PVDF sterilization membrane and preparation method thereof

Abstract

The present application relates to a kind of PVDF bacteria-removing membrane and its preparation method, bacteria-removing membrane includes porous body, non-oriented tortuous path has in porous body, one side of porous body is liquid inlet surface, the other side is liquid outlet surface, non-oriented tortuous path has in porous body, the PMI average pore size of bacteria-removing membrane is 0.15-0.4 μm, porosity is 35-75%, density is 0.4-0.8 g / cm 3 ;The crystallinity of bacteria-removing membrane is 30-50% by DSC method;Porous body has cross section fiber for forming porous structure on cross section, cross section fiber is stacked and fused by several granular PVDF particles, the SEM average diameter of cross section fiber is 150-500 nm;Under the action of suitable crystallinity, suitable density (the suitable number and density of cross section fiber and the degree of intensive), the suitable diameter of cross section fiber and suitable porosity, PVDF bacteria-removing membrane has higher retention capacity to bacteria, and has higher mechanical property (tensile strength and breaking elongation rate), has relatively higher flux, meets the demand of practical application.

Description

Technical Field

[0001] This invention relates to the field of antibacterial membrane materials technology, and in particular to a PVDF antibacterial membrane and its preparation method. Background Technology

[0002] In the 1960s, membranes with a pore size of 0.45 μm were considered "sterilization-grade" filtration membranes and were used in the pharmaceutical industry for sterilization filtration. With advancements in technology, a researcher in the United States discovered that a certain microorganism could survive in 10... 4 -10 6 cfu / cm 2 Under certain conditions, a 0.45μm filter membrane can penetrate, causing contamination of the culture medium after "sterilization" filtration. In the early 1980s, a filter membrane based on polyvinylidene fluoride (PVDF) was developed using the ASTM F838 bacterial retention standard method. Because the bubble point value of this membrane was approximately twice that of the traditional 0.45μm "sterilization-grade" membrane, it was named a 0.22μm membrane (sterilization membrane). The industry generally accepted that filter membranes that could pass the ASTM F838 test could be labeled with a pore size of 0.22μm or 0.2μm. However, this 0.22μm did not actually measure the pore size of the filter membrane; a new chapter in sterilization-grade filters had begun.

[0003] Chinese Patent Application No. 2018116400303 (applied by Shanghai Yiming Filtration Technology Co., Ltd.) discloses an ultra-high flux polyvinylidene fluoride microporous stretched membrane and its preparation method. The membrane is prepared using a combination of phase inversion and stretching film-forming processes, and has a pore size of 3-20 μm. This membrane possesses a large flux (in Examples 1-3, the flux of the flat sheet membrane is 50-72 ml / cm²). 2 (min). However, this membrane also has some shortcomings. The pore size of the membrane is too large to be used as a sterilization membrane. Because its pores are relatively large, it cannot guarantee efficient retention of bacteria. In order to ensure efficient retention of bacteria, existing researchers generally adopt various methods to reduce the size of the membrane pores. However, when the overall pore size of the membrane is reduced, the overall flux of the membrane will be significantly reduced (for example, if the membrane pores are reduced to half their original size, the flux may become one-quarter or even lower).

[0004] Chinese Patent Application No. 2008101474917 (applied by Tsinghua University) discloses a method for preparing porous polyvinylidene fluoride (PVDF) membranes. This method uses the tipps method to prepare the PVDF porous membrane. The membrane uses diphenyl carbonate, which has a high flash point (168°C), low volatility during membrane preparation, and can act as a plasticizer for PVDF, improving the elongation and toughness of the PVDF porous membrane, thus resulting in good tensile strength (the tensile strength of the sheet membranes in Examples 1-5 is 5.3-10.1 MPa). Simultaneously, the pore size of the porous membranes (the sheet membranes described in Examples 1-5) is 0.2-0.8 μm, exhibiting a certain ability to retain bacteria. However, the above porous membranes also have certain drawbacks, such as low flux, with the sheet membrane flux being 763-2597 L / (m²). 2 •hr•0.1MPa), i.e. 1.27-4.33ml / (cm 2 (0.1 MPa), the flux of the above porous membrane is less than 5 ml / (cm). 2 The current pressure is 0.1 MPa (min), which cannot meet the needs of practical applications.

[0005] Furthermore, in thermal membrane fabrication, methods to increase the crystallinity of the membrane are often employed to further enhance its tensile strength. It is generally believed that the higher the crystallinity of the membrane, the better its tensile strength. For example, the Journal of Industrial and Engineering Chemistry, 2018, 65:112-119 records that Mun J et al. used a "stretch coating modification" method to produce PVDF filter membranes with high crystallinity, film strength, and high water flux. The results showed that this method could change the crystal form of PVDF from α phase to β phase, increasing the crystallinity of the filter membrane from 53.3% to 78.4%, and improving the water flux, mechanical properties, and antifouling properties of the filter membrane. However, as the crystallinity of the membrane increases, the membrane becomes more brittle. Excessive crystallinity reduces the elongation at break of the membrane, making it unable to meet the needs of various processing. In particular, in the field of sterilization, in order to ensure that the sterilization membrane has a large surface area inside the sterilization filter, the sterilization membrane is usually folded for use. In this case, defects are likely to appear at the folds of the highly crystalline sterilization membrane, which can lead to bacterial leakage.

[0006] In summary, researchers have been seeking to develop a PVDF sterilization membrane that combines high retention capacity, high mechanical strength (high tensile strength and high tensile strength at break), and high throughput. Summary of the Invention

[0007] To address the aforementioned problems, this application aims to provide a PVDF sterilization membrane and a method for preparing the PVDF sterilization membrane. The prepared PVDF sterilization membrane exhibits high bacterial retention capacity, high mechanical properties, and relatively high flux, meeting the needs of practical applications.

[0008] The PVDF antibacterial membrane and its preparation method provided in this application adopt the following technical solution:

[0009] In a first aspect, this application provides a PVDF antibacterial membrane, which adopts the following technical solution:

[0010] A PVDF sterilizing membrane includes a porous body with non-directional tortuous pathways within it. One side of the porous body is a liquid inlet surface, and the other side is a liquid outlet surface. The average pore size (PMI) of the sterilizing membrane is 0.15-0.4 μm, preferably 0.2-0.35 μm, and the porosity is 35-75%, preferably 40-70%. The density of the sterilizing membrane is 0.4-0.8 g / cm³. 3 The preferred value is 0.45-0.75 g / cm³. 3 The crystallinity of the sterilization membrane, as measured by DSC, is 30-50%. The porous body has cross-sectional fibers for forming a porous structure. The cross-sectional fibers are formed by stacking and fusing several granular PVDF particles. The average SEM diameter of the cross-sectional fibers is 150-500 nm, preferably 200-450 nm.

[0011] This invention prepares a sterilizing membrane using a thermal method. The sterilizing membrane does not have any skin structure (dense structure). Each outer surface has a certain fiber structure, and these fibers intertwine to form pores of a certain size. In this invention, the non-directional tortuous pathways refer to irregularly oriented groove structures and / or discretely distributed pore structures, and each non-directional tortuous pathway is interconnected. Such a filter membrane structure helps to improve the membrane's fluid retention efficiency.

[0012] In the main cross-sectional structure of the antibacterial membrane of the present invention, it can be clearly seen that there are several granular objects in the cross-section, which we call PVDF particles (during the thermal film formation process, changes in external conditions, such as temperature and pressure, cause the generation of crystal nuclei, which continue to grow and aggregate to form PVDF particles). Furthermore, some PVDF particles will stack and fuse together to form a "strip-shaped" fiber structure, which we call cross-sectional fibers. The cross-sectional fibers are interconnected to form a porous structure.

[0013] The crystallinity of the PVDF sterilization membrane in this application, measured by DSC, is 30-50% (currently, the main methods for measuring crystallinity include DSC and XRD, and the data from different methods vary considerably). Contrary to conventional understanding (that better membrane crystallinity equates to better tensile strength), this application does not pursue excessively high crystallinity. A suitable crystallinity (30-50%) means that most of the molecular chains of the fibers inside the membrane matrix have arranged into an ordered and compact structure, with relatively suitable intermolecular forces, thus achieving a certain degree of... The tensile strength and elongation at break of the sterilizing membrane are improved. Furthermore, since the sterilizing membrane is used for sterilization, it must first be sterile. Therefore, it needs to be sterilized by high-temperature steam (121-130℃) before use. The suitable crystallinity of the sterilizing membrane also gives it good heat resistance; even under high-temperature steam sterilization, its pores are not easily deformed or collapsed, thus ensuring a relatively high flux in actual use. The density of the sterilizing membrane is 0.4-0.8 g / cm³. 3 A relatively high density means that there are more and denser fibers inside the membrane, which to some extent improves the tensile strength and tensile strength at break of the sterilization membrane. At the same time, the larger and denser fibers form more and more tortuous pathways, which to some extent improves the bacteria retention efficiency of the sterilization membrane. Of course, the density of the sterilization membrane cannot be too high; if the density is too high (greater than 0.8 g / cm³), it will be considered insufficient. 3 This, to some extent, means that the pathways within the porous matrix are too tortuous, which can actually reduce the flux of the filter membrane. The cross-sectional fibers also possess a suitable SEM average diameter, resulting in higher tensile strength and relatively higher flux for the overall membrane. If the SEM average diameter of the cross-sectional fibers is too small (too fine), the tensile strength and elongation at break of the sterilizing membrane will be low. If the SEM average diameter of the cross-sectional fibers is too large (too coarse), the coarse fibers will obstruct the feed liquid, thus reducing the flux of the sterilizing membrane. Simultaneously, the cross-sectional fibers, with their suitable SEM average diameter, have a relatively low effective specific surface area, which can also reduce the overall protein adsorption rate of the sterilizing membrane to some extent, thereby increasing the overall protein yield of the sterilizing membrane.

