CN114887500A

CN114887500A - Asymmetric cellulose filter membrane for virus removal and preparation method thereof

Info

Publication number: CN114887500A
Application number: CN202210813897.4A
Authority: CN
Inventors: 贾建东
Original assignee: Hangzhou Cobetter Filtration Equipment Co Ltd
Current assignee: Hangzhou Cobetter Filtration Equipment Co Ltd
Priority date: 2022-07-08
Filing date: 2022-07-12
Publication date: 2022-08-12
Also published as: WO2024007767A1; CN115608165B; CN115608165A

Abstract

The invention provides an asymmetric cellulose filter membrane for removing viruses and a preparation method thereof, wherein the filter membrane comprises a main body, one side surface of the main body is a first outer surface, and the other side surface of the main body is a second outer surface; the second outer surface has an average pore size of 15-40 nm; the average pore size of the first outer surface is at least 4 times greater than the average pore size of the second outer surface; the main body comprises a dirt containing layer and an intercepting layer for intercepting viruses, wherein one side of the dirt containing layer is a first outer surface, and one side of the intercepting layer is a second outer surface; the average pore diameter of the pollutant containing layer is larger than that of the interception layer; the average pore diameter variation gradient of the dirt containing layer is larger than that of the retention layer, so that the filter membrane has high dirt containing capacity; the cellulose filter membrane is integrally formed, does not need to be compounded, has stronger interception effect on viruses, high protein yield and higher flux; in addition, the invention also provides a preparation method of the filter membrane, and the preparation method is simple to operate, green and environment-friendly and suitable for large-scale popularization.

Description

Asymmetric cellulose filter membrane for virus removal and preparation method thereof

Technical Field

The invention relates to the technical field of membrane materials, in particular to an asymmetric cellulose filter membrane for virus removal and a preparation method thereof.

Background

The membrane technology is a new technology of modern high-efficiency separation, and compared with the traditional technologies of distillation, rectification and the like, the membrane technology has the advantages of high separation efficiency, low energy consumption, small occupied area and the like, and the core of the membrane separation technology is a separation membrane. Wherein the polymer filter membrane is a separation membrane which is prepared by taking an organic high molecular polymer as a raw material according to a certain process; wherein the polymer filter membrane can be subdivided into cellulose polymer filter membranes, polyamide polymer filter membranes, sulfone polymer filter membranes, polytetrafluoroethylene polymer filter membranes and the like according to different types of high molecular polymers; in addition, the membrane may be classified into a microfiltration membrane, an ultrafiltration membrane, a nanofiltration membrane and a reverse osmosis membrane according to the pore size of the membrane.

In recent years, biological drugs (particularly antibodies such as immunoglobulin) have been widely used because of their high therapeutic effect and few side effects. Since biological macromolecules such as antibodies are mainly produced by organisms such as animal cells, in order to be used as medicines, a fluid containing the biological macromolecules such as the antibodies needs to be separated and purified, and particularly, various parvoviruses (the murine parvovirus with the smallest particle size is about 20 nm) in the fluid are removed so as to ensure the safety of the corresponding biological medicines; at present, the most common mode for removing viruses in fluid is membrane separation, because the membrane separation technology has high separation efficiency and low energy consumption, can be carried out at normal temperature, can efficiently intercept various viruses, can not inactivate protein, and can efficiently recover various biological macromolecules.

For example, chinese patent CN1759924B (EMD mcirobo corporation) discloses a multi-layer composite ultrafiltration membrane (fig. 13 and 14); the composite ultrafiltration membrane comprises at least one first porous membrane layer having a first face and an equivalent second face, and at least one second porous membrane layer having an equivalent first face and a second face, the first layer overlying a junction with the second layer and having a porosity junction transition region from the equivalent first face of the second layer to the equivalent second face of the first layer, wherein at least one of the layers is an asymmetric ultrafiltration membrane; the membrane structure formed by compounding has stronger interception effect on parvovirus, and can obtain higher protein yield, thereby meeting the requirements of practical application; however, there are problems that, firstly, since the filter membrane is a composite membrane, the pore size changes (decreases) abruptly during the transition from one layer to another, which easily results in a large range of particle sizes remaining at the interface of the layers produced by co-casting, and such particle loading at the layer boundary results in a loss of the service life of the filter, i.e., a great reduction in service life; and the composite films are at risk of delamination/layer separation during pleating; in addition, the film forming material for preparing the composite film is mainly polyether sulfone, and two sides of the sulfone group of the polyether sulfone are benzene rings, so that the hydrophilicity of the composite film is poor, the final film forming has a certain adsorption effect on protein, the protein yield is general, and the economic benefit is reduced.

At the same time US20200238221a1 (siduris) also discloses a porous single layer polymer membrane having at least one major surface with a surface porosity of at least 40% and a total porosity of the polymer membrane of from 0.8 to 1.4 times the surface porosity of at least 40%; and the polymer film has an asymmetry factor of 1.5 to 10; the polymer film is a single-layer filter membrane, has good flux and long service life, and is mainly applied to filtering viruses, proteins or macromolecules; however, the average pore diameter of the polymer membrane is large, and only large-particle substances with the particle size of hundreds of nanometers can be intercepted, but parvovirus with the particle size of about 20nm cannot be intercepted.

In order to further increase the protein yield, chinese patent CN201580007740.0 (asahi chemical company application) also discloses a virus-removing membrane comprising cellulose for removing virus from a protein-containing solution, the virus-removing membrane having: a first side surface for supplying a solution containing a protein and a second side surface for discharging a permeate having passed through the virus-removal membrane, the membrane having an average pore diameter of 13nm to 21 nm; the membrane is made of cellulose materials and has strong hydrophilicity, so that the membrane has low protein adsorption rate while efficiently retaining viruses, and meanwhile, the membrane is a single-layer membrane and does not have the defects of sudden pore size change and easy separation between membrane layers; however, this membrane also has certain disadvantages; firstly, the virus-removing membrane is prepared by a cuprammonium method, namely, a membrane-forming substance is added into a cuprammonium solution for various treatments, and the preparation method not only pollutes the environment, but also has extremely high danger and is easy to cause great harm to the life safety of developers; secondly, the thickness of the virus membrane pollutant carrying layer (the area with the average pore diameter of more than 40nm in the cross section of the membrane is generally considered as the pollutant carrying layer) is very small, which can lead to the small pollutant carrying amount of the virus membrane; the large-particle impurities easily block the internal flow channel of the membrane, so that the service life of the virus membrane is short; in addition, the prepared virus removing membrane is a hollow fiber membrane, and the pressure resistance strength is low, so that the virus removing membrane component and the filter thereof are easy to damage, and the preparation process is relatively complex; in addition, the pressure resistance strength of the virus removing membrane is low, so that the pressure difference between the membrane before and after the membrane is small, the filtration speed is low, and the economic benefit per unit time is too low.

In view of the above, the development of virus-removing membranes is also limited to some extent by the presence of the above-mentioned problems.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide an asymmetric cellulose filter membrane for virus removal and a preparation method thereof, wherein the cellulose filter membrane is integrally formed without compounding, and the preparation process is relatively simple and environment-friendly; meanwhile, the prepared cellulose filter membrane has a strong virus interception effect, can obtain a high protein yield, and meets the requirements of practical application;

in order to achieve the purpose, the invention provides the following technical scheme:

an asymmetric cellulose-based filter membrane for removing viruses, comprising a body having a non-directional tortuous path therein, one surface of the body being a first outer surface and the other surface of the body being a second outer surface, the second outer surface having an average pore size of 15-40 nm; the average pore size of the first outer surface is at least 4 times greater than the average pore size of the second outer surface;

the main body comprises a dirt containing layer and a retention layer for retaining viruses, wherein one side of the dirt containing layer is a first outer surface, and one side of the retention layer is a second outer surface; the other side of the stain receiving layer and the other side of the trapping layer are in transition by continuous fibers;

the average pore diameter of the pollutant containing layer is larger than that of the interception layer; and the average pore diameter variation gradient of the pollutant containing layer is larger than that of the interception layer.

Compared with PES (polyether sulfone) and other organic polymer film-forming materials, the filter membrane made of the fiber membrane material has strong hydrophilicity, good biocompatibility, no toxicity and low adsorption quantity to various proteins (generally, the cellulose filter membrane is considered to be a membrane material which is least easy to adsorb proteins in the organic filter membrane); therefore, the membrane is particularly suitable for being used as a virus removal membrane;

in the membrane main body structure of the cellulose filter membrane provided by the invention, the pore diameters of holes on two outer surfaces of the filter membrane are different and have a certain difference; the holes on one of the outer surfaces have larger diameters, and the holes on the other outer surface have smaller diameters; wherein, the outer surface of one hole of the filter membrane with smaller aperture is called as the second outer surface in the invention, namely the second outer surface is the small hole surface (also liquid outlet surface) of the filter membrane, and the average aperture of the second outer surface is 15-40 nm; preferably, the second outer surface has an average pore size of 18 to 32 nm; the existence of the second outer surface (small pore surface) and the combined action of the non-directional tortuous path in the main body, wherein the non-directional tortuous path is a randomly oriented groove structure and/or a discretely distributed hole structure, and the non-directional tortuous paths are communicated with each other, so that the filtering precision of the filter membrane is improved, and the filter membrane also has higher retention effect on parvovirus;

the other outer surface of the filter membrane with larger pore diameter is called as a first outer surface in the invention, namely the first outer surface is a macroporous surface (also a liquid inlet surface) of the filter membrane, and the average pore diameter of the first outer surface is at least more than 4 times of the average pore diameter of the first outer surface; the existence of the first outer surface (macroporous surface) is beneficial to improving the membrane flux and accelerating the overall filtering speed of the membrane, so that the time for the fluid to pass through the filter membrane is short, and the time cost is low;

