CN116832628A

CN116832628A - Composite cellulose virus-removing filter membrane, preparation process thereof and virus-removing membrane assembly

Info

Publication number: CN116832628A
Application number: CN202310793848.3A
Authority: CN
Inventors: 贾建东
Original assignee: Hangzhou Cobetter Filtration Equipment Co Ltd
Current assignee: Hangzhou Cobetter Filtration Equipment Co Ltd
Priority date: 2023-06-30
Filing date: 2023-06-30
Publication date: 2023-10-03

Abstract

The application relates to a composite cellulose virus-removing filter membrane and a preparation process thereof, and a virus-removing membrane assembly, wherein the filter membrane comprises a nylon microporous membrane and a cellulose layer, one side of the nylon Long Weikong membrane is a liquid inlet surface, and a region, in which the cellulose layer is permeated, in the nylon microporous membrane is a permeation region; the thickness of the penetration area is 10-50 mu m; the liquid inlet surface comprises liquid inlet fibers and liquid inlet holes, the area ratio of the holes of the liquid inlet holes is 15-55%, the surface tension is 42-58 dyne/cm, and the thickness of the nylon microporous membrane is 40-120 mu m; the flux of the filter membrane is not less than 40L/h/m ² . The application further discloses a preparation process of the filter membrane and a virus removal membrane assembly comprising the filter membrane. The filter membrane has proper pore area rate and surface tensionThe nylon microporous membrane with force is used as a support, the thickness of the permeation area is controlled to improve the integrity of the composite membrane, and the possibility of stripping the nylon microporous membrane and the composite membrane is reduced, so that the composite membrane has high stripping strength and high flux which are difficult to achieve.

Description

Composite cellulose virus-removing filter membrane, preparation process thereof and virus-removing membrane assembly

Technical Field

The application relates to the field of membrane separation technology, in particular to a composite cellulose virus-removing filter membrane, a preparation process thereof and a virus-removing membrane component.

Background

In the production process of various biological agents, ensuring the virus safety of the biological agents is important, and high requirements on the virus safety of the biological agents are clearly required no matter whether the biological agents are in the new edition of Chinese pharmacopoeia or the ICH Q5A biotechnology product-virus safety evaluation. Also, as a result, viral clearance and/or viral inactivation steps during preparation of the biological agent become indispensable.

The membrane separation technology has the advantages of high separation efficiency, easy process amplification, difficult active substance denaturation in the separation process and the like, and is widely applied to virus removal steps of various biological agents. When the membrane separation technology is applied to a virus filtering process, a dead-end filtering mode is often adopted, and the main filtering driving force of the dead-end filtering is the pressure difference between two ends of a filtering membrane after the material liquid to be filtered is pressurized, so that the pressure of the material liquid to be filtered is further improved, and the filtering efficiency can be expected to be improved. However, the higher pressure of the feed liquid to be filtered increases the higher requirement on the pressure resistance of the filter membrane to avoid the reduction or even damage of the virus retention performance of the filter membrane at higher pressure.

As disclosed in chinese patent application publication No. CN105980038A (the application of the rising chemical industry company), a virus-removing film comprising cellulose having a surface on a first side to which a solution containing a protein is supplied and a surface on a second side from which a permeate which permeates the virus-removing film is discharged, has a log removal rate of 4 or more (LRV > 4) for porcine parvovirus (about 18 to 26 nm). The filter membrane is a cellulose filter membrane, and the good hydrophilicity of the cellulose filter membrane ensures that the cellulose filter membrane has low adsorption on protein; however, the intrinsic property of the softer texture of the cellulosic material determines that the three-dimensional network structure formed by the cellulose fibers in the cellulose filter is poor in mechanical strength, and the self-supporting performance of the cellulose filter is often insufficient, and the cellulose filter in this application can only bear 15psi of pressure, and is difficult to bear higher pressure. In the use process, the filter membrane is likely to be impacted by feed liquid, and the pressure resistance of the filter membrane is required to be high no matter whether the feed liquid with high pressure is used for the filter membrane in the virus filtering process or the impact is caused by equipment vibration and the like; filters which are difficult to withstand higher pressures may therefore have a lower service life, and may also in certain special application scenarios lead to a risk of virus leakage due to insufficient stability.

In order to improve the pressure resistance of the cellulose filter membrane, a support membrane layer with higher pressure resistance can be introduced on the basis of the cellulose layer to form a composite membrane structure, and the support membrane layer is often a microporous membrane or a non-woven substrate formed by polymer materials. The nonwoven substrate has high membrane pore openness, is easier to form a composite membrane structure with higher integrity with the casting solution, but has lower surface flatness, and nonwoven fibers are easy to penetrate and damage the casting solution, so that the risk of virus leakage is increased, and therefore, microporous membrane substrates with high integrity are widely adopted.

As disclosed in chinese patent application publication No. CN114173911a (filed by certolis corporation), a mechanically stable ultrafiltration membrane and a method for preparing the same, which is obtained by coating a first polymer solution and a second polymer solution on a support layer, and briefly treating the first polymer solution with a non-solvent-containing gas to form a damping region after the first polymer solution is cured, the damping region being capable of imparting a strong impact resistance (i.e., pressure resistance) to a composite membrane; the support layer may be a nonwoven web, a woven fabric or a polyester nonwoven, or may be a polypropylene, polyethylene, polyfiber, polyethersulfone or cellulose microfiltration membrane. The ultrafiltration membrane achieves a stronger impact resistance by forming a damping structure with a dense middle and loose two sides, however, such a membrane pore structure is not suitable for use in a virus-removing filter membrane. Because, unlike ultrafiltration membranes which often employ tangential flow filtration (feed liquid flow through a parallel membrane surface), virus removal membranes often employ dead-end filtration (feed liquid flow through a perpendicular membrane surface, also known as transmembrane filtration), dense damping structures within the membranes are likely to produce concentrated entrapment of particulate impurities in the feed liquid, thereby leading to rapid decline in the flux of the membranes and an excessively low service life of the membranes. Furthermore, the influence of the different support layers on the filter membrane is not described in this patent application, and in fact the support layers have a larger influence on the filter membrane as well.

A high bubble point filter membrane is disclosed in U.S. patent application publication No. US4824568A (milleipore CORP application) by coating PVDF or PES onto a 0.22 μm PVDF microporous substrate to form a composite membrane. The solvent in the casting solution can soften a part of PVDF substrate during coating, thereby greatly improving the peeling strength of the composite film. However, the erosion rate of the organic solvent to PVDF is very fast, for example, the PVDF microporous substrate film loses mechanical properties and permeability completely after soaking in NMP for 10 seconds, and dissolves completely within 2 minutes, which means that the high peel strength of the composite film obtained by softening the substrate tends to be at the expense of a decrease in permeability (i.e., flux), and both are difficult to achieve.

PES materials also have the problem of being intolerant to organic solvents with strong polarity, such as ketones, esters, halogenated hydrocarbons, dimethyl sulfoxide, and the like, and thus the composite membrane structure having PES microporous substrate membranes also has the problem. The cellulose material is softer, if the cellulose material is used as a substrate film, the mechanical properties of the composite film are likely to not meet the requirements, and the solvent in the cellulose casting solution is likely to soften the cellulose substrate film, so that the same problem of reduced permeability is generated. Compared with the materials, the nylon material has wider organic solvent resistance, so that the microporous membrane made of the nylon material is used as a substrate, the problem of flux reduction caused by the softening of the microporous substrate membrane by the solvent can be effectively solved, but the nylon substrate which cannot be softened means that the peeling strength of the composite membrane is reduced, and the integrity is reduced; therefore, it is difficult to achieve both flux and peel strength of the composite membrane.

How to obtain a composite membrane with higher flux and higher peel strength is a problem which is to be solved but is difficult to solve at present.

Disclosure of Invention

The application provides a composite cellulose virus-removing filter membrane and a preparation process thereof, and a virus-removing membrane component, wherein the virus-removing filter membrane uses a nylon microporous membrane as a support of a cellulose layer so as to improve the pressure resistance of the composite membrane, and the nylon microporous membrane has wider organic solvent resistance and is not easy to soften by an organic solvent in cellulose casting solution, so that a local compact structure is not easy to form; further, by controlling the nylon microporous membrane to have proper hole area ratio and surface tension, the cellulose casting membrane liquid can be properly permeated into the nylon microporous membrane to form a permeation area with the thickness of 10-50 mu m, and the permeation area can well improve the integrity of the cellulose layer and the nylon microporous membrane and reduce the possibility of stripping the cellulose layer and the nylon microporous membrane, so that the composite membrane has high stripping strength and high flux which are difficult to achieve.

In a first aspect, the application provides a supported composite cellulose virus-removing filter membrane, which adopts the following technical scheme:

the composite cellulose virus-removing filter membrane with the support comprises a nylon microporous membrane and a cellulose layer at least partially penetrating into the nylon microporous membrane, wherein one side of the nylon microporous membrane, which is far away from a regenerated fiber layer, is a liquid inlet surface, one side of the cellulose layer, which is far away from the nylon microporous membrane, is a liquid outlet surface, and a region, which is penetrated with the cellulose layer, in the nylon microporous membrane is a penetration region;

The thickness of the penetration area is 10-50 mu m;

the liquid inlet surface comprises liquid inlet fibers and liquid inlet holes, the liquid inlet fibers mutually encircle to form the liquid inlet holes, the hole area ratio of the liquid inlet holes is 15-55%, the surface tension of the liquid inlet surface is 42-58 dyne/cm, and the thickness of the nylon microporous membrane is 40-120 mu m;

the flux of the filter membrane is not less than 40L/h/m ² @30psi。

Optionally, the area ratio of the holes of the liquid inlet is 20% -50%; further optionally, the area ratio of the holes of the liquid inlet holes is 25% -45%.

Optionally, the surface tension of the liquid inlet surface is 45-55 dyne/cm; further alternatively, the surface tension of the liquid inlet surface is 50-55 dyne/cm.