[0014] When the crystallinity of the sterilizing membrane is 30-50%, it has a high overall density of 0.4-0.8 g / cm³. 3 (The membrane body contains a large number of dense fibers) and, in synergy with the membrane's internal fibers of suitable cross-sectional size, with an average SEM diameter of 150-500nm, the antibacterial membrane exhibits excellent tensile strength, tensile strength at break, and high bacterial retention capacity, which is unexpected.

[0015] Furthermore, the porosity of the PES sterilization membrane in this application is 35-75%. If the porosity is too low (less than 35%), it means that there is too much solid part inside the membrane, resulting in low flux of the sterilization membrane. If the porosity is too high (greater than 75%), the tensile strength of the sterilization membrane is low. The relatively high porosity and suitable PMI average pore size (0.15-0.4 μm) in this application combine to give the sterilization membrane good overall flux. Simultaneously, the sterilization membrane has a suitable density (0.4-0.8 g / cm³). 3 The membrane has a large number of fibers, which are relatively dense. The combination of a suitable average pore size of PMI and the overall tortuous pathway of the membrane results in high bacterial retention performance.

[0016] It is understood that the morphological parameters of the cross-section of the bactericidal membrane in this application can be measured by characterizing the membrane structure using a scanning electron microscope, followed by measurement using computer software (such as Matlab, NIS-Elements, etc.) or manually, and then performing corresponding calculations. During membrane fabrication, 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) is considered. When measuring the diameter of the cross-sectional fibers, the membrane cross-section can first be characterized 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 cross-sectional fibers in this area, and then calculate the average value to obtain the average diameter of the cross-sectional fibers. 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.

[0017] The density of the antibacterial membrane, as used in this invention, refers to a measure of mass within a specific volume, and a specific area, such as 100 cm², is selected. 2 (10cm x 10cm) or 400cm 2 (20cm x 20cm), the specific area size depends on the actual situation. Then measure the mass and thickness of the membrane within that area. Density equals the mass of the membrane divided by the area of ​​the membrane, then divided by the thickness of the membrane. The unit can be g / m³. 3 or kg / m 3 The porosity of a sterilizing membrane refers to the proportion of the membrane pore volume to the total volume. Membrane pores include open pores and closed pores. Commonly used porosity testing methods include mercury intrusion porosimetry, density method, and wet-dry membrane weighing method. This application uses the wet-dry membrane weighing method for measurement. Of course, those skilled in the art can obtain the above parameters through other measurement methods, and the above measurement methods are for reference only.

[0018] The average pore size (PMI) of the sterilizing membrane can be directly measured using a PMI pore size analyzer. The crystallinity of the sterilizing membrane can be directly measured using a DSC analyzer.

[0019] Optionally, the SEM average diameter of the PVDF particles is 80-350 nm, preferably 100-300 nm.

[0020] By adopting the above technical solution, the diameter of PVDF particles can reflect the thickness of the cross-sectional fibers to a certain extent. The average diameter of PVDF is 80-350 nm. If the particle size of PVDF is too small, the resulting retained fibers will be relatively fine, and the overall tensile strength of the membrane will be too low. If the particle size of PVDF is too large, the resulting retained fibers will be relatively coarse. During filtration, the coarser fibers may obstruct the feed liquid, resulting in a low membrane flux. Furthermore, if some PVDF particles have a diameter that is too large and some have a diameter that is too small, the resulting retained fibers will be uneven in thickness, which will also easily lead to a decrease in the tensile strength and flux of the membrane.

[0021] PVDF particles possess a suitable particle size, ensuring that the retained fibers have an appropriate diameter (neither too coarse nor too fine) and that the fiber thickness is more uniform. Furthermore, the overall membrane exhibits a suitable density, ranging from 0.4 to 0.8 g / cm³. 3 Furthermore, the membrane as a whole possesses a suitable degree of crystallinity, with a crystallinity of 30-50%. Under the synergistic effect of these factors, the antibacterial membrane exhibits excellent tensile strength, tensile strength at break, and relatively high flux.

[0022] The particle size of PVDF particles can be obtained by using a scanning electron microscope to characterize the morphology of the membrane structure, measuring the particle size of all PVDF particles on that area, and then calculating the average particle size of the PVDF particles.

[0023] Optionally, the ratio between the SEM average diameter of the cross-sectional fiber and the PMI average pore size of the sterilization membrane is 0.4-3 nm / nm; the average SEM length of the cross-sectional fiber is 600-2000 nm.

[0024] There should be a suitable ratio between the average diameter of the cross-section fibers and the average pore size (PMI) of the sterilizing membrane. If the ratio is too small, the cross-section fibers will be too fine and / or the average PMI pore size will be too large. If the cross-section fibers are too fine, the overall tensile strength of the sterilizing membrane will be low. If the average PMI pore size is too large, it will also reduce the retention performance of the sterilizing membrane to some extent. At the same time, excessively fine cross-section fibers may not be able to provide effective support for the pores inside the sterilizing membrane. If a sudden situation occurs during filtration, such as a sudden power outage and immediate restoration, the instantaneous flow rate of the feed liquid will suddenly increase, and the internal pore structure of the sterilizing membrane may collapse. If the ratio is too large, the cross-section fibers will be too coarse and / or the average PMI pore size will be too small. If the cross-section fibers are too coarse, the resistance of the sterilizing membrane to the feed liquid will be too great, which will also reduce the flow rate of the sterilizing membrane to some extent. Although the average PMI pore size can increase the retention capacity of the sterilizing membrane to some extent, it will also reduce the flow rate of the sterilizing membrane.

[0025] In addition to having a suitable thickness (diameter), the cross-sectional fiber also has a suitable length, that is, the cross-sectional fiber as a whole has a suitable length-to-diameter ratio. If the cross-sectional fiber is too long, it is easy for the cross-sectional fiber to break during the fluid filtration process, which will affect the retention efficiency. If the cross-sectional fiber is too short, it means to some extent that the cross-sectional fiber is too thick, and the resistance of the fluid passing through the filter membrane will increase greatly, which will reduce the flux of the filter membrane.

[0026] The cross-sectional fibers have suitable thickness, suitable length, and suitable density and crystallinity. Under the synergistic effect of these four factors, the filter membrane further possesses excellent tensile strength, tensile strength at break, and relatively suitable flux.

[0027] The average length of the cross-sectional fibers can be obtained by characterizing the morphology of the membrane structure using a scanning electron microscope, selecting a certain area, measuring the length of all cross-sectional fibers in that area, and then calculating the average length of the cross-sectional fibers.

[0028] Optionally, some of the PVDF particles are stacked and fused together to form irregularly shaped support blocks, the SEM average area of ​​which is 0.5-2 μm. 2 .

[0029] In the main cross-sectional structure of the sterilizing membrane of this invention, it can be clearly seen that, unlike the "strip-shaped" fiber structure, there are also several "block-shaped irregular" structures in the cross-section, which we call support blocks. These support blocks exist in small quantities within the porous main body. The small number of evenly distributed support blocks significantly reinforce the porous main body, further improving the tensile strength and elongation at break of the sterilizing membrane. The support blocks have a suitable area (average area of ​​0.5-2 μm²). 2If the area is too small, it will not be able to reinforce the porous body; if the area is too large, it may block the pores and flow channels in the porous body, thereby reducing the flux of the sterilization membrane.

[0030] The average area of ​​the support blocks can be obtained by characterizing the morphology of the membrane structure using a scanning electron microscope, selecting a certain area, measuring the area of ​​all support blocks on that area, and then calculating the average area of ​​the support blocks.

[0031] Optionally, the pore area ratio of the liquid inlet surface is less than the porosity of the sterilization membrane, and the difference between the pore area ratio of the liquid inlet surface and the porosity of the sterilization membrane is 5-20%; the pore area ratio of the liquid outlet surface is greater than the pore area ratio of the liquid inlet surface but less than the porosity of the sterilization membrane.

[0032] The sterilizing membrane of this application possesses a suitable porosity, enabling it to achieve a high flux. Simultaneously, a suitable difference (5-20%) exists between the porosity of the sterilizing membrane and the pore area ratio of the inlet surface. This ensures a suitable flow rate and flow path for the feed liquid when it instantaneously enters the membrane, further enhancing the overall flux of the sterilizing membrane. If the difference is too small, a large amount of feed liquid instantaneously flows into the inlet surface, easily causing blockage and collisions within the flow path, increasing the flow resistance within the sterilizing membrane, and thus reducing its flux. If the difference is too large, a smaller amount of feed liquid instantaneously enters the inlet surface, while there are more flow paths within the membrane, resulting in relatively greater resistance to the feed liquid and a decrease in the flux of the sterilizing membrane. The liquid inlet and liquid outlet surfaces have a suitable pore area ratio, which means that the liquid inlet and liquid outlet surfaces have a suitable solid part, so that the porous body near the liquid inlet and liquid outlet surfaces has high tensile strength and tensile strength at break, that is, the sterilization membrane as a whole has high tensile strength and tensile strength at break.

[0033] Optionally, the solid portion of the liquid inlet surface has a plurality of reinforcing nodes, the reinforcing nodes having a granular structure, and some adjacent reinforcing nodes being connected by a first surface fiber; the SEM average diameter of the reinforcing nodes is 250-750nm, preferably 300-700nm, and the SEM average diameter of the first surface fiber is 100-500nm, preferably 150-450nm.

