controls the average fiber solidity rate within the range of 25% to 55%, ensuring that each layer has sufficient dirt-holding space to accommodate a small amount of deposited bacteria and maintaining low filtration resistance in each layer. Simultaneously, it retains enough fiber solidity to cooperate with adjacent sieve layers to guarantee retention function, further achieving the effect of "moderate single-layer retention and multi-layer synergistic accumulation." This promotes uniform distribution of bacteria along the membrane thickness direction and ensures the overall membrane's cumulative retention reliability and sterilization performance while maintaining low filtration resistance. If the average fiber solidity rate is too high (>55%), the dirt-holding space is insufficient, and a single layer will saturate prematurely, forming a concentrated clogging pattern similar to traditional symmetrical membranes. Furthermore, the pore area ratio of a single layer is too small, resulting in excessive filtration resistance and affecting flux performance. If the average fiber solidity rate is too low (<25%), the pore connectivity between adjacent sieve layers increases, and the fiber surface is insufficient to provide reliable retention sites. The retention capacity of a single layer is too low, making it difficult to ensure the overall membrane's sterilization effect even with multiple layers stacked.

[0028] The average fiber solidity of the sieve layer is tested by characterizing the cross-section of the filter membrane using a scanning electron microscope or other microscopic observation equipment. An appropriate magnification is selected (enough to clearly show the edges of the fiber structure and pores) to obtain an electron microscope image. A straight line is drawn along the membrane surface direction (i.e., perpendicular to the thickness direction of the filter membrane) on the obtained electron microscope image. The total length of the line is recorded, and the total length of all fibers covering the line is calculated. The ratio of the total length of all fibers to the total length of the line is the fiber solidity percentage Z1 on that line. The thickness is then measured at intervals... + Draw another straight line at the distance, and measure the fiber solid percentage Z2 on the line. The average of Z1 and Z2 is the fiber solid percentage of one sieve layer. Measure the fiber solid percentage of at least 5 sieve layers according to the aforementioned method. The average of the fiber solid percentages of the 5 sieve layers is the average fiber solid percentage of the sieve layer.

[0029] Optionally, the average fiber width of the microporous body The average fiber width of the microporous body is 0.15-0.35 μm. The average pore size of the microporous body The ratio is 0.25-0.45.

[0030] Understandably, control / To control the simultaneous change of both. Since the average pore size (0.3-1 μm) of this application is larger than the pore size of conventional asymmetric sterilization membranes, in such a macroporous structure, if the fibers are too fine, the membrane is prone to pore collapse under filtration pressure differential, leading to a sharp drop in flux and retention failure. Therefore, in the macroporous system of this application, it is necessary to use coarser fibers (…). The pore size (≥0.15μm) provides reliable mechanical support for these large pores, maintaining the stability of the three-dimensional network structure. The larger the pore size, the coarser the fiber. At the same time, the coarser fiber also provides a larger retention area, partially compensating for the influence of large pores on the retention probability of a single layer. However, the fiber cannot be too coarse (the ratio between the two should not exceed 0.45) to avoid the fiber being too coarse and occupying too much flow space, increasing the filtration resistance and affecting the flux performance of the filter membrane.

[0031] Optionally, the pore size in the filter is less than 0.7 mm. The main retention holes account for 20%-40% of the total number of micropores.

[0032] By adopting the above technical solution, the proportion of main retention pores is controlled within the range of 20% to 40%. Main retention pores are the small pore structures in each sieve layer that primarily perform bacterial retention. In conventional membrane structures, because 20% to 40% of the pores are insufficient to cover all flow channels, a large amount of feed liquid will bypass these high-resistance pores and tend to flow through the lower-resistance large pores, resulting in poor retention capacity. However, in the sieve layer structure of n=100 to 400 layers in this application, because the 20% to 40% of main retention pores in each layer are randomly distributed, bacteria inevitably encounter the main retention pores repeatedly during layer-by-layer flow and are retained in conjunction with the fiber structure, significantly increasing the cumulative retention probability and meeting the requirements of high bacterial load during large-volume feed filtration. Simultaneously, the 60% to 80% relatively large pore area ensures the total flow area of ​​each layer, and the flux loss caused by the stacking of hundreds of sieve layers is greatly reduced, further ensuring a balance between overall membrane retention capacity and flux.

[0033] The method for measuring the proportion of main retention pores in the microporous body is as follows: referring to the above, use Nano Measure software to measure the radial dimension of at least 50 filter pores, and count those with a radial dimension less than 0.7. The number of filter pores can be used to calculate the proportion of main retention pores in the microporous body.

[0034] Optionally, the average shape factor of the filter pores Less than 0.25.