Optionally, the flux of the filter membrane is not less than 50L/h/m ² @30psi; further alternatively, the filter membrane has a flux of not less than 60L/h/m ² @30psi; further alternatively, the filter membrane has a flux of not less than 70L/h/m ² @30psi; further alternatively, the filter membrane has a flux of not less than 80L/h/m ² @30psi; further alternatively, the filter membrane has a flux of not less than 90L/h/m ² @30psi; further alternatively, the filter membrane has a flux of not less than 100L/h/m ² @30psi。

By adopting the technical scheme, the composite membrane is obtained by compounding the nylon micropores and the cellulose layer, and the cellulose layer which plays a main role in virus interception in the composite membrane adopts a cellulose film-forming material with good hydrophilicity, so that the composite membrane has higher protein yield, and the concentration and purity of active proteins in filtrate are ensured. The introduction of the nylon microporous membrane greatly improves the intrinsic defect of softer texture of the cellulose film-forming material, which means that the filtration efficiency can be improved by further improving the filtration pressure and the production cost can be reduced for the virus removal filtration process taking the pressure as the filtration driving force, thus having very positive effects. However, as mentioned above, the introduction of the nylon microporous membrane often brings about the problem that the flux and the delamination resistance are difficult to be combined, and the conventional composite membrane is often required to be replaced at present; if the nylon microporous membrane is softened by a solvent, the delamination resistance and the pressure resistance of the prepared composite membrane can be improved, but the local solid content of the casting solution can be obviously improved after the nylon microporous membrane is locally softened, and a relatively compact membrane structure is obtained after re-split-phase solidification, so that the flux and the loading capacity are synchronously reduced; if the solvent in the casting solution cannot soften the nylon microporous membrane (compared with a nonwoven substrate which is more open), a composite membrane with higher integrity is difficult to obtain, and the nylon microporous membrane and the cellulose layer are easy to peel off under higher use pressure, so that unnecessary and unexpected risks are brought to the virus filtration process.

The inventors of the present application found that, on the basis of specific selection of a nylon microporous membrane having good resistance to an organic solvent and thus not easily softened by a solvent as a substrate, by controlling the pore area ratio of the inlet level of the nylon microporous membrane to 15 to 55% and the surface tension to 42 to 58dyne/cm, it is possible to ensure obtaining a permeation zone having a thickness of 10 to 50. Mu.m, so that the composite membrane obtained has not only a thickness of 40L/h/m or more ² Pass at 30psi, and also have high delamination resistance.

This is probably due to the fact that for a substantially symmetrical nylon microporous membrane (substantially symmetrical means that the pore diameter maintains a small gradient of variation along the thickness of the membrane, e.g., less than 5nm/μm), the morphology of the surfaces on both sides of the membrane has a small difference, and therefore, the rough morphology of the surfaces on both sides can be obtained by observing the morphology of the liquid inlet surface, and the characterization of the morphology parameters of the liquid inlet surface also characterizes the morphology parameters of the side of the nylon microporous membrane in contact with the cellulose casting solution to a certain extent.

The pore area ratio of the liquid inlet surface of the nylon microporous membrane is controlled to be not less than 15%, the surface tension is not less than 42dyne/cm, the cellulose casting solution and the nylon microporous membrane are easy to wet, the casting solution is not difficult to permeate into the nylon microporous membrane due to overlarge wetting resistance, and on the basis of ensuring the wettability of the casting solution and the nylon microporous membrane, the surface of the nylon microporous membrane has enough microporous structure to generate capillary phenomenon on the cellulose casting solution, so that the cellulose casting solution is promoted to permeate into the nylon microporous membrane, a permeation area with the thickness not less than 10 mu m is obtained, and the prepared composite membrane has good delamination resistance.

However, the inventors of the present application have unexpectedly found that as the pore area ratio and the surface tension of the liquid inlet surface of the nylon microporous membrane are increased, the thickness of the permeation region in the composite membrane is increased, and as the thickness of the permeation region is increased, the delamination resistance of the virus-free membrane is not increased linearly, but rather, the tendency of rapid increase followed by a slow increase speed is substantially presented, i.e., the influence of the thickness of the permeation region on the delamination resistance of the composite membrane has a marginal decreasing effect. This is probably because, when peeling the composite layer structure, the region where peeling is most likely to occur tends to be located near the composite interface of the layer structure, i.e., the delamination resistance of the composite film is mainly dependent on the structure near the composite interface of the layer structure, and therefore, the farther the distance from the composite interface is, the smaller the influence on the delamination resistance between the layer structures is. Also, as a result, when the thickness of the permeation zone is too large (e.g., greater than 50 μm), too far from the composite interface, the influence on the delamination resistance of the composite membrane is already small, and further increase of the thickness of the permeation zone inevitably results in increase of the feed liquid resistance of the permeation zone.

Correspondingly, the flux and the loading of the composite membrane decrease first a little and then at a faster rate. When the pore area ratio of the liquid inlet surface of the nylon microporous membrane is controlled to be not less than 55% and the surface tension is not less than 58dyne/cm, the flux and the loading capacity of the composite membrane are obviously reduced on the basis of keeping the delamination resistance basically unchanged. This is probably due to the fact that the too high pore area ratio and surface tension of the liquid inlet surface can further promote a large amount of casting solution to permeate into the nylon microporous membrane, so that a permeation area with an excessive thickness (such as more than 50 μm) is obtained, and the excessive thickness of the permeation area forms excessive blockage to the inner pore structure of the nylon microporous membrane, and the permeation area has larger resistance and lower dirt receiving space, so that flux and loading capacity are reduced.

Further, the thickness of the nylon microporous membrane is controlled to be 40-120 mu m, so that the composite membrane can be ensured to have the required high pressure resistance, the possibility of rising feed liquid resistance caused by excessively thick nylon microporous membrane can be reduced, and the composite membrane is ensured to have higher flux on the basis of having the high pressure resistance.

It can be understood that the measurement mode of various surface morphology parameters (such as thickness, fiber diameter, aperture, hole area rate and the like) of the composite membrane can be obtained by using a scanning electron microscope to perform morphology characterization on the membrane structure, then using computer software (such as Matlab, NIS-Elements and the like) or manually to perform measurement and corresponding calculation; in the preparation of the membrane, the characteristics such as pore size distribution are substantially uniform in the direction perpendicular to the membrane thickness (the direction is a planar direction if the membrane is in the form of a flat plate membrane; the direction is perpendicular to the radial direction if the membrane is in the form of a hollow fiber membrane); the overall average pore size in the plane can be reflected by determining the average pore size of a partial region in the corresponding plane. In practice, the surface (or cross-section) of the film may be characterized by electron microscopy to obtain a corresponding SEM image and selecting an area, e.g., 1 μm ² (1 μm by 1 μm) or 25 μm ² (5 μm by 5 μm), measuring the shape parameters such as pore diameter and fiber diameter of all holes on the specific area by corresponding computer software or manually, and calculating to obtain the final productThe average pore diameter, average fiber diameter and other morphological parameters of the region; of course, the person skilled in the art can also obtain the above parameters by other measuring means, which are only used as reference.

Alternatively, the average diameter of the liquid inlet fiber is 150-450 nm, and the SEM measurement average pore diameter of the liquid inlet hole is 700-2000 nm.

By adopting the technical scheme, on the basis of 15-55% of the area ratio of the holes of the liquid inlet surface and 42-58 dyne/cm of the surface tension, the liquid inlet fiber with the average diameter of 150-450 nm and the liquid inlet hole with the average diameter of 700-2000 nm measured by SEM are preferable, so that the nylon microporous membrane has more preferable liquid resistance and more preferable flux; the nylon microporous membrane can also have further preferable casting solution resistance and further preferable internal pore wall structure (the pore wall of the pore structure is actually the surface of the fiber structure, so that the thicker the fiber is, the generally lower the specific surface area) so as to ensure that the casting solution is easy to permeate and has more pore wall structure with the casting solution permeated into the nylon microporous membrane to generate interaction force with the nylon microporous membrane, so as to improve the delamination resistance of the composite membrane; but not the problem that the casting solution is difficult to permeate because of smaller and denser pore structures, so that the delamination resistance is reduced.

For example, for a nylon microporous membrane with a specific pore area ratio and surface tension, if the average diameter of the liquid inlet fibers is too large (e.g., greater than 450 nm) and the average pore diameter of the liquid inlet pores is too large (e.g., greater than 2000 nm), this means that the liquid inlet surface has a large pore coarse fiber structure and the number of liquid inlet pores is small (on the basis of a certain pore area ratio, the larger the area of a single pore is, the smaller the number of pores is). Although the large pore structure of the liquid inlet surface can promote the penetration of the casting solution into the interior of the nylon microporous membrane, so as to improve the integrity of the composite membrane, the coarse fiber and small amount of large pore structure also mean that the nylon microporous membrane has a lower specific surface area, even if the casting solution penetrates into the nylon microporous membrane, the pore wall structure for the casting solution to adhere to and generate interaction force with the casting solution is also less, so that even if the penetration area is provided, the further preferable delamination resistance performance is not provided. If the average size of the liquid inlet fiber is small (e.g. less than 150 nm) and the average pore size of the liquid inlet hole is too small (e.g. less than 700 nm), the liquid inlet surface has a small pore fiber structure, which means that the number of liquid inlet holes is large and the specific surface area of the nylon microporous membrane is relatively large. While a larger specific surface area tends to mean more interaction force with the casting solution permeated into the interior of the nylon microporous membrane, too small a pore size tends to mean an increase in the difficulty of permeation of the casting solution, and thus has an unpreferable delamination resistance. In addition, small pore fibril structure tends to mean a denser pore structure within the nylon microporous membrane that forms a higher tortuosity feed liquid flow path, and a more tortuosity feed liquid path tends to mean a higher feed liquid resistance, so that the composite membrane also has a non-preferred flux.