[0034] The inlet surface of the sterilization membrane is distributed with reinforcing nodes of appropriate particle size. Some adjacent reinforcing nodes are connected by first surface fibers, and there are certain gaps between adjacent first fibers to allow fluid to pass through. Therefore, the reinforcing nodes can be considered as relatively dense areas with low porosity on the inlet surface of the membrane. Since the reinforcing nodes are relatively coarse, their presence can improve the overall tensile strength of the membrane, as well as the overall pressure resistance of the membrane, especially ensuring the stability of the membrane pore structure at the inlet surface, making it less prone to collapse or deformation.

[0035] The reinforcing nodes should have a suitable particle size (250-750nm). If the particle size is too small, it will not provide sufficient reinforcement, resulting in low overall tensile strength of the sterilization membrane. If the particle size is too large, it may block the pores near the inlet surface, increasing the resistance of the fluid passing through the filter membrane and making the overall porosity of the membrane too small, thus resulting in low overall flux of the sterilization membrane. The first surface fibers should have a suitable average diameter (100-500nm). If the first surface fibers are too fine, they are prone to breakage when a large amount of fluid passes through the inlet surface, thus failing to provide stable sterilization filtration and resulting in low overall mechanical properties of the sterilization membrane. If the first surface fibers are too coarse, the porosity of the membrane inlet surface and even the whole membrane will be too low, resulting in low overall flux, excessive pressure loss, high energy consumption, and low economic efficiency.

[0036] In this invention, the reinforcing nodes and the first surface fibers both have suitable average diameters; at the same time, the sterilization membrane has suitable density and crystallinity, and the sterilization membrane has cross-sectional fibers of suitable length and thickness. Under the synergistic effect of these features, the sterilization membrane as a whole has excellent tensile strength and relatively high flux.

[0037] Furthermore, the inlet surface is the first area within the membrane to directly bear the pressure of the feed liquid. Under certain special operating conditions, such as a sudden power outage followed by immediate restoration, the instantaneous pressure of the feed liquid will change abruptly, and the inlet surface will be subjected to more feed liquid impacts. This necessitates that the inlet surface possess higher pressure resistance. The presence of reinforcing nodes ensures the wide application range of this sterilization membrane. Under certain special circumstances, the membrane pores will not change, ensuring that the sterilization membrane can stably and efficiently retain bacteria for a long time. In addition, the inlet surface possesses higher pressure resistance, meaning that the inlet side of the sterilization membrane can withstand higher pressure, thereby increasing the pressure difference between the inlet and outlet sides of the sterilization membrane. This allows for the application of greater pressure, further increasing the filtration rate of the sterilization membrane, i.e., further increasing the flux of the sterilization membrane, and thus also improving the economic efficiency of the sterilization membrane per unit time.

[0038] In practical use, the sterilization membrane in a sterilization filter is usually folded. Compared to the non-folded areas, the folded areas of the sterilization membrane are more prone to breakage, leading to a relatively higher probability of bacterial leakage. This may be because, under higher pressure, the folded areas of the sterilization membrane have more potential points for excessive deformation / structural collapse. However, the PVDF sterilization membrane provided by this invention can reduce the probability of bacterial leakage at the folded areas to a certain extent. This is likely because the PVDF sterilization membrane provided in this application has several reinforcing nodes at the folded areas. These reinforcing nodes significantly strengthen the folded areas, thereby minimizing the probability of excessive deformation / structural collapse and ensuring a longer service life for the sterilization membrane during filtration.

[0039] The special membrane pore fiber structure at the liquid inlet surface of the sterilization membrane in this invention significantly improves the overall mechanical properties of the sterilization membrane. Under various conditions, the membrane pores are not easy to collapse or deform, and can stably play a sterilization role for a long time.

[0040] The average particle size of the reinforcing nodes and the average diameter of the first surface fibers can be obtained by characterizing the morphology of the liquid inlet surface structure of the membrane using a scanning electron microscope, selecting a certain area, measuring the particle size of all reinforcing nodes and the diameter of the first surface fibers on that area, and then calculating to obtain the average particle size of the reinforcing nodes and the average diameter of the first surface fibers.

[0041] Optionally, the pore area ratio of the liquid inlet surface is 15%-45%, preferably 20-40%, and the ratio of the SEM average diameter of the reinforcing node to the SEM average diameter of the first surface fiber is 1.5-6.

[0042] By adopting the above technical solution, the liquid inlet surface has a suitable pore area ratio. If the pore area ratio of the liquid inlet surface is too small, the amount of liquid entering the sterilization membrane instantaneously will be less, and the flux of the sterilization membrane will be relatively low. If the pore area ratio of the liquid inlet surface of the sterilization membrane is too large, the area of ​​the solid part of the liquid inlet surface will be relatively small, thereby reducing the overall tensile strength of the sterilization membrane.

[0043] The average diameter of the reinforcing nodes should have a suitable ratio to the average diameter of the first surface fibers. Generally, the average diameter of the reinforcing nodes should be larger than that of the first surface fibers, meaning the reinforcing nodes are thicker than the first surface fibers. The reinforcing nodes provide reinforcement to the first surface fibers, improving their tensile strength and thus the overall tensile strength of the sterilization membrane. If the ratio is too small, the reinforcing nodes and the first surface fibers are considered to be roughly the same size, either both too thick or both too thin. This would result in either insufficient overall membrane flux or low overall membrane tensile strength. Conversely, if the ratio is too large, the reinforcing nodes are too thick, while the first surface fibers are too thin. Although the reinforcing nodes improve the pressure resistance of the inlet surface, the thinness of the first surface fibers still leads to insufficient pressure resistance at the inlet surface, causing the membrane pores at the inlet surface to collapse easily. This results in unstable sterilization efficiency and prolonged high-efficiency sterilization.

[0044] The liquid inlet surface has a suitable pore area ratio, a first surface fiber of suitable thickness, and a node structure with suitable particle size. Under the synergistic effect of the three, the sterilization membrane as a whole has high tensile strength and relatively high flux.

[0045] The porosity of the liquid inlet surface can be obtained by using a scanning electron microscope to characterize the morphology of the liquid inlet surface, selecting a certain area, measuring the area of ​​all the pores on that area, and then calculating the porosity of the liquid inlet surface.

[0046] Optionally, the liquid inlet surface has a plurality of large holes with a diameter of not less than 600 nm, and the sum of the pore areas of the large holes accounts for 4%-25% of the liquid inlet surface area, preferably 8%-22%.

[0047] By adopting the above technical solution, some of the pores in the liquid inlet surface have large pores with a diameter of not less than 600 nm, which significantly improves the overall flux of the sterilization membrane. The proportion of the sum of the pore areas of the large pores to the total area of ​​the liquid inlet surface is appropriate. If the proportion is too large, the solid part of the porous body near the liquid inlet surface will be relatively small, resulting in low tensile strength and tensile strength at break of the sterilization membrane. If the proportion is too small, the flux of the sterilization membrane cannot be significantly improved.

[0048] The pore diameter and the proportion of the pore area of ​​macropores can be determined by using a scanning electron microscope to characterize the morphology of the membrane structure, selecting a certain area, measuring the pore diameter and pore area of ​​all macropores on that area, and simultaneously calculating the sum of the pore areas and the proportion of the area of ​​macropores on that surface.

[0049] Optionally, the solid portion of the liquid inlet surface has a plurality of reinforcing aggregates, which are formed by the stacking of reinforcing nodes. The reinforcing aggregates are located at the edge of the macropore, and the SEM average area of ​​the reinforcing aggregates is 1-5 μm. 2 The sum of the SEM areas of the enhanced aggregates accounts for 2-20% of the inlet surface area.

[0050] By adopting the above technical solution, the reinforcing aggregate is formed by stacking and fusing reinforcing nodes. The SEM area of ​​the reinforcing aggregate is larger than that of the reinforcing nodes, and the reinforcing performance of the reinforcing aggregate on the porous body near the liquid inlet surface is relatively better than that of the reinforcing nodes. At the same time, the reinforcing aggregate is located at the edge of the large pores, and the reinforcing aggregate plays a significant reinforcing role on the porous body at the edge of the large pores, so that the sterilization membrane as a whole has high tensile strength.

[0051] The area of ​​the enhanced aggregate should be increased; the proportion of the enhanced aggregate area to the liquid inlet surface area should not be too small, otherwise it will not be able to fully reinforce the porous body at the edge of the large pores; at the same time, it should not be too large, otherwise the enhanced aggregate may block the pore structure of the liquid inlet surface, thereby reducing the flux of the sterilization membrane.

[0052] Meanwhile, the presence of enhanced aggregates also increases the pressure resistance near the macropores of the sterilization membrane to some extent, minimizing the probability of structural collapse of the macropores under high pressure. This allows the inlet side of the sterilization membrane to withstand higher pressure, thereby increasing the membrane's flux to some extent. Furthermore, under certain special operating conditions (such as a sudden increase in pressure or a sudden increase in the instantaneous flux of the feed liquid), the macroporous structure is less prone to collapse, further extending the service life of the sterilization membrane.

[0053] The average SEM area of ​​the reinforcing aggregates can be obtained by characterizing the morphology of the membrane structure using a scanning electron microscope, selecting a certain area, measuring the area of ​​all reinforcing aggregates, and then calculating the average area of ​​the reinforcing aggregates.

[0054] Optionally, the liquid outlet surface includes a block structure for forming a porous structure and a second surface fiber, with adjacent block structures connected by the second surface fiber; the pore area ratio of the liquid outlet surface is 18-48%, preferably 20%-45%, and the difference between the pore area ratio of the liquid outlet surface and the pore area ratio of the liquid inlet surface is 1-10%.

[0055] The special membrane pore fiber structure at the liquid inlet and liquid outlet of the sterilization membrane in this invention significantly improves the overall tensile strength of the sterilization membrane. Under various conditions, the membrane pores are not easy to collapse or deform, and can play a stable sterilization role for a long time. That is, this invention obtains a sterilization membrane with good mechanical properties and relatively high flux.

