CN116116247A

CN116116247A - Asymmetric cuprammonium cellulose filter membrane for removing viruses and preparation process thereof

Info

Publication number: CN116116247A
Application number: CN202310223227.1A
Authority: CN
Inventors: 贾建东; 相黎超
Original assignee: Hangzhou Cobetter Filtration Equipment Co Ltd
Current assignee: Hangzhou Cobetter Filtration Equipment Co Ltd
Priority date: 2023-03-09
Filing date: 2023-03-09
Publication date: 2023-05-16

Abstract

The application relates to an asymmetric cuprammonium cellulose filter membrane for removing viruses and a preparation process thereof, wherein the filter membrane comprises a porous main body with a non-directional tortuous path, the two sides of the porous main body are respectively provided with a first surface and a second surface, and the porous main body comprises a pre-filtering layer, a separating layer and a protecting layer which are used for intercepting viruses; the bubble point of the filter membrane is 1-1.7 MPa; the SEM measurement average pore diameter of the protective layer is larger than that of the separation layer and smaller than that of the pre-filter layer; the protection coefficient B of the protection layer is 5-100 nm/mu m; the protection factor B is calculated by the following formula: b=d/h; the SEM measurement average pore diameter d of the pore structure of the second outer surface is 100-500 nm; the thickness of the filter membrane is 20-80 mu m; the application further discloses a preparation process of the filter membrane. On the basis of the thickness of the filter membrane of 20-80 mu m, the average pore diameter d is 100-500 nm by controlling the protection coefficient B of the protection layer and combining SEM measurement of the second outer surface of the filter membrane, so that the protection layer can be ensured to have both high protection effect and low flux influence.

Description

Asymmetric cuprammonium cellulose filter membrane for removing viruses and preparation process thereof

Technical Field

The application relates to the field of membrane separation technology, in particular to an asymmetric cuprammonium cellulose filter membrane for virus removal and a preparation process thereof.

Background

The membrane separation technology is a technology for separating, classifying, enriching, purifying and the like a mixed system by taking concentration difference, pressure difference, potential difference, chemical potential difference or the like as driving force. The membrane separation technology has the advantages of low pollution, high separation efficiency, low energy consumption, no need of adding chemical reagents, separation of systems (such as azeotropic systems) which cannot be separated by the conventional method, mild separation conditions, difficult change of the properties of active substances and the like, and is widely applied to the field of biological medicine.

Various biological agent products in the biomedical field are likely to have viruses due to raw material introduction, introduction during production and the like, and once the viruses are not cleared and directly injected into a patient, serious safety risks are generated. Therefore, as in the related documents of the "Chinese pharmacopoeia" of 2020 edition and the "ICH Q5A biotechnological product-virus safety evaluation", the virus safety of biological agents is clearly and highly required. In the production of various biological agents, virus removal and/or virus inactivation steps must be performed to ensure the safety of the biological agent. And the report of the virus safety evaluation test result must be attached for examination when the medicine is declared, and the report content directly influences the examination result.

US patent US4629563 discloses the preparation of asymmetric microporous membranes by non-solvent induced phase separation, for which later US5171445 is improved, reducing the casting temperature and the gel temperature, simplifying the process; in addition, patents US5866059, US7125493, US6045899 and US4976859 all disclose polyethersulfone membranes having a distinct asymmetric structure. However, the membrane materials of the filter membranes are polyethersulfone, and the hydrophilicity of the polyethersulfone material is still poor even though the polyethersulfone material is subjected to hydrophilic modification, so that the adsorption rate of the protein is high, the quality of the biological agent is reduced, the cost is improved, the filter membranes are rapidly blocked, the flux is rapidly attenuated, and the service life is short. And all the filters have the same problem that the separation layer is positioned on the surface of the filter membrane and is easy to be damaged mechanically.

In the Chinese patent application document with the application publication number of CN113842792A, an asymmetric PES filter membrane for removing viruses is disclosed, the PES filter membrane comprises a main body, the main body comprises a prefilter layer and a separating layer for intercepting viruses, and the other side of the prefilter layer and the other side of the separating layer are transited by continuous fibers; the PES filter membrane is prepared by only one casting solution, is integrally formed and does not need to be compounded. The PES membrane has a typical double-layer structure (a large-aperture pre-filter layer and a small-aperture separation layer) and has a good virus interception effect (LRV > 4), but the PES membrane has the problem of lower loading capacity due to the selection of PES materials. In addition, the average pore diameter of the filter membrane is reduced from one side to the other side along the thickness direction, so that the separation layer with the smallest pore diameter is positioned on the surface of the filter membrane, and is easy to be damaged mechanically, and the mechanical stability is also often poor.

Japanese patent application publication No. JP1984204911a discloses that regenerated cellulose membrane (RC membrane) has good clearance ability for aids virus (about 100 nm) and that good protein yield is often obtained due to low adsorptivity for active substances (proteins) due to good hydrophilic property of cellulose. However, it has poor clearance ability (LRV < 4) against viruses having a size of 20 to 100nm such as hepatitis B virus (about 42 nm), nAB type hepatitis virus (30 to 60 nm), murine parvovirus (about 20 nm), and thus has failed to meet the current stringent virus clearance requirements.

As disclosed in chinese patent application publication No. CN114887500a, an asymmetric cellulose filter membrane for removing viruses and a method for preparing the same are disclosed, the cellulose filter membrane comprises a main body, two sides of the main body are a first outer surface and a second outer surface, the pore diameter of the first outer surface is at least 4 times that of the second outer surface, the average pore diameter of the second outer surface is 15-40nm, the main body comprises a nano-dirt layer and a interception layer, the average pore diameter of the nano-dirt layer is larger than that of the interception layer, and the average pore diameter variation gradient of the nano-dirt layer is larger than that of the interception layer. The cellulose filter membrane has good interception effect on small-size viruses, and has good hydrophilicity (the cellulose is generally considered to be the most hydrophilic organic film forming material) because the film forming material of the cellulose filter membrane is cellulose, so that the low adsorption of the filter membrane on proteins is ensured. The filter membrane has both higher LRV and higher protein yield, but its rejection layer is also located on the membrane surface, and is susceptible to mechanical damage.

In chinese patent application publication No. CN105980038A, a virus-removing film is disclosed, which comprises cellulose, has 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 that permeates the virus-removing film is discharged, and has a log removal rate of 4 or more (LRV > 4) for porcine parvovirus (about 18 to 26 nm). The inorganic salt is added into the casting solution to change the diffusion speed of particles formed by cellulose concentrated phase, thereby influencing the micro-phase separation speed, controlling the size of pores from the surface to the inside of the membrane, the degree of change of the size of the pores in the membrane thickness direction, and the like. It is mentioned that in the cross section of the filter membrane the pore size decreases from the first side towards the second side and then changes to increase, whereby the membrane structure, which serves as a virus-retaining capacity, is located inside the filter membrane and is thus not susceptible to mechanical damage. And because the film forming material is cellulose raw material, the specificity adsorption of the filter film to protein is low. However, the cellulose membrane has a thinner prefilter layer, which is prone to clogging and thus affects its service life; more importantly, although the separation layer of the cellulose membrane is located internally, the larger pore size of the layer structure near the liquid exit surface can provide a protective effect on the separation layer, it is anticipated that the additional introduction of the layer structure will result in a certain decrease in the flux of the filter membrane.

The separation layer of the membrane in the patent publication No. CN101227965B is also located inside the membrane, and its average pore diameter increases in the thickness direction from the separation layer to both sides, and although the separation layer located inside is not susceptible to mechanical damage, the flux of such a membrane structure is not high.

Therefore, the filter membrane with good virus interception effect, the layer structure with the virus interception effect is not easy to damage and has high flux is a problem which is needed to be solved at present and is difficult to solve.