Therefore, for a nylon microporous membrane having a liquid inlet surface with a hole area ratio of 15 to 55% and a surface tension of 42 to 58dyne/cm, it is preferable to control the average diameter of the liquid inlet fiber to 150 to 450nm and the average pore diameter of the liquid inlet hole measured by SEM to 700 to 2000nm, so as to obtain further preferable combination properties.

Optionally, in the liquid inlet surface, the liquid inlet fiber with the diameter not smaller than 1.3 times of the average diameter is coarse fiber, and the ratio of the coarse fiber in the liquid inlet fiber is not more than 25%.

By adopting the technical scheme, the crude fiber can play a part of structural reinforcement effect to improve the pressure resistance of the composite membrane, and on the other hand, the existence of the crude fiber often means the reduction of the local specific surface area for the membrane casting liquid to adhere to and generate interaction force with the membrane casting liquid.

Optionally, the connection points of the adjacent liquid inlet fibers are connection points, the average diameter of the connection points is larger than that of the liquid inlet fibers, and 2.5-4.5 liquid inlet fibers are connected to each connection point on average.

By adopting the technical scheme, the fibers do not exist independently, but form a three-dimensional network structure, wherein the fiber structure forms a framework part of the three-dimensional network structure, pores of the three-dimensional network structure are membrane pore structures, and joints of the fibers are connection points; and the morphology structure of the liquid inlet surface can show the whole three-dimensional network structure to a certain extent.

The connecting point is used as a connecting structure between fibers, has a larger diameter compared with the fibers, and the larger diameter of the connecting point means that the connecting point has good connection and supporting effects on a local fiber structure, so that the local stability of the three-dimensional network structure after being pressed is improved, and the pressure resistance of the nylon microporous membrane is improved. Correspondingly, the connection points have larger diameters and thus larger feed liquid resistance than the fibers, and the presence of the connection points can increase the irregularity of the membrane pore structure, thereby increasing the resistance of the membrane pore structure to feed liquid. Therefore, the liquid inlet fiber connected to each connecting point is not too much, so that the insufficient reinforcing effect of the connecting point is avoided; the quantity of liquid inlet fibers connected to each connecting point is not too small, so that larger liquid resistance is avoided, and the flux of the composite membrane is reduced.

Optionally, the zeta potential of the liquid inlet surface at the pH value of 7 is between-2 mV and-40 mV.

By adopting the technical scheme, on the basis that the surface morphology of the nylon microporous membrane is approximately the same, the inventor of the application surprisingly discovers that the zeta potential of the nylon microporous membrane can also influence the delamination resistance and flux of the finally prepared composite membrane, and the adoption of the nylon microporous membrane with the zeta potential of-2 mV to-40 mV can further preferably obtain the good delamination resistance of the composite membrane. It should be noted that although it is well known that nylon materials are inherently negatively charged, it is quite unexpected that the zeta potential of the nylon materials is preferably controlled to provide a composite membrane with better delamination resistance.

This is probably because the cellulose-based material has a large number of hydroxyl groups, and thus, when the cellulose-based material is phase-separated in a non-solvent coagulation bath (e.g., water), the hydroxyl groups on the cellulose-based material may be ionized to have a weak negative charge. If the nylon microporous membrane is provided with excessive negative electricity (e.g. zeta potential is less than-40 mV), excessive electrostatic force is generated between the nylon microporous membrane with a large amount of negative electricity and the casting solution, the bonding fastness between the casting solution and the wall of the nylon microporous membrane is reduced, and even if the nylon microporous membrane has a permeable area with the same thickness, the cellulose layer and the nylon microporous membrane are more easily stripped, so that the delamination resistance of the composite membrane is reduced.

However, if the zeta potential of the nylon microporous membrane is controlled to be greater than-2 mV and even positively charged, it is often necessary to positively modify the nylon microporous membrane, and in virus removal applications, negatively charged active protein materials are often present in the feed solution, and less negatively charged or even positively charged nylon microporous membranes will likely cause adsorption of the protein active materials, resulting in a decrease in protein yield, which is an undesirable result for the expensive protein active materials. Therefore, in the application, the nylon microporous membrane with zeta potential of-2 mV to-40 mV is preferably adopted, and the low adsorption of the composite membrane to the protein in the feed liquid can be ensured on the basis of ensuring the delamination resistance of the composite membrane.

It is understood that the cellulose material may be regenerated cellulose material obtained by hydrolyzing cellulose derivative, or cellulose derivative having hydroxyl group.

Optionally, in the liquid inlet surface, the liquid inlet holes with the aperture of SEM measurement not smaller than 1.3 times of the average aperture of SEM measurement are large holes, the liquid inlet holes with the aperture of SEM measurement not larger than 0.5 times of the average aperture of SEM measurement are small holes, and the number of large holes in all the liquid inlet holes is 10-30%, and the number of the large holes is not more than 25% smaller than Kong Zhanbi.

By adopting the technical scheme, macropores in the liquid inlet surface can promote the casting solution to permeate into the nylon microporous membrane, so that the number of macropores is not too small (such as less than 10%), but excessive macropores (such as more than 30%) can lead to too low specific surface area of the nylon microporous membrane, so that the interaction area between the nylon microporous membrane and the casting solution is reduced, and the delamination resistance of the composite membrane is reduced. Similarly, the specific surface area of the nylon microporous membrane can be properly increased by a certain amount of small pore occupation ratio, so that the delamination resistance of the composite membrane is improved, but the small pore occupation ratio Kong Zhanbi is not too high (such as more than 25 percent) so as to avoid excessive small pores not only generating excessive resistance to feed liquid, but also affecting the flux of the composite membrane and the permeation of casting membrane liquid.

Optionally, the liquid inlet surface is taken as the position of the nylon microporous membrane thickness 0, the surface of one side far away from the liquid inlet surface is taken as the position of the nylon microporous membrane thickness 1, the aperture change coefficient X of the nylon microporous membrane is less than or equal to 0.4, and X is calculated by the following formula:

in the above, D _0.1 Average pore diameter, D, was measured for SEM in the region of 0 to 0.1 film thickness of nylon microporous membrane ₁ Average pore diameter, D, was measured for SEM in the region of 0.9 to 1 film thickness of nylon microporous membrane _{Are all} For D _0.1 And D ₁ Average value of (2).

By adopting the technical scheme, the aperture change coefficient of the nylon microporous membrane represents the aperture change degree of the nylon microporous membrane in the film thickness direction to a certain extent, and the nylon microporous membrane with the aperture change coefficient not more than 0.4 is selected and used in the application, which means that the aperture change of the nylon microporous membrane in the thickness direction is smaller, and the nylon microporous membrane has a structure which is approximately symmetrical or slightly asymmetrical. The substantially symmetrical nylon microporous membrane reduces the variation in permeation resistance due to membrane pore variation, thereby providing a composite membrane having more uniform delamination resistance throughout.

If the pore diameter change coefficient of the nylon microporous membrane is too large, the pore structure of the nylon microporous membrane has a larger change gradient along the film thickness direction, and the position of the film thickness 1 (namely, one side surface of the nylon microporous membrane, which is contacted with casting solution), if the membrane pores of the nylon microporous membrane are rapidly enlarged, the region near the film thickness 1 of the nylon microporous membrane has a pore structure with higher density, the casting solution is difficult to permeate, and the casting solution permeated into the nylon microporous membrane is difficult to fill the pore structure of the nylon microporous membrane with the enlarged pore diameter, so that good interaction between the casting solution and the pore wall structure of the nylon microporous membrane is difficult to ensure, and the delamination resistance performance of the composite membrane is reduced. If the membrane pores of the nylon microporous membrane become smaller rapidly, the region near the membrane thickness 1 of the nylon microporous membrane has a pore structure with higher porosity, namely the region naturally has lower specific surface area, and the interaction area between the casting solution near the region and the pore wall structure of the nylon microporous membrane is smaller, so that the delamination resistance of the composite membrane is reduced; in addition, the membrane pores of the nylon microporous membrane become smaller rapidly, which means that the rapid increase of the permeation resistance of the casting solution easily causes the thickness of the permeation area to be too low, which also affects the delamination resistance of the composite membrane.

Optionally, the ratio of the average fiber diameter in the area with the film thickness of 0 to 0.1 of the nylon microporous film to the average fiber diameter in the area with the film thickness of 0.4 to 0.5 of the nylon microporous film is 0.7 to 1.3; the ratio of the average fiber diameter in the region of 0.4-0.5 film thickness of the nylon microporous film to the average fiber diameter in the region of 0.9-1 film thickness of the nylon microporous film is 0.7-1.3.

Optionally, the difference between the average fiber diameter in the area with the film thickness of 0-0.1 and the average fiber diameter in the area with the film thickness of 0.4-0.5 is not more than 50nm; the difference between the average fiber diameter in the area of 0.4-0.5 film thickness of the nylon microporous film and the average fiber diameter in the area of 0.9-1 film thickness of the nylon microporous film is not more than 50nm.

By adopting the technical scheme, the aperture change coefficient of the nylon microporous membrane can represent the integral pore structure change trend of the nylon microporous membrane, but the morphological structure change trend inside the nylon microporous membrane is difficult to clearly represent. If the nylon microporous membrane is equally divided into two parts according to the membrane thickness, and the morphology structures of the two parts of membrane structures are respectively represented, the morphology structure change trend inside the nylon microporous membrane can be further represented.

The average fiber diameter of the upper and lower parts of the nylon microporous membrane has no larger mutation, which indicates that the upper and lower parts of the nylon microporous membrane have approximately symmetrical structures, thereby further ensuring the compound uniformity of the compound membrane and ensuring the compound membrane to have relatively uniform delamination resistance.