[0056] Compared to the inlet surface, the outlet surface does not require as much pressure resistance, thus eliminating the need for reinforcing nodes and improving the overall membrane flux. However, in practical applications, the area near the outlet surface still needs to have good mechanical properties. In this invention, the outlet surface includes a block structure for forming a porous structure and second surface fibers. The block structure is formed by stacking and fusing several second surface fibers. The presence of the block structure also increases the tensile strength of the area near the outlet surface to a certain extent, thereby facilitating various processing procedures.

[0057] The difference between the pore area ratio of the outlet surface and the inlet surface should be 1%-10%. A suitable difference ensures a suitable flow rate difference between the inlet and outlet surfaces, resulting in a larger flow rate of the liquid at the outlet surface. This promotes the flow of the liquid from the inlet to the outlet surface, increasing the flow velocity. In other words, the liquid near the outlet surface exerts a drag force on the liquid near the inlet surface, further increasing the flux of the sterilizing membrane. If the difference between the pore area ratios of the outlet and inlet surfaces is small, the flow rate difference between the inlet and outlet surfaces is small, reducing the drag force of the liquid near the outlet surface on the liquid near the inlet surface, thus reducing the overall flux of the sterilizing membrane. If the difference between the pore area ratios of the outlet and inlet surfaces is large, the instantaneous flow rate of the liquid at the outlet surface is large. The amount of liquid flowing into the inlet surface instantaneously cannot meet the timely outflow, easily causing blockage of the flow channels within the membrane, thus reducing the overall flux of the sterilizing membrane.

[0058] The sterilizing membrane has suitable pore area ratios on both its inlet and outlet surfaces, with a suitable difference between the pore area ratios of the inlet and outlet surfaces, and also possesses suitable porosity, resulting in a relatively high flux. Simultaneously, the special membrane structure at the inlet and outlet surfaces of the sterilizing membrane enables it to possess not only relatively high flux but also high tensile strength and elongation at break.

[0059] The porosity of the liquid outlet surface can be obtained by characterizing the morphology of the liquid outlet surface of the membrane using a scanning electron microscope, selecting a certain area, measuring the area of ​​all pores on that area, and calculating the porosity of the liquid outlet surface.

[0060] Optionally, the SEM average diameter of the second surface fiber is 100nm-450nm, preferably 150nm-400nm, and the SEM average pore size of the liquid outlet surface is 500nm-1400nm, preferably 600nm-1200nm.

[0061] In this invention, the second surface fiber has a suitable average diameter, and the liquid outlet surface has a suitable average pore size. Under the synergistic effect of the two, the porous body near the liquid outlet surface of the sterilization membrane has high tensile strength and relatively high flux.

[0062] If the average diameter of the SEM of the second surface fibers is too small, it is easy for a large amount of fluid to break when passing through the liquid outlet, thus failing to achieve stable sterilization filtration and also resulting in low overall mechanical properties of the sterilization membrane. If the average diameter of the SEM of the second surface fibers is too large, the relatively coarse second surface fibers will have greater resistance to the liquid, resulting in a decrease in the overall flux of the sterilization membrane. If the average pore size of the liquid outlet is too large, the porous body near the liquid outlet will not have sufficient tensile strength (mechanical properties). If the average pore size of the liquid outlet is too small, the flux of the porous body near the liquid outlet will be low.

[0063] The average diameter of the second surface fibers and the average pore size of the liquid outlet surface can be calculated by characterizing the morphology of the liquid outlet surface of the membrane using a scanning electron microscope, selecting a certain area, measuring the diameter of all fibers and pores on that area, and then calculating the average diameter of the second surface fibers and the average pore size of the liquid outlet surface.

[0064] Optionally, the ratio of the average SEM pore size of the liquid outlet surface to the average SEM diameter of the second surface fiber is 2-8, and the ratio of the average SEM diameter of the first surface fiber to the average SEM diameter of the second surface fiber is 0.4-3, preferably 0.5-2.

[0065] There should be a suitable ratio between the average SEM pore size of the liquid outlet surface and the average SEM diameter of the second surface fiber. If the ratio between the average SEM pore size of the liquid outlet surface and the average SEM diameter of the second surface fiber is too large, that is, the average SEM pore size of the liquid outlet surface is relatively too large and / or the average SEM diameter of the second surface fiber is relatively too small, the supporting effect of the second surface fiber on the pores of the liquid outlet surface will be weak. At the same time, the excessively fine second surface fiber will lead to a weak overall tensile strength of the sterilization membrane.

[0066] If the ratio between the average SEM pore size of the liquid outlet surface and the average SEM diameter of the second surface fiber is too small, that is, the average SEM pore size of the liquid outlet surface is relatively too small and / or the average SEM diameter of the second surface fiber is relatively too large, the coarse second surface fiber will create greater resistance to the liquid, which may lead to a decrease in the flux of the sterilization membrane.

[0067] The liquid outlet surface has second surface fibers of suitable thickness, pores of suitable size, and a suitable ratio between the pore diameter and the diameter of the second surface fibers. At the same time, the liquid outlet surface has a block structure. Under the synergistic effect of these four factors, the sterilization membrane as a whole has high tensile strength (mechanical properties) and relatively high throughput.

[0068] By controlling the ratio of the average diameter of the first surface fiber to the average diameter of the second surface within a suitable range, and simultaneously ensuring that the inlet surface and the outlet surface have suitable pore area ratios, the overall flux of the sterilization membrane is further improved through the synergistic effect of these three factors.

[0069] Optionally, the average SEM area of ​​the block structure is 0.5-3.5 μm. 2 The sum of the SEM areas of the blocky structures on the liquid outlet surface is 1.2 to 4.5 times the sum of the SEM areas of the second surface fibers.

[0070] By adopting the above technical solution, the area of ​​the blocky structure on the liquid outlet surface is larger than the area of ​​the second surface fibers. The relatively large number of blocky structures increases the tensile strength of the porous body near the liquid outlet surface. A suitable SEM area ratio is crucial between the blocky structure and the second surface fibers. If the ratio between the SEM areas of the blocky structure and the second surface fibers is too small, the overall tensile strength of the sterilization membrane will be too low. If the ratio between the SEM areas of the blocky structure and the second surface fibers is too large, it may lead to a decrease in the pore area ratio of the liquid outlet surface, thereby reducing the overall flux of the sterilization membrane.

[0071] The liquid outlet surface of the sterilization membrane has a block structure, and the area of ​​the block structure has a suitable ratio to the area of ​​the second surface fiber. At the same time, the liquid outlet surface has a suitable pore area ratio. Under the synergistic effect of the two, the sterilization membrane as a whole has high mechanical properties and relatively high throughput.

[0072] The sum of the SEM areas of the blocky structures emerging from the liquid surface can be obtained by characterizing the membrane structure using scanning electron microscopy, measuring the SEM areas of all blocky structures, and then calculating the sum of the SEM areas of the blocky structures. The sum of the SEM areas of the second surface fibers can also be obtained using a similar method.

[0073] Optionally, the thickness of the sterilizing membrane is 80-160 μm, preferably 100-140 μm; the tensile strength of the sterilizing membrane is 4-10 MPa, and the elongation at break is 20-50%; the LRV of the sterilizing membrane against *Pseudomonas degenerativeae* is at least 7, and the flux of the sterilizing membrane is 8-14 ml / (cm²). 2 (·min·1bar); the specific surface area of ​​the sterilizing membrane is 1.5-10m². 2 / g.

[0074] By adopting the above technical solution, the membrane thickness can be determined by characterizing the membrane structure using a scanning electron microscope, followed by calculation using computer software (such as Matlab, NIS-Elements, etc.) or manual measurement. When the membrane thickness is too small, its mechanical properties will be low; simultaneously, due to the short filtration time, effective filtration will be impossible. When the membrane thickness is too large, the filtration time will be too long, resulting in excessive time costs. The thickness of the sterilizing membrane in this invention is 80-160 μm (preferably 100-140 μm), ensuring that the sterilizing membrane has high mechanical properties. The sterilizing membrane of this invention has relatively high porosity, resulting in relatively high flux. At 20°C and 1 bar pressure, the flux of the sterilizing membrane of this invention is 8-14 ml / (cm²). 2 (min). That is, the present invention obtains a sterilization membrane with high mechanical properties and relatively high throughput.

[0075] Tensile strength is a crucial indicator for evaluating the mechanical properties of filter membranes. Under certain conditions, a higher tensile strength indicates better mechanical properties. Tensile strength refers to the membrane's ability to withstand parallel tensile forces. During testing, the membrane sample is subjected to a tensile load until it breaks. The tensile strength can be calculated based on the maximum tensile load at failure and the change in the membrane sample's dimensions (length). Tensile strength can be measured using a universal tensile testing machine. The testing methods for tensile strength are well-known in the field; for example, ASTM D790 or ISO 178 details the procedures for tensile strength testing. The antibacterial membrane of this invention exhibits a tensile strength of 4-10 MPa and an elongation at break of 20-50%, demonstrating that it possesses high tensile strength, good mechanical properties, and significant industrial practical value, fully meeting market demands.

[0076] Using *Pseudomonas quinquefolius* (ATCC19146) with a diameter of 0.3-0.4 μm, a bacterial challenge was conducted under the standard ASTM F838-2015ae1. The sterilization membrane prepared in this application showed an LRV greater than 7 against *Pseudomonas quinquefolius*, ensuring that the sterilization membrane has high sterilization efficiency.

[0077] The specific surface area of ​​the antibacterial membrane is 1.5-10 m². 2 / g, where specific surface area refers to the total area of ​​a unit mass of material. The sterilization membrane has a suitable specific surface area, so when the liquid is filtered through the PVDF sterilization membrane, the possibility of the effective substances in the liquid being adsorbed in the sterilization membrane channel is greatly reduced.