Disclosure of Invention

Aiming at the defects of the prior art, the application aims to provide an asymmetric cuprammocellulose filter membrane for removing viruses and a preparation process thereof, and a separating layer which has a virus interception effect of the filter membrane is positioned inside the filter membrane, so that the filter membrane is not easy to be damaged mechanically; the bubble point of the filter membrane is 1-1.7 MPa, so that a good interception effect on small-size viruses can be achieved; furthermore, the average pore diameter d is 100-500 nm by controlling the protection coefficient B of the protection layer to be 5-100 nm/mu m and combining with SEM measurement of the second outer surface of the filter membrane, so that the separation layer structure of the filter membrane is not easy to be damaged mechanically, the influence of the introduced protection layer structure on the flux of the filter membrane is small, and the filter membrane still has higher flux. Therefore, the filter membrane in the application not only has good virus interception effect, but also has higher flux and mechanical damage resistance.

The application provides an asymmetric cuprammonium cellulose filter membrane for virus removal and a preparation process thereof, which adopts the following technical scheme:

in a first aspect, the present application provides an asymmetric cuprammonium cellulose filter membrane for virus removal, which adopts the following technical scheme:

an asymmetric cuprammonium cellulose filter membrane for virus removal comprises a porous main body, wherein a non-directional tortuous path is arranged in the porous main body, one side surface of the porous main body is a first outer surface, the other side surface of the porous main body is a second outer surface,

the porous main body comprises a pre-filtering layer, a separating layer for intercepting viruses and a protective layer, wherein one side of the pre-filtering layer is a first outer surface, and one side of the protective layer is a second outer surface; the pre-filtering layer, the separation layer and the protective layer are transited by continuous fibers;

the bubble point of the filter membrane is 1-1.7 MPa;

the SEM measurement average pore diameter of the protective layer is larger than that of the separation layer and smaller than that of the pre-filter layer;

the protection coefficient B of the protection layer is 5-100 nm/mu m; the protection coefficient B is calculated by the following formula:

B＝d/h；

in the above formula, d is the SEM measurement average pore diameter of the pore structure of the second outer surface, and the unit is nm; h is the thickness of the protective layer, and the unit is mu m;

D is 100-500 nm;

the thickness of the filter membrane is 20-80 mu m.

By adopting the technical scheme, the filter membrane in the application takes the cellulose raw material with good hydrophilicity as a film forming material, so that the adsorption rate of protein is lower, and the filter membrane has higher protein yield; the bubble point of the filter membrane is 1-1.7 MPa, so that the filter membrane can have good interception effect on small-size viruses (such as model virus PP7 phage of miniviruses specified in PDA TR41 or common murine parvoviruses) so as to ensure the virus safety of each biological agent.

In addition, in the filter membrane structure of this application, the separating layer is located between prefilter layer and the protective layer, and not expose on the surface of filter membrane, because the separating layer is located inside the protective layer, therefore, outside mechanical failure power needs to destroy the protective layer earlier, just can further destroy the separating layer structure, because the region that plays virus interception effect in the filter membrane is the separating layer, even if the partial structure of protective layer is destroyed, if the separating layer structure is not destroyed, the risk is still lower for the virus leakage of filter membrane, consequently, set up the separating layer and be located inside the protective layer greatly reduced because outside mechanical failure leads to the possibility that the virus was revealed, the security has been improved. It is noted that the protective layer of different structure has different effects on the protective effect of the separation layer and on the flux of the filter membrane.

On the basis of the thickness of the filter membrane being 20-80 mu m, when the SEM measurement average pore diameter d of the pore structure of the second outer surface of the filter membrane is 100-500 nm and the protection coefficient of the protection layer is 5-100 nm/mu m, the protection layer not only can form a good protection effect on separation layers, but also can reduce the possibility of damage of the separation layers, and the flux of the filter membrane is still higher, so that the filter membrane has high virus interception effect, high flux and high mechanical damage resistance.

This is probably because the filter membranes with different thicknesses have different mechanical properties, and when the pore structure of the filter membrane is changed, the properties such as flux and the like are affected to different degrees, so that the protection factor B of the protective layer needs to be based on the filter membrane with a specific thickness to ensure that the filter membrane with the specific thickness has good mechanical damage resistance and higher flux after being introduced into the protective layer with the specific protection factor B. For a filter membrane with a thickness of 20-80 μm, when the protection coefficient B of the protection layer is too small (such as less than 5nm/μm), it indicates that the thickness of the protection layer is too large and/or the average pore diameter of the pore structure of the second outer surface of the filter membrane is too small as measured by SEM, and the structure of the protection layer with large thickness and small pore diameter forms larger resistance to feed liquid, which may cause larger reduction of the flux of the filter membrane; when the protection coefficient B of the protection layer is too large (e.g. greater than 100nm/μm), it indicates that the thickness of the protection layer is too small and/or the average pore diameter of the pore structure of the second outer surface of the filter membrane is too large as measured by SEM, which means that the structure of the protection layer with small thickness and large pore diameter not only means that the possibility of defects generated in the separation layer during the membrane manufacturing process is increased, but also means that the mechanical damage resistance of the protection layer is insufficient, so that the separation layer of the filter membrane is easy to be damaged during the assembly and use process. Therefore, the protection coefficient B of the protection layer needs to be controlled within a certain range to ensure that the filter membrane has both higher flux and higher mechanical damage resistance.

It should be noted that the SEM measurement of the thickness h of the protective layer alone or the pore structure of the second outer surface alone is not significant, since even if the thickness of the protective layer is large, the effect on the flux may be small if the pore structure of the protective layer is large in pore size; even if the thickness of the protective layer is small, if the pore structure of the protective layer is small in pore diameter, a large influence on the flux may be generated. Therefore, the relationship between the thickness of the protective layer and the average pore diameter of the pore structure of the second outer surface needs to be comprehensively considered, and when the protective coefficient B of the protective layer is 5-100 nm/μm, the protective layer can form a good protective effect on separation, and the flux influence on the filter membrane is small, so that the filter membrane has higher flux and good mechanical damage resistance.

It is understood that in the present application, the separation layer refers to a region with an average pore diameter measured by SEM of less than 50nm in the relevant field of view of the SEM image, and since the pore diameter of the pore structure of the filter membrane in the present application is first smaller and then larger from the first outer surface to the second outer surface, the two sides of the separation layer in the present application have regions with larger pore diameters compared to the separation layer, wherein the macroporous region near the first outer surface (liquid inlet side) is a prefilter layer, the macroporous region near the second outer surface (liquid outlet side) is a protective layer, and the average pore diameter measured by SEM of the protective layer is smaller than the average pore diameter measured by SEM of the prefilter layer.

The measurement mode of various surface morphology parameters (such as thickness, fiber diameter, aperture, area porosity and the like) of the filter membrane can be realized by using a scanning electron microscope to perform morphology characterization on the membrane structure, then computer software (such as Matlab, NIS-Elements and the like) or manual measurement is used for performing 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 average pore size of the whole on the plane can be reflected by measuring the average pore size of a partial region on 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 multiplied by 5 μm), the specific area size is determined according to the actual situation, the corresponding computer software or manual measurement is used for measuring the pore diameters, fiber diameters and other morphological parameters of all holes on the area, and then calculation is carried out to obtain the average pore diameter (namely, SEM measurement average pore diameter), average fiber diameter (namely, SEM measurement average fiber diameter) and other morphological parameters of the area; of course, the person skilled in the art can also obtain the above parameters by other measuring means, which are only used as reference.

The bubble point of the filter membrane in the present application means that after the filter membrane is wetted with a liquid having a surface tension of 0.012N/M (the liquid is FX3250 perfluorocarbon of 3M company), the wetted filter membrane is slowly pressurized with nitrogen, and when bubbles are continuously generated on the surface of the wetted filter membrane, the pressure of the nitrogen at this time is recorded, that is, the bubble point of the filter membrane, and the unit of the bubble point is MPa.

Optionally, the protection coefficient B of the protection layer is 10-90 nm/μm, d is 150-450 nm, and the hole area ratio of the second outer surface is 5-20%.