It is understood that the difference between the average fiber diameter in the region of 0 to 0.1 film thickness of the nylon microporous film and the average fiber diameter in the region of 0.4 to 0.5 film thickness of the nylon microporous film, or the difference between the average fiber diameter in the region of 0.4 to 0.5 film thickness of the nylon microporous film and the average fiber diameter in the region of 0.9 to 1 film thickness of the nylon microporous film means the difference between the average fiber diameters in both regions, and the values thereof are positive numbers.

Optionally, the permeable region includes nylon fibers and cellulose fibers, the nylon fibers mutually encircle to form primary pores, the cellulose fibers are located in the primary pores, the cellulose fibers mutually encircle and divide the primary pores into a plurality of secondary pores, and the SEM measurement average pore diameter of the secondary pores is smaller than that of the primary pores.

By adopting the technical scheme, on the basis that the thickness of a permeation area is 10-50 mu m, the casting solution permeates into the pore structure in the nylon microporous membrane, and the influence on the porosity of the nylon microporous membrane is difficult to avoid, so that the resistance of the nylon microporous membrane is improved; of course, on the basis of the same casting solution coating thickness, as the thickness of the casting solution penetrating into the nylon microporous membrane increases (i.e. the thickness of the penetrating area increases), the total thickness of the composite membrane will decrease, because the thickness of the pure cellulose layer which does not penetrate into the nylon microporous membrane will be reduced, and the pure cellulose layer with lower thickness tends to have lower resistance to the feed solution. Thus, the permeation process of the casting solution is accompanied by the improvement of the feed solution resistance of the nylon microporous membrane and the reduction of the feed solution resistance of the pure cellulose layer.

It is further preferred in the present application to introduce secondary pore structures in the permeate region, which are formed by surrounding and entangling the cellulose fibers in the permeate region with each other, separating the pore structures (i.e., primary pores) of the nylon microporous membrane. The secondary holes enable a large number of passages for feed liquid to flow in the primary holes in the permeation area, and compared with the primary holes without the secondary hole structure, the special macroporous sleeve small hole structure can obviously reduce feed liquid resistance of the permeation area; as mentioned above, the thickness of the pure cellulose layer will decrease with the increase of the thickness of the permeable region, and the liquid resistance of the pure cellulose layer will decrease. In short, the introduction of the secondary pores in the permeable zone only increases the resistance of the permeable zone to a small extent on the basis of the reduced resistance of the pure cellulose layer, thus allowing the composite membrane to have a better flux on the basis of good delamination resistance (thickness assurance of the permeable zone).

Optionally, the region with the thickness of 10 μm at the side of the infiltration region close to the prefilter region is a boundary region, the region with the thickness of 5 μm at the side of the boundary region close to the liquid inlet surface is an upper boundary region, the region with the thickness of 5 μm at the side of the boundary region close to the liquid outlet surface is a lower boundary region, and the SEM measurement average pore diameter of the secondary pores in the infiltration region is larger than that of the secondary pores in the boundary region; the average diameter of the cellulose fibers in the interface region is not less than 50nm.

By adopting the technical scheme, as described above, the influence of each part in the permeation zone on the delamination resistance of the composite membrane is not the same, wherein the area with the greatest influence on the delamination resistance of the composite membrane is located near the composite interface of each layer of membrane structure. The inventors of the present application have found that for a composite membrane of the specific structure of the present application, the region of the permeation zone (i.e., the interfacial zone) near the composite interface, which is about 10 μm thick, has a greater impact on the delamination resistance of the virus-free membrane.

It is further preferred according to the present application that the SEM-measured average pore size of the secondary pores in the permeate region is set to be larger than the SEM-measured average pore size of the secondary pores in the interface region, which means that the secondary pores in the interface region have smaller pore sizes and higher densities, and that the denser, more entangled cellulose fibers in the interface region can ensure sufficiently high delamination resistance of the composite membrane, despite the smaller cellulose fiber diameters in the interface region. Of course, although cellulose fibers having smaller diameters in the interface region have smaller flow resistance to the feed liquid, cellulose fibers having too small diameters (e.g., less than 50 nm) may still cause the cellulose fibers at the interface where the delamination resistance of the composite film is most affected to be easily broken, and the delamination resistance of the composite film is lowered, so that the cellulose fibers in the interface region should not have diameters lower than 50nm.

Therefore, the application controls the interface area to have a more compact three-dimensional cellulose fiber skeleton structure compared with the whole permeation area, and the diameter of cellulose fibers in the cooperative coordination interface area is not less than 50nm, so that the virus-removing membrane has higher delamination resistance and higher flux.

Alternatively, the SEM measurement average pore diameter of the secondary pores in the lower junction region is 100-200 nm; the average pore diameter of the secondary pores in the upper boundary region is 120-220 nm as measured by SEM.

By adopting the technical scheme, the pore diameters of the secondary pores in the lower junction region and the upper junction region are further controlled on the basis that the average pore diameter of the SEM measurement of the liquid inlet surface of the nylon microporous membrane is 700-2000 nm and is a substantially symmetrical membrane. For the boundary area of a special macroporous sleeve small pore structure, the pore size of the secondary pores greatly influences the delamination resistance of the composite membrane and the feed liquid resistance of the permeation area on the basis of the approximate definition of the pore size of the primary pores.

As described above, the region having the greatest influence on the delamination resistance of the composite membrane is located in the region near the composite interface, that is, the junction region having the greatest influence on the delamination resistance of the virus-removing membrane in the permeation region, and the lower junction region having the greatest influence on the delamination resistance of the virus-removing membrane in the junction region. And because the secondary pores in the permeable zone of the composite membrane in the application have a substantially asymmetric structure, the secondary pores with the smallest pore diameter in the whole permeable zone are located in the junction zone and are located near the lower junction zone, and therefore, the lower junction zone and the upper junction zone in turn in the permeable zone have the greatest influence on the flux of the composite membrane.

Because the lower junction area is provided with a secondary pore structure with a relatively smaller pore diameter, in order to ensure low influence of the whole permeation area on the flux of the composite membrane, a low feed liquid resistance pore structure with a 'macroporous sleeve pore' in the lower junction area needs to be ensured; however, in order to ensure that the composite membrane still has high delamination resistance, the secondary pore structure in the 'macroporous sleeve pore' structure is not suitable to have an oversized pore diameter, so that the phenomenon of delamination is easy to generate due to insufficient compactness of the cellulose fiber skeleton structure. Therefore, the pore diameter of the secondary pores in the lower junction region is preferably controlled to be 100-200 nm, so that the composite membrane has good delamination resistance and high flux.

Similarly, the morphology structure of the upper interface region has relatively great influence on the feed liquid resistance of the permeation region and the delamination resistance of the composite membrane. If the pore size of the secondary pores in the upper boundary region is too large (e.g., greater than 220 nm), it is indicated that the density of the cellulosic fibrous skeleton in the upper boundary region is low, and although the resistance of the upper boundary region to the feed liquid is reduced, the entanglement of the cellulosic fibers between the upper and lower boundary regions is reduced, and the cellulosic fibers in the upper boundary region are difficult to inhibit breakage of the cellulosic fibers in the lower boundary region, resulting in insufficient delamination resistance of the composite membrane; in addition, on the basis of the secondary pore structure with smaller pore diameter in the lower junction region, if the pore diameter of the secondary pore structure in the upper junction region is too large, which means that a larger pore diameter variation gradient exists in the secondary pore in the junction region along the thickness direction, concentrated interception of impurity particles is easy to cause (concentrated interception means that large particle substances and small particle substances are intercepted in a small range region), and concentrated interception of the impurity particles often means rapid blockage of the local pore structure of the composite membrane, so that the service life of the composite membrane is too low. If the aperture of the secondary holes in the upper junction area is too small (for example, less than 120 nm), although the more compact cellulose fiber skeletons in the upper junction area form entanglement with the cellulose fiber skeletons in the lower junction area, the delamination resistance of the composite membrane can be further improved; however, on the basis of the lower junction region with the denser secondary pore structure, the upper junction region with the denser secondary pore structure is further introduced, so that the whole junction region has the denser secondary pore structure, larger feed liquid resistance is formed, and the lower flux of the composite membrane is caused. Therefore, on the basis that the lower junction area has a denser secondary pore structure, the composite membrane can have more preferable flux and delamination resistance by further preferably controlling the pore diameter of the secondary pore structure of the upper junction area

Optionally, the ratio of the SEM measured average pore diameter of the primary pores to the SEM measured average pore diameter of the secondary pores in the lower boundary region is 4-10; the ratio of the SEM measured average pore diameter of the primary pores to the SEM measured average pore diameter of the secondary pores in the upper boundary region is 3 to 9.

By adopting the technical scheme, no matter the structure of the special macroporous sleeve small holes is arranged in the upper junction area or the lower junction area, wherein the primary holes with larger pore diameters determine the porosity of the nylon microporous membrane, and besides the influence on the permeation resistance of the casting solution, the flux and the supporting capacity of the nylon microporous membrane are determined to a great extent. If the primary pore diameter is too large, the nylon microporous membrane has a larger flux but tends to have a lower supporting capacity; if the primary pore diameter is too small, the nylon microporous membrane has a good supporting effect, but cannot guide the feed liquid to pass through with a larger flux and enter the cellulose layer.

In addition, although the size of the primary pores largely determines the flux of the microporous membrane, the flux is still determined by the superposition of feed liquid resistances everywhere for the whole virus removal membrane, and the secondary pores with relatively smaller pore diameters besides nylon fibers with larger fiber sizes are arranged in the boundary region. By limiting the aperture ratio of the primary holes and the secondary holes, the density of nylon fibers with larger feed liquid resistance in the primary holes can be reacted to a great extent, and the density of cellulose fibers with larger feed liquid resistance in the secondary holes can be reacted. The ratio of the apertures of the primary aperture to the secondary aperture is too large, which means that the primary aperture is too large to obtain a sufficient supporting effect, and the primary aperture has a secondary aperture structure with too small aperture, and the secondary aperture with too small aperture will generate larger feed liquid resistance. The ratio of the apertures of the primary aperture to the secondary aperture is too small, which means that the primary aperture is too small to have more compact nylon fibers, while the aperture of the secondary aperture in the primary aperture is larger, and the secondary aperture with larger aperture has smaller resistance to the feed liquid, but the too loose cellulose fiber structure can cause the defect of the delamination resistance of the virus removal membrane, and the more compact nylon fiber structure can also form larger resistance to the feed liquid, so that the flux of the virus removal membrane is reduced.