the average pore size between the first outer surface and the second outer surface is different and has a certain difference, which indicates that the cellulose filter membrane is an asymmetric membrane, so that the overall membrane has higher filtration speed, larger pollutant carrying capacity and longer service life; but also can ensure that the parvovirus (particularly the parvovirus with the grain diameter of about 20 nm) has stronger trapping capacity and meets the requirement of practical application;

and through observing the membrane main body structure, the average pore size of the main body is found to be changed from the area close to the first outer surface to the area close to the second outer surface, namely the average pore size of the membrane main body is gradually changed along with the thickness (but in a certain small area, the pore size is probably not changed basically), and no mutation occurs, so that the filter membrane is proved to be integrally formed without processes such as compounding and the like;

the whole filter membrane main body is mainly divided into two areas in the thickness direction, wherein one area is a dirt containing layer comprising a first outer surface, the pore diameter of an inner hole of the dirt containing layer is relatively large (the average pore diameter of the dirt containing layer is larger than that of an interception layer), the dirt containing layer is mainly used for intercepting large-particle impurities in fluid, the dirt containing layer has large dirt containing amount and high flow speed, the pre-filtration effect is achieved on the fluid, meanwhile, the interception layer is protected, and the integral membrane is guaranteed to have high mechanical strength; the other area is an interception layer comprising a second outer surface, the aperture of the inner hole of the interception layer is relatively small, and the interception layer is mainly used for intercepting fine particle impurities such as parvovirus in fluid, plays a role in separation and ensures that the filter membrane has higher capacity of catching various viruses; therefore, the filter membrane is particularly suitable for being used as a virus removal membrane, and when the filter membrane is actually used, the first outer surface (a big hole surface) is used as a liquid inlet surface, and the second outer surface (a small hole surface) is used as a liquid outlet surface;

the average pore diameter variation gradient in the invention refers to the variation value of the average pore diameter under unit thickness; the larger the value, the faster the pore diameter changes with thickness; the smaller the value, the smaller the variation of the pore diameter with the film thickness; the average pore size variation gradient is calculated by the difference between the maximum pore size and the minimum pore size (in nm)/the thickness between the two locations in a region (the distance between the maximum pore size and the minimum pore size in μm in this region); note: if a certain thickness exists at the position of the smallest aperture in the area, the thickness between the two positions refers to the smallest thickness between the position of the largest aperture and the position of the smallest aperture; the average pore size variation gradient of the fouling-containing layer is greater than the average pore size variation gradient of the retention layer (i.e., the pore size of the fouling-containing layer changes faster with thickness and the pore size of the retention layer changes slower with thickness), thus demonstrating that the pore size is substantially decelerated with thickness change in the direction of the membrane body from the first outer surface to the second outer surface; the average pore diameter of the interception layer is smaller, and the change gradient of the average pore diameter is smaller, namely, in the interception layer, the pore diameter of the pores is very small along with the change of the membrane thickness, even not along with the change of the membrane thickness, so that the pore diameters of the pores in the interception layer are all smaller, which is very favorable for efficiently intercepting various fine particle impurities, such as parvovirus (about 20 nm) in protein, and has very high purification efficiency;

the cellulose filter membrane is integrally formed, and the average pore diameter of the membrane main body is gradually changed along with the thickness, so that mutation is avoided; it indicates that the pore size of the pores in the vicinity of the fouling layer close to the rejection layer is also smaller, in order to ensure a higher flux for the membrane as a whole; the average pore diameter of the whole pollutant-containing layer is required to be larger, so that the pollutant-containing layer is required to have a relatively larger average pore diameter change gradient, which ensures that the pore diameter of the holes in the interception layer is smaller; the pollutant-containing layer has larger pollutant-containing amount, and the service life of the membrane is longer; meanwhile, the integral flux of the membrane is ensured to be higher, the flux attenuation is slower, and the unit economic benefit is high;

further, the other side of the soil receptive layer (the side of the soil receptive layer facing away from the first outer surface) and the other side of the retention layer (the side of the retention layer facing away from the second outer surface) transition in continuous fibers, it being understood that "continuous" means that substantially all of the fibers are integrally connected to one another, e.g., integrally formed, without the need for additional adhesives or the like to attach them to one another, and the network of fibers cannot be separated from one another unless torn by an external force; at the same time, the continuous network-like fibers are interconnected with the first outer surface and the second porous surface; the cellulose filter membrane is uniform in material, namely the whole membrane is made of cellulose materials, and no change exists in material;

in the context of the present invention, an asymmetric membrane is understood to be a membrane in which the fouling-receiving layer and the rejection layer are both composed of the same material, the two layers being combined into one integral structure and being formed directly during the membrane preparation process; in the transition from the fouling layer to the rejection layer, there is only a change in the membrane structure; in contrast, for example, composite membranes, which have a multilayer structure and in which a dense layer as a rejection layer is applied in a separate process step to a porous, frequently microporous, support layer or support membrane, the materials of which the support layer and rejection layer are composed often also being different;

the measurement mode of the average pore diameter of the membrane surface can be realized by performing morphology characterization on a membrane structure by using a scanning electron microscope, then performing measurement by using computer software (such as Matlab, NIS-Elements and the like) or manually, and performing corresponding calculation; in the production of the membrane, various characteristics such as the pore size distribution in the direction perpendicular to the thickness of the membrane (the direction is a planar direction if the membrane is in the form of a flat sheet membrane; the direction is perpendicular to the radial direction if the membrane is in the form of a hollow fiber membrane) are substantially uniform and substantially uniform; the average pore size of the whole of the plane can be reflected by the average pore size of a partial region on the corresponding plane. In practice, the surface of the membrane can be characterized by an electron microscope to obtain a corresponding SEM image, and since the pores on the surface of the membrane are substantially uniform, a certain area, such as 1 μm, can be selected ² (1 μm by 1 μm) or 25 μm ² (5 μm multiplied by 5 μm), the specific area size being determined according to the actual situation, and then using a corresponding meterMeasuring the pore diameters of all pores on the area by computer software or manually, and then calculating to obtain the average pore diameter of the surface; of course, the skilled person can also obtain the above parameters by other measuring means, which are only used as reference.

As a further improvement of the invention, the average pore diameter variation gradient of the pollutant containing layer is at least larger than the average pore diameter variation gradient of the retention layer by more than 3 nm/mum;

the second outer surface is provided with a plurality of second holes in a circular hole shape, and the hole area rate of the second holes on the second outer surface is 2% -15%.

In order to further ensure that the pore diameter of the holes in the interception layer is small (high interception efficiency for various parvoviruses), and simultaneously further ensure that the flux of the whole membrane is high and the filtration speed is high; therefore, the difference between the average pore diameter change gradient of the pollutant containing layer and the average pore diameter change gradient of the interception layer cannot be too small, and when the difference is too small, or the average pore diameter of the whole membrane is too large, the interception efficiency of various parvoviruses (the particle diameter is about 20 nm) is too low; or the average pore diameter of the whole membrane is too small, so that the whole flux of the membrane is too low, the time cost is too large, and the economic benefit per unit time is too low, and the average pore diameter change gradient of the pollutant receiving layer is at least larger than the average pore diameter change gradient of the interception layer by more than 3 nm/mum and has a proper difference value; the aperture of the holes in the interception layer is further ensured to be smaller, which is beneficial to efficiently intercepting various parvoviruses, and the integral flux of the membrane is further improved;

a certain number of second holes with certain apertures are formed in the second outer surface of the membrane, and the second holes in the second outer surface are of a circular hole-shaped structure, some of the second holes are circular, and some of the second holes are oval; and the hole area ratio (the ratio of the sum of the second hole areas to the membrane area) of the second holes on the second outer surface is 2% -15%, the hole area ratio is lower, namely the second outer surface is relatively dense; the second holes with certain hole diameters and the second outer surface with corresponding hole area rates further ensure that the filter membrane has high interception efficiency on various parvoviruses (the particle size is about 20 nm).

The method for testing the area rate of the holes can be that after the film structure is subjected to morphology characterization by using a scanning electron microscope, computer software (such as Matlab, NIS-Elements and the like) or manual measurement is carried out, and corresponding calculation is carried out; selecting a certain area, e.g. 1 μm ² (1 μm by 1 μm) or 25 μm ² (5 μm multiplied by 5 μm), the specific area is determined according to the actual situation, the hole areas of all holes on the area are measured by corresponding computer software or manually, then calculation and summation are carried out, and the sum is divided by the corresponding area, so that the hole area rate of the surface is obtained; of course, the skilled person can also obtain the above parameters by other measuring means, and the above measuring means is only used for reference; furthermore, the average diameter of the first fibers in subsequent features may also be obtained by a similar method (i.e. the average of the diameters of several first fibers over an area).

As a further improvement of the invention, the first outer surface comprises a plurality of strip-shaped continuous first fibers, and a first hole in a circular hole shape is formed between adjacent continuous first fibers in a surrounding manner; the average diameter of the first fiber is 100-250 nm; the average pore diameter of the first pores is 200-600 nm; the first holes have a hole area ratio of 5-25% on the first outer surface.

In the membrane body structure of the filter membrane provided by the invention, a plurality of first fibers are clearly seen on the first outer surface of the membrane, the first fibers are in a strip-shaped structure, and the first holes on the first outer surface are formed by encircling the first fibers; the average diameter of the first fibers is 100-250nm, so that the thick and thin first fibers ensure the stability of the first holes, are convenient for performing certain pre-filtration on fluid and intercepting impurity particles with certain particle size; meanwhile, the mechanical strength of the membrane is ensured, the requirement of practical application is met, and various processing treatments are suitable for being carried out;

in addition, a certain number of first holes with a certain pore diameter exist on the first outer surface of the membrane, and the factors such as the pore diameter size, the number and the shape of the holes of the membrane have great influence on the properties such as the filtration precision (interception efficiency) and the flow rate of the membrane; the first holes on the first outer surface are round hole-shaped structures, some first holes are round, and some first holes are oval; the average pore diameter of the first pores is 200-600nm (preferably 250-550 nm); and the area ratio of the first holes on the first outer surface is 5-25% (the ratio of the sum of the areas of the first holes to the area of the membrane), and the first holes with a certain pore size and the first outer surface with the corresponding area ratio of the holes jointly ensure that the filter membrane has a larger flow velocity, so that fluid can rapidly pass through the porous membrane, the filtering time is shortened, the tensile strength is higher, and the requirements of practical application are met.