[0078] Secondly, this application provides a method for preparing a PVDF antibacterial membrane, which adopts the following technical solution:

[0079] A method for preparing a PVDF antibacterial membrane includes the following steps:

[0080] S1. PVDF resin is added to a solvent system composed of compound A and compound B and stirred and mixed until homogeneous to form a mixture; wherein compound A is the solvent of PVDF resin; compound B is the non-solvent of PVDF resin; the solid content of PVDF resin in the mixture is 20%-45%; and the mass of compound A in the solvent system is greater than the mass of compound B.

[0081] S2. The mixture is heated and melted at a temperature of 140℃-220℃ to form a casting liquid, which is then extruded through a die to form a liquid film on a carrier; the extrusion temperature of the die is 180℃-220℃.

[0082] S3. During the process from the extrusion of the liquid film from the die head to the liquid film remaining relatively stationary with the carrier, the liquid film undergoes longitudinal extension, with an extension ratio of 1.5 times to 10 times.

[0083] S4. The longitudinally extended liquid film is subjected to phase separation and solidification at a temperature of 15℃-60℃ to form a green film. During phase separation and solidification, the temperatures on both sides of the liquid film are different. One side of the liquid film is the air side, and the other side is the carrier side. The temperature of the air side is 5℃-15℃ lower than that of the carrier side. The phase separation and solidification time is 3s-25s.

[0084] S5: Extract the solvent system with the extraction solution to remove the solvent system from the biofilm and obtain the original biofilm;

[0085] S6: Heat set the original film. During heat setting, control the longitudinal shrinkage rate and transverse shrinkage rate of the original film surface to be no more than 10%. The heat setting temperature is 60-120℃ and the setting time is 3-12 hours to obtain the sterilization film.

[0086] Preferably, the molecular weight of the PVDF resin in the mixture is 100,000 to 1,000,000; and the mass percentage of compound A in the solvent system is 60-80%.

[0087] Compound A is at least one of dicyclohexyl phthalate, diphenyl methyl phosphate, tricresyl phosphate, diethyl phthalate, dibutyl phthalate, dipropyl carbonate, triacetin, and diacetin.

[0088] Compound B is at least one of dioctyl adipate, castor oil, soybean oil, glycerin, dioctyl phthalate, and paraffin oil.

[0089] Preferably, in S2, the die extrusion temperature is 3°C-15°C lower than the heating and melting temperature; in S4, when the liquid film is solidified by phase separation, air is blown on the air side of the liquid film, and the air velocity is 1m / min-20m / min.

[0090] Preferably, the viscosity of the casting solution in S2 is 20,000-100,000 CPS; the movement speed of the carrier in S3 is 1-10 m / min; and the extraction solution in S5 is at least one of hexane, methanol, ethanol, ethylene glycol and isopropanol, with an extraction temperature of 25℃-60℃ and an extraction time of 8h-64h.

[0091] This invention prepares a PVDF sterilization membrane using a thermal method; this membrane is a flat sheet membrane. The preparation of the sterilization membrane begins with mixing various materials to form a mixture, which includes PVDF resin and a corresponding solvent system. The solid content of the PVDF resin in the mixture is 20%-45%, where solid content is the mass percentage of PVDF resin in the mixture. A relatively high solid content makes it easier to obtain a sterilization membrane with small pore size and high tensile strength. Furthermore, the molecular weight of the PVDF resin in the mixture is 100,000-1,000,000, preferably 100,000-400,000. If the molecular weight is too low, the mechanical strength of the sterilization membrane will be too low; if the molecular weight is too high, it is difficult to form a high-porosity filter membrane, resulting in a low flux. By selecting a PVDF resin with a certain number-average molecular weight, the prepared PVDF sterilization membrane has sufficient mechanical strength and a relatively high flux. Furthermore, the crystallinity of the PVDF resin particles is 50%-80%, and the relatively high solid content of PVDF in the mixture ensures that the sterilization membrane as a whole possesses suitable crystallinity.

[0092] The solvent system consists of compound A and compound B. Compound A is a solvent for PVDF resin. A solvent is defined as a compound that can completely dissolve PVDF resin to form a homogeneous solution when heated to at most its boiling point. In this invention, compound A is specifically at least one of dicyclohexyl phthalate, diphenyl methyl phthalate, tricresyl phosphate, diethyl phthalate, dibutyl phthalate, dipropyl carbonate, triacetin, and diacetin. Compound B is a non-solvent for PVDF resin. A non-solvent is a compound that cannot dissolve PVDF resin to form a homogeneous solution when heated to at most its boiling point. Compound B increases the phase separation temperature between the polyolefin polymer and compound A. Adding compound B is beneficial for controlling the pore size and other characteristics of the sterilizing membrane, thus facilitating the acquisition of a sterilizing membrane with ideal pore size. In this invention, compound B is specifically at least one of dioctyl adipate, castor oil, soybean oil, glycerin, dioctyl phthalate, and paraffin oil.

[0093] Compared to using a single solvent as the solvent system, this invention uses a mixture of solvent and non-solvent as the corresponding solvent system. This solvent system makes it easier to form the required pore size and porosity in the biofilm formed after the liquid membrane phase separation, making it easier to retain bacteria. The required PMI in this application has an average pore size of 0.15-0.4 μm and a porosity of 35-75% for the sterilization membrane. This is because while the liquid membrane is undergoing liquid-liquid phase separation and solidification due to temperature changes (phase separation solidification via thermal method), diffusion exchange occurs between the non-solvent and the solvent, thereby further improving the phase separation solidification rate.

[0094] The second step is to put the mixture into an extruder and heat and melt it at a temperature of 140-220℃, so that the PVDF resin is completely melted in the corresponding solvent system to form a uniform and stable casting liquid. Then, it is extruded through a die (die forming) to form a flat liquid film. The die extrusion temperature is 180-220℃. Preferably, the die extrusion temperature is 3℃-15℃ lower than the heating and melting temperature. This ensures that the temperature of each area of ​​the liquid film is basically the same during extrusion, which is conducive to more uniform subsequent phase separation and curing, and thus obtaining a sterilization film with more uniform pores.

[0095] The third step involves longitudinally extending the flat liquid film during the process from extrusion through the die to its relative stillness with the carrier. The extension ratio is 1.5 to 10 times. This extension ratio can be controlled by the carrier's movement speed and the die's extrusion speed; it is the ratio of the carrier's movement speed to the die's extrusion speed. During this process, the sudden drop in pressure and temperature cause microphase separation within the liquid film, resulting in the formation of a certain number and diameter of crystal nuclei. These nuclei grow and aggregate to form PVDF particles. Some of these PVDF particles stack and fuse together, forming "strip-shaped" cross-sectional fibers. These fibers interconnect to create a porous structure. Simultaneously, the liquid film... Longitudinal extension is performed, and the extension ratio is controlled to be 1.5-10 times. Appropriate longitudinal extension of the liquid film ensures that the sterilization membrane has suitable pore size, porosity, and crystallinity, thereby guaranteeing high retention efficiency and relatively high flux. Preferably, the carrier's movement speed is controlled to be 1-10 m / min to ensure an appropriate longitudinal extension ratio of the liquid film. Preferably, the casting solution viscosity is controlled to 20,000-100,000 CPS. If the casting solution viscosity is too high, the liquid film is prone to breakage during longitudinal extension; if the casting solution viscosity is too low, the mechanical strength of the casting solution cannot be guaranteed. Therefore, by controlling the casting solution viscosity and an appropriate extension ratio, it is easier to obtain a PVDF sterilization membrane with high mechanical strength (high tensile strength, high elongation at break), high retention efficiency, and high flux.

[0096] The fourth step involves phase separation and curing of the longitudinally extended liquid film at a temperature of 15-60℃ to form a green film. At higher temperatures, the solvent system composed of compounds A and B can form a single homogeneous solution with the PVDF resin. However, as the system temperature decreases, the homogeneous solution undergoes phase separation and curing. In this invention, the phase separation and curing time is 3-25 seconds, which is relatively short and facilitates obtaining the desired ideal membrane pore structure. That is, the ideal membrane pore structure is formed by controlling the temperature difference and the phase separation time.

[0097] Furthermore, the solidification rates on both sides of the liquid film are required to be basically the same. Due to the different heat transfer efficiencies of the air side and the carrier side, the temperatures on both sides of the liquid film are different during solidification. The temperature on the air side is 5-15°C lower than that on the carrier side, so that the film formation is basically symmetrical along the thickness direction. Furthermore, air is blown on the air side at a speed of 1m / min-20m / min. During phase separation curing, the selection of factors such as the curing temperature and curing time is extremely critical. These factors determine the curing speed and whether an ideal membrane structure and pore size can be obtained. In preparing the PVDF sterilization membrane using the above method, this invention unexpectedly obtained a PVDF sterilization membrane with reinforcing nodes and reinforcing aggregates on the liquid inlet surface. Furthermore, it was unexpectedly discovered that this membrane possesses excellent tensile strength, tensile strength at break, and pressure resistance. This may be because, during phase separation, one side of the liquid film is the carrier side, and the other side is the air side. The roughness of the liquid film on the air side after phase separation curing is relatively high. At the same time, under the combined action of air blowing, reinforcing nodes and reinforcing aggregate structures are formed, which enhance the mechanical strength and pressure resistance of the liquid inlet surface.

[0098] The fifth step is to remove the solvent system from the biofilm using an extractant to obtain the original biofilm. The extractant is at least one of n-hexane, methanol, ethanol, ethylene glycol, and isopropanol. The extraction temperature is 25-60℃ and the extraction time is 8-64h. By selecting appropriate extractants and extraction conditions, the solvent system is completely removed from the biofilm.