Optionally, the average diameter of the cellulose fibers in the lower interface region is not less than 40nm, and the ratio of the average pore diameter to the average diameter of the cellulose fibers measured by SEM of primary pores in the lower interface region is 10 to 25; the average diameter of the cellulose fiber in the upper boundary region is not less than 60nm, and the ratio of the average pore diameter to the average diameter of the cellulose fiber measured by SEM of the primary pores in the upper boundary region is 8 to 20.

By adopting the technical scheme, the morphology structure of small holes and fine fibers in the lower junction region can greatly improve the delamination resistance of the composite membrane through a compact three-dimensional network skeleton structure. However, if the cellulose fiber diameter in the lower interface region is too small, the cross-sectional area will become one fourth as the cellulose fiber diameter is halved, and the mechanical properties of the fiber are not linearly reduced but exponentially reduced; therefore, the skeleton structure formed by cellulose fiber with too small diameter (such as less than 40 nm) can not obtain the required mechanical property even if the skeleton structure is compact, and fiber fracture still easily occurs under the action of external force to cause layering phenomenon.

In addition, the specific primary holes have a secondary hole structure, so that the lower junction area is provided with special large-hole sleeve small holes and large-hole fine fiber structures, and for the lower junction area with the primary holes with larger apertures, the existence of the secondary holes and the fine fibers combine to enable the feed liquid to be subjected to smaller resistance by the secondary holes. Therefore, the special macroporous sleeve small holes and the fine fiber structures in the large holes in the lower junction area not only can enable the virus removal membrane to have good delamination resistance, but also have small resistance to feed liquid, so that the virus removal membrane has high flux.

Because the upper boundary region has a secondary pore structure with a larger pore diameter than that of the lower boundary region, even if the cellulose fiber with a relatively larger diameter (such as not less than 60 nm) is provided, the secondary pore structure with a larger pore diameter and the primary pore structure with a larger pore diameter (the ratio of the secondary pore structure to the cellulose fiber is 8-20) can ensure that the upper boundary region is provided with a channel for the circulation of feed liquid, and the upper boundary region is provided with a special large pore sleeve small pore (the small pore is larger than that of the lower boundary region) and a structure of fine fibers in the large pore (the fiber diameter is larger than that of the lower boundary region), so that the resistance of the upper boundary region to the feed liquid can be ensured to be smaller.

In addition, the larger-sized secondary pore structure of the upper boundary region relative to the lower boundary region means that the three-dimensional network skeleton structure formed by cellulose fibers in the upper boundary region has higher porosity, and the three-dimensional network skeleton with higher porosity is combined with the cellulose fibers with relatively larger matched diameters, so that the cellulose fibers in the upper boundary region can have good breaking strength even though the porosity is higher; therefore, the upper junction area closer to the composite interface has low feed liquid resistance, and the delamination resistance of the composite membrane can be further improved.

Optionally, the loading of the filter membrane is not lower than 200L/m ² The retention rate of the peel strength of the filter membrane is not lower than 0.8@30 psi for 2 h.

By adopting the technical scheme, the loading capacity of the filter membrane greatly reflects the service life of the filter membrane, and the filter membrane belongs to a composite membrane, but also has higher loading capacity on the basis of ensuring high delamination resistance.

The current general method for evaluating the delamination resistance of the composite membrane is to test the 180 DEG peel strength of the composite membrane, but the 180 DEG peel strength only can reflect the delamination resistance of the composite membrane in the initial state, and the filtration membrane is applied to a continuous pressure-bearing process for virus removal filtration, which is likely to be accompanied by the change of morphology structure at the composite interface of the composite membrane (such as fracture of cellulose fibers with extremely small diameter in the interface area after long-time pressure bearing, etc.). The change of the morphology structure at the composite interface of the composite membrane is likely to cause the change of the flux, the virus interception capacity and the like of the composite membrane, so that the retention rate of the peel strength of the composite membrane after the composite membrane is subjected to feed liquid pressure for a long time is limited, and the performance of the composite membrane in practical application can be reflected.

According to the application, the retention rate of the stripping strength of the filter membrane after 2h treatment of the feed liquid with the pressure of 30psi is not lower than 0.8, so that the filter membrane can be ensured to have stable and good delamination resistance and flux in practical application.

In a second aspect, the application provides a virus removal membrane assembly, which adopts the following technical scheme:

a virus-removing membrane module comprising the filter membrane of any one of the preceding claims and the number of the filter membranes is 1-3 layers, wherein the interception capability of the membrane module for PP7 phage reaches LRV > 4.

Optionally, the membrane component comprises 1 layer of the filter membrane, and the interception capacity of the filter membrane for PP7 phage reaches LRV > 5; preferably, the membrane module has an entrapment capacity for PP7 phage of LRV > 6.

Optionally, the membrane component comprises 2 layers of the filter membranes, and the interception capacity of the filter membranes for PP7 phage reaches LRV > 6; preferably, the membrane module has an entrapment capacity for PP7 phage of LRV > 7.

In a third aspect, the application provides a preparation process of a supported composite cellulose virus-removing filter membrane, which adopts the following technical scheme:

a preparation process of a supported composite cellulose virus-removing filter membrane comprises the following steps:

s1, preparing a casting solution, wherein the casting solution at least comprises a cellulose polymer, a first good solvent and a first non-solvent, the mass ratio of the first non-solvent is 2-4%, the solid content of the casting solution is 10-25%, the viscosity of the casting solution is 5000-20000 cps, and the first non-solvent is small molecular alcohol;

S2, pouring, namely pouring the casting film liquid onto a carrier to form a liquid film, compounding a nylon microporous film on the liquid film, wherein the compounding speed of the nylon microporous film is 0.5-2.5 m/S, and then placing the carrier in a negative pressure environment with the air pressure of 0.7-0.85 bar for 15-30S to obtain a compound semi-finished film;

s3, curing to form a film, immersing the carrier in a curing bath, and curing for at least 5min to obtain a green film, wherein the curing bath comprises a second good solvent and a second non-solvent, and the second good solvent accounts for 5-15wt% in the curing bath;

s4, regenerating cellulose, and placing the raw film in a regeneration bath to hydrolyze and regenerate the raw film to obtain the cellulose virus-removing film.

By adopting the technical scheme, the existing film-making process of the composite film with the support layer generally comprises the steps of directly coating film casting liquid on the microporous film support layer, and obtaining the required composite film through a series of post-treatment. The film-making process mainly relies on the gravity of the casting solution to enable the casting solution to partially permeate into the substrate, and no driving force for driving the rest casting solution to permeate into the substrate is generated, in fact, as the substrate is positioned on the carrier side and the liquid casting solution is positioned on the upper surface of the substrate, even if external acting force is applied, the liquid casting solution firstly acts on the casting solution, and unexpected defects and the like are likely to be generated under the action of the external acting force, so that the difficulty of applying the external driving force by the film-making process is higher; in addition, when the casting solution permeates into the substrate, air in the pore structure of the substrate is necessarily extruded and forced to be discharged, which obviously increases the permeation difficulty of the casting solution, and since the lower surface of the substrate is directly contacted with the carrier, the pore structure of the substrate is largely shielded, the air in the substrate is difficult to be discharged from the lower surface of the substrate, and if the air is discharged upwards, the casting solution with higher viscosity needs to be penetrated, and if the air in the substrate does not completely penetrate the casting solution and remains in the liquid film, the cellulose layer after phase separation solidification is likely to have macropore defects caused by bubbles.

In the application, a film making process of single-layer pouring and microporous film back cover is specifically adopted, namely, firstly, a casting film liquid is poured on a carrier, and then, a nylon microporous film is covered on a liquid film which is already poured. Compared with the process of coating the casting solution on the microporous membrane substrate, the process of coating the microporous membrane back cover ensures that air in the microporous membrane can be simply discharged upwards after the casting solution permeates into the microporous membrane, so that the resistance of the permeation of the casting solution is not easily formed, and air bubbles are not easily remained in the casting solution, thereby causing defects. In addition, the specific microporous membrane back cover process of the application makes it possible to further improve the permeability of the casting solution in the nylon microporous membrane, and the microporous membrane back cover process is matched with the negative pressure treatment after the compounding of the nylon microporous membrane, so that the casting solution can be promoted to permeate into the nylon microporous membrane and defects are not easy to be introduced into the cellulose layer. This is because, when the liquid film composited with the nylon microporous film is placed in a negative pressure environment (the negative pressure is that the ambient air pressure is smaller than the atmospheric pressure), the negative pressure acts on the nylon microporous film first to suck out the air inside the nylon microporous film, and the negative pressure formed after the air inside the nylon microporous film is sucked out again draws in the casting solution, so that a permeation area with the required thickness is obtained. And the liquid film is positioned on the carrier side, so that defects caused by instability of the liquid film due to integral stress are not easy to occur.

In order to ensure that a cellulose layer formed after phase separation and solidification of the casting solution has good virus interception effect, the solid content of the casting solution needs to be controlled, if the solid content of the casting solution is lower than 10%, the cellulose layer structure obtained by phase separation and solidification is likely to be too high in porosity, and the composite membrane has higher flux but is too high in virus leakage risk; if the solid content of the casting solution is higher than 25%, the casting solution with higher solid content can often obtain a cellulose layer with higher density after phase separation and solidification, and the flux of the composite membrane is reduced although the risk of virus leakage is lower, so that the filtration efficiency is reduced. The solid content of the casting solution is controlled to be 10-25%, and the mixed solvent of good solvent and non-solvent is used as curing bath in the curing and film forming stage to regulate and control the phase separation speed of the casting solution (the addition of the good solvent can properly delay the phase separation of the casting solution gel), so that the casting solution in the permeation zone is phase-separated at a proper slow speed, the possibility of forming a dense pore structure in the permeation zone is reduced, thereby the permeation zone has lower feed liquid resistance, and the composite film has high flux and high delamination resistance.