As a further improvement of the invention, the average pore diameter variation gradient of the cellulose filter membrane is 2-7nm/1 μm;

the ratio of the average pore size of the first outer surface to the average pore size of the second outer surface is 6-30;

the area ratio of the holes on the first outer surface is at least 3% greater than the area ratio of the holes on the second outer surface.

The filter membrane is integrally formed, and the pore size of the filter membrane is gradually changed along with the integral thickness of the membrane (in a certain area, the pore size may not be changed along with the membrane thickness basically), so that mutation is avoided; therefore, the speed of the change of the pore diameter of the membrane along with the thickness is reflected by the size of the change gradient of the average pore diameter, the larger the value of the change gradient is, the faster the change of the pore diameter is, and the smaller the value of the change gradient is, the smaller the change of the pore diameter is; the average pore diameter change gradient of the filter membrane is 2-7nm/1 mu m, and the filter membrane has a proper pore diameter change gradient value, which shows that the pore diameter of the filter membrane changes with thickness to a certain extent, the pore diameter of the filter membrane does not change too fast, and overlarge pores do not exist (when the pores of the pollutant-containing layer are overlarge, the integral mechanical strength of the filter membrane is too low, the filter membrane is not pressure-resistant, and is easy to damage under the action of pressure), so that the pollutant-containing layer can play a certain supporting role on the interception layer, the integral filter membrane has good mechanical strength and is pressure-resistant, and is not easy to damage under larger pressure; the aperture change gradient cannot be too small, so that the interception efficiency is too low or the flux is too low, and the requirement of practical application cannot be met; the whole membrane has the aperture change gradient, so that the high-efficiency interception of the membrane on viruses can be ensured, and the membrane also has higher flux and higher pollutant carrying capacity.

In the invention, the pore size of the filter membrane is gradually changed along with the whole thickness of the membrane (in a certain region, the pore size may not be changed along with the membrane thickness basically), and mutation does not occur; except that the change gradient of the average pore diameter can basically reflect the change condition of the pore diameter of the membrane along with the thickness; the characteristic of the ratio of the average pore diameters of the two outer surfaces can further better reflect the change of the pore diameter of the membrane along with the thickness; the ratio of the average pore sizes of the two outer surfaces can be called an asymmetry factor, and the smaller the value is (the closer to 1), the stronger the symmetry of the two outer surfaces of the filter membrane is; the larger the value, the larger the asymmetry of the two outer surfaces of the filter membrane; the ratio of the average pore size of the first outer surface to the average pore size of the second outer surface is measured to be 6-30, preferably 10-25, indicating that the two outer surfaces of the filter membrane of the present invention are asymmetric and have suitable asymmetry; the asymmetry not only ensures that the filter membrane has larger flux and longer service life; the high virus interception efficiency of the filter membrane is ensured, and the actual requirement is met;

it is known that factors such as the pore size and the number of pores of the membrane, the shape of the pores and the like can greatly influence the properties such as the filtration precision (interception efficiency) and the flow rate of the membrane; according to the invention, the area rate of the holes on the first outer surface is at least more than 3% greater than that of the holes on the second outer surface, namely, the area rate of the holes on the first outer surface (big hole surface) is greater, and the area rate of the holes on the second outer surface (small hole surface) is smaller, so that fluid can rapidly pass through the first outer surface (big hole surface), and the first outer surface has a pre-filtering effect on the fluid, so that the integral membrane has good flux; and the second outer surface (a small pore surface) is compact, so that various parvoviruses (particularly mouse parvoviruses with the particle size of about 20 nm) can be efficiently intercepted, the parvoviruses are not easy to leak, and the requirement of practical application is met.

As a further improvement of the invention, the cellulose filter membrane has a PMI average pore diameter of 15-40nm, a thickness of 70-120 μm and a porosity of 25-55%.

The average pore size of the filter membrane is tested by a PMI pore size tester, the PMI average pore size of the filter membrane is 15-40nm (preferably 18-30nm), and the filter membrane has strong interception effect on nano-scale parvovirus (even the murine parvovirus with the particle size of 20 nm) through a tortuous path of a main body structure and certain thickness of the membrane, can meet the requirement of practical application and is suitable for being used as a virus membrane;

the thickness of the film can be measured by using a scanning electron microscope to perform morphology characterization on the film structure, and then using computer software (such as Matlab, NIS-Elements and the like) or manually measuring and then calculating; of course, the skilled person can also obtain the above parameters by other measuring means (e.g. freeze drying, measurement with measuring tools in advance), and the above measuring means is only used for reference; when the thickness of the film is too small, the mechanical strength of the film is low; meanwhile, as the filtering time is too short, effective filtering cannot be carried out; when the thickness of the membrane is too large, the filtration time is too long, and the time cost is too large; the thickness of the cellulose filter membrane is 70-120 mu m, so that the cellulose filter membrane not only has higher mechanical strength, but also can carry out effective filtration, and has higher filtration efficiency, shorter filtration time and lower time cost;

when the porosity of the membrane is too high, the tensile strength of the membrane is too low, the mechanical property of the membrane is poor, the industrial practical value is low, and the market demand cannot be met; when the porosity of the membrane is too low, on one hand, the flow rate of the membrane is influenced, so that the filtering speed of the membrane is low, the filtering time is long, and the time cost is high; on the other hand, the pollution capacity of the membrane is too low, the service life is too short, the membrane needs to be replaced in a short time, and the economic cost is greatly improved; therefore, the filter membrane needs to have a suitable porosity, which is closely related to the material of the filter membrane; the filter membrane is made of cellulose materials, on the basis, the porosity of the filter membrane is 25-55%, and under the combined action of the porosity and the membrane materials, the membrane not only has good tensile strength, but also has high filtering speed, high flow rate, high pollutant carrying capacity, long service life and low economic cost, and can intercept more impurity particles.

As a further improvement of the invention, the average pore diameter of the pollutant-containing layer is 80-300nm, and the porosity is 35-70%; the thickness of the stain containing layer accounts for 70-90% of the thickness of the film;

the average pore diameter variation gradient of the pollutant carrying layer is 3-9 nm/mu m.

In the main structure of the membrane, the area with the aperture larger than 40nm is a pollutant-containing layer, and the area with the aperture smaller than or equal to 40nm is a trapping layer; compared with the interception layer, the pore diameter of the pollutant containing layer is larger, and the porosity is higher; tests show that the average pore diameter of the pollutant carrying layer is 80-300nm (preferably 120-250 nm), and the porosity is 35-70% (preferably 40-65%); the filter membrane is ensured to have higher flow velocity, and can also play a sufficient role in intercepting large-particle impurities (such as large-particle-size viruses and other impurities) without influencing the interception of subsequent parvoviruses; the thickness of the pollutant-containing layer accounts for 70-90% of the whole thickness of the membrane, which indicates that most areas of the membrane are the pollutant-containing layer, and under the combined action of large aperture and high porosity, the whole membrane is ensured to have high flux, high filtering speed, low time cost, high pollutant-containing amount, long service life and slow flux attenuation.

The average pore diameter change gradient of the dirt-containing layer is too large, namely the pore diameter of the membrane changes too fast along with the thickness, so that the integral mechanical strength of the membrane is too low, the dirt-containing layer cannot provide a supporting function for the interception layer, and the requirement of practical application cannot be met; the average pore diameter change gradient of the dirt-containing layer is too small, namely when the pore diameter of the membrane changes too slowly along with the thickness, the interception efficiency of the filter membrane on various parvoviruses is too low (the average pore diameter of the whole membrane is too large), or the integral flux of the filter membrane is too small, the filtering time is too long, and the time cost is too large (the average pore diameter of the whole membrane is too small); the average aperture change gradient of the pollutant-containing layer is 3-9 nm/mum, the pollutant-containing layer has proper average aperture change gradient, the aperture size is more reasonable along with the thickness change, and simultaneously, under the combined action of the larger average aperture of the corresponding pollutant-containing layer, the pollutant-containing layer is ensured to have larger pollutant-containing amount, and the service life of the membrane is longer; meanwhile, the integral flux of the membrane is ensured to be higher, the flux attenuation is slower, and the unit economic benefit is high; in addition, the small pore diameter of the holes in the interception layer can be ensured, and the high-efficiency interception of the whole filter membrane on the virus is not influenced.

The average pore diameter, porosity, thickness and other parameters of the pollutant carrying layer can be measured by tearing the filter membrane, dividing the filter membrane into the pollutant carrying layer and the interception layer, and then testing the corresponding parameters of the pollutant carrying layer; or the film cross-sectional structure is subjected to morphology characterization by using a scanning electron microscope, and then is measured and measured by using computer software (such as Matlab, NIS-Elements and the like) or manually; of course, the skilled person can also obtain the above parameters by other measuring means, and the above measuring means is only used for reference;

as a further improvement of the present invention, the average pore size of the area of the soil-receiving layer on the side close to the first outer surface is larger than the average pore size of the area of the soil-receiving layer on the side close to the second outer surface;

and the average pore diameter variation gradient of the area of the pollutant carrying layer close to the first outer surface is larger than that of the area of the pollutant carrying layer close to the second outer surface.