[0035] Understandably, the average shape factor The smaller the shape factor, the closer the cross-sectional shape of the filter pores is to a regular circle. Compared to irregular pores, such as elongated or irregularly shaped pores, stress concentration occurs at the ends and sharp corners. Even under normal filtration pressure differential, these areas will preferentially deform, leading to a chain reaction of collapse. Circular pores, on the other hand, distribute pressure evenly along the circumference of the pore wall, with no obvious stress concentration points. Even with a larger pore size, structural instability is less likely to occur. Therefore, controlling the average shape factor of the filter pores to below 0.25 helps ensure the pressure resistance of the filter membrane. Furthermore, considering the overall uniformity and balanced stress characteristics of the symmetrical membrane structure of this application, coupled with the high purity of the treated liquid and the relatively mild filtration pressure, even with a large pore size, the filter membrane of this application still exhibits good pressure resistance and structural stability.

[0036] In addition, the circular pores have a consistent diameter in all directions, eliminating the problem of directional bacterial leakage that may occur with narrow pores along their long axis. This results in more precise retention and further enhances the sterilization reliability of the filter membrane.

[0037] Average shape factor of filter pores The measurement method is as described above: using Nano Measure software, measure the dimensions L1, L2, L3, and L4 in the four radial directions of each filter pore, and calculate the average value of L1, L2, L3, and L4. The radial dimension of this filter hole is obtained through the formula... Calculate the shape factor M of the filter aperture. Using this method, calculate the shape factors M of at least 50 filter apertures. The arithmetic mean of these at least 50 shape factors M is the average shape factor of the filter aperture. .

[0038] Optionally, the fibers on the liquid inlet surface are first fibers, the pores between the first fibers form liquid inlet holes, at least a portion of the first fibers have particles protruding from the liquid inlet surface, a plurality of the particles form a particle layer, the pores between the particles form flow channels of the particle layer, the flow channels communicate with the liquid inlet holes, and the porosity of the particle layer is 50%-80%.

[0039] By adopting the above technical solution, a granular layer formed by protruding particles is set on the inlet surface, with an open porosity of 50%~80%. That is, in addition to the microporous main body with the inlet and outlet surfaces as boundaries, the filter membrane also includes a granular layer structure attached to the inlet surface. The large open porosity of the granular layer achieves ultra-low feed resistance. Compared with the inlet skin layer that is prone to appear in conventional PES filter membranes, it further reduces the resistance barrier near the inlet surface and increases the filtration flux. Moreover, the presence of the granular layer distributes the feed liquid quickly and evenly across the entire inlet surface of the membrane with extremely low resistance, so that bacteria are already in a spatially dispersed state when they enter the microporous main body. Furthermore, the granular layer is composed of different particles, and the channel walls are uneven, which disturbs the feed liquid as it passes through, thereby increasing the probability of collision between bacteria and fibers inside the filter membrane. Combined with the hundreds of layers of sieving structure of the microporous main body, the retention capacity and bacterial dispersion uniformity of the filter membrane are further increased, i.e., high bacterial loading effect.

[0040] Optionally, the ratio of the porosity on the particle layer to the area of ​​the inlet holes on the inlet surface is 1.3-3.

[0041] Among them, the porosity on the particle layer refers to The area ratio of the inlet holes on the inlet surface refers to .

[0042] Understandably, the larger the ratio of the two, the greater the porosity on the particle layer is compared to the porosity on the inlet surface. As mentioned above, this helps to reduce resistance and increase the turbulence of the feed liquid, thereby improving the flux and sterilization performance of the filter membrane. However, the ratio of the two should not be too large, lest the particle layer become too permeable and the inlet surface become too dense, causing abrupt changes at the interface (similar to a sudden decrease in pore size), resulting in greater resistance and retention at the inlet surface, which in turn affects the flux and sterilization performance of the filter membrane.

[0043] The porosity of the particle layer and the proportion of the inlet pore area on the inlet surface are measured as follows: The inlet surface of the filter membrane is characterized using a scanning electron microscope or other microscopic observation equipment. An appropriate magnification is selected (enough to make the particle edges clearly visible, such as 5000x, 10000x, etc.) to obtain the corresponding microscopic image. This microscopic image is then imported into ImageJ measurement software for measurement. The specific steps are as follows: ① Open the image and adjust the pixels; Open the image in the image processing software ImageJ, and select Image>Type>8-bit to convert the electron microscope image into an 8-bit grayscale image; ② Set the scale; Use the line tool from the toolbar to draw a straight line within the scale area, making the drawn line the same length as the scale on the electron microscope image. Select Analyze > Set Scale, enter the length of the scale in "Known Distance" (for example, enter 1000), enter the unit in "Unit of length" (for example, enter μm), and select OK; ③ Image binarization; Select Image>Adjust>Threshold... to divide the electron microscope image into thresholds to obtain a binarized image, ensuring that all particles in the image are basically selected and the areas outside the particles are basically not selected; ④ Set measurement parameters; In Analyze>Set Measurements, ensure that the required measurement parameters such as "Area" are checked, and then select OK; ⑤ Data Measurement; In Analyze > Analayze Particles, set “Size (μm^2)” to 0.001-Infinity, set “Show” to “Outlines”, and confirm that the boxes for “Display results”, “Exclude on edges”, and “Include holes” are checked. Select OK, and the area ratio of the particles will be obtained directly in the Summary screen. Subtract the area ratio of the particles from 100% to get the porosity of the particle layer.