By adopting the technical scheme, on the basis that the protection coefficient B of the protection layer is 10-90 nm/mu m and d is 150-450 nm, when the hole area ratio of the second outer surface of the filter membrane is 5-20%, the filter membrane further has higher flux and mechanical damage resistance. This is probably due to the fact that the second outer surface, as a region directly contacting the external mechanical force, has a very important influence on the mechanical failure resistance of the protective layer, and the hole area ratio of the second outer surface is also greatly influenced in addition to the SEM measurement average pore diameter of the hole structure of the second outer surface. If the pore area ratio of the second outer surface is too low (for example, lower than 5%), it indicates that the second outer surface is relatively dense, and the relatively dense second outer surface has better mechanical damage resistance, but too low pore area ratio often means that the feed liquid is subjected to relatively high resistance near the second outer surface during filtration, so that the flux of the filter membrane is relatively low; if the hole area ratio of the second outer surface is too high (for example, higher than 20%), it means that the second outer surface is low in density, and the material liquid is relatively high in flux due to low resistance, but the too high hole area ratio of the second outer surface means that the mechanical damage resistance is poor, and good protection on separation cannot be formed, so that the possibility of mechanical damage to the separation layer is greatly improved.

Alternatively, the SEM measurement average pore diameter of the protective layer is 100-300 nm, and the porosity of the protective layer is 35-65%.

Through adopting above-mentioned technical scheme, because outside mechanical failure often need destroy protective layer structure before can further destroy the separating layer structure that is located the protective layer in advance, consequently, the protection effect influence of the anti-mechanical failure ability of protective layer to the separating layer is great. In order to ensure that the protective layer has a good protective effect on separation and also to give consideration to SEM measurement of the protective layer, the average pore diameter and porosity need to be controlled within a certain range. This is because, if the SEM measurement of the protective layer has an average pore size and/or porosity that is too small (e.g., the SEM measurement has an average pore size of less than 100nm and/or porosity of less than 35%), it is indicated that the protective layer has a denser three-dimensional network structure, and thus has a stronger resistance to mechanical damage, and thus has a better protective effect on separation; however, too dense a three-dimensional network structure also means too great a resistance to the feed liquid, resulting in a decrease in the flux of the filter membrane. If the SEM measurement of the protective layer has an average pore diameter and/or a porosity that is too large (e.g., the SEM measurement has an average pore diameter that is greater than 300nm and/or a porosity that is greater than 65%), it indicates that the three-dimensional network structure of the protective layer has a lower density, and although the three-dimensional network structure with a lower density has a lower resistance to feed liquid and a smaller flux impact on the filter membrane, the three-dimensional network structure with a too low density also means that the mechanical damage resistance is weaker, and once the protective layer structure is damaged, the possibility of damaging the exposed separation layer is greatly improved, and the risk of virus leakage is greatly increased.

Optionally, the SEM measurement average pore size of the protective layer increases gradually from the side near the first outer surface to the side near the second outer surface, and the SEM measurement average pore size of the protective layer near the first outer surface increases at a smaller rate than the SEM measurement average pore size of the protective layer near the second outer surface.

By adopting the technical scheme, the average pore diameter increase speed measured by the SEM on the side of the protective layer close to the first outer surface is smaller than that measured by the SEM on the side of the protective layer close to the second outer surface, that is, the pore diameter of the pore structure of the protective layer is slowly increased and then rapidly increased along the flowing direction of the feed liquid. This means that the mechanical failure resistance of the protective layer is rapidly increased in the opposite direction to the flow of the feed liquid (i.e., in the direction of action of the external mechanical failure force), and the mechanical failure resistance is kept high in a certain range, thereby ensuring a good protective effect for the separation layer. It should be noted that the SEM measurement average pore size of the protective layer is not preferred to be changed at a faster rate all the time, because, although the rapid decrease in SEM measurement average pore size of the protective layer along the direction of action of external mechanical failure force can ensure that the protective layer further has better resistance to mechanical failure, the rapid decrease in pore structure pore size also tends to mean a rapid decrease in the flux of the filter membrane; likewise, the SEM measurement average pore diameter of the protective layer is not preferably changed at a slow rate at all times, so as not to cause insufficient protection effect for the separation layer due to insufficient mechanical failure resistance of the protective layer.

Optionally, the SEM measured average fiber diameter of the protective layer is greater than the SEM measured average fiber diameter of the separating layer and less than the SEM measured average fiber diameter of the pre-filter layer; the separation layer has an SEM measurement average fiber diameter of 30 to 100nm.

By adopting the above technical scheme, the SEM measurement average pore diameter of the protective layer is larger than that of the separation layer, and the possibility of structural collapse under the action of external mechanical failure is greater, so that the pore structure of the protective layer needs to be supported by a fiber structure with larger size.

It should be noted that at present, a dead-end filtration mode is generally adopted for virus removal filtration, which means that the whole filter membrane is subjected to a large pressure of the feed liquid to be filtered, and the intrinsic characteristic of the cellulose raw material is that the texture is softer, so that the structure is easy to collapse when the filter membrane is subjected to the pressure. The separation layer is used as a structure for mainly intercepting viruses in the filter membrane, has a relatively small pore diameter and a compact three-dimensional network structure, is a region with larger influence on the virus interception capacity and flux of the filter membrane, and can cause great reduction of the flux of the filter membrane once the pore structure at the separation layer is collapsed. This is because, if the edge of the pore structure in the separation layer is regarded as a virtual three-dimensional sphere, when the pore diameter of the pore structure is reduced to half, the volume of the virtual sphere of the pore structure will be reduced to one eighth, and the sectional area of the passage through which the feed liquid formed by the pore structure passes will be reduced to one fourth. Thus, a small decrease in pore size of the pore structure in the separation layer will likely result in a large decrease in the flux of the filter membrane, requiring strict control of the size of the fibrous structure in the separation layer, and if the SEM measurement of the separation layer is too small (e.g., less than 30 nm) the average fiber diameter of the separation layer is too small, although the separation layer has a relatively dense three-dimensional network structure, too small fiber diameter will not form an effective support for the pore structure of the separation layer, which is difficult to form when the filter membrane is subjected to a large pressure of feed liquid (e.g., 30 psi) as a whole, and will likely result in a large decrease in the flux of the filter membrane once the pore structure is collapsed under pressure. If the SEM measurement of the separation layer is too small (e.g. greater than 100 nm) the larger fiber diameter in combination with the denser three-dimensional network structure can form an effective support for the pore structure of the separation layer, but the fiber structure itself acts as a solid part of the separation layer, which has a higher resistance to feed liquid, resulting in a lower flux of the filter membrane even in the unpressurized state. Therefore, the dimensions of the fibrous structure of the separating layer need to be tightly controlled.

Optionally, the ratio of the SEM measured average fiber diameter of the protective layer to the SEM measured average fiber diameter of the separation layer is 1.1 to 1.7; the ratio of the SEM measurement average fiber diameter of the pre-filter layer to the SEM measurement average fiber diameter of the protective layer is 1.2-2; the mean fiber diameter of the SEM measurement of the protective layer is 40-130 nm.

By adopting the technical scheme, although the protective layer is positioned near the second outer surface (namely the liquid surface) of the filter membrane and is not directly subjected to the pressure of feed liquid, the pressure of feed liquid borne by the pore structure of the protective layer is relatively small; however, in order to obtain good resistance to mechanical damage, the size of the fibrous structure in the protective layer still needs to be large. If the average fiber diameter of the SEM measurement of the fiber structure in the protective layer is too small (for example, less than 40 nm), the pore structure of the protective layer is less supported by the fiber structure, and the pore structure is easily damaged even if the pressure is small; in addition, the fibrous structure with the undersize protective layer has relatively weak mechanical damage resistance and weak protective effect on the separation layer. If the average fiber diameter of the fiber structure in the protective layer is too large (for example, greater than 130 nm) by SEM measurement, although the protective layer has strong mechanical damage resistance and is not easily deformed by compression, the fiber structure serves as a solid part in the protective layer, forming a barrier to the flow of feed liquid, and too large the average fiber diameter by SEM measurement means too large resistance to the feed liquid, thereby resulting in a decrease in the flux of the filter membrane.