Preferably, the pore size of the membrane pores in the soil-receiving layer of the present invention changes with the deceleration of the membrane thickness (in the direction from the first outer surface toward the second outer surface), i.e., in the region of the soil-receiving layer on the side near the first outer surface, the pore size of the pores is relatively large, and the pore size of the pores changes rapidly with the thickness (the average pore size change gradient value is large); in the area of the pollutant-containing layer close to the second outer surface, the pore diameter of the pores is relatively small, and the pore diameter of the pores changes slowly along with the thickness (the average pore diameter change gradient value is small), so that the transition from the pollutant-containing layer to the interception layer is very natural without any mutation, and the membrane is ensured to have high mechanical strength integrally; compared with a membrane structure in which the pore diameter of the membrane pores in the dirt-containing layer is basically in equal gradient change along with the thickness, the filter membrane in which the pore diameter of the dirt-containing layer is in deceleration change along with the thickness has larger dirt-containing amount and higher flux, and plays a good role in pre-filtering fluid.

As a further improvement of the invention, the pollutant carrying layer further comprises a leather layer area, and one side of the leather layer area comprises a first outer surface; the thickness of the skin layer region is 1-15 μm, the porosity of the skin layer region is 10-55%, and the average pore diameter of the region on the side close to the first outer surface in the skin layer region is smaller than the average pore diameter of the region on the side close to the trapping layer in the skin layer region.

In the filter membrane prepared by the invention, in the sewage containing layer of a part of the filter membrane, the pore diameter of the membrane pores is reduced along with the thickness (no matter the pore diameter is reduced by an equal gradient or a deceleration gradient) in the direction from the first outer surface (liquid inlet surface) to the second outer surface (liquid outlet surface), and the pores existing on the first outer surface are the pores with the largest pore diameter in the integral structure of the membrane; however, in the dirt-containing layer of a part of the filter membrane, in the direction from the first outer surface (liquid inlet surface) to the second outer surface (liquid outlet surface), the pore diameter of the membrane pores is firstly increased and then reduced along with the thickness, and the area of the membrane overall structure with the pores with the largest pore diameter is the area close to the first outer surface, but not the first outer surface; in the main structure of the filter membrane, the area of the inner hole of the dirt-containing layer, the hole diameter of which increases along with the thickness, is called a leather layer area; when the dirt-containing layer of the filter membrane comprises a skin layer area, the side of the skin layer area, which is far away from the interception layer, is the first outer surface; the existence of the skin layer region is beneficial to improving the tensile strength of the membrane, and simultaneously, a supporting and protecting function is further provided for the interception layer, so that the whole membrane is more pressure-resistant, is not easy to break and has longer service life; it has been found, moreover, that the thickness of the skin region is from 1 to 15 μm (as preferred from 3 to 10 μm) and the porosity is from 10 to 55%; the skin layer area has proper thickness and porosity, which can not only improve the supporting strength of the membrane, but also can not influence the integral filtering speed and pollutant carrying capacity of the membrane.

As a further improvement of the invention, the average pore diameter of the interception layer is 20-40nm, and the porosity is 10-45%; the thickness of the interception layer is 5-25 μm; the average pore diameter variation gradient of the interception layer is 0-3nm/1 mu m.

The interception layer is an area for intercepting parvovirus in the main structure of the filter membrane; the aperture size and the thickness of the interception layer can have great influence on the interception efficiency of the virus; the average pore diameter of the interception layer is 20-40nm, and the pore diameter of the pores in the interception layer is smaller, so that the filter membrane has higher interception efficiency on impurities with small particle size (particularly parvovirus with the particle size of 20 nm), meets the requirement of practical application, and is particularly suitable for being applied to the field of virus removal; in the prior art, the thickness of some filter membrane retention layers is very small (basically about 1-3 um), especially some filter membranes with general hydrophilic performance (such as polyethersulfone filter membranes), because the smaller the membrane pores, the stronger the adsorption capacity of the filter membranes, and therefore if the thickness of the retention layer of the filter membranes with general hydrophilic performance is a little larger, the proteins are easily adsorbed, thereby resulting in the low yield of the proteins (the PES membrane has a certain adsorption effect on the proteins, and when the pore diameter is small, the adsorption effect is more obvious, and therefore the thickness of the separation layer of the PES membrane is relatively thin); however, the method has certain problems that the virus is easy to leak, and the high-efficiency interception of the filter membrane cannot be kept all the time;

the cellulose filter membrane has strong hydrophilicity and basically does not have the adsorption effect on protein; according to the invention, the small-hole area (the thickness of the interception layer is 5-25 μm) with larger thickness ensures low protein adsorption, and simultaneously has high interception efficiency, and the virus has no risk of leakage; meanwhile, the thickness of the trapping layer is not too large, and the integral flux of the membrane is basically not influenced; meanwhile, the porosity of the interception layer is 10-45%, which shows that the interception layer can play a sufficient and sufficient retention role on parvovirus, the loading capacity of the membrane is high, and the service life of the membrane is further prolonged;

the average pore diameter variation gradient of the trapping layer is 0-3nm/1 μm, and the average pore diameter variation gradient is smaller. Thus, the pore diameter of the holes inside the trapping layer is slightly changed with the thickness, even does not change; under the combined action of the filter membrane and the smaller average pore diameter of the interception layer, the high-efficiency interception of the filter membrane on viruses can be further improved, even the mouse parvovirus with the particle size of 20nm can be efficiently intercepted, the leakage risk does not exist, and the service life is long.

The average pore diameter, porosity, thickness and other parameters of the interception layer can be measured by tearing the filter membrane, dividing the filter membrane into the interception layer and the pollutant carrying layer, and then testing the corresponding parameters of the interception layer; or the film cross-sectional structure is subjected to morphology characterization by using a scanning electron microscope, and then is measured and measured by using computer software (such as Matlab, NIS-Elements and the like) or manually; in addition, the thickness of the interception layer can also be subjected to interception test by using 20nm colloidal gold as impurity particles, the length of the 20nm colloidal gold interception area in the filter membrane is the thickness of the interception layer, and the specific test method can refer to Chinese patent CN 105980037B-membrane for removing viruses; of course, the skilled person can also obtain the above parameters by other measuring means, which are only used as reference.

As a further improvement of the present invention, the average pore size within the rejection layer in the direction of the membrane thickness from the first outer surface to the second outer surface is substantially constant with thickness; or the average pore diameter in the trapping layer becomes continuously smaller with the thickness; or the average pore diameter in the trapping layer is firstly reduced and then increased along with the thickness.

The main structure of the formed membrane can be influenced by controlling and adjusting corresponding preparation parameters, and filter membranes with different structures are prepared; observing the main structure of the filter membrane, and finding that the average pore diameter of the pores in the retention layer of a part of the filter membrane is not basically changed along with the thickness (namely the average pore diameter change gradient is 0);

the average pore diameter of the pores in the interception layer of the other part of the filter membrane is continuously reduced along with the thickness, and the position with the minimum pore diameter of the pores in the interception layer is on the second outer surface, so that the interception layer structure is beneficial to ensuring the interception efficiency; the average pore diameter of the holes in the interception layer of a part of the filter membrane is reduced and then increased along with the thickness, and the interception layer structure is favorable for improving the integral flux of the membrane on the premise of ensuring the interception efficiency; different interception layer structures, the thickness of the interception layer and the average pore size of the interception layer are acted together, so that the filter membrane has high interception efficiency on parvovirus, and the filter membrane has high flux and mechanical strength integrally.

As a further improvement of the invention, the ratio of the average pore size of the fouling layer to the average pore size of the rejection layer is 2.5 to 9.5: 1; the thickness of the dirt containing layer is at least 35 mu m larger than that of the interception layer.

The main structure of the filter membrane is mainly divided into two areas, wherein the area with relatively larger hole diameter is a pollutant accommodating layer, and the area with relatively smaller hole diameter is a trapping layer; after measurement, the ratio of the average pore diameter of the pollutant containing layer to the average pore diameter of the retention layer is 2.5-9.5: 1 (preferably 4-9: 1), on the one hand, the fiber membrane type filter membrane is described as an asymmetric membrane, and the pore diameter of the pores of the asymmetric membrane varies with the thickness; on the other hand, the membrane aperture of the invention can not change too fast along with the thickness, and no overlarge holes exist; meanwhile, the membrane has a reasonable membrane pore structure, and the membrane pore diameter is reasonably changed along with the thickness, so that the efficient interception of the filter membrane on viruses is further ensured, the filter membrane can be ensured to have faster flux, and the filter membrane has larger pollutant carrying capacity.

On the premise of ensuring that the filter membrane has high interception efficiency, the separation layer is expected to be thin (the thickness is relatively small), and the difference between the thickness of the dirt containing layer and the thickness of the interception layer is large, so that the filter membrane has large flux; the thickness of the dirt containing layer is at least 35 mu m larger than that of the interception layer, and the membrane main body structure further indicates that most areas in the filter membrane are the dirt containing layer, and the separation layer is very thin, so that the filter membrane has larger flux and high filtering speed; meanwhile, the filter membrane also has large dirt holding capacity, long service life and slow flux attenuation.

As a further improvement of the invention, the pollutant containing layer comprises prefilter fibers forming a porous structure, and the prefilter fibers are in a strip-shaped structure; the interception layer comprises separation fibers forming a porous structure, and the separation fibers are in a strip-shaped structure; one side of the prefiltration fiber close to the interception layer is connected with one side of the separation fiber close to the pollutant containing layer; the pre-filter fibers have an average diameter of 40-100 nm; the mean diameter of the separation fiber is 20-90 nm.

In the membrane body structure of the filter membrane provided by the invention, the fiber structure does not change along with the membrane thickness, the pre-filtering fiber strip structure in the sewage accommodating layer can be clearly seen, and the separating fiber in the intercepting layer is also in a strip structure; the filter membrane is integrally formed, and no composite exists; the pre-filtering fiber and the separating fiber in the strip structure form a dirt holding layer and an intercepting layer with proper porosity and pore distribution, so that the whole membrane has higher flow speed and high virus intercepting efficiency; the average diameter of the pre-filtering fiber is 40-100nm, and the average diameter of the separating fiber is 20-90nm, so that the thick pre-filtering fiber and the thick separating fiber can ensure that the stability of the inner holes of the pollutant receiving layer and the intercepting layer is stronger, the collapse or the contraction is not easy to happen, and the stability of the flow rate of the fluid is further ensured; finally, the membrane has high mechanical strength and filtration stability, and can be efficiently filtered for a long time; therefore, the filter membrane is particularly suitable for being applied to the field of virus removal;

the thickness degree of the fiber section can be regarded as the diameter of the fiber, and the average diameter of the second fiber in the invention can be calculated by using a scanning electron microscope to perform morphology characterization on the cross-sectional structure of the filter membrane and then using computer software (such as Matlab, NIS-Elements and the like) or manually to perform measurement; it will of course be appreciated that the above parameters may also be obtained by other measurement means by a person skilled in the art.