[0044] Repeat steps ①-⑤, except that in step ③, ensure that all entities in the image are basically selected, and the area where the hole structure is located is basically not selected; in step ⑤, directly obtain the area ratio of the first fiber on the liquid inlet surface in the Summary screen, and subtract the area ratio of the first fiber on the liquid inlet surface from 100% to get the area ratio of the liquid inlet hole on the liquid inlet surface.

[0045] Secondly, this application provides a method for preparing a sterilizing filter membrane, comprising the following steps: S1. Prepare a casting solution, wherein the casting solution comprises polyethersulfone, a good solvent for casting, and a non-solvent for casting, and the solid content of the casting solution is 5-10 wt%. S2. Casting film: The casting liquid is cast onto the carrier to form a liquid film; S3. Phase separation and solidification: The liquid film is placed in a coagulation bath for phase separation and solidification to obtain a primary film. The coagulation bath contains a good coagulation solvent, a coagulation non-solvent system, and a surfactant. The content of the coagulation non-solvent system in the coagulation bath is 50-65 wt%, and the coagulation non-solvent system contains at least a small molecule alcohol, and the content of the small molecule alcohol in the coagulation non-solvent system is 80-100 wt%, with the remainder being water. The content of the surfactant in the coagulation bath is 0.5-1 wt%. The temperature of the coagulation bath is 40-50°C, and the temperature of the coagulation bath is lower than the temperature of the carrier. S4. Heat treatment: The primary membrane is heat-treated in a water bath for 5-10 minutes to obtain a retreated membrane. The temperature of the water bath is 70-80℃. S5. Post-processing: The reprocessed membrane is at least cleaned and dried to obtain the sterile filter membrane.

[0046] The above method provides a process for preparing the aforementioned symmetrical macroporous PES membrane. Specifically, the coagulation bath is rapidly and synchronously penetrated into the entire thickness direction of the liquid membrane, followed by a slower phase separation rate to allow uniform phase separation and solidification within the liquid membrane, forming a symmetrical membrane. In particular, when preparing the filter membrane, a higher solid content in the casting solution results in more film-forming polymers, tending to form a denser membrane pore structure. Conversely, a lower solid content results in fewer film-forming polymers, making it easier to form a relatively looser membrane pore structure. Therefore, this application achieves the required filtration precision by adjusting the casting solution to have a lower solid content, and by controlling the casting solution to have a lower permeation resistance. Combined with subsequent coagulation bath and heat treatment to control the pore size, the filter membrane exhibits a relatively large pore structure. Here, the solid content refers to the mass ratio of polyethersulfone in the casting solution. The casting solution is then cast onto a carrier to form a liquid membrane, and the final membrane thickness is controlled by controlling the thickness of the cast liquid membrane.

[0047] Subsequently, the liquid membrane is placed in a coagulation bath for phase separation and solidification. By controlling a specific phase separation and solidification process, the core mechanism is "rapid permeation + slow phase separation" to obtain the required basic symmetrical sterilization filter membrane. The proportion of non-solvents in the coagulation bath is relatively low; therefore, the phase separation driving ability of the coagulation bath is relatively weak, avoiding the formation of small-sized pore structures and large permeation resistance to the coagulation bath due to rapid phase separation and solidification of the liquid membrane in the coagulation bath. Furthermore, while the small-molecule alcohol in the coagulation bath, as a non-solvent, can promote phase separation, its driving force for phase separation is less than that of water. Due to its smaller molecular size and lower surface tension, it can promote the penetration of the coagulation bath into the liquid film. The addition of a small amount of surfactant (0.5-1 wt%) to the coagulation bath can further accelerate the penetration rate. Simultaneously, the relatively high temperature of the coagulation bath (40-50℃, but not too high to avoid accelerating the phase separation rate) reduces the viscosity of both the coagulation bath and the liquid film, further increasing the penetration rate. It is understood that the closer to the support, the greater the mass transfer resistance, and the more difficult the coagulation bath becomes. This application addresses this by creating a temperature difference between the coagulation bath and the support (the temperature of the coagulation bath is lower than the temperature of the support), i.e., creating a temperature gradient, so that the temperature is higher closer to the support. This results in a lower viscosity of the liquid film closer to the support, thereby compensating for the difference in mass transfer resistance caused by the extended penetration path and ensuring that the penetration rate is consistent throughout the film thickness direction. In summary, a high proportion of good solvent in the coagulation bath, the primary use of small molecule alcohols as non-solvents (weak non-solvents), and the control of coagulation bath temperature, surfactants, and the temperature difference between the coagulation bath and the carrier ensure a fast and uniform permeation rate in the coagulation bath. Due to the fast permeation rate and weak phase separation driving force, almost no phase separation or very low phase separation occurs throughout the liquid film during permeation. Therefore, phase separation and solidification of the entire liquid film mostly occur after permeation is basically complete, with very little difference in the phase separation initiation points across the entire film. The phase separation process after permeation proceeds slowly, allowing sufficient time for the polyethersulfone molecular chains of the film-forming material to move and aggregate, forming a polymer-rich phase, thereby effectively controlling the fiber width and its uniformity. Simultaneously, solvent and non-solvent molecules can also migrate and aggregate sufficiently, promoting the full growth and uniformity of the pore structure throughout. This results in a macroporous symmetrical membrane with highly consistent pore size and fiber width across the entire membrane thickness.