Compared with the protective layer, the pre-filtering layer is a part of the filter membrane structure directly subjected to the feed liquid pressure, and the pore diameter of the pre-filtering layer is larger than that of the separating layer and the protective layer, so that the pore structure is required to be supported by a fiber structure with larger diameter in order to ensure that the pre-filtering layer does not deform excessively when being pressed. Thus, the diameter of the fibrous structure in the prefilter layer is larger than the protective layer (e.g., not less than 1.2 times the fiber diameter of the protective layer) to ensure that the filter membrane is less prone to collapse of the pore structure when subjected to the greater pressure of the feed liquid. The fiber diameter of the pre-filtering layer is not too large (for example, the ratio of the fiber diameter of the pre-filtering layer to the fiber diameter of the protective layer is larger than 2 times), and although the pre-filtering layer can indeed obtain stronger self-supporting capability, the feed liquid is subjected to larger resistance of a thicker fiber structure, the flux is easy to reduce, and the dirt receiving amount of the pre-filtering layer is easy to reduce due to larger fiber structure size.

Alternatively, the ratio of the SEM measurement average pore diameter to the SEM measurement average fiber diameter of the protective layer is 0.8 to 3.

By adopting the above technical scheme, although the protective layer is not directly subjected to the pressure of the feed liquid, the protective layer needs to have sufficient mechanical damage resistance to ensure a good protective effect for the separation layer. On the basis of the protection coefficient of the protection layer being 5-100 nm/mu m, the ratio of the SEM measurement average pore diameter to the SEM measurement average fiber diameter of the protection layer is further limited, so that the good protection effect of the protection layer on the separation layer and the influence on the flux of the filter membrane can be further ensured.

If the ratio of the SEM measured average pore diameter to the SEM measured average fiber diameter of the protective layer is too large (e.g., greater than 3), it is indicated that the pore diameter of the pore structure of the protective layer is too large or the diameter of the fiber structure is too small, and although such structure has a small influence on the flux of the filter membrane, the mechanical damage resistance is weak and is easily damaged by external force; if the ratio of the SEM measured average pore diameter of the protective layer to the SEM measured average fiber diameter is too small (e.g., less than 0.8), it is indicated that the pore size of the pore structure of the protective layer is too small or the diameter of the fiber structure is too large, and although such a structure has relatively good resistance to mechanical damage, the material liquid is too hindered, resulting in a lower flux of the filter membrane.

Optionally, the first outer surface includes a plurality of first fibers that are long and mutually staggered, the staggered positions of the first fibers form nodes, the adjacent and staggered first fibers mutually encircle to form holes, the average diameter of the first fibers measured by SEM is 50-180 nm, and the area ratio of the holes of the first outer surface is 10-50%.

By adopting the technical scheme, when the surface morphology of the filter membrane is observed through the SEM image of the filter membrane, the first outer surface can be found to have a relatively obvious fiber structure (namely first fibers), the fibers are of an elongated strip-shaped structure and mutually staggered to form a node structure, the node structure has a larger radial dimension compared with the fiber structure, so that a three-dimensional network structure near the first outer surface can be better supported, and the node structure and the first fibers have reasonable dimensions so as to ensure that the first outer surface with a larger pore diameter hole structure has better pressure resistance. If the diameter of the first fiber is too large (for example, greater than 180 nm), the thicker first fiber can provide the first outer surface with stronger pressure resistance, but has weaker guiding capability for the feed liquid; if the diameter of the first fiber is too small (e.g., less than 50 nm), the supporting effect on the pore structure of the first outer surface is weak, and the pressure resistance of the first outer surface as a direct bearing material liquid pressure is insufficient.

The holes formed around the first fibers as the solid portions are used for guiding the feed liquid into the filter membrane, so that the first outer surface needs a larger hole area rate (such as not less than 10%) to prevent the feed liquid from being blocked by excessive solid portions on the second outer surface and not easy to enter the filter membrane; the pore area ratio of the first outer surface is not too large (e.g., greater than 50%), because the main area affecting the flux of the filter membrane is a separation layer, and further improvement of the pore area ratio of the first outer surface does not further improve the flux of the filter membrane, but rather causes excessive decrease in the pressure resistance of the first outer surface.

Alternatively, the SEM measured average pore size of the first outer surface is 300-4500 nm, and the ratio of the SEM measured average pore size of the first outer surface to the SEM measured average pore size of the second outer surface is 2-40.

By adopting the above technical solution, if the SEM measurement of the first outer surface has too small average pore diameter (e.g. less than 300 nm), the guiding capability of the feed liquid is likely to be too low, the feed liquid is difficult to enter the filter membrane, although the feed liquid can be promoted to enter the filter membrane by further increasing the feed liquid pressure in theory, the softer texture of the cellulose membrane makes the filter membrane easily collapse and break down in structure under larger pressure, so that the pressure of the feed liquid is not necessarily set too high. If the SEM of the first outer surface measures an average pore size that is too large (e.g., greater than 4500 nm), the pore structure of the first outer surface that is too large requires greater support, although the feed liquid is more likely to enter the interior of the filter membrane through the pore structure on the first outer surface, otherwise collapse of the structure is likely to occur.

Alternatively, the average pore diameter of the prefilter layer is 200-700 nm as measured by SEM, and the porosity of the prefilter layer is 40-75%.

By adopting the technical scheme, the prefilter layer mainly plays a role in filtering large-particle matters in the feed liquid, if the SEM measurement average pore diameter of the prefilter layer is too large (such as larger than 700 nm), the prefilter layer with a large pore diameter pore structure generally has larger nano-dirt quantity, but the trapping effect on the large-particle matters is insufficient, and once the large-particle matters leak from the prefilter layer, the rapid blocking of the separation layer and the rapid attenuation of the flux of the filter membrane are likely to be caused. In addition, too large an average pore size measured by SEM of the pre-filter layer also means a decrease in pressure resistance of the pre-filter layer, which would lead to a decrease in both the flux and the loading of the filter membrane once the pre-filter layer collapses under the effect of the higher pressure of the feed liquid. Therefore, although increasing the SEM measurement average pore size of the pre-filter layer within a certain range is beneficial to increasing the loading capacity of the filter membrane and reducing the flux attenuation speed of the filter membrane, the SEM measurement average pore size of the pre-filter layer is not too large, but rather the loading capacity of the filter membrane is reduced and the flux attenuation speed is increased. The average pore size of the prefilter layer measured by SEM is not too small (e.g. less than 200 nm), and the prefilter layer serving as a prefilter for prefiltering large particulate matters in the feed liquid needs to have a large dirt receiving space for the large particulate matters so as not to be blocked by the large particulate matters rapidly, thereby leading to rapid attenuation of flux.

Optionally, the SEM measurement average pore size of the pre-filter layer gradually decreases from the side near the first outer surface to the side near the second outer surface, and the SEM measurement average pore size increase rate of the pre-filter layer on the side near the first outer surface is greater than the SEM measurement average pore size increase rate of the pre-filter layer on the side near the second outer surface; the SEM measurement of the prefilter layer shows an average pore size gradient of (60-200) nm/μm.

By adopting the technical scheme, in order to reduce the possibility of blocking the separation layer by large-particle substances in the feed liquid, the pre-filtering layer is required to have good interception effect on the large-particle substances in the feed liquid and have enough space to accommodate the intercepted large-particle substances. The pore diameter of the pore structure of the pre-filtering layer is firstly reduced at a faster speed, so that the interception capability of the pre-filtering layer on large particulate matters is rapidly improved, and the possibility that the large particulate matters leak to block the separating layer is reduced; the pore size of the prefilter layer pore structure is then reduced at a relatively slow rate to avoid a rapid, excessive reduction in pore size of the pore structure to reduce the likelihood of too low a fouling receiving space and localized concentrated entrapment of impurities resulting in rapid decay of the through-holes. In order to ensure that the prefilter has higher dirt holding capacity, is not easy to block, has good interception effect on large granular substances, and has the advantages that the SEM measurement average pore diameter change gradient of the prefilter layer is not too large or too small, when the SEM measurement average pore diameter change gradient is too small (such as less than 60 nm/mum), the prefilter layer can intercept the large granular substances only through a larger pore diameter matched with a laminated pore structure, and the risk of leakage of the large granular substances is higher although the dirt holding capacity is larger; when the SEM measurement average pore diameter variation gradient is too large (e.g., greater than 200nm/μm), the pore diameter of the prefilter layer pore structure is rapidly reduced, which, although being capable of forming good retention for large particulate matter, also means a rapid drop in the fouling receiving space, thereby making the fouling receiving capacity of the prefilter layer insufficient and susceptible to clogging.