As a further improvement of the invention, the cellulose filter membrane is made of cellulose polymer with acetyl of 0-40% by mass.

As a further improvement of the present invention, the cellulose-based filter membrane comprises at least one of nitrocellulose, cellulose acetate and regenerated cellulose.

In the present invention, the film-forming material is a cellulose-based polymer having 0 to 40% by mass of acetyl groups (i.e., the mass fraction of acetyl groups in the cellulose-based polymer is 0 to 40%), and preferably, the cellulose-based polymer is at least one (either one or more kinds of cellulose-based substances) of cellulose nitrate, cellulose acetate (including cellulose diacetate and cellulose triacetate), and regenerated cellulose; the cellulose polymers are easy to dissolve in corresponding organic solvents and have good film-forming and fiber-forming properties; the prepared film has strong hydrophilicity, is not easy to adsorb effective substances (mainly protein) in fluid, and has high economic benefit and long service life; and the cellulose polymer has wide sources, is convenient to obtain and has lower cost.

As a further improvement of the present invention, the first water contact angle of the cellulose-based filter membrane is 25 ° to 70 °; the cellulose filter membrane has the tensile strength of 6-15MPa and the elongation at break of 5-40 percent; the flux of the cellulose filter membrane is more than 300L h ^-1 *m ^-2 @30 psi; the LRV of the cellulose filter membrane to virus impurities is not less than 4; the protein yield of the cellulose filter membrane is not lower than 98%;

under the action of 30psi pressure, 0.4g/L IVIG solution is used as test solution, and the initial flux of the filter membrane is 300- ^-1 *m ^-2 @30psi, and the loading of the filter is not less than 300L/m until the flux attenuation of the filter is 75 percent as an end point ² 。

Generally, the more hydrophilic the membrane, the less readily the membrane adsorbs the proteins in the fluid, i.e., the higher the protein yield; the contact angle test is carried out on the first outer surface and the second outer surface of the cellulose filter membrane, and the test finds that the first water contact angle of the first outer surface and the second outer surface is 25-70 degrees, namely the first water contact angle of the cellulose filter membrane is 25-70 degrees (the smaller the contact angle is, the more hydrophilic the cellulose filter membrane is), so that the cellulose filter membrane is very hydrophilic as a whole and has low adsorption to various proteins, therefore, the cellulose filter membrane has high protein yield and further ensures the economic benefit;

important indexes for evaluating the mechanical strength of the filter membrane are the tensile strength and the elongation at break of the filter membrane; under certain conditions, the higher the tensile strength of the filter membrane is, the better the mechanical strength of the filter membrane is; tensile strength refers to the ability of a film to withstand parallel stretching; when the film is tested under a certain condition, the film sample is acted by a tensile load until the film sample is damaged, and the tensile strength and the elongation at break of the film can be calculated according to the maximum tensile load corresponding to the damage of the film sample, the change of the size (length) of the film sample and the like; tensile strength, elongation at break, can be measured by a universal tensile tester, tensile strength testing methods are well known in the art, for example, tensile strength testing procedures are explained in detail in ASTM D790 or ISO 178; the tensile strength of the filter membrane is 6-15 MPa; the elongation at break is 5-40%, which shows that the filter membrane of the invention has larger tensile strength and elongation at break, better mechanical property and higher industrial practical value, and can completely meet the market demand.

The permeation flux is also called the permeation rate, flux for short, and refers to the amount of substance that a filter membrane passes through the unit membrane area in a unit time under a certain working pressure in the separation process; the flux reflects the speed of the filtration; the higher the flux, the faster the filtration rate of the membrane; the flux of the filter membrane of the invention is more than 300L x h ^-1 *m ^-2 @30psi, its flux is great, indicates that the filtration rate of filter membrane is faster, when guaranteeing to hold back efficiency, and the fluid can rapid through filtration membrane, and the time cost is lower, and economic benefits is higher.

The trapped viruses mainly aim at various viruses with the particle size of 20nm and above (such as mouse parvovirus, the particle size of which is about 20 nm), and the LRV of the filter membrane to various viruses is not lower than 4 after trapping tests, which shows that the filter membrane has very high trapping rate to the viruses, plays a role in sufficiently retaining virus impurities and meets the requirements of practical application; in addition, the protein yield of the filter membrane is not lower than 98%, which indicates that the effective substance protein in the fluid is not easy to be adsorbed on the membrane, on one hand, the membrane pores are not blocked, and the filter membrane still has longer service life, on the other hand, the content change of the effective substance protein in the fluid is ensured to be very small, the protein is not lost basically, and the economic benefit is ensured; for the test method of virus impurities, reference may be made to patent-CN 105980037B-membrane for virus removal, CN 101816898B-ultrafiltration membrane and its preparation method, CN 1759924B-ultrafiltration membrane and its preparation method, etc.

IVIG is an injected immunoglobulin, which is a protein model of antibodies; in the invention, IVIG acetate buffer solution with the concentration of 0.4g/L is used as the test solution (except IVI in the test solution)G, no other protein, no corresponding viral impurities), when the flux of the filter membrane is reduced to 25% of the initial flux (flux is reduced by 75%) under the pressure of 30psi, the volume of the test solution flowing through the filter membrane is not less than 300L/m ² Namely, the loading capacity of the filter membrane is not lower than 300L/m2, thereby further illustrating that the filter membrane has lower nonspecific adsorption and longer service life;

on the other hand, the invention also provides a preparation method of the asymmetric cellulose filter membrane for virus removal, which comprises the following steps:

s1: preparing a casting solution, and casting the casting solution on a carrier to form a liquid film; the casting solution comprises the following substances in parts by weight: 10-30 parts of a film-forming polymer; 15-40 parts of a first organic solvent; 30-75 parts of a pore-forming agent; the film-forming polymer is a cellulose polymer; the first organic solvent is at least one of acetone, dioxane, dimethylacetamide, N-methylpyrrolidone, acetic acid, propionic acid, butyric acid and valeric acid;

the pore-forming agent is a non-solvent substance with the surface tension lower than 35dyne/cm, and the substance is mutually soluble with the coagulating bath;

s2: immersing the liquid film into a coagulating bath for split-phase curing, wherein the temperature of the coagulating bath is 15-45 ℃, and the duration is 20-60s, so as to obtain a film; the coagulating bath is water or ethanol.

As a further improvement of the invention, the temperature of the casting film liquid is 15-40 ℃; the pore-forming agent is at least one of formamide, ethanol, 1-propanol, isopropanol, n-butanol, 1-pentanol, 2-pentanol and diethylamine.

As a further improvement of the invention, the liquid film is immersed into pre-phase-separating liquid for pre-phase-separating before being immersed into a coagulating bath for phase-separating solidification, and the pre-phase-separating time is 2-10 s; wherein the pre-phase separation liquid comprises a second organic solvent and a non-solvent, and the content of the non-solvent is 0-30%; the second organic solvent is mutually soluble with the first organic solvent; the second organic solvent is at least one of acetone, dioxane, dimethylacetamide, N-methylpyrrolidone, acetic acid, propionic acid, butyric acid and valeric acid; the non-solvent is water or ethanol.

As a further improvement of the invention, the formed film is put into sodium hydroxide solution for hydrolysis, the hydrolysis temperature is 20-40 ℃, and the hydrolysis time is 15-45 min; and (4) drying after hydrolysis to form a solid film.

When the cellulose filter membrane is prepared, a membrane casting solution is prepared firstly, and the membrane casting solution comprises a membrane forming polymer, a first organic solvent and a pore-forming agent; wherein the film-forming polymer is a cellulose-based polymer having 0 to 40% by mass of acetyl groups (i.e., the mass fraction of acetyl groups in the cellulose-based polymer is 0 to 40%), and preferably, the cellulose-based polymer is at least one of cellulose nitrate, cellulose acetate (including cellulose diacetate and cellulose triacetate), and regenerated cellulose; the cellulose polymers are easy to dissolve in corresponding organic solvents and have good film-forming and fiber-forming properties; the prepared film has strong hydrophilicity, and is not easy to adsorb effective substances (mainly protein) in fluid; the first organic solvent is used for fully dissolving the corresponding cellulose polymer, and is dissolved by the coagulating bath during phase separation, so that the cellulose polymer is separated out to form a filter membrane with a certain pore size; in addition, pore-forming agent is added in the casting solution, in the prior art, the added pore-forming agent is generally selected from high specific surface tension substances such as polyvinylpyrrolidone (surface energy is about 60-65 dyne/cm), and the substances are relatively easy to enrich and pore-form; when the liquid film is immersed into a coagulating bath (such as water and ethanol), the liquid film close to the air side is firstly contacted with the coagulating bath, so that the liquid film close to the air side can be subjected to rapid phase separation, the pore-forming agent is separated out from the liquid film, and a compact surface layer with small pore diameter is formed on the side close to the air side (the side far away from the carrier), although the pore diameter of the pores in the compact surface layer is small, the entrapment efficiency of the formed film is too low and the pollutant carrying capacity is low due to the too small thickness, and almost no carrying capacity (the service life is very short) can not form a virus removal film which can be practically applied; non-solvents with low surface tension are generally not used as pore-forming agents because these materials are not easily enriched and the pore-forming effect is relatively poor; in an accidental experiment, a low-surface-tension non-solvent substance (a non-solvent substance with the surface tension lower than 35dyne/cm and mutually soluble with the coagulation bath; preferably at least one of formamide, ethanol, 1-propanol, isopropanol, n-butanol, 1-pentanol, 2-pentanol and diethylamine) is used as a pore-forming agent by mistake, but surprisingly, the addition of the low-surface-tension non-solvent substance can quickly mutually dissolve with the coagulation bath, and the coagulation bath can quickly enter the side close to the liquid film with the help of the low-surface-tension substance, so that the area close to the carrier side is quickly subjected to phase separation to form a corresponding small-hole area, namely a trapping layer, and the liquid film far away from the carrier side (air side) forms a corresponding large-hole area, namely a dirt accommodating layer due to the relatively slow phase separation speed; the membrane casting solution system can be used for obtaining a filter membrane with an ideal membrane aperture size and membrane aperture structure under the combined action of the membrane casting solution system and proper phase-splitting curing time (the temperature of a coagulation bath is 15-45 ℃, the duration time is 20-60s, and the coagulation bath is water or ethanol); in addition, the casting solution system is only suitable for cellulose film formation and is not suitable for polyether sulfone, the inventor conjectures that the system has a certain relation with the structural shape of the film forming material, and the cellulose material is more hydrophilic, so the system is suitable for the system and can form an ideal film structure;