[0048] Next, the nascent membrane, after phase separation and solidification, is heat-treated in a water bath (specifically, at 70-80°C for 5-10 minutes) to further shrink the pore size formed in the aforementioned process steps. This step is performed because, in order to obtain a more uniform and symmetrical membrane, the aforementioned steps control the solid content of the casting solution to be low and the content of the non-solvent system to be low, resulting in larger membrane pores. Further heat treatment shrinks the pores, ensuring that the final filter membrane has a macropore structure of a suitable size (not too large). Furthermore, by controlling the filter membrane thickness, the number of sieve layers in the filter membrane can be further controlled.

[0049] In summary, this application reduces permeation resistance and increases permeation driving force by controlling the coagulation bath temperature, the temperature difference between the coagulation bath and the carrier, and the coagulation bath system. This ensures that the coagulation bath rapidly penetrates the entire liquid film, weakens the adverse effects of permeation rate differences on the phase separation uniformity within the liquid film, and lays the foundation for the formation of a symmetrical membrane. Furthermore, by using a lower content of the non-solvent system for coagulation and selecting a weak non-solvent small molecule alcohol to control the formation of a relatively slow coagulation phase separation rate, a symmetrical membrane with relatively consistent pore size, fibrous structure, and other structural characteristics is formed.

[0050] Optionally, the liquid film is pretreated before phase separation and solidification. Specifically, the liquid film is transferred to a pretreatment chamber at a temperature of 5-10°C, and saturated vapor of the good solvent of the casting liquid is introduced into the chamber for a pretreatment time of 4-8 seconds.

[0051] It is understandable that steam pretreatment of the liquid film before phase separation and solidification is to form the aforementioned particle layer in situ on the inlet surface. At low temperatures, the good solvent vapor of the casting solution condenses on the air-side surface of the liquid film, causing localized dilution of the liquid film on the air side. This reduces the solid content in localized areas of the liquid film on the air side. For casting solutions with already low solid content, coupled with a coagulation bath system with low phase separation driving force, it is difficult for the air side of the liquid film to form a continuous three-dimensional network structure during subsequent phase separation and solidification. Instead, a looser particle structure forms and adheres to the lower-level fibrous structure. By controlling the pretreatment time and dilution conditions, the degree of dilution of the particle layer can be controlled, thereby controlling the porosity of the particle layer. Due to the low-temperature environment and the pretreatment time of only 4-8 seconds, the liquid film as a whole has a high viscosity. The dilution effect is concentrated on the surface of the liquid film, and the internal composition of the liquid film is unaffected—the main body of the liquid film still forms a symmetrical macroporous structure in the subsequent coagulation bath according to the aforementioned "rapid penetration + slow phase separation" mechanism.

[0052] Optionally, the casting solution further includes a penetrant with a surface tension not exceeding 35 dyne / cm, wherein the content of the penetrant is 10-30 wt%. The temperature difference between the coagulation bath and the carrier is 5-10℃.

[0053] By adopting the above technical solution, a penetrant with a surface tension not exceeding 35 dyne / cm (content 10~30wt%) is added to the casting solution, and a temperature difference of 5~10℃ is maintained between the coagulation bath and the carrier. The role of the penetrant is to reduce the interfacial tension between the casting solution and the coagulation bath, reduce the resistance of the coagulation bath to penetrating into the liquid film, and promote the diffusion rate of the solvent system in the liquid film into the coagulation bath and the penetration rate of the coagulation bath into the liquid film, further ensuring the control mechanism of "rapid penetration + slow phase separation". Furthermore, the carrier temperature is 5~10℃ higher than the coagulation bath temperature, which allows for more precise control of the temperature gradient during the penetration process, avoiding situations where the temperature difference is too large, causing the coagulation bath to penetrate too quickly, resulting in excessively rapid phase separation, or too small, making it difficult to ensure the consistency of the penetration rate.

[0054] Optionally, the good solvent for casting and the good solvent for coagulation are at least one selected from butyl lactate, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-Methylpyrrolidone, N-methylpyrrolidone, tetramethylurea, caprolactam, methyl acetate, ethyl acetate, N-ethylpyrrolidone, dioxane, diethyl succinate, chloroform, and tetrachloroethane. The non-solvent in the casting solution is water; The small molecule alcohol in the solidification non-solvent system is at least one of methanol, ethanol, and isopropanol; The surfactant is at least one selected from Tween 80, Tween 20, sodium dodecyl sulfate, sodium dodecyl sulfonate, hexadecyltrimethylammonium bromide, and hexadecyltrimethylammonium chloride. The penetrant is at least one of isopropanol, ethanol, and ethylene glycol.