In addition, in order to promote the membrane casting solution to permeate into the nylon microporous membrane so as to obtain a required permeation area capable of improving the delamination resistance of the composite membrane, the membrane casting solution is added with 2-4% of small molecular alcohol by mass, and the small molecular alcohol has lower surface tension, so that the surface tension of the membrane casting solution can be reduced to a certain extent, and the wettability of the membrane casting solution and the nylon microporous membrane is improved, and therefore, the addition amount of the small molecular alcohol in the membrane casting solution is not lower than 2%; however, the addition of the small molecular weight alcohol as a non-solvent for the cellulose polymer to the casting solution increases the viscosity of the casting solution, and the casting solution has an excessively high permeation resistance, and it is difficult to form a permeation region of a sufficient thickness, so that the addition amount of the small molecular weight alcohol in the casting solution is not preferably higher than 4%. The viscosity of the casting solution can be controlled to be 5000-20000 cps (at 25 ℃) by controlling the adding amount of the small molecular alcohol to be 2-4% and the solid content of the casting solution to be 10-25%, so that the permeation resistance of the casting solution is not excessively large, a permeation area with the required thickness is obtained, and the prepared composite film can be ensured to have good virus interception performance.

In summary, the application combines a specific microporous membrane back cover process with a specific casting solution added with small molecular alcohol, a negative pressure treatment process and a curing bath to control the phase separation speed, thereby ensuring that the casting solution with higher viscosity can well permeate into the nylon microporous membrane to form a permeation area with required thickness, and the pore structure in the permeation area is not too compact to influence flux.

Optionally, before immersing the composite semi-finished film in the curing bath, performing pre-gel treatment on the composite semi-finished film, specifically, immersing the composite semi-finished film in the pre-gel bath after standing for 20-30 s, wherein the pre-gel time is 20-30 s, and the pre-gel film is obtained, the pre-gel bath at least comprises a third good solvent and a third non-solvent, and the ratio of the third non-solvent is 5-20wt%.

By adopting the technical scheme, the pre-gel bath is further introduced to pretreat the composite semi-finished membrane, the ratio of non-solvent in the pre-gel bath is controlled to be 5-20% (namely, the good solvent is relatively high, the effect of promoting gel phase separation is poor), the casting solution in the permeation zone can be diluted by the pre-gel bath, and the casting solution in the permeation zone forms solid content gradient change in the thickness direction (because the closer to the composite interface is the mass transfer process of the pre-gel bath, the larger the resistance is, the closer to the composite interface is the permeation zone, the higher the solid content is), and in combination with the curing bath with the specific adoption of the good solvent with the ratio of 5-15%, an obvious macroporous sleeve pore structure can be formed in the permeation zone, the existence of the secondary pores greatly reduces the resistance of the permeation zone to the feed liquid, so that the permeation zone not only can improve the delamination resistance of the composite membrane, but also has small influence on flux.

It should be noted that surface aperturing of cellulosic materials is difficult (this is related to its own characteristics, rapid phase separation in the solidification liquid is fast, and rapid phase separation easily results in a small pore structure, and high density), whereas the preparation process of coating the casting liquid means that even if the casting liquid is pretreated in a certain pretreatment manner, since the microporous membrane support layer is located on the support side, the pretreatment system is difficult to permeate the microporous membrane support layer with holes masked, and the pretreatment system needs to penetrate the whole layer of casting liquid to pretreat the interface between the casting liquid and the microporous membrane support layer, which is not practical, and therefore, even if pretreatment is performed, a pore structure of a larger size is obtained only on the side of the casting liquid away from the microporous membrane support layer, and thus a permeation region of high density is more easily formed, resulting in a decrease in flux and load. Therefore, the pregelatinization treatment in the present application is matched with the microporous membrane back cover process, thereby obtaining a further preferable secondary pore structure. It can be understood that even though the pre-gel treatment is not performed, the phase separation speed of the permeable region is controlled by controlling the proportion of the curing bath, and the permeable region has no preferred secondary pore structure, but has higher flux compared with a common composite membrane due to the fact that the pore structure is not compact.

Optionally, the temperature of the pre-gel bath is 50-70 ℃, the pre-gel bath is also added with penetrating agent with surface tension not higher than 20dyne/cm, and the concentration of the penetrating agent in the pre-gel bath is 1-3 wt%.

Optionally, the penetrating agent is at least one of hexafluoroisopropanol or trifluoroethanol.

By adopting the technical scheme, a small amount of penetrating agent with low surface tension is added into the pregelatinized bath, the temperature of the pregelatinized bath is controlled to be 50-70 ℃ higher, the penetrating capacity of the pregelatinized bath can be improved, the pregelatinized bath has a further preferable pretreatment effect, and the penetrating area is more stable and has a secondary pore structure.

Optionally, in the step S2, the nylon microporous membrane is tempered for 1-3 min in an environment with a temperature of 50-70 ℃ before being compounded, and then is compounded into a liquid membrane.

By adopting the technical scheme, the higher the temperature of the casting solution is, the lower the viscosity is, and on the basis that the solid content is unchanged and the casting solution is added with small molecular alcohol to improve the wettability of the casting solution, the viscosity of the casting solution is properly reduced to further promote the penetration of the casting solution into the nylon membrane. However, if the viscosity of the casting solution as a whole is too low, the dimensional stability of the liquid film deposited on the support is poor, and therefore, it is not preferable to heat the whole liquid film to a high temperature. Based on the above problems, the method of temperature regulating treatment is specifically adopted in the application, and the temperature is controlled to be higher before the nylon microporous membrane is compounded, so that after the nylon microporous membrane is compounded on the liquid membrane, the temperature at the compounding interface of the liquid membrane and the nylon microporous membrane is properly increased, the viscosity of the casting solution at the compounding interface is reduced, and the casting solution with better wettability is matched with the casting solution added with small molecular alcohol, so that the permeation resistance of the casting solution can be further reduced, and the required permeation area is obtained.

Optionally, the cellulose polymer is at least one of diacetyl cellulose, triacetyl cellulose, propionic acid cellulose, phthalic acid acetic acid cellulose, acetic acid butyric acid cellulose and acetic acid propionic acid cellulose;

the first good solvent and the second good solvent are at least one of acetone, dioxane, dimethylacetamide, N-methylpyrrolidone, acetic acid, propionic acid, butyric acid and valeric acid;

the small molecular alcohol is at least one of ethanol, 1-propanol, isopropanol, n-butanol and isobutanol.

In summary, the present application includes at least one of the following beneficial technical effects:

1. according to the application, the nylon microporous membrane is particularly adopted as the support of the cellulose layer, so that the pressure resistance of the composite membrane can be remarkably improved, and the nylon microporous membrane is not easy to soften by an organic solvent in cellulose casting solution, so that a local compact structure is not easy to form;

2. According to the application, the nylon microporous membrane with zeta potential of-2 mV to-40 mV is adopted, so that the binding fastness of the nylon microporous membrane and the cellulose materials in the casting solution can be improved, and the delamination resistance of the composite membrane is improved;

3. according to the application, a secondary pore structure is further introduced into the permeation region to form a special macroporous sleeve pore structure, and the cellulose skeleton structure forming the secondary pores is mutually entangled with the inside of the primary pores, so that the composite membrane has higher delamination resistance, and due to the existence of the secondary pores, the permeation region has a large number of passages for the flow of feed liquid, so that the feed liquid resistance of the permeation region is lower, and therefore, the composite membrane not only has higher delamination resistance, but also has higher flux.

Drawings

FIG. 1 is a cross-sectional scanning electron microscope image of a composite film according to example 1 of the present application, wherein the upper layer is a nylon microporous film, the lower layer is a cellulose layer, and the magnification is 500X.

FIG. 2 is a scanning electron microscope image of the liquid inlet surface of the composite film of example 1 of the present application, with magnification of 5000X.

FIG. 3 is a scanning electron microscope image of the compound film of example 1 of the present application at a magnification of 20000×.

FIG. 4 is a cross-sectional scanning electron microscope image of a nylon microporous membrane in the composite membrane of example 1 of the present application near the liquid inlet surface, and the magnification in the image is 10000×.

FIG. 5 is a cross-sectional scanning electron microscope image of the nylon microporous membrane in the middle of the composite membrane in the thickness direction of example 1 of the present application, and the magnification in the image is 10000×.

FIG. 6 is a cross-sectional scanning electron microscope image of the side of the nylon microporous membrane close to the permeation zone in the composite membrane of example 1 of the present application, and the magnification in the image is 10000×.

FIG. 7 is a cross-sectional scanning electron micrograph of the permeate region of the composite membrane of example 1 of the present application at 5000X magnification.

FIG. 8 is a further enlarged scanning electron microscope image of the cross section of the permeated region in the composite membrane of example 1 of the present application, and the magnification in the image is 10000×.

FIG. 9 is a further enlarged scanning electron microscope image of the cross section of the permeated region in the composite membrane of example 1 of the present application, and the magnification in the image is 20000×.

Detailed Description

The present application will be described in further detail with reference to fig. 1 to 9.

The embodiment of the application relates to a composite cellulose virus-removing filter membrane, a preparation process thereof and a virus-removing membrane component.