Alternatively, the separation layer has an average pore diameter of 20 to 45nm as measured by SEM, the separation layer has a thickness of 5 to 45 μm, and the ratio of the separation layer to the thickness of the porous body is 20 to 60%.

By adopting the above technical solution, the virus removal filter must be ensured to have low risk of virus leakage, while the separation layer in the filter is the region that plays a role in virus entrapment. In order to ensure good virus retention by the filter, the separation layer should not have too large an average pore size (e.g., greater than 45 nm) and too small a thickness (e.g., less than 5 μm) as measured by SEM, so as to prevent virus leakage from the separation layer having a smaller thickness and/or a larger pore size. However, the protective layer structure has a relatively larger pore diameter, and cannot form a good virus trapping effect, so that once the virus leaks from the separation layer, the virus penetrates through the protective layer with a high probability, and the leakage risk is caused.

Optionally, the porosity of the filter membrane is 10-60%; the tensile strength of the filter membrane is 6-15 MPa, the elongation at break is 5-40%, and the elastic modulus is 20-80 MPa; the flux of the filter membrane is more than 60 L.h ^-1 m ^-2 @30psi; the protein yield of the filter membrane is not lower than 98%.

By adopting the technical scheme, the filter membrane with the specific structure has good virus interception capability, higher flux and good protection effect on the separation layer structure.

In a second aspect, the present application provides a process for preparing an asymmetric cellulose filter membrane for virus removal, which adopts the following technical scheme:

the preparation process of the asymmetric cellulose filter membrane for virus removal comprises the following process steps:

s1, preparing a casting solution, namely dissolving cotton fibers in a copper ammonia solution to form the casting solution, wherein the solid content of the casting solution is 7-10%, and the copper content of the casting solution is 3-5%;

s2, casting, namely casting the casting film on a carrier to obtain a liquid flat shaped forming film, wherein a first outer surface of the forming film is in contact with the carrier, and a second outer surface of the forming film is exposed to the environment;

s3, preprocessing, namely preprocessing the second outer surface of the formed film, and blowing acetone steam with relative humidity of 40-80%, acetone concentration of 15-55 v/v and air speed of 0.05-0.5 m/S onto the second outer surface of the formed film, wherein the time of exposing the formed film to the acetone steam is 30-120S, so as to form a green film;

s4, solidifying and phase-splitting, namely immersing the raw film into a coagulating bath for further phase-splitting and solidifying to obtain a hydrated cellulose film, wherein the coagulating bath is an aqueous solution of acid, the concentration of hydrogen ions in the coagulating bath is 0.5-3 mol/L, the concentration of penetrating agents is 0.1-5 wt%, and the acid is at least one of acetic acid and sulfuric acid; the penetrating agent is at least one of ethanol, 1-propanol, isopropanol, n-butanol, 1-pentanol and 2-pentanol;

S5, post-treatment, namely sequentially carrying out acid washing regeneration and water washing on the hydrated cellulose membrane to obtain the cellulose filter membrane.

By adopting the technical scheme, the film forming material of the filter film is cuprammonium fiber, and as one of regenerated fibers, the cuprammonium fiber has obvious advantages, and is different from the mode that cellulose acetate, cellulose nitrate and other compounds are hydrolyzed to remove the acetic acid group and the nitric acid group to regenerate the cellulose, the problem of degree of hydrolysis does not exist (insufficient hydrolysis can remain cellulose ester compounds with poor hydrophilicity, and excessive hydrolysis can cause hydrolytic damage of regenerated cellulose). The cellulose copper amide compound is a five-membered chelate compound, and the regeneration process thereof is to release cellulose from a cyclic chelate state, so that the process is easy to carry out, almost no damage is caused to cellulose molecules, and even if the cellulose copper amide compound which is not released exists, the cellulose copper amide compound cannot form fibers, and does not become a composition of a filter membrane. Therefore, the filter membrane prepared by the cuprammonium method has extremely high cellulose proportion and almost no damage to the fiber structure of the cellulose, so that the filter membrane has better hydrophilicity and higher mechanical property.

In step S3, the liquid formed film obtained by casting is further pretreated in the present application, because it is relatively difficult to open pores on the surface of the cellulose raw material, and if the liquid film is directly immersed in the coagulation bath, the second outer surface directly contacting with the coagulation bath is likely to rapidly phase-separate and form a relatively dense film structure, so that the protective layer structure with a pore structure having a relatively large pore diameter cannot be formed. Therefore, the liquid formed film is specifically placed in acetone vapor for treatment, and acetone can promote the phase separation of the film casting liquid on the surface of the formed film, but compared with a liquid coagulation bath, the acetone vapor has limited acetone content and relatively weak phase separation promoting effect, so that the film casting liquid on the surface is separated at a slower speed. The slower sharing speed and longer pretreatment time can ensure that the casting solution has enough time to form a polymer-rich phase with larger size and a solvent-rich phase with larger size, and the required protective layer structure can be formed after the solvent-rich phase is removed.

In order to ensure that the protective layer has small influence on the flux of the filter membrane under the premise of having good separation protective effect, the protective layer has a protective coefficient in a specific range, acetone vapor is limited in the application, and the dilution degree, the phase separation speed, the pretreatment phase separation time and the like of the casting film liquid near the second outer surface are controlled by controlling the relative humidity of the acetone vapor, the concentration of the acetone vapor, the air flow speed and the pretreatment time, so that the protective layer with good protective effect and low flux influence is obtained.

The forming film is placed in a wet air flow with the relative humidity of 40-80%, the acetone concentration of 15-55 v/v% and the air speed of 0.05-0.5 m/s, so that the moisture in the wet air can be promoted to be condensed on the surface of the casting film liquid, and the casting film liquid is promoted to form gradient change of solid content in the thickness direction through mass transfer in the casting film liquid in a longer pretreatment time (30-120 s), so that a required protective layer structure is formed when the film is immersed in a coagulating bath; and acetone can promote the preliminary phase separation of the casting solution to form a corresponding pore structure.

The influence of the acetone gas flow on the pretreatment effect is critical, if the relative humidity in the acetone gas flow is too low (such as less than 40%), the acetone concentration is too low (such as less than 15 v/v%), the wind speed is too low (such as less than 0.05 m/s), the phase separation promotion effect of the acetone gas flow with too low concentration on the casting film liquid is poor, and the uniformity of the casting film liquid is reduced in a longer pretreatment time, so that the aperture uniformity inside the finally formed filter film is easily reduced. In addition, the moisture in the acetone vapor is difficult to condense and form dilution on the casting film liquid, namely, the gradient change of the solid content is difficult to form in the casting film liquid, so that a structure with higher density is formed by solidification phase separation when the casting film liquid near the second outer surface contacts a solidification bath, and the flux of the filter film is greatly influenced. If the relative humidity in the acetone gas flow is too high (such as more than 80%), the acetone concentration is too high (such as more than 55 v/v%), the wind speed is too high (such as more than 0.5 m/s), excessive moisture is condensed and diluted to form casting solution in a long pretreatment time, and a pore structure with too large pore diameter is easily formed at the second outer surface, so that the protection effect of the protection layer is insufficient, and a good protection effect on the separation layer is difficult to form. In addition, too high concentration of acetone vapor has too strong a sharing promoting effect on the casting solution, and is likely to be phase-separated and solidified when the casting solution is not sufficiently diluted, thereby leading to formation of a dense structure. Therefore, the relative humidity of the acetone vapor, the acetone concentration, the wind speed, etc. need to be strictly controlled to ensure that a protective layer structure having a suitable protective coefficient is obtained.