[0055] The penetrant itself is actually a non-solvent. Adding not only strong non-solvent water to the casting solution, but also a penetrant (weak non-solvent) can further improve the thermodynamic stability of the casting solution and increase the phase separation threshold.

[0056] Compared with the prior art, this application has the following beneficial technical effects: 1. The symmetrical filter membrane provided in this application has a structure of large pores and multiple sieving layers, which enables the filter membrane to have both high throughput and high bacterial load when filtering large volumes of low turbidity liquid.

[0057] 2. This application achieves further optimized throughput performance and high retention capacity by further adjusting the solid content of the sieve layers and the coordination between the number of sieve layers and the pore size, and by setting a particle layer on the inlet surface.

[0058] 3. By adjusting the shape and distribution of the filter pores, this application can not only bring about further optimized flux performance and high sterilization performance, but also ensure the mechanical properties of the symmetrical filter membrane. Attached Figure Description

[0059] Figure 1 This is a scanning electron microscope schematic diagram of the cross-section of the filter membrane prepared in Example 1, where the magnification is 500×; Figure 2 This is a scanning electron microscope schematic diagram of the cross-section of the filter membrane prepared in Example 1, where the magnification is 5000×; Figure 3 This is a scanning electron microscope schematic diagram of the liquid inlet surface of the filter membrane prepared in Example 1, with a magnification of 5000×. Detailed Implementation

[0060] The present application will be further described below through specific embodiments and comparative examples.

[0061] Example 1 This embodiment discloses a method for preparing a PES sterilization filter membrane, including the following steps: First, the casting solution is prepared, comprising the following components: 7.5 wt% polyethersulfone, 65 wt% dimethylformamide (a good solvent for casting), 12.5 wt% water (a non-solvent for casting), and 15 wt% isopropanol (a penetrant). Then, the casting solution is poured to form a liquid film; Next, the liquid film is pretreated by transferring it to a pretreatment chamber at 7°C for 6 seconds and introducing saturated vapor of a good solvent for casting into the chamber. The liquid film was then placed in a coagulation bath at 45°C for phase separation and solidification to obtain the primary film. The temperature of the coagulation bath was 7°C lower than that of the carrier. The coagulation bath contained the following components: 39.2 wt% of a good coagulation solvent (dimethylformamide), 0.8 wt% of a surfactant (Tween 80), and 60 wt% of a non-solvent system. The non-solvent system consisted of a small molecule alcohol (ethanol) and water, with the small molecule alcohol (ethanol) containing 90 wt% and the water containing 10 wt%. The nascent membrane was then heat-treated in a water bath at 75°C for 7 minutes to obtain the retreated membrane. Finally, the reprocessing membrane is cleaned and dried to obtain the sterile filter membrane.

[0062] Example 2-8 The difference between Examples 2-8 and Example 1 lies in the different process parameters. The specific process parameters are detailed in Table 1. It should be noted that: (1) In Examples 6-7, the liquid membrane was not pretreated before phase separation and solidification when preparing the filter membrane; (2) In Examples 6-7, the good solvent for casting liquid was NN-methylpyrrolidone, the good solvent for coagulation was NN-methylpyrrolidone, the permeabilizer was ethanol, the surfactant was sodium dodecyl sulfate, and the small molecule alcohol was isopropanol. The various components of the other examples are the same as those of Example 1.

[0063] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the filter membrane in Comparative Example 1 is an asymmetric membrane, and the process includes the following steps: First, the casting solution is prepared, which is divided into a first casting solution and a second casting solution. The first casting solution contains the following components: 7 wt% polyethersulfone, 65 wt% dimethylformamide (DMF), and 28 wt% water. The second casting solution contains the following components: 15 wt% polyethersulfone, 65 wt% dimethylformamide (DMF), and 20 wt% water. Then, the first casting liquid and the second casting liquid are poured onto the carrier to form a liquid film, wherein the second casting liquid is poured onto the carrier and the first casting liquid is poured above the second casting liquid. Next, the liquid film is pretreated by transferring it to a pretreatment chamber at 7°C for 6 seconds and introducing saturated vapor of a good solvent for casting into the chamber. The liquid film was then placed in a coagulation bath at 40°C for phase separation and solidification to obtain the primary film. The coagulation bath contained the following components: 25 wt% of a good coagulation solvent (dimethylformamide) and 75 wt% of a non-coagulation solvent (water). Finally, the nascent membrane is cleaned and dried to obtain the sterile filter membrane.

[0064] Comparative Examples 2-5 The difference between Comparative Examples 2-5 and Example 1 lies in the different process parameters. The specific process parameters are detailed in Table 1. All components of Comparative Examples 2-5 are the same as those of Example 1. It should be noted that in Comparative Examples 2-3, the liquid membrane was not pretreated before phase separation and solidification when preparing the filter membrane.