[0099] The sixth step is to heat-set the extracted raw film at a temperature of 60-120℃ for 3-12 hours. After heat-setting, the sterilizing film is obtained. The purpose of heat-setting is twofold: firstly, to eliminate the internal stress generated by extraction, and secondly, to finalize the shape of the membrane pores, ensuring that the pores remain essentially unchanged, thus obtaining the PVDF sterilizing film with the desired pore structure. Furthermore, during heat-setting, the longitudinal and transverse shrinkage rates of the raw film surface are controlled to be no more than 10%, ensuring high fusion of PVDF crystal particles in the thickness direction of the sterilizing film, thereby ensuring the formation of cross-sectional fibers of suitable thickness and density. Simultaneously, the combined effect of setting at a relatively low temperature (60-120℃) for a long time (3-12 hours) and controlling the longitudinal and transverse shrinkage rates of the raw film to be no more than 10% further controls the overall crystallinity of the sterilizing film to be relatively suitable.

[0100] The resulting sterilization membrane not only has excellent bacterial retention performance, but also high tensile strength and relatively large throughput. The time required for the liquid to pass through the flat sheet membrane is short, the time cost is low, and it has a wide range of applications, making it particularly suitable for sterilization.

[0101] This application provides the following beneficial effects: the PVDF sterilization membrane and the method for preparing the sterilization membrane provided in this application exhibit excellent mechanical properties (tensile strength and elongation at break), and the high retention efficiency and relatively high flux greatly improve the performance of the PVDF sterilization membrane. The preparation method provided by this invention can conveniently, quickly, and effectively prepare the above-mentioned sterilization membrane. Attached Figure Description

[0102] Figure 1 This is a scanning electron microscope (SEM) schematic diagram of the cross-section of the sterile membrane prepared in Example 1, with a magnification of 500×.

[0103] Figure 2 This is a scanning electron microscope (SEM) schematic diagram of the cross-section of the sterile membrane prepared in Example 1, with a magnification of 2000×.

[0104] Figure 3 This is a scanning electron microscope (SEM) schematic diagram of the cross-section of the sterile membrane prepared in Example 1, with a magnification of 5000×.

[0105] Figure 4 This is a scanning electron microscope (SEM) schematic diagram of the liquid inlet surface of the sterile membrane prepared in Example 1, with a magnification of 5000×.

[0106] Figure 5 This is a scanning electron microscope (SEM) schematic diagram of the liquid outlet surface of the sterile membrane prepared in Example 1, with a magnification of 5000×.

[0107] Figure 6 This is a scanning electron microscope (SEM) schematic diagram of the cross-section of the sterile membrane prepared in Example 3, with a magnification of 2000×.

[0108] Figure 7 This is a scanning electron microscope (SEM) schematic diagram of the cross-section of the sterile membrane prepared in Example 3, with a magnification of 5000×. Detailed Implementation

[0109] Example 1

[0110] This application discloses a method for preparing a PVDF antibacterial membrane, comprising the following steps:

[0111] S1. Mixing: PVDF resin is added to a solvent system composed of compound A and compound B and stirred until homogeneous to form a mixture. The number average molecular weight of PVDF resin is 500,000, and the crystallinity of PVDF resin is 65%. The solid content of PVDF resin particles is 30%. Compound A is dicyclohexyl phthalate (solvent), and compound B is dioctyl adipate (non-solvent). In the solvent system, the mass percentage of compound A is 70%, and the mass percentage of compound B is 30%.

[0112] S2. Extrusion film formation: The mixture is heated and melted at a temperature of 200℃ to form a casting liquid, which is then extruded through a die to form a liquid film on a carrier; the die extrusion temperature is 190℃; the viscosity of the casting liquid is 60,000 CPS.

[0113] S3, Longitudinal Extension; During the process of the liquid film being extruded from the die head until it remains relatively stationary with the carrier, the liquid film is longitudinally extended by a factor of 6; The carrier's movement speed is 6 m / min;

[0114] S4. Phase separation curing: The longitudinally extended liquid film is subjected to phase separation curing at a temperature of 40°C to form a green film; one side of the liquid film is the air side and the other side is the carrier side. The temperature of the air side is 10°C lower than that of the carrier side. The phase separation curing time is 14s; the air side of the liquid film is blown with an air velocity of 10m / min.

[0115] S5: Extraction; The solvent system is extracted with an extractant to remove the solvent system from the membrane and obtain the original membrane; The extractant is n-hexane, the extraction temperature is 40℃, and the extraction time is 48h;

[0116] S6: Heat setting; The original film is heat set, and the longitudinal shrinkage rate and transverse shrinkage rate of the original film surface are controlled to be no more than 10% during heat setting. The heat setting temperature is 80℃ and the setting time is 8h to obtain the sterilization film.

[0117] Example 2

[0118] S1. Mixing: PVDF resin is added to a solvent system composed of compound A and compound B and stirred until homogeneous to form a mixture. The number average molecular weight of PVDF resin is 800,000, and the crystallinity of PVDF resin is 50%. The solid content of PVDF resin particles is 25%. Compound A is dibutyl phthalate (solvent), and compound B is dioctyl phthalate (non-solvent). In the solvent system, the mass percentage of compound A is 60%, and the mass percentage of compound B is 40%.

[0119] S2. Extrusion film formation: The mixture is heated and melted at a temperature of 190°C to form a casting liquid, which is then extruded through a die to form a liquid film on a carrier; the die extrusion temperature is 180°C; the viscosity of the casting liquid is 50,000 CPS.

[0120] S3, Longitudinal Extension; During the process of the liquid film being extruded from the die head until it remains relatively stationary with the carrier, the liquid film is longitudinally extended by a factor of 9; The carrier's movement speed is 9 m / min;

[0121] S4. Phase separation curing: The longitudinally extended liquid film is subjected to phase separation curing at a temperature of 30°C to form a green film; one side of the liquid film is the air side and the other side is the carrier side. The temperature of the air side is 5°C lower than that of the carrier side. The phase separation curing time is 5s. Air is blown onto the air side of the liquid film at a wind speed of 2m / min.

[0122] S5: Extraction; The solvent system is extracted with an extractant to remove the solvent system from the biofilm and obtain the original membrane; The extractant is ethanol, the extraction temperature is 35℃, and the extraction time is 36h;

[0123] S6: Heat setting; The original film is heat set, and the longitudinal shrinkage rate and transverse shrinkage rate of the original film surface are controlled to be no more than 10% during heat setting. The heat setting temperature is 65℃ and the setting time is 4h to obtain the sterilization film.

[0124] Example 3

[0125] S1. Mixing: PVDF resin is added to a solvent system composed of compound A and compound B and stirred until homogeneous to form a mixture. The number average molecular weight of PVDF resin is 420,000, and the crystallinity of PVDF resin is 75%. The solid content of PVDF resin particles is 42%. Compound A is dibutyl phthalate (solvent), and compound B is dioctyl phthalate (non-solvent). In the solvent system, the mass percentage of compound A is 80%, and the mass percentage of compound B is 20%.

[0126] S2. Extrusion film formation: The mixture is heated and melted at a temperature of 220℃ to form a casting liquid, which is then extruded through a die to form a liquid film on a carrier; the die extrusion temperature is 210℃; the viscosity of the casting liquid is 85,000 CPS.

[0127] S3, Longitudinal Extension; During the process of the liquid film being extruded from the die head until it remains relatively stationary with the carrier, the liquid film is longitudinally extended by a factor of 2; The carrier's movement speed is 2 m / min;

[0128] S4. Phase separation curing: The longitudinally extended liquid film is subjected to phase separation curing at a temperature of 55°C to form a green film; one side of the liquid film is the air side and the other side is the carrier side. The temperature of the air side is 12°C lower than that of the carrier side. The phase separation curing time is 13s; the air side of the liquid film is blown with an air velocity of 14m / min.

[0129] S5: Extraction; The solvent system is extracted with an extractant to remove the solvent system from the membrane and obtain the original membrane; The extractant is isopropanol, the extraction temperature is 60℃, and the extraction time is 8h;

[0130] S6: Heat setting; The original film is heat set, and the longitudinal shrinkage rate and transverse shrinkage rate of the original film surface are controlled to be no more than 10% during heat setting. The heat setting temperature is 115℃ and the setting time is 10h to obtain the sterilization film.

[0131] Example 4

[0132] S1. Mixing: PVDF resin is added to a solvent system composed of compound A and compound B and stirred until homogeneous to form a mixture. The number average molecular weight of PVDF resin is 600,000, and the crystallinity of PVDF resin is 55%. The solid content of PVDF resin particles is 22%. Compound A is toluene diphenyl phosphate (solvent), and compound B is castor oil (non-solvent). In the solvent system, the mass percentage of compound A is 65%, and the mass percentage of compound B is 35%.

[0133] S2. Extrusion film formation: The mixture is heated and melted at a temperature of 195°C to form a casting liquid, which is then extruded through a die to form a liquid film on a carrier; the die extrusion temperature is 190°C; the viscosity of the casting liquid is 30,000 CPS.

[0134] S3, Longitudinal Extension; During the process of the liquid film being extruded from the die head until it remains relatively stationary with the carrier, the liquid film is longitudinally extended by a factor of 7; The carrier's movement speed is 7 m / min;

[0135] S4. Phase separation curing: The longitudinally extended liquid film is subjected to phase separation curing at a temperature of 40°C to form a green film; one side of the liquid film is the air side and the other side is the carrier side. The temperature of the air side is 7°C lower than that of the carrier side. The phase separation curing time is 9s; the air side of the liquid film is blown with an air velocity of 18m / min.