It should be noted that in order to enable better dilution of the casting solution with the moisture in the wet gas flow, the temperature of the wet gas flow may be controlled to be higher than the temperature of the casting solution, so that the moisture in the wet gas flow is more likely to condense to the surface of the casting solution.

In step S4, the pretreated green membrane is placed in a dilute acid solution, so that the casting membrane liquid phase can be promoted to be separated into a solvent-rich phase and a polymer-rich phase, wherein the polymer-rich phase is solidified to form a solid structure of the filter membrane, and the solvent-rich phase is removed to form a pore structure of the filter membrane. In the process, the coagulating bath needs to permeate and soak into the casting solution to induce the phase separation in the casting solution, the viscosity of the casting solution is higher, the blocking force of the coagulating bath is larger, and the distribution uniformity of the coagulating bath in the casting solution is poorer; the further added penetrating agent can improve the penetrating property of the coagulating bath, promote the coagulating bath to permeate in the casting film liquid, thereby improving the distribution uniformity of the coagulating bath in the casting film liquid, and obtaining a pore structure with higher pore diameter uniformity.

The penetrant added in the coagulating bath can promote the coagulating bath to quickly permeate in the casting film liquid and enable the casting film liquid to quickly phase-separate, so that a separating layer structure with relatively smaller pore diameter is obtained, and a separating layer area with a smaller pore diameter pore structure can cause larger obstruction to further permeation of the coagulating bath, so that the phase-separating speed of the casting film liquid near the carrier side is reduced, and a pre-filtering layer structure with larger pore diameter compared with the separating layer is designed.

Optionally, ammonia gas is introduced in the cotton fiber dissolving process, and inorganic salt accounting for 0.1-1.5% of the total mass of the casting solution is also added in the casting solution, wherein cations of the inorganic salt are one or more of sodium, potassium, calcium and magnesium, and anions of the inorganic salt are one or more of sulfate radical, sulfite radical, silicate radical or carbonate.

By adopting the technical scheme, compared with regenerated fibers such as acetate fibers and nitrocellulose fibers, the cuprammonium cellulose also has certain defects, for example, as the mechanism of dissolving the cellulose by the cuprammonium solution is approximately that the hydrogen bond action of the cellulose is reduced by the coordination action of cuprammonium ions in the cuprammonium solution and hydrogen ions in the cellulose, the hydrogen bonds in cellulose molecules and between chains are broken, and thus the cellulose is dissolved. In the whole dissolving process, enough copper ammonia ions in the copper ammonia solution are required to be ensured so as to ensure the stable and rapid dissolution of cotton fibers. The inventor of the application found that when cotton fibers are dissolved by the cuprammonium solution, the dissolution rate and dissolution amount of the cotton fibers can be obviously improved by introducing ammonia gas, and the effect is obviously better than that of the conventional mode of adding concentrated ammonia water and the like, and the effect is probably due to the fact that as the cuprammonium solution continuously dissolves cellulose, the concentration of cuprammonium complex ions in the system is reduced, and the dissolution performance of the cuprammonium solution on cellulose is also inevitably reduced. The ammonia gas is introduced to promote copper hydroxide and the like to be further converted into copper ammonia ions, so that the concentration of the copper ammonia ions in the system is supplemented, and the dissolution speed and the dissolution amount of cotton fibers are ensured. Although the addition of concentrated aqueous ammonia or the like can supplement ammonium ions, the addition of concentrated aqueous ammonia dilutes the entire system and even results in a significant decrease in the solid content of the system, thereby affecting the subsequent extrusion film-forming step. The concentration of ammonium ions in the system can be increased by adding ammonia, the influence on the system is small, and the introduced ammonia also has a self-stirring effect, so that the dissolution rate and the dissolution amount of cotton fibers can be remarkably increased by introducing ammonia into the system.

The addition of the inorganic salt can adjust the phase separation speed of the casting solution in the coagulating bath, so as to ensure that the phase separation uniformity of the casting solution is higher, and a more uniform pore structure is obtained.

Optionally, the step S1 specifically includes the following process steps:

s11, preparing copper ammonia solution, mixing and stirring copper hydroxide powder and ammonia water, introducing ammonia gas in the stirring process, and stirring until copper hydroxide is not dissolved any more, thus obtaining copper ammonia solution;

s12, dissolving cellulose, stirring, putting cotton fibers into a cuprammonium solution, continuing stirring after adding until the cotton fibers are completely wetted, then introducing ammonia gas, stirring until the cotton fibers are completely dissolved, and adding inorganic salt to obtain the casting solution.

By adopting the technical scheme, the phase separation performance of the casting solution can be improved by adding the inorganic salt into the casting solution, but the adding time of the inorganic salt is important. The inventors of the present application have unexpectedly found that if the inorganic salt and the cotton fiber are added directly to the cuprammonium solution simultaneously, the dissolution rate of the cotton fiber will be significantly reduced; if the addition time of the inorganic salt is changed into the dissolution of the cotton fiber, the dissolution rate of the cotton fiber is obviously faster under the condition that the inorganic salt is not added, which is quite unexpected, and the dissolution rate of the cuprammonium solution to the cellulose is not directly related to the inorganic salt.

This is probably because copper ammonia ions in copper ammonia solution generally exist in two forms, namely complex alkali and complex salt, and the complex alkali can play a role in dissolving cellulose, and the generation of complex salt can be promoted by the premature addition of inorganic salt, so that the complex alkali content is reduced, and the complex alkali ratio for promoting the dissolution of cellulose is reduced, and at this time, even though the concentration of copper ammonia ions is the same, the dissolution capacity is reduced.

It is understood that the filter membrane in the present application may be a flat plate membrane or a hollow fiber membrane. When the filter membrane is a hollow fiber membrane, the preparation process can be as follows:

s1, preparing a casting solution, namely dissolving cotton fibers in a copper ammonia solution to form the casting solution, wherein the solid content of the casting solution is 7-10%, the copper content is 3-5%, and the inorganic salt content is 0.1-1.5%; the cation of the inorganic salt is one or more of sodium, potassium, calcium and magnesium, and the anion of the inorganic salt is one or more of sulfate radical, sulfite radical or carbonate; the method comprises the steps of carrying out a first treatment on the surface of the

S2, extruding, namely extruding the casting film liquid into a film, wherein the die head temperature is 15-35 ℃, and obtaining a formed film;

s3, pre-phasing the materials,

s31, internally phase-separating, namely, when spinning is carried out by using a casting solution, extruding the casting solution and an internal core solution together to obtain hollow membrane wires, exposing the hollow membrane wires to air, and carrying out phase-separating on the inner surfaces of the membrane wires, wherein the internal core solution is an aqueous acetone solution with the weight percent of 60-80;

S32, external phase separation, namely immersing the membrane wires into external core liquid from air to separate phases on the outer surfaces of the membrane wires, wherein the external core liquid is 30-50wt% of acetone aqueous solution, and ammonium salt is added into the external core liquid, and the concentration of the ammonium salt is 0.1-1mol/L;

s4, solidifying and phase-splitting, namely immersing the primary membrane into a coagulating bath for further phase-splitting and solidifying to obtain a hydrated cellulose membrane, wherein the coagulating bath is an aqueous solution of acid, the concentration of hydrogen ions in the coagulating bath is 0.5-3 mol/L, the addition amount of penetrating agents is 0.1-5 wt%, and the acid is at least one of acetic acid and sulfuric acid;

s5, post-treatment, namely sequentially carrying out acid washing and water washing on the hydrated cellulose membrane to obtain the cellulose filter membrane.