[0065] Table 1. Process parameters of Examples 1-8 and Comparative Examples 2-5 ; 1. Structural Characterization The required data can be obtained by characterizing the membrane structure of the bactericidal filter membranes obtained in each embodiment and comparative example using scanning electron microscopy; the morphological parameters of the membrane structures of Examples 1-8 and Comparative Examples 1-5 are recorded in the following table: Table 2. Morphological parameters of the filter membranes in Examples 1-8 and Comparative Examples 1-5 ; It should be noted that although the membrane preparation process is synchronous, that is, the fiber width and the pore size of the membrane increase synchronously, in Table 2, the filter membrane with a larger fiber width in different embodiments does not necessarily have a larger pore size. This is because in this application, the factors affecting the pore size include not only the phase separation rate, but also the degree of heat treatment and the solid content of the casting solution. Even if filter membranes with the same fiber width are prepared by the same phase separation rate in different embodiments, the pore size of the two filter membranes can be controlled to be different by controlling the degree of shrinkage during heat treatment.

[0066] II. Performance Testing and Performance Data Filtration performance and retention performance tests: The standard for testing the bacterial retention capacity of filter membranes is ASTM F838-20, which requires a minimum bacterial count of 10 CFU / cm² based on the effective filtration area of ​​the filter membrane. 2 A challenge test was conducted on a filter membrane using a suspension of the defective shortwave monoclonal bacteria (ATCC 19146). Considering the potential for higher total microbial loads on large-volume solutions with some microbial contamination, a PBS buffer spiked with bacteria was used as the test solution, with all other test conditions remaining constant. The solution was prepared at approximately 10 CFU / cm³. 2 10 8 CFU / cm 2 10 9 CFU / cm 2 Three bacterial challenge levels were used to test the bacterial retention performance of the filter membrane. By increasing the bacterial challenge level, the high microbial load condition generated when filtering a bulky microbially contaminated feed solution was simulated, and three sets of logarithmic reduction values ​​(LRV) were obtained. LRV = log 10 (Total bacteria count / Permeate bacteria count), LRV>7 means that more than 99.99999% of bacteria are retained, which is considered to have reached the sterilization level. When conducting retention performance testing, the flux data at the beginning of filtration for 10 seconds is taken as the initial flux, and the flux data at the end of filtration is taken as the endpoint flux. (Initial flux - endpoint flux) / initial flux * 100% is the flux decay rate.

[0067] Specifically, the sterilizing filter membranes obtained in the various embodiments or comparative examples are prepared as needle filters with an effective filtration diameter of 47 mm, or the membrane modules are clamped and sealed in a stainless steel filter fixture, using a dead-end filtration method, with a test pressure of 0.03 MPa. For detailed operating procedures, please refer to ASTM F838-20.

[0068] The test data for the antibacterial filter membranes prepared in each embodiment and comparative example are detailed in Table 3.

[0069] Table 3 Performance test data of each antibacterial filter membrane ; It should be noted that in Table 3, 10 CFU / cm³ is used. 2 As a bacterial challenge level, LRV > 7 indicates that no bacteria were detected in the permeate, but at 10 7 CFU / cm 2 An LRV of less than 7 (e.g., 6.3 in Comparative Example 4) at the bacterial challenge level indicates the presence of bacteria in the permeate. A lower LRV indicates a higher concentration of bacteria in the permeate, meaning a greater amount of bacteria have leaked. Similarly, an LRV of 10... 8 CFU / cm 2 As a bacterial challenge level, LRV > 8 indicates that no bacteria were detected in the permeate, but LRV > 10 indicates that no bacteria were detected in the permeate. 8 CFU / cm 2 An LRV of less than 8 (e.g., 7.7 in Example 2) at the bacterial challenge level indicates the presence of bacteria in the permeate. A lower LRV indicates a higher concentration of bacteria in the permeate, meaning more bacteria have leaked. A LRV of 10... 9 CFU / cm 2 As a bacterial challenge level, LRV > 9 indicates that no bacteria were detected in the permeate, but LRV > 10 indicates that no bacteria were detected in the permeate. 9 CFU / cm 2 When the LRV (Level of Permeability) is less than 9 (e.g., 8.3 in Example 2), it means that bacteria are detected in the permeate. The smaller the LRV, the more bacteria are detected in the permeate, i.e., the more bacteria are leaked.

[0070] in conclusion In summary, as shown in Table 3, the bactericidal filter membranes of Examples 1-8 all exhibited higher LRVs at higher bacterial challenge levels. This indicates that the symmetrical membrane of this application has a high bacterial loading capacity. Furthermore, the LRVs of the filter membranes in Examples 1-8 were consistently greater than 7 at all three bacterial challenge levels, demonstrating that the symmetrical membrane of this application also meets the sterilization requirements under high bacterial load conditions. In contrast, the asymmetric membrane in Comparative Example 1, although at 10... 7 CFU / cm 2It can achieve sterilization at the lowest bacterial challenge level, but significant bacterial leakage occurs at higher bacterial challenge levels, even at level 10. 9 CFU / cm 2 When the bacterial challenge level is less than 7, its LRV is less than 7, which cannot meet the industry's sterilization requirements. In addition, as the bacterial challenge level increases, its LRV drops from 7.1 to less than 6.2, indicating that its bacterial loading capacity is limited and it is difficult to meet the high bacterial loading requirements for large-volume liquid filtration.