[0136] S5: Extraction; The solvent system is extracted with an extractant to remove the solvent system from the biofilm and obtain the original biofilm; The extractant is methanol, the extraction temperature is 35℃, and the extraction time is 24h;

[0137] S6: Heat setting; The original film is heat set, and the longitudinal shrinkage rate and transverse shrinkage rate of the original film surface are controlled to be no more than 10% during heat setting. The heat setting temperature is 70℃ and the setting time is 5h to obtain the sterilization film.

[0138] Example 5

[0139] S1. Mixing: PVDF resin is added to a solvent system composed of compound A and compound B and stirred until homogeneous to form a mixture. The number average molecular weight of PVDF resin is 450,000, and the crystallinity of PVDF resin is 70%. The solid content of PVDF resin particles is 38%. Compound A is dicyclohexyl phthalate (solvent), and compound B is castor oil (non-solvent). In the solvent system, the mass percentage of compound A is 72%, and the mass percentage of compound B is 28%.

[0140] S2. Extrusion film formation: The mixture is heated and melted at a temperature of 205℃ to form a casting liquid, which is then extruded through a die to form a liquid film on a carrier; the die extrusion temperature is 195℃; the viscosity of the casting liquid is 75,000 CPS.

[0141] S3, Longitudinal Extension; During the process of the liquid film being extruded from the die head until it remains relatively stationary with the carrier, the liquid film is longitudinally extended by a factor of 5; The carrier's movement speed is 5 m / min;

[0142] S4. Phase separation curing: The longitudinally extended liquid film is subjected to phase separation curing at a temperature of 20°C to form a green film; one side of the liquid film is the air side and the other side is the carrier side. The temperature of the air side is 5°C lower than that of the carrier side. The phase separation curing time is 10s; the air side of the liquid film is blown with an air velocity of 7m / min.

[0143] S5: Extraction; The solvent system is extracted with an extractant to remove the solvent system from the membrane and obtain the original membrane; the extractant is glycerol, the extraction temperature is 40℃, and the extraction time is 64h;

[0144] S6: Heat setting; The original film is heat set, and the longitudinal shrinkage rate and transverse shrinkage rate of the original film surface are controlled to be no more than 10% during heat setting. The heat setting temperature is 100℃ and the setting time is 99h to obtain the sterilization film.

[0145] Example 6

[0146] S1. Mixing: PVDF resin is added to a solvent system composed of compound A and compound B and stirred until homogeneous to form a mixture. The number average molecular weight of PVDF resin is 400,000, and the crystallinity of PVDF resin is 80%. The solid content of PVDF resin particles is 45%. Compound A is diacetate (solvent), and compound B is soybean oil (non-solvent). In the solvent system, the mass percentage of compound A is 67%, and the mass percentage of compound B is 33%.

[0147] S2. Extrusion film formation: The mixture is heated and melted at a temperature of 200℃ to form a casting liquid, which is then extruded through a die to form a liquid film on a carrier; the die extrusion temperature is 185℃; the viscosity of the casting liquid is 90,000 CPS.

[0148] S3, Longitudinal Extension; During the process of the liquid film being extruded from the die head until it remains relatively stationary with the carrier, the liquid film is longitudinally extended by a factor of 4; The carrier's movement speed is 4 m / min;

[0149] S4. Phase separation curing: The longitudinally extended liquid film is subjected to phase separation curing at a temperature of 48°C to form a green film; one side of the liquid film is the air side, and the other side is the carrier side. The temperature of the air side is 8°C lower than that of the carrier side. The phase separation curing time is 16s.

[0150] S5: Extraction; The solvent system is extracted with an extractant to remove the solvent system from the membrane and obtain the original membrane; the extractant is glycerol, the extraction temperature is 45℃, and the extraction time is 24h;

[0151] S6: Heat setting; The original film is heat set, and the longitudinal shrinkage rate and transverse shrinkage rate of the original film surface are controlled to be no more than 10% during heat setting. The heat setting temperature is 90℃ and the setting time is 3h to obtain the sterilization film.

[0152] Example 7

[0153] S1. Mixing: PVDF resin is added to a solvent system composed of compound A and compound B and stirred until homogeneous to form a mixture. The number average molecular weight of PVDF resin is 480,000, and the crystallinity of PVDF resin is 50%. The solid content of PVDF resin particles is 28%. Compound A is diacetate (solvent), and compound B is soybean oil (non-solvent). In the solvent system, the mass percentage of compound A is 60%, and the mass percentage of compound B is 40%.

[0154] S2. Extrusion film formation: The mixture is heated and melted at a temperature of 200℃ to form a casting liquid, which is then extruded through a die to form a liquid film on a carrier; the die extrusion temperature is 200℃; the viscosity of the casting liquid is 40,000 CPS.

[0155] S3, Longitudinal Extension; During the process of the liquid film being extruded from the die head until it remains relatively stationary with the carrier, the liquid film is longitudinally extended by a factor of 5; The carrier's movement speed is 5 m / min;

[0156] S4. Phase separation curing: The longitudinally extended liquid film is subjected to phase separation curing at a temperature of 50°C to form a green film; one side of the liquid film is the air side and the other side is the carrier side. The temperature of the air side is 10°C lower than that of the carrier side. The phase separation curing time is 13s; the air side of the liquid film is blown with an air velocity of 5m / min.

[0157] S5: Extraction; The solvent system is extracted with an extractant to remove the solvent system from the membrane and obtain the original membrane; the extractant is glycerol, the extraction temperature is 50℃, and the extraction time is 12h;

[0158] S6: Heat setting; The original film is heat set, and the longitudinal shrinkage rate and transverse shrinkage rate of the original film surface are controlled to be no more than 10% during heat setting. The heat setting temperature is 100℃ and the setting time is 5h to obtain the sterilization film.

[0159] Comparative Example 1

[0160] S1. Mixing: PVDF resin is added to a solvent system composed of compound A and compound B and stirred until homogeneous to form a mixture. The number average molecular weight of PVDF resin is 450,000, and the crystallinity of PVDF resin is 55%. The solid content of PVDF resin particles is 55%. Compound A is diacetate (solvent), and compound B is soybean oil (non-solvent). In the solvent system, the mass percentage of compound A is 65%, and the mass percentage of compound B is 35%.

[0161] S2. Extrusion film formation: The mixture is heated and melted at a temperature of 200℃ to form a casting liquid, which is then extruded through a die to form a liquid film on a carrier; the die extrusion temperature is 190℃; the viscosity of the casting liquid is 100,000 CPS.

[0162] S3, Phase Separation Curing; The longitudinally extended liquid film is subjected to phase separation curing at a temperature of 35°C to form a green film; One side of the liquid film is the air side, and the other side is the carrier side. The temperature of the air side is 10°C lower than that of the carrier side. The phase separation curing time is 10s; Air is blown onto the air side of the liquid film at a wind speed of 5m / min.

[0163] S4: Extraction; The solvent system is extracted with an extractant to remove the solvent system from the membrane and obtain the original membrane; the extractant is glycerol, the extraction temperature is 40℃, and the extraction time is 36h;

[0164] S5: Heat setting; The original film is heat set at 100℃ for 6 hours to obtain a sterile film.

[0165] Comparative Example 2

[0166] S1. Mixing: PVDF resin is added to a solvent system containing only compound A and stirred until homogeneous to form a mixture; the number average molecular weight of PVDF resin is 100,000, and the crystallinity of PVDF resin is 50%; the solid content of PVDF resin particles is 40%; compound A is diacetate (solvent).

[0167] S2. Extrusion film formation: The mixture is heated and melted at a temperature of 200℃ to form a casting liquid, which is then extruded through a die to form a liquid film on a carrier; the die extrusion temperature is 190℃; the viscosity of the casting liquid is 63,000 CPS.

[0168] S3, Longitudinal Extension; During the process of the liquid film being extruded from the die head until it remains relatively stationary with the carrier, the liquid film is longitudinally extended by a factor of 3; The carrier's movement speed is 3 m / min;

[0169] S4. Phase separation curing: The longitudinally extended liquid film is subjected to phase separation curing at a temperature of 60°C to form a green film; one side of the liquid film is the air side and the other side is the carrier side. The temperature of the air side is 10°C lower than that of the carrier side. The phase separation curing time is 15s.

[0170] S5: Extraction; The solvent system is extracted with an extractant to remove the solvent system from the membrane and obtain the original membrane; the extractant is glycerol, the extraction temperature is 40℃, and the extraction time is 36h;

[0171] S6: Heat setting; The original film is heat set at a temperature of 120℃ for 5 hours to obtain a sterile film.

[0172] The surface and cross-sectional morphology of the filter membranes prepared in Examples 1-7 and Comparative Examples 1-2 were characterized using scanning electron microscopy, and various tests were performed to obtain the corresponding data, which are as follows:

[0173]

[0174]

[0175]

[0176] Furthermore, the PVDF sterilization membranes prepared in Examples 1-7 were subjected to high-temperature steam sterilization (125°C, 30 min). The flux of the sterilization membrane was still maintained at more than 90% of the original flux. This indicates that the sterilization membrane of the present invention has good heat resistance and its pores are not easily deformed or collapsed at high temperatures.

[0177] As shown in the table above, the PVDF sterilization membranes prepared in Examples 1-7 of this invention all possess ideal crystallinity, density, and cross-sectional fibers with suitable diameters (thickness), which is beneficial for the PVDF sterilization membranes to have high mechanical strength (high tensile strength and high tensile strength at break), relatively high flux, and sufficient retention of bacteria. The sterilization membrane in Comparative Example 1 has excessively high density and excessively large cross-sectional fiber diameter (excessively thick fibers), resulting in an overly dense three-dimensional network structure and excessively low internal porosity. Although its tensile strength is relatively high, its flux significantly fails to meet practical application requirements. The sterilization membrane in Comparative Example 2 has excessively large pores, resulting in an excessively large average pore size of PMI. Even with a large thickness, it still cannot sufficiently retain bacteria, and this membrane cannot be used as a sterilization membrane.