the reasonable formula of the casting solution can greatly influence the structure and performance of the finally formed filter membrane, such as the aperture, the thickness, the flow rate and the like of the filter membrane; the reasonable formula of the casting solution ensures that the finally prepared filter membrane has proper thickness and obtains ideal aperture; further, the inventive casting solutions can be cast manually (e.g., by pouring, casting, or spreading by hand on a casting surface) or automatically (e.g., poured or otherwise cast on a moving bed); a variety of apparatus known in the art can be used for casting. Casting equipment includes, for example, mechanical coaters, including doctor blades, or spray/pressurized systems. As is known in the art, a variety of casting speeds are suitable, such as casting speeds of about 2 to 6 feet per minute (fpm), and the like, as the case may be;

On the premise of ensuring the retention efficiency, the market hopes that the flux of the filter membrane is as large as possible; more fluid can be filtered in a shorter time, and the economic benefit per unit time is higher; the required flux of the filter membrane is larger, so that the porosity of the whole filter membrane is required to be larger; in order to further increase the flux of the cellulose-based filter membrane as a whole, it is desirable that the filter membrane has a high porosity; in order to make the filter membrane have more ideal porosity, the liquid membrane is subjected to phase splitting solidification and pretreatment, namely, the liquid membrane is subjected to pre-phase splitting firstly, namely, the liquid membrane enters a pre-phase solution, wherein the pre-phase solution is a mixture of a second organic solvent and a non-solvent, the second organic solvent can be mutually soluble with the first organic solvent, and the second organic solvent can be the same as or different from the first organic solvent; the non-solvent is water or ethanol, the presence of the non-solvent can help the liquid film near the air side to carry out phase separation, and the liquid film is carried out due to the fact that the content of the non-solvent is 0-30% and the content of the non-solvent is extremely low

Slowly phase-separating to form a hole with a larger aperture near the air side; due to the difference of the pre-phase-separating liquid and the pre-phase-separating time, the position with the largest pore diameter of the holes of the final filter membrane is the first outer surface or the position close to the first outer surface; and because partial holes with larger pore diameters are formed in the pre-separation phase, the coagulation bath can be more easily invaded into the liquid film close to the carrier side, the phase separation is more sufficient, and the finally formed filter membrane has higher porosity and higher flux.

The cellulose filter membrane is put into a sodium hydroxide aqueous solution with the concentration of 0.005mol/L-0.03mol for hydrolysis, and then is dried after hydrolysis, wherein the drying can be natural drying or drying in an oven, so as to form a solid membrane; the solid membrane after hydrolysis and drying has better hydrophilicity and lower nonspecific adsorption to protein, thereby further improving the protein yield and the economic benefit.

The invention has the beneficial effects that: the asymmetric cellulose filter membrane for removing viruses comprises a main body, wherein one side surface of the main body is a first outer surface which is a macroporous surface, the second outer surface is a microporous surface, and the average pore diameter of the second outer surface is 15-40 nm; the first outer surface is a macroporous surface, and the average pore diameter of the first outer surface is at least more than 4 times of the average pore diameter of the second outer surface; the main body comprises a dirt containing layer and an intercepting layer for intercepting viruses, the main body comprises a dirt containing layer and an intercepting layer for intercepting the viruses, one side of the dirt containing layer is a first outer surface, and one side of the intercepting layer is a second outer surface; the other side of the stain containing layer and the other side of the interception layer are in transition by continuous fibers, so that the filter membrane is integrally prepared and formed by only one membrane casting solution without compounding, and the preparation process is relatively simple; the average pore diameter of the pollutant containing layer is larger than that of the interception layer; the average pore diameter variation gradient of the dirt containing layer is larger than that of the interception layer, and the pore diameter is changed along with the thickness in a deceleration way, so that the filter membrane has a stronger interception effect on parvovirus, can obtain higher protein yield, has higher flux, high filtering speed, larger loading capacity and long service life, and meets the requirements of practical application; is particularly suitable for the field of virus removal; in addition, the invention also provides a preparation method of the filter membrane, and the preparation method is convenient, quick and effective, simple to operate, green and environment-friendly, and suitable for large-scale popularization.

Drawings

FIG. 1 is a Scanning Electron Microscope (SEM) image of a first external surface of a filter membrane prepared according to example 1, at a magnification of 5K ×;

FIG. 2 is a Scanning Electron Microscope (SEM) image of the second outer surface of the filter membrane prepared in example 1 at a magnification of 20K ×;

FIG. 3 is a Scanning Electron Microscope (SEM) image of a longitudinal section of a filter membrane prepared according to example 1, wherein the magnification is 2K ×;

FIG. 4 is a further magnified Scanning Electron Microscope (SEM) image of a longitudinal section of the filter membrane prepared in example 1 at a magnification of 20K;

FIG. 5 is a Scanning Electron Microscope (SEM) image of the longitudinal section skin region of the filter membrane prepared in example 5 closest to the first outer surface at a magnification of 10K;

FIG. 6 is a Scanning Electron Microscope (SEM) image of the longitudinal section skin region of the filter membrane prepared in example 5, furthest from the first outer surface, at a magnification of 10K;

FIG. 7 is a Scanning Electron Microscope (SEM) image of the longitudinal cross-section stain-containing layer (non-skin region) of the filter membrane prepared in example 5, far from the retention layer, wherein the magnification is 10K;

FIG. 8 is a Scanning Electron Microscope (SEM) image of a stain-containing layer (non-skin region) near a retention layer of a longitudinal section of the filter membrane prepared in example 5, wherein the magnification is 10K ×;

FIG. 9 is a Scanning Electron Microscope (SEM) image of a longitudinal section of the filter membrane prepared in example 5, taken away from the second outer surface, at a magnification of 10K ×;

FIG. 10 is a Scanning Electron Microscope (SEM) image of a longitudinal section, near a second outer surface, of a filter membrane prepared in example 5 at a magnification of 10K ×;

FIG. 11 is a schematic view of a filter flux testing apparatus according to the present invention;

FIG. 12 is a schematic view of a testing apparatus for performing a retention efficiency test on a filter membrane using colloidal gold according to the present invention;

FIG. 13 is a Scanning Electron Microscope (SEM) image of the cross section of the multi-layer composite ultrafiltration membrane prepared in the patent CN 1759924B;

FIG. 14 is a schematic diagram of a compounding device in the preparation of a multi-layer composite ultrafiltration membrane according to patent CN 1759924B.

Detailed Description

In order to more clearly explain the overall concept of the present application, the following detailed description is given by way of example. In the following examples, raw materials and equipment for preparing the filtration membranes were commercially available, unless otherwise specified. Wherein the structural morphology of the filter membrane is characterized by adopting a scanning electron microscope with the model number of S-5500 provided by Hitachi company.

Example 1a method for preparing an asymmetric cellulose-based filter membrane for virus removal, comprising the steps of:

s1: preparing a casting solution, and casting the casting solution on a carrier to form a liquid film; wherein the casting solution comprises the following substances in parts by weight: 12 parts of a film-forming polymer; 17 parts of a first organic solvent; 58 parts of pore-forming agent;

the film-forming polymer is cellulose diacetate; the first organic solvent is acetone; the pore-forming agent is ethanol; the temperature of the casting solution is 34 ℃;

s2: immersing the liquid film into a coagulating bath for split-phase curing, wherein the temperature of the coagulating bath is 24 ℃, and the duration time is 32s, and preparing a film; the coagulation bath is water.

The filter membrane comprises a dirt-containing layer and a retention layer, wherein the pore diameter variation gradient of the dirt-containing layer is larger than that of the retention layer; in the pollutant containing layer, the average pore diameter of the area close to one side of the first outer surface is larger than that of the area close to one side of the second outer surface of the pollutant containing layer; and in the pollutant carrying layer, the average pore diameter variation gradient of the area close to one side of the first outer surface is larger than that of the area close to the second outer surface of the pollutant carrying layer; the average pore size in the trapping layer becomes smaller with a continuous gradient of thickness.

Example 2 a method for preparing an asymmetric cellulose-based filter membrane for virus removal, comprising the steps of:

s1: preparing a casting solution, and casting the casting solution on a carrier to form a liquid film; the casting solution comprises the following substances in parts by weight: 24 parts of a film-forming polymer; 34 parts of a first organic solvent; 34 parts of a pore-forming agent; the film-forming polymer is cellulose triacetate; the first organic solvent is dioxane; the pore-forming agent is formamide; the temperature of the casting solution is 18 ℃;

s2: immersing the liquid film into a coagulating bath for split-phase curing, wherein the temperature of the coagulating bath is 18 ℃, and the duration time is 48s, so as to obtain a film; the coagulation bath is water.