Example 1

The embodiment discloses a preparation process of a composite cellulose virus-removing filter membrane, which comprises the following process steps:

S1, preparing a casting solution, wherein the casting solution is prepared from a cellulose polymer, a first good solvent and a first non-solvent, and defoaming treatment is carried out after the preparation is completed, so that the casting solution is obtained. In the prepared casting film liquid, the mass ratio of the first non-solvent is 3%, the mass ratio of the cellulose polymer is 18% (i.e. the solid content is 18%), the viscosity is 13000cps, and the first non-solvent is small molecular alcohol and the small molecular alcohol is ethanol. In this embodiment, the cellulose polymer is cellulose diacetate, and the first good solvent is dimethylacetamide.

S2, pouring, namely pouring the casting film liquid onto a carrier (the carrier is a steel belt in the embodiment) to form a liquid film, compositing a nylon microporous film on the liquid film, and adjusting the temperature of the nylon microporous film in an environment with the temperature of 60 ℃ for 2min before compositing, wherein the compositing speed of the nylon microporous film is 1.5m/S; the support was then subjected to a negative pressure environment at a gas pressure of 0.78bar for 20s to obtain a composite semi-finished film. And then standing the composite semi-finished film for 25 seconds, immersing the composite semi-finished film into a pre-gel bath, wherein the pre-gel bath is prepared from 15wt% of a third non-solvent, 2wt% of a penetrating agent and 83wt% of a third good solvent, the temperature of the pre-gel bath is 60 ℃, the pre-gel treatment time is 25 seconds, and the pre-gel film is obtained after the pre-treatment is completed. In this embodiment, the third non-solvent is water, the third good solvent is dimethylacetamide, and the penetrating agent is trifluoroethanol. The morphology parameters and other types of the nylon microporous membrane used in the example are shown in Table 1.

S3, curing to form a film, immersing the carrier in a curing bath for 7min to obtain a green film, wherein the curing bath comprises a second good solvent and a second non-solvent, the second good solvent accounts for 10wt% in the curing bath, and in the embodiment, the second good solvent is dimethylacetamide and the second non-solvent is water;

s4, regenerating cellulose, placing the raw film in a regeneration bath to hydrolyze and regenerate the raw film, and obtaining the cellulose virus-removing film; in this example, a sodium hydroxide aqueous solution having a concentration of 0.1mol/L and a temperature of 40℃was used as the regeneration bath, and the green film was hydrolyzed and regenerated in the regeneration bath for 80 minutes.

Example 2

Example 2 differs from example 1 mainly in that the nylon microporous membrane used in this example is the same as that in example 1, but is used by being turned over on the basis of example 1, and the formulation of the casting solution and various process parameters are adjusted. The options such as various morphological parameters of the nylon microporous membrane used in this example are shown in table 1, the formulation of the casting solution is different, and the adjustment of various technological parameters is shown in table 2.

Example 3

Example 3 differs from example 1 mainly in that in this example, a nylon microporous membrane with higher density (i.e. smaller pore diameter) is selected, and the formulation of the casting solution and various process parameters are adjusted. The options such as various morphological parameters of the nylon microporous membrane used in this example are shown in table 1, the formulation of the casting solution is different, and the adjustment of various technological parameters is shown in table 2.

Example 4

Example 4 differs from example 1 mainly in that in this example, a nylon microporous membrane with lower density (i.e. larger pore diameter) is selected, and the formulation of the casting solution and various process parameters are adjusted. The options such as various morphological parameters of the nylon microporous membrane used in this example are shown in table 1, the formulation of the casting solution is different, and the adjustment of various technological parameters is shown in table 2.

Example 5

Example 5 differs from example 1 mainly in that this example uses a nylon microporous membrane that is denser than example 3, and the liquid inlet surface of the nylon microporous membrane has liquid inlet fibers with a lower average diameter and liquid inlet holes with a smaller average diameter as measured by SEM; in addition, the temperature adjustment treatment is not performed on the nylon microporous membrane before compounding, namely the nylon microporous membrane is in a room temperature state during compounding, and the formula of the casting solution and various process parameters are adjusted. The options such as various morphological parameters of the nylon microporous membrane used in this example are shown in table 1, the formulation of the casting solution is different, and the adjustment of various technological parameters is shown in table 2.

Example 6

Example 6 differs from example 1 mainly in that in this example, a nylon microporous membrane having a lower density than that of example 4 was selected, and the liquid inlet surface of the nylon microporous membrane had liquid inlet fibers having a higher average diameter and liquid inlet holes having a larger average diameter measured by SEM, and the formulation of the casting solution and various process parameters were adjusted. The options such as various morphological parameters of the nylon microporous membrane used in this example are shown in table 1, the formulation of the casting solution is different, and the adjustment of various technological parameters is shown in table 2.

Example 7

Example 7 differs from example 1 mainly in that in this example, a nylon microporous membrane with a smaller zeta potential (the larger the absolute value of the negative number, the smaller the zeta potential is considered to be), and the formulation of the casting solution and various process parameters are adjusted. The options such as various morphological parameters of the nylon microporous membrane used in this example are shown in table 1, the formulation of the casting solution is different, and the adjustment of various technological parameters is shown in table 2.

Example 8

Example 8 differs from example 1 mainly in that the pregelatinization treatment was not performed and the formulation of the casting solution and various process parameters were adjusted. The options such as various morphological parameters of the nylon microporous membrane used in this example are shown in table 1, the formulation of the casting solution is different, and the adjustment of various technological parameters is shown in table 2.

Comparative example

Comparative example 1

Comparative example 1 differs from example 1 mainly in that the microporous support layer in this comparative example is a PVDF microporous membrane instead of a nylon microporous membrane, and in addition, the present comparative example adopts a preparation process of casting a membrane casting solution on the PVDF microporous membrane, and does not adopt a preparation process of a microporous membrane back cover, and specific process steps are as follows:

S2, pouring, namely firstly placing the PVDF microporous membrane on a carrier, placing the carrier loaded with the PVDF microporous membrane in an environment of 70 ℃ for 3min, and then pouring the casting solution into the PVDF microporous membrane at the pouring speed of 1.5m/S to obtain the PVDF microporous membrane loaded with the liquid membrane, namely the composite semi-finished membrane. The composite semi-finished film was then placed in a pre-gel bath, which was prepared from 5wt% water, 2wt% trifluoroethanol and 93wt% dimethylacetamide, at a temperature of 65 ℃ for 25 seconds, and the pre-gel film was obtained after the pre-treatment was completed.

S3, curing to form a film, immersing the carrier in a curing bath, wherein the curing treatment time is 7min, the raw film is obtained, the curing bath is prepared from water and dimethylacetamide, and the ratio of the dimethylacetamide in the curing bath is 10wt%.

Comparative example 2

Comparative example 2 differs from example 1 mainly in that the comparative example uses nylon micropores with too high density, and does not carry out negative pressure treatment after compounding the nylon microporous membrane onto a liquid membrane, and in addition, the pre-gel bath in the comparative example adopts the mixed volume of pure good solvent and penetrating agent, does not add non-solvent, and adjusts the formulation of the casting solution and various process parameters. The options such as various morphological parameters of the nylon microporous membrane used in the comparative example are shown in Table 1, the formulation of the casting solution is different, and the adjustment of various technological parameters is shown in Table 2.

Comparative example 3

Comparative example 3 differs from example 1 mainly in that nylon micropores with too low a density are selected and subjected to an appropriate negative pressure treatment after compounding the nylon microporous membrane onto a liquid membrane, and in that the pre-gel treatment is not performed in this comparative example, and the formulation of the casting solution and various process parameters are adjusted. The options such as various morphological parameters of the nylon microporous membrane used in the comparative example are shown in Table 1, the formulation of the casting solution is different, and the adjustment of various technological parameters is shown in Table 2.

Table 1 morphological parameters of microporous membranes used in examples and comparative examples

Table 2 examples, comparative examples casting solution ratios and process parameters

Performance detection and performance data

1. Virus challenge test

The virus challenge test method is carried out by referring to the relevant regulations in PDATR41, and the mode virus is PP7 phage or hepatitis B virus, the mode protein is IVIG, and Buffer is PBS; and recording the change of flux and load with time in the test process to obtain the LRV, flux and load of the filter membrane.

2. Delamination resistance Property

The unused composite films obtained in each example and comparative example were tested for 180 ° peel strength with a universal tensile tester, and the test results were recorded as B ₀ The method comprises the steps of carrying out a first treatment on the surface of the The composite film after 2h treatment with feed solution at 30psi was then tested for 180 ° peel strength, and the test result was designated B ₁ The method comprises the steps of carrying out a first treatment on the surface of the Peel strength retention of B ₁ /B ₀ 。

Wherein, the morphology parameters of the composite films in each example and comparative example are shown in Table 3 in detail; the virus retention and delamination resistance of the composite membranes of the examples and comparative examples are shown in Table 4.

TABLE 3 morphological parameters of composite films in examples and comparative examples

TABLE 4 Virus rejection Properties and delamination resistance Properties of composite membranes of examples and comparative examples

Conclusion(s)

By comparing the technical schemes of examples 1 to 4 and the various performance parameters in the table above, it is not difficult to find that on the basis of selecting a nylon microporous membrane as a substrate, the finally prepared composite membrane has higher delamination resistance and good flux and loading capacity by controlling the morphological parameters (such as the area ratio of the holes of the liquid inlet surface, the surface tension and the like) of the nylon microporous membrane.

By comparing the technical solutions of example 1 and examples 5-6 with the performance parameters in the table above, it is readily found that even if non-preferred nylon microporous membranes (such as the higher density nylon microporous membrane in example 5 and the lower density nylon microporous membrane in example 6) are selected, they still have higher delamination resistance and flux, loading.

By comparing the technical solutions of example 1 and example 7 and the various performance parameters in the table above, it is not difficult to find that, although example 7 has a significantly larger thickness of the permeation region than example 1, the delamination resistance of both is similar, probably because the nylon microporous membrane zeta potential used in example 7 is smaller, and a larger electrostatic force is generated between the nylon microporous membrane zeta potential and the casting solution, resulting in a decrease in delamination resistance, thereby having similar delamination resistance to example 1 with a significantly lower thickness of the permeation region.