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

1. the separating layer with virus interception effect in the filter membrane is positioned in the filter membrane, so that the filter membrane is not easy to be damaged mechanically; the bubble point of the filter membrane is 1-1.7 MPa, so that a good interception effect on small-size viruses can be achieved; furthermore, on the basis of the thickness of the filter membrane of 20-80 mu m, the average pore diameter d is 100-500 nm by controlling the protection coefficient B of the protective layer to be 5-100 nm/mu m and combining with the SEM measurement of the second outer surface of the filter membrane, so that the separation layer structure of the filter membrane is not easy to be damaged mechanically, the flux influence of the introduced protective layer structure on the filter membrane is less, and the filter membrane still has higher flux;

2. The preparation process of the filter membrane in the application is a copper ammonia method, and the filter membrane with good performance can be ensured to be obtained by introducing ammonia gas and preprocessing a liquid membrane obtained by tape casting when cotton fibers are dissolved.

Drawings

FIG. 1 is a schematic cross-sectional view of a filter membrane of the present application, wherein the filter membrane is a flat membrane, and the magnification of the scanning electron microscope is 4k×.

FIG. 2 is a schematic cross-sectional view of a typical filter membrane of the present application, wherein the filter membrane is a hollow fiber membrane, and the magnification of the present scanning electron microscope is 2.5K×.

FIG. 3 is a scanning electron microscope image of the cross-sectional structure of the filter membrane of example 6 of the present application, magnification in the image being 4k×.

FIG. 4 is a scanning electron microscope image of the first outer surface of the filter membrane of example 6 of the present application, at a magnification of 5K.

FIG. 5 is a scanning electron microscope image of the second outer surface of the filter membrane of example 6 of the present application, at a magnification of 5K.

FIG. 6 is a scanning electron microscope image of the cross-sectional structure of the filter membrane of example 7 of the present application, the magnification in the image being 6K×.

FIG. 7 is a scanning electron micrograph of a first outer surface of the filter membrane of example 7 of the present application at 5K× magnification.

FIG. 8 is a scanning electron micrograph of the second outer surface of the filter according to example 7 of the present application, at 5K× magnification.

Detailed Description

The present application is described in further detail below in conjunction with figures 1-8.

Example 1

The embodiment of the application discloses a preparation process of an asymmetric cellulose filter membrane for virus removal, which comprises the following process steps:

s1, preparing a casting film liquid, which specifically comprises the following steps:

s12, dissolving cellulose, stirring, putting cotton fibers into a cuprammonium solution, continuing stirring after adding until the cotton fibers are completely wetted, then introducing ammonia gas, stirring until the cotton fibers are completely dissolved, and adding inorganic salt to obtain the casting solution. The prepared casting film liquid has a solid content of 9.1% and a copper content of 4.2%.

S2, casting, namely casting the casting film on a carrier to obtain a liquid flat shaped forming film, wherein a first outer surface of the forming film is in contact with the carrier, and a second outer surface of the forming film is exposed to the environment.

S3, preprocessing, namely, blowing acetone steam with the relative humidity of 65%, the acetone concentration of 35v/v% and the wind speed of 0.25m/S to the second outer surface of the formed film exposed to the air, wherein the time of exposing the formed film to the acetone steam is 70S, and obtaining the green film after the preprocessing is finished.

S4, solidifying and phase-separating, namely immersing the obtained green film into a coagulating bath to promote the film casting solution to further phase-separate and solidify, so as to obtain a hydrated cellulose film; wherein the coagulating bath is an aqueous acetic acid solution with a hydrogen ion concentration of 1.7mol/L, and a penetrant with a concentration of 2.5wt% is present in the coagulating bath, and in the embodiment, ethanol is used as the penetrant.

S5, post-treatment, sequentially carrying out acid washing regeneration and water washing on the hydrated cellulose membrane, wherein the acid washing liquid used in the acid washing regeneration is sulfuric acid water solution with the concentration of 10wt%, the water washing can be carried out after the acid washing is carried out until the color of the hydrated cellulose membrane is changed from blue to white, the pH value is neutral during the water washing, and the cellulose filter membrane is obtained after the water washing.

Example 2

The difference between the embodiment 2 and the embodiment 1 is that when the casting solution is prepared, inorganic salt is further added into the system, the adding node of the inorganic salt is that after cotton fibers are completely dissolved, the adding amount of the inorganic salt is 0.8% of the total mass of the casting solution, and sodium sulfate is selected as the inorganic salt; the remaining process parameters are detailed in table 1.

Example 3

Example 3 is different from example 2 mainly in that the inorganic salt is added to the copper ammonia solution together with the cotton fiber at the point of adding the inorganic salt when preparing the casting solution; the remaining process parameters are detailed in table 1. When the casting solution was prepared, it was observed that the dissolution rate of the cotton fibers was slower than that in example 2, but the cotton fibers were all dissolved in the end of both example 3 and example 2, indicating that the addition time point of the inorganic salt had an effect on the dissolution rate of the cotton fibers, but did not have a significant effect on the solubility of the cotton fibers.

Examples 4 to 6

Examples 4 to 6 differ from example 2 mainly in the formulation of the casting solution and in the various process parameters, as detailed in table 1.

Example 7 differs from example 2 mainly in that no ammonia gas was introduced in both steps S11 and S21, and the formulation of the casting solution and the process parameters were appropriately adjusted, as shown in table 1.

It should be noted that, in the preparation of the casting solution with a relatively high solid content in example 7, since ammonia gas was not introduced during the copper ammonia solution preparation and the dissolution of the cotton fibers, flocculent cotton fibers could be observed in the casting solution even after a long period of stirring dissolution, which means that the cotton fibers were not completely dissolved, and the solid content in the casting solution should be lower than the theoretical value (the solid content of the casting solution was calculated as the addition mass of the cotton fibers, and the cotton fibers in examples 1 to 6 were all substantially completely dissolved, so that the solid content of the casting solution was considered to be the same as the theoretical calculated value). Furthermore, since no ammonia gas was introduced, the dissolution rate of the cotton fibers was significantly slower than in examples 1 to 6. In order to avoid the undissolved flocculent cotton fibers from blocking equipment, the casting solution is filtered and then subjected to the subsequent film making process.

Comparative example 1

Comparative example 1 differs from example 2 mainly in that the pretreatment of step S3 was not performed, i.e., the cast liquid-state molded film was directly immersed in a coagulation bath for phase-separation solidification, and the formulation of the casting liquid and the respective process parameters were adjusted, as shown in table 1.

Comparative example 2

Comparative example 2 differs from example 2 mainly in that in step S3, the relative humidity of acetone vapor is lower than 40% and the acetone concentration is lower than 15v/v%, and the formulation of the casting solution and the respective process parameters are adjusted as shown in table 1.

Comparative example 3

Comparative example 3 is different from example 2 mainly in that the relative humidity of acetone vapor is higher than 80% and the acetone concentration is higher than 55v/v% in step S3, and the formulation of the casting solution and the respective process parameters are adjusted as shown in table 1.

Table 1 casting solution formulations and process parameters for each example, comparative example

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Performance detection and data

The morphology parameters of the filter membranes prepared in each example and comparative example are shown in Table 2:

TABLE 2 morphological parameters of the filters prepared in examples and comparative examples

The performance parameters of the filter membranes prepared in each example and comparative example are shown in Table 3:

TABLE 3 Performance parameters of the filter membranes prepared in examples and comparative examples

Conclusion(s)

It is clear from comparing the schemes and data of examples 1 and 2-3 that whether or not the addition of the inorganic salt has a small effect on the solubility of the cotton fiber, but has a certain effect on the dissolution rate of the cotton fiber, particularly the addition time node of the inorganic salt, if the inorganic salt is added together with the cotton fiber, the dissolution rate of the cotton fiber will be reduced, possibly due to the formation of complex salt caused by the addition of the inorganic salt, and the concentration of complex alkali will be reduced.

As can be seen from the comparison of the protocols and data of examples 2 and 7, when preparing the cuprammonium solution and dissolving the cotton fibers, the introduction of ammonia gas can not only increase the solubility of the cotton fibers, but also increase the dissolution rate of the cotton fibers.