[0071] Regarding flux performance, the initial flux of the filter membranes obtained in each embodiment and comparative example did not change significantly under the three bacterial challenge levels, but the flux decay rate gradually increased. This is understandable, as the same filter membrane has the same initial flux at the beginning of filtration, but as the amount of challenged bacteria increases, the amount of bacteria retained also increases, and the flux decay rate becomes larger and larger. The filter membranes in Examples 1-8 all had high initial flux, and even at the maximum challenge level (10... 9 CFU / cm 2 When the flux decay rate is less than 35%, it can maintain a high flux performance while ensuring excellent sterilization ability and high bacterial load capacity. This is beneficial to meeting the requirements of manufacturers for ultra-high flux and high bacterial load capacity when filtering large volumes of low-turbidity liquids.

[0072] By comparing the morphology and performance data of Example 1 and Examples 5-7, it can be seen that the filter membrane prepared in Example 1 has a better performance at 10... 8 CFU / cm 2 At a bacterial challenge level of greater than 8, indicating no bacterial leakage and good bacterial load capacity, but at higher levels of 10... 9 CFU / cm 2 Although the LRV was 8.5 at the bacterial challenge level, it was less than 9, indicating bacterial leakage. Further adjustments to the pore size, the number of sieve layers, and the symmetry of the filter membrane not only improved the LRV to 10... 8 CFU / cm 2 When the bacterial challenge level is greater than 8, the bacterial load capacity of the filter membrane can be further improved at higher bacterial challenge levels, especially the filter membrane of Example 7 at 10. 9 CFU / cm 2 No bacterial leakage was observed at the bacterial challenge level (LRV greater than 9). Furthermore, compared with Example 4, Example 8 shows that, with essentially the same pore size and number of sieve layers, the more symmetrical filter membrane has a better bacterial loading capacity.

[0073] Compared with Examples 4 and 7, Example 1 shows that in 10 8 CFU / cm 2At bacterial challenge levels, only the filter membrane of Example 4 showed bacterial leakage, at 10 9 CFU / cm 2 At the bacterial challenge level, the LRV of the filter membrane in Example 1 was less than that in Example 7 and greater than that in Example 4. Under the three bacterial challenge levels, the flux of the filter membrane in Example 1 was greater than that in Example 7 and less than that in Example 4, and the flux decay rate was less than that in Example 7 and greater than that in Example 4. This indicates that both the LRV and flux performance of the filter membrane require the coordinated operation of pore size and the number of sieve layers, rather than relying on the control of a single variable. It will not continuously increase or decrease with the increase of pore size, nor will it continuously increase or decrease with the increase of the number of sieve layers. Instead, it has a better overall effect when both pore size and the number of sieve layers are close to a certain intermediate range, which can ensure both the high bacterial loading capacity of the filter membrane and excellent flux performance.

[0074] Furthermore, comparing Example 3 with Example 2 and Example 6 with Example 5, it can be found that even if the number of sieve layers and the pore size can each be taken to a reasonable value, if the ratio of the two is unbalanced (too large or too small), it will also lead to a decrease in LRV or flux performance. In addition, the lack of a particulate layer in the filter membrane in Example 6 is also a factor that leads to a decrease in flux compared to Example 5.

[0075] The comparison between Comparative Examples 2-5 and Examples 4 and 7 further illustrates the synergistic relationship between the number of sieve layers and the pore size. Neither too large nor too small is suitable. Specifically, comparing Comparative Example 2 with Example 7 shows that even with an increased pore size, too many sieve layers lead to a low initial flux and a high flux decay rate. Conversely, comparing Comparative Example 4 with Example 4 shows that even with a smaller pore size, too few sieve layers result in insufficient overall retention capacity of the filter membrane, such as at 10 CFU / cm². 2 The LRV was 6.3 at the bacterial challenge level, which did not meet the sterilization requirements. Comparing Comparative Example 3 with Example 7, it is clear that even with fewer sieve layers in the filter membrane, excessively small pore sizes can lead to a decrease in initial flux and an increase in flux attenuation rate. Furthermore, compared to Example 4, in Comparative Example 5, even with more sieve layers in the filter membrane, excessively large pore sizes still resulted in bacterial leakage, such as at 10 CFU / cm². 2 The LRV is 6.7 when it is considered a bacterial challenge level, which does not meet the sterilization requirements.