By comparing the technical schemes of example 1 and example 8 and the various performance parameters in the table above, it is not difficult to find that the flux and the loading of the composite membrane are reduced even if the pore diameter of the secondary pore is reduced without the pre-gel treatment, but the composite membrane still has higher flux, loading and delamination resistance. That is, the scheme of example 8, although not the preferred scheme, still has a relatively good overall performance.

By comparing the technical schemes of example 1 and comparative example 1 and the various performance parameters in the table above, it is not difficult to find that comparative example 1, which uses PVDF microporous membrane and does not use microporous membrane back cover process, has better delamination resistance but has poorer flux and loading properties and basically no practical value as compared to example 1 which uses nylon microporous membrane. This is probably due to the fact that the good solvent in the casting solution is not only a good solvent for diacetate fibers, but also a good solvent for PVDF, which can soften or even partially dissolve the PVDF microporous membrane, thereby resulting in a cellulose-PVDF mixed casting solution with higher solid content at the composite interface, where after split-phase solidification, a pore structure with higher density will be produced, which can improve the binding fastness between the cellulose layer and the PVDF microporous membrane layer, but has a larger influence on the flux and loading of the composite membrane. In addition, an alkali solution with a certain concentration is needed for hydrolysis regeneration, and PVDF is not alkali-resistant, which can damage the mechanical properties and permeability of PVDF micropores.

By comparing the technical schemes of example 1 and comparative examples 2 to 3 and the various performance parameters in the above table, it is not difficult to find that even if a nylon microporous membrane is used as the substrate of the composite membrane, if a nylon microporous membrane with specific morphology and physicochemical parameters is not selected, the composite membrane with high delamination resistance performance, high flux and loading can not be obtained. As in comparative example 2, the nylon microporous membrane has too low a liquid inlet surface pore area ratio and too low a surface tension, and the finally prepared composite membrane has too thin permeation area (less than 10 μm and only 5 μm), so that the delamination resistance cannot be satisfied (the strength retention rate is 0, meaning that the delamination phenomenon occurs obviously under the condition of 30 psi), and the practical application value is lost. As in comparative example 3, the nylon microporous membrane had a too high inlet level hole area ratio and a too high surface tension, and the casting solution was easily wetted and permeated into the nylon microporous membrane, and formed an excessively thick permeation zone (more than 50 μm and up to 68 μm), and although the prepared composite membrane had good delamination resistance, the flux and the loading were both small, and had no use value.

The present embodiment is only for explanation of the present application and is not to be construed as limiting the present application, and modifications to the present embodiment, which may not creatively contribute to the present application as required by those skilled in the art after reading the present specification, are all protected by patent laws within the scope of claims of the present application.

Claims

1. A composite cellulose virus-removing filter membrane, which is characterized in that: the nylon microporous membrane comprises a nylon microporous membrane and a cellulose layer which at least partially permeates into the nylon microporous membrane, wherein one side of the nylon microporous membrane, which is far away from a regenerated fiber layer, is a liquid inlet surface, one side of the cellulose layer, which is far away from the nylon microporous membrane, is a liquid outlet surface, and a region, which is permeated with the cellulose layer, in the nylon microporous membrane is a permeation region;

the thickness of the penetration area is 10-50 mu m;

the flux of the filter membrane is not less than 40L/h/m ² @30psi。

2. The composite cellulose virus-removing filter of claim 1, wherein: the average diameter of the liquid inlet fiber is 150-450 nm, and the SEM measurement average pore diameter of the liquid inlet hole is 700-2000 nm.

3. The composite cellulose virus-removing filter of claim 1, wherein: in the liquid inlet surface, liquid inlet fibers with the diameter not smaller than 1.3 times of the average diameter are coarse fibers, and the proportion of the coarse fibers in the liquid inlet fibers is not more than 25%.

4. The composite cellulose virus-removing filter of claim 1, wherein: the connection points of the adjacent liquid inlet fibers are connection points, the average diameter of the connection points is larger than that of the liquid inlet fibers, and 2.5-4.5 liquid inlet fibers are connected to each connection point on average.

5. The composite cellulose virus-removing filter of claim 1, wherein: the zeta potential of the liquid inlet surface at the pH value of 7 is-2 mV to-40 mV.

6. The composite cellulose virus-removing filter of claim 1, wherein: in the liquid inlet level, liquid inlet holes with the aperture of SEM measurement not smaller than 1.3 times of the average aperture of SEM measurement are large holes, liquid inlet holes with the aperture of SEM measurement not larger than 0.5 times of the average aperture of SEM measurement are small holes, and the number of large holes in all liquid inlet holes is 10-30%, and the number of large holes is not more than 25% smaller than Kong Zhanbi.

7. The composite cellulose virus-removing filter of claim 1, wherein: taking the liquid inlet surface as the position of the nylon microporous membrane thickness 0, taking the surface of one side far away from the liquid inlet surface as the position of the nylon microporous membrane thickness 1, wherein the aperture change coefficient X of the nylon microporous membrane is less than or equal to 0.4, and X is calculated by the following formula:

8. The complex cellulose virus-removing filter of claim 7, wherein: the ratio of the average fiber diameter in the area with the film thickness of 0-0.1 to the average fiber diameter in the area with the film thickness of 0.4-0.5 is 0.7-1.3; the ratio of the average fiber diameter in the region of 0.4-0.5 film thickness of the nylon microporous film to the average fiber diameter in the region of 0.9-1 film thickness of the nylon microporous film is 0.7-1.3.

9. The complex cellulose virus-removing filter of claim 7, wherein: the difference between the average fiber diameter in the area with the film thickness of 0-0.1 and the average fiber diameter in the area with the film thickness of 0.4-0.5 is not more than 50nm; the difference between the average fiber diameter in the area of 0.4-0.5 film thickness of the nylon microporous film and the average fiber diameter in the area of 0.9-1 film thickness of the nylon microporous film is not more than 50nm.

10. The composite cellulose virus-removing filter of claim 1, wherein: the infiltration area comprises nylon fibers and cellulose fibers, the nylon fibers mutually encircle to form primary holes, the cellulose fibers are positioned in the primary holes, the cellulose fibers mutually encircle and divide the primary holes into a plurality of secondary holes, and the SEM measurement average pore diameter of the secondary holes is smaller than that of the primary holes.

11. The composite cellulose virus-removing filter of claim 10, wherein: the region with the thickness of 10 mu m at one side of the infiltration region close to the prefilter region is a boundary region, the region with the thickness of 5 mu m at one side of the boundary region close to the liquid inlet surface is an upper boundary region, the region with the thickness of 5 mu m at one side of the boundary region close to the liquid outlet surface is a lower boundary region, and the SEM measurement average pore diameter of the secondary pores in the infiltration region is larger than that of the secondary pores in the boundary region; the average diameter of the cellulose fibers in the interface region is not less than 50nm.

12. The composite cellulose virus-removing filter of claim 11, wherein: SEM measurement average pore diameter of the secondary pores in the lower junction region is 100-200 nm; the average pore diameter of the secondary pores in the upper boundary region is 120-220 nm as measured by SEM.

13. The composite cellulose virus-removing filter of claim 11, wherein: the ratio of the SEM measurement average pore diameter of the primary pores to the SEM measurement average pore diameter of the secondary pores in the lower boundary region is 4-10; the ratio of the SEM measured average pore diameter of the primary pores to the SEM measured average pore diameter of the secondary pores in the upper boundary region is 3 to 9.

14. The composite cellulose virus-removing filter of claim 11, wherein: the average diameter of cellulose fiber in the lower junction area is not less than 40nm, and the ratio of the average pore diameter to the average diameter of cellulose fiber measured by SEM of primary pores in the lower junction area is 10-25; the average diameter of the cellulose fiber in the upper boundary region is not less than 60nm, and the ratio of the average pore diameter to the average diameter of the cellulose fiber measured by SEM of the primary pores in the upper boundary region is 8 to 20.

15. The composite cellulose virus-removing filter of claim 1, wherein: the loading capacity of the filter membrane is not lower than 200L/m ² The retention rate of the peel strength of the filter membrane is not lower than 0.8@30 psi for 2 h.

16. A virus removal membrane module, characterized in that: comprising the filter membrane according to any one of claims 1 to 15 in an amount of 1 to 3 layers, the membrane module having an interception capacity of LRV > 4 for PP7 phage.

17. The process for preparing the composite cellulose virus-removing filter membrane according to any one of claims 1 to 15, which is characterized in that: the method comprises the following steps:

18. The process for preparing the composite cellulose virus-removing filter membrane according to claim 17, wherein the process comprises the following steps: before immersing the composite semi-finished film in a curing bath, pre-gelling treatment is carried out on the composite semi-finished film, specifically, after the composite semi-finished film is kept stand for 20-30 s, the composite semi-finished film is immersed in the pre-gelling bath, the pre-gelling time is 20-30 s, the pre-gelling film is obtained, the pre-gelling bath at least comprises a third good solvent and a third non-solvent, and the ratio of the third non-solvent is 5-20wt%.

19. The process for preparing the composite cellulose virus-removing filter membrane according to claim 18, wherein: the temperature of the pregelatinized bath is 50-70 ℃, the pregelatinized bath is also added with penetrating agent with the surface tension not higher than 20dyne/cm, and the concentration of the penetrating agent in the pregelatinized bath is 1-3 wt%.

20. The process for preparing the composite cellulose virus-removing filter membrane according to claim 17, wherein the process comprises the following steps: in the step S2, the temperature of the nylon microporous membrane is regulated for 1-3 min in an environment with the temperature of 50-70 ℃ before the nylon microporous membrane is compounded, and then the nylon microporous membrane is compounded into a liquid membrane.

21. The process for preparing the composite cellulose virus-removing filter membrane according to claim 17, wherein the process comprises the following steps:

the cellulose polymer is at least one of cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose acetate phthalate, cellulose acetate butyrate and cellulose acetate propionate;