The filter membrane comprises a dirt-containing layer and a retention layer, wherein the pore diameter variation gradient of the dirt-containing layer is larger than that of the retention layer; in the pollutant containing layer, the average pore diameter of the area close to one side of the first outer surface is larger than that of the area close to one side of the second outer surface of the pollutant containing layer; and in the pollutant carrying layer, the average pore diameter variation gradient of the area close to one side of the first outer surface is larger than that of the area close to the second outer surface of the pollutant carrying layer; the average pore size within the trapping layer is substantially constant with thickness.

Example 3 a method for preparing an asymmetric cellulose-based filter membrane for virus removal, comprising the steps of:

s1: preparing a casting solution, and casting the casting solution on a carrier to form a liquid film; the casting solution comprises the following substances in parts by weight: 20 parts of a film-forming polymer; 28 parts of a first organic solvent; 42 parts of a pore-forming agent; the film-forming polymer comprises 10 parts of cellulose diacetate and 10 parts of cellulose triacetate; the first organic solvent is dimethylacetamide; the pore-forming agent is 2-amyl alcohol; the temperature of the casting solution is 28 ℃;

s2: immersing the liquid film into a coagulating bath for split-phase curing, wherein the temperature of the coagulating bath is 34 ℃, and the duration time is 40s, and preparing a film; the coagulating bath is water.

The filter membrane comprises a dirt-containing layer and a retention layer, wherein the pore diameter variation gradient of the dirt-containing layer is larger than that of the retention layer; in the pollutant containing layer, the average pore diameter of the area close to one side of the first outer surface is larger than that of the area close to one side of the second outer surface of the pollutant containing layer; and in the pollutant carrying layer, the average pore diameter variation gradient of the area close to one side of the first outer surface is basically the same as that of the area close to the second outer surface of the pollutant carrying layer; the average pore diameter in the trapping layer is reduced and then increased along with the thickness.

Example 4 a method for preparing an asymmetric cellulose-based filter membrane for virus removal, comprising the steps of:

s1: preparing a casting solution, and casting the casting solution on a carrier to form a liquid film; the casting solution comprises the following substances in parts by weight: 14 parts of a film-forming polymer; 20 parts of a first organic solvent; 50 parts of a pore-forming agent; the film-forming polymer is cellulose diacetate; the first organic solvent is N-methyl pyrrolidone;

the pore-forming agent is ethanol; the temperature of the casting solution is 32 ℃;

s2: immersing the liquid film into a pre-phase separation liquid for pre-phase separation, wherein the pre-phase separation time is 7.5 s; wherein the pre-split phase liquid comprises a second organic solvent and a non-solvent, and the content of the non-solvent is 5%; the second organic solvent is N-methyl pyrrolidone; the non-solvent is water.

S3: immersing the liquid film into a coagulating bath for split-phase curing, wherein the temperature of the coagulating bath is 30 ℃, and the duration time is 24s, so as to prepare a film; the coagulating bath is water.

Example 5 a method for preparing an asymmetric cellulose-based filter membrane for virus removal, comprising the steps of:

s1: preparing a casting solution, and casting the casting solution on a carrier to form a liquid film; the casting solution comprises the following substances in parts by weight: 16 parts of a film-forming polymer; 23 parts of a first organic solvent; 62 parts of a pore-forming agent; the film-forming polymer is cellulose diacetate; the first organic solvent is acetone; the pore-forming agent is diethylamine; the temperature of the casting solution is 36 ℃;

s2, immersing the liquid film into a pre-phase separation liquid for pre-phase separation, wherein the pre-phase separation time is 5S; wherein the pre-phase separation liquid comprises a second organic solvent and a non-solvent, and the content of the non-solvent is 20%; the second organic solvent is acetone; the non-solvent is water;

s3: immersing the liquid film into a coagulating bath for split-phase curing, wherein the temperature of the coagulating bath is 25 ℃, and the duration time is 28s, so as to obtain a film; the coagulating bath is water.

The filter membrane comprises a dirt-containing layer and a retention layer, wherein the pore diameter variation gradient of the dirt-containing layer is larger than that of the retention layer; wherein the soil receiving layer comprises a skin region comprising a first outer surface; in the pollutant containing layer (in the direction from the first outer surface to the second outer surface), the pore diameter of the membrane pores is increased and then decreased along with the thickness; the average pore size in the trapping layer becomes smaller with a continuous gradient of thickness.

Example 6 a method for preparing an asymmetric cellulose-based filter membrane for virus removal, comprising the steps of:

s1: preparing a casting solution, and casting the casting solution on a carrier to form a liquid film; the casting solution comprises the following substances in parts by weight: 21 parts of a film-forming polymer; 30 parts of a first organic solvent; 66 parts of a pore-forming agent; the film-forming polymer is nitrocellulose; the first organic solvent is dioxane; the pore-forming agent is isopropanol; the temperature of the casting solution is 24 ℃;

s2, immersing the liquid film into a pre-phase separation liquid for pre-phase separation, wherein the pre-phase separation time is 7S; the pre-split phase liquid comprises a second organic solvent and a non-solvent, and the content of the non-solvent is 15%; the second organic solvent is dioxane; the non-solvent is ethanol;

s3: immersing the liquid film into a coagulating bath for split-phase curing, wherein the temperature of the coagulating bath is 32 ℃, and the duration time is 44s, so as to obtain a film; the coagulating bath is ethanol.

The filter membrane comprises a dirt-containing layer and a retention layer, wherein the pore diameter variation gradient of the dirt-containing layer is larger than that of the retention layer; in the pollutant containing layer, the average pore diameter of the area close to one side of the first outer surface is larger than that of the area close to one side of the second outer surface of the pollutant containing layer; in the pollutant carrying layer, the average pore diameter variation gradient of the area close to one side of the first outer surface is larger than that of the area close to the second outer surface of the pollutant carrying layer; the average pore diameter in the trapping layer is reduced and then increased along with the thickness.

Example 7 a method for preparing an asymmetric cellulose-based filter membrane for virus removal, comprising the steps of:

s1: preparing a casting solution, and casting the casting solution on a carrier to form a liquid film; the casting solution comprises the following substances in parts by weight: 26 parts of a film-forming polymer; 36 parts of a first organic solvent; 36 parts of a pore-forming agent; the film-forming polymer is cellulose triacetate; the first organic solvent is acetic acid; the pore-forming agent is 1-amyl alcohol; the temperature of the casting solution is 26 ℃;

s2: immersing the liquid film into a pre-phase-splitting liquid for pre-phase splitting before the liquid film is immersed into a coagulating bath for phase splitting solidification, wherein the pre-phase-splitting time is 9 s; wherein the pre-phase separation liquid is a second organic solvent; the second organic solvent is butyric acid;

s3: immersing the liquid film into a coagulating bath for split-phase curing, wherein the temperature of the coagulating bath is 36 ℃, and the duration time is 52s, so as to obtain a film; the coagulating bath is water.

The filter membrane comprises a dirt-containing layer and a retention layer, wherein the pore diameter variation gradient of the dirt-containing layer is larger than that of the retention layer; in the pollutant containing layer, the average pore diameter of the area close to one side of the first outer surface is larger than that of the area close to one side of the second outer surface of the pollutant containing layer; and in the pollutant carrying layer, the average pore diameter variation gradient of the area close to one side of the first outer surface is basically the same as that of the area close to the second outer surface of the pollutant carrying layer; the average pore size within the trapping layer is substantially constant with thickness.

Example 8 a method for preparing an asymmetric cellulose-based filter membrane for virus removal, comprising the steps of:

s1: preparing a casting solution, and casting the casting solution on a carrier to form a liquid film; the casting solution comprises the following substances in parts by weight: 18 parts of a film-forming polymer; 26 parts of a first organic solvent; 70 parts of pore-forming agent; the film-forming polymer comprises 10 parts of cellulose diacetate and 8 parts of cellulose triacetate;

the first organic solvent is valeric acid; the pore-forming agent is 1-propanol; the temperature of the casting film liquid is 38 ℃;

s2: immersing the liquid film into a pre-phase separation liquid for pre-phase separation, wherein the pre-phase separation time is 8 s; wherein the pre-phase separation liquid is a second organic solvent; the second organic solvent is propionic acid;

s3: immersing the liquid film into a coagulating bath for split-phase curing, wherein the temperature of the coagulating bath is 27 ℃, and the duration time is 36s, and preparing a film; the coagulating bath is water;

s4: placing the formed film in 0.01mol/L sodium hydroxide aqueous solution for hydrolysis at 25 deg.C for 20 min; and (4) drying after hydrolysis to form a solid film.

The filter membrane comprises a dirt-containing layer and a retention layer, wherein the pore diameter variation gradient of the dirt-containing layer is larger than that of the retention layer; in the pollutant containing layer, the average pore diameter of the area close to one side of the first outer surface is larger than that of the area close to one side of the second outer surface of the pollutant containing layer; and in the pollutant carrying layer, the average pore diameter variation gradient of the area close to one side of the first outer surface is basically the same as that of the area close to the second outer surface of the pollutant carrying layer; the average pore size in the trapping layer becomes smaller with a continuous gradient of thickness.

Example 9 a method for preparing an asymmetric cellulose-based filter membrane for virus removal, comprising the steps of:

s1: preparing a casting solution, and casting the casting solution on a carrier to form a liquid film; the casting solution comprises the following substances in parts by weight: 28 parts of a film-forming polymer; 38 parts of a first organic solvent; 38 parts of a pore-forming agent; the film-forming polymer is cellulose triacetate; the first organic solvent is dimethylacetamide;

the pore-forming agent is n-butyl alcohol; the temperature of the casting film liquid is 20 ℃;

s2, immersing the liquid film into a pre-phase separation liquid for pre-phase separation, wherein the pre-phase separation time is 4S; wherein the pre-phase separation liquid comprises a second organic solvent and a non-solvent, and the content of the non-solvent is 25%;

the second organic solvent is dimethylacetamide; the non-solvent is water;

s3: immersing the liquid film into a coagulating bath for split-phase curing, wherein the temperature of the coagulating bath is 21 ℃, and the duration time is 56s, so as to obtain a film; the coagulating bath is water;

s4, placing the formed film in 0.025mol/L sodium hydroxide aqueous solution for hydrolysis, wherein the hydrolysis temperature is 35 ℃, and the hydrolysis time is 40 min; and (4) drying after hydrolysis to form a solid film.