[0076] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A PES antibacterial filter membrane, characterized in that, It includes an inlet surface, an outlet surface, and a microporous body bounded by the inlet surface and the outlet surface. The microporous body is composed of a network fiber structure. The pores of the network fiber structure constitute the filter pores within the microporous body. The filter pores are interconnected to form a tortuous path, which connects the inlet surface and the outlet surface. The microporous body is composed of n sieve layers, where the number of sieve layers n is between 100 and 400, and n is obtained by the following formula: Where H is the thickness of the microporous body, in μm. The average pore size of the microporous body is expressed in μm. The average fiber width of the microporous body is expressed in μm, wherein the average pore diameter is... X1, X2, and X3 are the arithmetic mean of X1, X2, and X3. The cross-section of the microporous body is divided into three continuous regions of equal thickness along the thickness direction, and the microstructure of these three continuous regions is characterized. The average pore diameters X1, X2, and X3 of each region are measured, and the average fiber width is... The arithmetic mean of the average fiber widths D1, D2, and D3 of the three consecutive regions; The average pore size of the microporous body The thickness is 0.3-1 μm; The microporous body has a symmetrical structure, which means that the coefficient of variation C of the fiber width in the three continuous regions of the microporous body is less than 0.

15.

2. The antibacterial filter membrane according to claim 1, characterized in that, The number n of the sieve layers and the average pore size of the microporous body The ratio is 190-600μm -1 .

3. The antibacterial filter membrane according to claim 1, characterized in that, The average fiber solidity of the sieve layer is 25%-55%.

4. The antibacterial filter membrane according to claim 1, characterized in that, The average fiber width of the microporous body The average fiber width of the microporous body is 0.15-0.35 μm. The average pore size of the microporous body The ratio is 0.25-0.

45.

5. The antibacterial filter membrane according to claim 1, characterized in that, The pore size of the filter is less than 0.7 mm. The main retention holes account for 20%-40% of the total number of micropores.

6. The antibacterial filter membrane according to claim 1, characterized in that, The average shape factor of the filter pore Less than 0.

25.

7. The antibacterial filter membrane according to claim 1, characterized in that, The fibers on the liquid inlet surface are first fibers, and the pores between the first fibers form liquid inlet holes. At least a portion of the first fibers have particles protruding from the liquid inlet surface. A plurality of the particles form a particle layer, and the pores between the particles form flow channels in the particle layer. The flow channels are connected to the liquid inlet holes, and the porosity of the particle layer is 50%-80%.

8. The antibacterial filter membrane according to claim 7, characterized in that, The ratio of the porosity on the particle layer to the area of ​​the inlet holes on the inlet surface is 1.3-3.

9. A method for preparing a sterilizing filter membrane as described in any one of claims 1-8, characterized in that, Includes the following steps: S1. Prepare a casting solution, wherein the casting solution comprises polyethersulfone, a good solvent for casting, and a non-solvent for casting, and the solid content of the casting solution is 5-10 wt%. S2. Casting film: The casting liquid is cast onto the carrier to form a liquid film; S3. Phase separation and solidification: The liquid film is placed in a coagulation bath for phase separation and solidification to obtain a primary film. The coagulation bath contains a good coagulation solvent, a coagulation non-solvent system, and a surfactant. The content of the coagulation non-solvent system in the coagulation bath is 50-65 wt%, and the coagulation non-solvent system contains at least a small molecule alcohol, with the content of the small molecule alcohol in the coagulation non-solvent system being 80-100 wt%, and the remainder being water. The content of the surfactant in the coagulation bath is 0.5-1 wt%. The temperature of the coagulation bath is 40-50°C, and the temperature of the coagulation bath is lower than the temperature of the carrier. S4. Heat treatment: The primary membrane is heat-treated in a water bath for 5-10 minutes to obtain a retreated membrane. The temperature of the water bath is 70-80℃. S5. Post-processing: The reprocessed membrane is at least cleaned and dried to obtain the sterile filter membrane.

10. The method for preparing the sterilizing filter membrane according to claim 9, characterized in that, Before phase separation and solidification, the liquid film is pretreated. Specifically, the liquid film is transferred to a pretreatment chamber at a temperature of 5-10°C, and saturated vapor of the good solvent of the casting liquid is introduced into the chamber. The pretreatment time is 4-8 seconds.

11. The method for preparing the sterilizing filter membrane according to claim 9, characterized in that, The casting solution also includes a penetrant with a surface tension not exceeding 35 dyne / cm, and the content of the penetrant is 10-30 wt%; the temperature difference between the coagulation bath and the carrier is 5-10℃.

12. The method for preparing the sterilizing filter membrane according to claim 11, characterized in that, The good solvent for casting and the good solvent for coagulation are at least one selected from butyl lactate, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-N-methylpyrrolidone, N-methylpyrrolidone, tetramethylurea, caprolactam, methyl acetate, ethyl acetate, N-ethylpyrrolidone, dioxane, diethyl succinate, chloroform, and tetrachloroethane; the non-solvent for casting is water. The small molecule alcohol in the solidification non-solvent system is at least one of methanol, ethanol, and isopropanol; The surfactant is at least one selected from Tween 80, Tween 20, sodium dodecyl sulfate, sodium dodecyl sulfonate, hexadecyltrimethylammonium bromide, and hexadecyltrimethylammonium chloride. The penetrant is at least one of isopropanol, ethanol, and ethylene glycol.

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