[0178] By observing Examples 3 and 6, it can be found that although the overall porosity and pore area ratio of the inlet surface of the filter membranes in Examples 3 and 6 are similar, and the pore area ratio of the outlet surface of the filter membrane in Example 6 is slightly greater than that of the filter membrane in Example 3, the flux of the filter membrane in Example 6 is significantly less than that of the filter membrane in Example 3. The ratio between the average diameter of the cross-sectional fibers of the filter membrane in Example 6 and the average pore size of the PMI of the sterilizing membrane is too large, and the cross-sectional fibers are too coarse. Therefore, the resistance of the sterilizing membrane to the feed liquid is too large, which reduces the flux of the sterilizing membrane to a certain extent.

[0179] By observing Examples 3 and 5, it can be found that although the overall porosity of the filter membrane in Example 5 is significantly higher than that in Example 3, the flux of the filter membrane in Example 3 is still significantly higher than that in Example 5. This may be because the pore area ratio of the liquid inlet surface in Example 5 is too small. Furthermore, the difference between the porosity of the sterilization membrane and the pore area ratio of the liquid inlet surface is greater than 20%. The difference is too large, so the amount of liquid entering the liquid inlet surface instantaneously is small, while there are many flow paths inside the membrane. The resistance encountered by the liquid in the flow path is relatively large, and the flux of the sterilization membrane is further reduced.

[0180] By observing Examples 2 and 7, it can be found that the filter membrane in Example 7 has a higher density, crystallinity, and cross-sectional fiber thickness than the filter membrane in Example 2. However, the tensile strength of the filter membrane in Example 2 is greater than that of the filter membrane in Example 7. This may be because the inlet surface of the filter membrane in Example 2 contains reinforcing nodes and reinforcing aggregates, while the filter membrane in Example 7 does not contain reinforcing nodes and reinforcing aggregates. Since the reinforcing nodes and reinforcing aggregates reinforce the porous body near the inlet surface, the tensile strength of the filter membrane in Example 2 is greater than that of the filter membrane in Example 7.

[0181] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A PVDF antibacterial membrane, comprising a porous body, one side of which is a liquid inlet surface and the other side of which is a liquid outlet surface, wherein the porous body has non-directional tortuous pathways, characterized in that, The sterilization membrane has an average PMI pore size of 0.15-0.4 μm and a porosity of 35-75%. The density of the sterilizing membrane is 0.4-0.8 g / cm³. 3 ; The crystallinity of the antibacterial membrane, as measured by DSC, is 30-50%. The porous body has cross-sectional fibers on its cross-section for forming a porous structure. The cross-sectional fibers are formed by stacking and fusing several granular PVDF particles. The average SEM diameter of the cross-sectional fibers is 150-500 nm.

2. The PVDF antibacterial membrane according to claim 1, characterized in that, The average SEM diameter of the PVDF particles is 80-350 nm.

3. The PVDF antibacterial membrane according to claim 2, characterized in that, The average SEM diameter of the PVDF particles is 100-300 nm.

4. The PVDF antibacterial membrane according to claim 1, characterized in that, The ratio between the average SEM diameter of the cross-sectional fiber and the average PMI pore size of the sterilization membrane is 0.4-3 nm / nm; the average SEM length of the cross-sectional fiber is 600-2000 nm.

5. The PVDF antibacterial membrane according to claim 1, characterized in that, Some of the PVDF particles are stacked and fused together to form a blocky, irregular cross-sectional support. The average SEM area of ​​the cross-sectional support is 0.5-2 μm. 2 .

6. The PVDF antibacterial membrane according to claim 1, characterized in that, The pore area ratio of the liquid inlet surface is less than the porosity of the sterilization membrane, and the difference between the porosity of the sterilization membrane and the pore area ratio of the liquid inlet surface is 5%-20%; the pore area ratio of the liquid outlet surface is greater than the pore area ratio of the liquid inlet surface but less than the porosity of the sterilization membrane.

7. The PVDF antibacterial membrane according to claim 1, characterized in that, The solid portion of the liquid inlet surface has several reinforcing nodes, which are granular structures. Some adjacent reinforcing nodes are connected by a first surface fiber. The SEM average diameter of the reinforcing nodes is 250-750 nm, and the SEM average diameter of the first surface fiber is 100-500 nm.

8. The PVDF antibacterial membrane according to claim 7, characterized in that, The porosity of the liquid inlet surface is 15%-45%, and the ratio of the SEM average diameter of the reinforcing node to the SEM average diameter of the first surface fiber is 1.5-6.

9. The PVDF antibacterial membrane according to claim 1, characterized in that, The liquid inlet surface has a number of large holes with a diameter of not less than 600 nm, and the sum of the pore areas of the large holes accounts for 4%-25% of the liquid inlet surface area.

10. A PVDF antibacterial membrane according to claim 9, characterized in that, The solid portion of the liquid inlet surface has several reinforcing aggregates, which are formed by the accumulation of reinforcing nodes. The reinforcing aggregates are located at the edge of the macropore, and the SEM average area of ​​the reinforcing aggregates is 1-5 μm. 2 The sum of the SEM areas of the enhanced aggregates accounts for 2-20% of the inlet surface area.

11. The PVDF antibacterial membrane according to claim 1, characterized in that, The liquid outlet surface includes a block structure for forming a porous structure and a second surface fiber, and adjacent block structures are connected by the second surface fiber; the pore area ratio of the liquid outlet surface is 18-48%, and the difference between the pore area ratio of the liquid outlet surface and the pore area ratio of the liquid inlet surface is 1-10%.

12. The PVDF antibacterial membrane according to claim 11, characterized in that, The average SEM diameter of the second surface fiber is 100-450 nm, and the average SEM pore size of the liquid outlet surface is 500-1400 nm.

13. The PVDF antibacterial membrane according to claim 11, characterized in that, The ratio of the average SEM pore size of the liquid outlet surface to the average SEM diameter of the second surface fiber is 2-8; the ratio of the average SEM diameter of the first surface fiber to the average SEM diameter of the second surface fiber is 0.5-2.

14. The PVDF antibacterial membrane according to claim 11, characterized in that, The average SEM area of ​​the blocky structure is 0.5-3.5 μm. 2 The sum of the SEM areas of the blocky structures on the liquid outlet surface is 1.2 to 4.5 times the sum of the SEM areas of the second surface fibers.

15. The PVDF antibacterial membrane according to claim 1, characterized in that, The thickness of the sterilization membrane is 80-160 μm; The antibacterial membrane has a tensile strength of 4-10 MPa and an elongation at break of 15-60%. The sterilization filter membrane has an LRV of at least 7 against defective Pseudomonas aeruginosa. The flux of the sterilization membrane is 8-14 ml / (cm²). 2 (min·1 bar); The specific surface area of ​​the sterilization membrane is 1.5-10 m². 2 / g.

16. A method for preparing a PVDF antibacterial membrane according to any one of claims 1-15, characterized in that, Includes the following steps: S1. Add PVDF resin to a solvent system composed of compound A and compound B and stir to mix until homogeneous to form a mixture; wherein compound A is the solvent of PVDF resin; compound B is the non-solvent of PVDF resin; the solid content of PVDF resin in the mixture is 20%-45%; and the mass of compound A in the solvent system is greater than the mass of compound B. S2. The mixture is heated and melted at a temperature of 140℃-220℃ to form a casting liquid, which is then extruded through a die to form a liquid film on a carrier; the extrusion temperature of the die is 180℃-220℃. S3. During the process from the extrusion of the liquid film from the die head to the liquid film remaining relatively stationary with the carrier, the liquid film undergoes longitudinal extension, with an extension ratio of 1.5 times to 10 times. S4. The longitudinally extended liquid film is subjected to phase separation and solidification at a temperature of 15℃-60℃ to form a green film. During phase separation and solidification, the temperatures on both sides of the liquid film are different. One side of the liquid film is the air side, and the other side is the carrier side. The temperature of the air side is 5℃-15℃ lower than that of the carrier side. The phase separation and solidification time is 3s-25s. S5: Extract the solvent system with the extraction solution to remove the solvent system from the biofilm and obtain the original biofilm; S6: Heat set the original film. During heat setting, control the longitudinal shrinkage rate and transverse shrinkage rate of the original film surface to be no more than 10%. The heat setting temperature is 60-120℃ and the setting time is 3-12 hours to obtain the sterilization film.

17. The method for preparing a PVDF antibacterial membrane according to claim 16, characterized in that, The PVDF resin in the mixture described in S1 has a molecular weight of 100,000 to 1,000,000; the crystallinity of the PVDF resin is 50% to 80%. The mass percentage of compound A in the solvent system is 60%-80%; Compound A is at least one of dicyclohexyl phthalate, diphenyl methyl phosphate, tricresyl phosphate, diethyl phthalate, dibutyl phthalate, dipropyl carbonate, triacetin, and diacetin. Compound B is at least one of dioctyl adipate, castor oil, soybean oil, glycerin, dioctyl phthalate, and paraffin oil.

18. The method for preparing a PVDF antibacterial membrane according to claim 16, characterized in that, The die extrusion temperature in S2 is 3°C-15°C lower than the heating and melting temperature; During the phase separation and solidification of the liquid film in S4, air is blown on the air side of the liquid film at a speed of 1m / min-20m / min.

19. The method for preparing a PVDF antibacterial membrane according to claim 16, characterized in that, The viscosity of the casting solution in S2 is 20,000-100,000 CPS; The speed of the carrier in S3 is 1-10 m / min; The extractant in S5 is at least one of hexane, methanol, ethanol, ethylene glycol and isopropanol, with an extraction temperature of 25℃-60℃ and an extraction time of 8h-64h.

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