It is apparent from the comparison of the protocol and data of example 2 and comparative example 1 that the filter membrane did not produce a protective layer structure, but a dense skin layer structure, although a higher LRV could be obtained, the flux was lower and the filtration efficiency was lower, since no pretreatment was performed. In addition, as no protective layer structure exists, after 10 times of disassembly and assembly, the retention rate of the LRV is obviously reduced, which indicates that the separation layer with the virus interception effect is damaged by multiple times of disassembly and assembly, so that the virus interception capacity is obviously reduced, and the virus safety requirement cannot be met.

As can be seen from comparing the schemes and data of example 2 and comparative example 2, an improper pretreatment process (ultra-long treatment time and low humidity, low acetone concentration, etc.) will result in an increased thickness of the protective layer but a smaller pore size, resulting in an excessively low protection factor B, while a large thickness and dense protective layer can significantly improve the protection effect for the separation layer, the flux of the filter membrane is clearly lower.

As can be seen from comparing the schemes and data of example 2 and comparative example 3, the improper pretreatment process (shorter treatment time and high humidity, high acetone concentration, etc.) will make the protective layer structure have too small thickness and large pore diameter, resulting in too high protective coefficient B, although the low thickness and loose protective layer has less influence on the flux of the filter membrane, LRV, etc., LRV retention is significantly reduced after 10 disassembly, which means that the protective effect of the protective layer on the separation layer is significantly reduced when the protective coefficient B is too high.

The present embodiment is merely illustrative of the present application and is not intended to be limiting, and those skilled in the art, after having read the present specification, may make modifications to the present embodiment without creative contribution as required, but is protected by patent laws within the scope of the claims of the present application.

Claims

1. An asymmetric cellulose filter membrane for virus removal, comprising a porous body, wherein a non-directional tortuous path is arranged in the porous body, one side surface of the porous body is a first outer surface, and the other side surface of the porous body is a second outer surface, and the asymmetric cellulose filter membrane is characterized in that:

the bubble point of the filter membrane is 1-1.8 MPa;

B＝d/h；

d is 100-500 nm;

the thickness of the filter membrane is 20-80 mu m.

2. An asymmetric cellulose filter membrane for virus removal according to claim 1, wherein: the protection coefficient B of the protection layer is 10-90 nm/mu m, d is 150-450 nm, and the area ratio of the holes on the second outer surface is 5-20%.

3. An asymmetric cellulose filter membrane for virus removal according to claim 1, wherein: the SEM measurement average pore diameter of the protective layer is 100-300 nm, and the porosity of the protective layer is 35-65%.

4. An asymmetric cellulose filter membrane for virus removal according to claim 1, wherein: the SEM measurement average pore diameter of the protective layer gradually increases from the side close to the first outer surface to the side close to the second outer surface, and the SEM measurement average pore diameter increase speed of the side close to the first outer surface of the protective layer is smaller than the SEM measurement average pore diameter increase speed of the side close to the second outer surface of the protective layer.

5. An asymmetric cellulose filter membrane for virus removal according to claim 1, wherein: the SEM measured average fiber diameter of the protective layer is greater than the SEM measured average fiber diameter of the separating layer and less than the SEM measured average fiber diameter of the pre-filter layer; the separation layer has an SEM measurement average fiber diameter of 30 to 100nm.

6. An asymmetric cellulose filter membrane for virus removal according to claim 1, wherein: the ratio of the SEM measurement average fiber diameter of the protective layer to the SEM measurement average fiber diameter of the separation layer is 1.1 to 1.7; the ratio of the SEM measurement average fiber diameter of the pre-filter layer to the SEM measurement average fiber diameter of the protective layer is 1.2-2; the mean fiber diameter of the SEM measurement of the protective layer is 40-130 nm.

7. An asymmetric cellulose filter membrane for virus removal according to claim 1, wherein: the ratio of the SEM measurement average pore diameter to the SEM measurement average fiber diameter of the protective layer is 0.8 to 3.

8. An asymmetric cellulose filter membrane for virus removal according to claim 1, wherein: the first outer surface comprises a plurality of strip-shaped first fibers which are staggered mutually, the staggered parts of the first fibers form nodes, the adjacent and staggered first fibers mutually encircle to form holes, the average diameter of the first fibers is 50-180 nm through SEM measurement, and the area ratio of the holes of the first outer surface is 10-50%.

9. An asymmetric cellulose filter membrane for virus removal according to claim 1, wherein: the SEM measurement average pore diameter of the first outer surface is 300-4500 nm, and the ratio of the SEM measurement average pore diameter of the first outer surface to the SEM measurement average pore diameter of the second outer surface is 2-40.

10. An asymmetric cellulose filter membrane for virus removal according to claim 1, wherein: the SEM measurement average pore diameter of the pre-filtering layer is 200-700 nm, and the porosity of the pre-filtering layer is 40-75%.

11. An asymmetric cellulose filter membrane for virus removal according to claim 1, wherein: the SEM measurement average pore diameter of the pre-filtering layer gradually decreases from the side close to the first outer surface to the side close to the second outer surface, and the SEM measurement average pore diameter increase speed of the pre-filtering layer on the side close to the first outer surface is larger than that of the pre-filtering layer on the side close to the second outer surface; the SEM measurement of the prefilter layer shows an average pore size gradient of (60-200) nm/μm.

12. An asymmetric cellulose filter membrane for virus removal according to claim 1, wherein: the average pore diameter of the separation layer is 20-45 nm as measured by SEM, the thickness of the separation layer is 5-45 μm, and the ratio of the separation layer to the thickness of the porous body is 20-60%.

13. An asymmetric cellulose filter membrane for virus removal according to claim 1, wherein: the porosity of the filter membrane is 10-60%; the tensile strength of the filter membrane is 6-15 MPa, the elongation at break is 5-40%, and the elastic modulus is 20-80 MPa; the flux of the filter membrane is more than 60 L.h ^-1 m ^-2 @30psi; the filter membraneThe protein yield of (2) is not lower than 98%.

14. The process for preparing an asymmetric cellulose filter membrane for virus removal according to any one of claims 1 to 13, wherein: the method comprises the following process steps:

s2, forming a film, namely extruding the film casting solution into a film to obtain a formed film;

s3, preprocessing the second outer surface of the formed film to promote the second outer surface of the formed film to be subjected to pre-split phase to obtain a green film;

15. The process for preparing an asymmetric cellulose filter membrane for virus removal according to claim 14, wherein: ammonia gas is introduced in the cotton fiber dissolving process, inorganic salt accounting for 0.1-1.5% of the total mass of the casting solution is also added into the casting solution, the cation of the inorganic salt is one or more of sodium, potassium, calcium and magnesium, and the anion of the inorganic salt is one or more of sulfate radical, sulfite radical, silicate radical or carbonate.

16. The process for preparing an asymmetric cellulose filter membrane for virus removal according to claim 15, wherein: the step S1 specifically comprises the following process steps:

17. The process for preparing an asymmetric cellulose filter membrane for virus removal according to any one of claims 14 to 16, wherein: the method comprises the following process steps: the filter membrane is a flat membrane, and the steps S2 and S3 specifically comprise the following process steps:

s3, preprocessing, namely preprocessing the second outer surface of the formed film, and blowing acetone steam with relative humidity of 40-80%, acetone concentration of 15-55 v/v and air speed of 0.05-0.5 m/S onto the second outer surface of the formed film, wherein the time of exposing the formed film to the acetone steam is 30-120S, so as to form a green film.

18. The process for preparing an asymmetric cellulose filter membrane for virus removal according to any one of claims 14 to 16, wherein: the method comprises the following process steps: the filter membrane is a hollow fiber membrane, and the steps S2 and S3 specifically comprise the following process steps:

s3, pre-phasing the materials,

s32, external phase separation, namely immersing the membrane wires into external core liquid from air to separate phases on the outer surfaces of the membrane wires, wherein the external core liquid is 30-50wt% of acetone aqueous solution, and ammonium salt is added into the external core liquid, and the concentration of the ammonium salt is 0.1-1mol/L.