The filter membrane comprises a dirt-containing layer and a retention layer, wherein the pore diameter variation gradient of the dirt-containing layer is larger than that of the retention layer; wherein the soil receiving layer comprises a skin region comprising a first outer surface; in the pollutant-containing layer (in the direction from the first outer surface to the second outer surface), the aperture of the membrane pores is increased and then decreased along with the thickness; the average pore size within the trapping layer is substantially constant with thickness.

Example 10 a method for preparing an asymmetric cellulose-based filter membrane for virus removal, comprising the steps of:

s1: preparing a casting solution, and casting the casting solution on a carrier to form a liquid film; the casting solution comprises the following substances in parts by weight: 22 parts of a film-forming polymer; 32 parts of a first organic solvent; 46 parts of a pore-forming agent;

the film-forming polymer comprises 10 parts of cellulose diacetate and 12 parts of cellulose triacetate;

the first organic solvent is N-methyl pyrrolidone; the pore-forming agent is isopropanol; the temperature of the casting film liquid is 30 ℃;

s2: immersing the liquid film into a pre-phase-splitting liquid for pre-phase splitting before the liquid film is immersed into a coagulating bath for phase splitting solidification, wherein the pre-phase-splitting time is 6.5 s; the pre-split phase liquid comprises a second organic solvent and a non-solvent, and the content of the non-solvent is 10%;

the second organic solvent is N-methyl pyrrolidone; the non-solvent is water;

s3: immersing the liquid film into a coagulating bath for split-phase curing, wherein the temperature of the coagulating bath is 38 ℃, and the duration time is 42s, so as to obtain a film; the coagulating bath is water;

s4: placing the formed film in 0.02mol/L sodium hydroxide aqueous solution for hydrolysis, wherein the hydrolysis temperature is 30 ℃, and the hydrolysis time is 30 min; and (4) drying after hydrolysis to form a solid film.

The filter membrane comprises a dirt-containing layer and a retention layer, wherein the pore diameter variation gradient of the dirt-containing layer is larger than that of the retention layer; wherein the soil receiving layer comprises a skin region comprising a first outer surface; in the pollutant containing layer (in the direction from the first outer surface to the second outer surface), the pore diameter of the membrane pores is increased and then decreased along with the thickness; the average pore size in the trapping layer decreases and then increases with thickness.

Comparative example 1

The pore-forming agent ethanol in the example 1 is replaced by polyvinylpyrrolidone, and the preparation is carried out under the same conditions; the detection shows that a compact surface layer exists in the membrane, the pore diameter of the compact surface layer is small and is 20-30nm, but the thickness of the compact surface layer is small and is about 1um, and the compact surface layer does not have a carrying capacity at all, so that the virus removing membrane capable of being practically applied is formed.

Firstly, the following steps: structural characterization

Carrying out morphology characterization on the membrane structure of the nanoscale polymer filtering membrane obtained in each embodiment by using a scanning electron microscope, and then obtaining required data; the specific results are as follows:

table 1: structural and integral features of the outer surface of the filter membrane

	Flat of the first outer surface Average pore diameter/nm	A first hole on the first outer surface Area ratio of holes/%)	Flattening of the first fiber Average diameter/nm	Flat second outer surface Average pore diameter/nm	Second hole on second outer surface Area ratio of holes/%)
						Practice of Example 1	410	16	162	18	9
Practice of Example 2	520	21	200	32	12
						Practice of Example 3	480	19	190	26	11
Practice of Example 4	440	17	170	20	11
						Practice of Example 5	320	14	125	19	9
Practice of Example 6	400	15	155	28	11
						Practice of Example 7	540	22	210	34	14
Practice of Example 8	460	18	180	21	10
						Practice of Example 9	340	15	130	33	11
Practice of Example 10	300	14	120	27	10

Table 2-cellulose filter membrane bulk structural features:

	is thick and thick Degree- μm	Pores of Rate/%)	PMI averaging Pore size/nm	Membrane overall average pore diameter Gradient of change μm/1 μm	The average pore size of the first outer surface and ratio of average pore diameters of the second outer surface	Area ratio of holes on the first outer surface and the difference in the area ratio of the holes of the outer surfaces%
							Practice of Example 1	80	34	18	4.90	23	7
Practice of Example 2	100	36	22	4.88	16	9
							Practice of Example 3	95	35	20	4.78	18	8
Practice of Example 4	80	41	19	5.25	22	6
							Practice of Example 5	90	40	19	3.34	17	5
Practice of Example 6	95	45	19	3.92	14	4
							Practice of Example 7	110	50	22	4.60	16	8
Practice of Example 8	85	43	20	5.16	22	8
							Practice of Example 9	105	49	22	2.92	10	4
Practice of Example 10	90	46	20	3.03	11	4

Table 3-soil-receiving layer structural features:

	average of soil layer Pore size/nm	Hole of pollutant-receiving layer Void fraction/%)	Thickness of soil layer Degree/um	Change of average pore diameter of pollutant carrying layer Chemical gradient nm/mum	Prefiltration fiber flat Average diameter/nm	Thickness of the skin zone Degree/. mu.m	Holes in the skin zone Void fraction/%)
								Practice of Example 1	190	44	68	5.44	75	/	/
Practice of Example 2	240	48	78	6.15	90	/	/
								Practice of Example 3	225	46	77	5.71	85	/	/
Practice of Example 4	210	53	67	5.97	80	/	/
								Practice of Example 5	150	51	76	4.85	55	8	36
Practice of Example 6	185	58	75	4.80	70	/	/
								Practice of Example 7	248	63	86	5.81	92	/	/
Practice of Example 8	215	54	72	5.83	83	/	/
								Practice of Example 9	170	61	81	4.93	65	10	44
Practice of Example 10	160	56	73	5.07	60	6	40

Table 4-structural features of the rejection layer:

	average pore diameter/nm	Porosity/%	Thickness/um	Mean pore diameter variation gradient nm/mum	Separation ofAverage diameter of fiber/nm
						Example 1	27	19	12	1.83	41
Example 2	35	21	22	0.36	58
						Example 3	30	20	18	1.27	50
Example 4	28	26	13	1.54	45
						Example 5	27	25	14	1.50	43
Example 6	32	29	20	1.00	54
						Example 7	37	33	24	0.25	64
Example 8	29	28	13	1.46	48
						Example 9	36	31	24	0.29	61
Example 10	31	30	17	1.29	52

Note: as can be seen from Table 4, the average pore size variation gradient of the retention layer of the filtration membranes obtained in example 2, example 7 and example 9 was less than 0.5 nm/. mu.m, and it is believed that the pore size does not substantially vary with the membrane thickness.

As can be seen from tables 1-4, the filter membranes prepared in the embodiments 1-10 of the present invention all have ideal membrane structures, and the filter membranes are integrated into a membrane, and do not undergo a composite process, so that the process preparation is simple; the filter membrane is an asymmetric membrane, has a reasonable membrane structure, ensures high-efficiency interception of viruses, has higher flux and loading capacity, is long in service life, and is suitable for being applied to the field of virus removal due to low protein adsorption;

characteristic features

The membrane flux is calculated as follows:

the membrane flux (J) is calculated as: j = V/(T × a) formula:

j- -Membrane flux Unit: l H-1 m-2

V- -sample volume (L); t- -sampling time (h); a- -effective area of film (m2)

The operation conditions adopted for measuring the separation performance of the filter membrane are as follows: the feed liquid is deionized water, the operating pressure is 30psi, the operating temperature is 25 ℃, and the pH of the solution is 7; the throughput testing apparatus is shown in fig. 11;

	first water contact angle/°	flux/L h-1 m-2@30psi	Tensile strength/MPa	Elongation at break/%	L/m2 loading
						Example 1	50	400	11	16	500
Example 2	36	460	10	18	580
						Example 3	42	440	11	16	540
Example 4	48	500	9	20	620
						Example 5	46	480	9	21	600
Example 6	60	550	8	28	670
						Example 7	34	580	7	30	700
Example 8	44	530	9	22	650
						Example 9	32	570	8	27	690
Example 10	40	560	8	26	680

As can be seen from the above table, the filter membranes prepared in examples 1-10 have excellent hydrophilicity, and the first contact angles thereof are all small; meanwhile, the filter has high flux and high loading capacity, high filtering speed and long service life; the product also has good tensile strength and elongation at break, and high processing practicability; furthermore, it can be seen that the membrane obtained in example 4 has a higher porosity and a higher flux when comparing example 1 with example 4, which also indicates that it is preferable to perform pre-phase separation by immersing the liquid membrane in a pre-phase separation liquid before immersing the liquid membrane in a coagulation bath for phase separation and solidification.

Note: when there is a certain difference between the first water contact angles of the two outer surfaces of the membrane, the first water contact angle of the membrane of the present invention is the average value of the first water contact angles of the two outer surfaces.

Furthermore, the following test methods were used in the 114 th paragraph of the CN 201010154974.7-ultrafiltration membrane and the preparation method thereof: performing a virus retention test:

the virus used is a murine parvovirus with a particle size of 20 nm;

after testing, the LRV of the virus impurities with the particle size of 20nm of the filter membranes prepared in the examples 1-10 is not lower than 4, thereby showing that the filter membranes of the invention have sufficient and sufficient retention effect on the virus with the particle size of 20nm and above; and the protein yield of the filter membrane is not lower than 98 percent; the filter is therefore particularly suitable for use in the field of virus removal.

And (3) testing the filtering precision: the filtration membranes obtained in each example were tested for interception efficiency; intercepting particles: colloidal gold with particle size of 20nm

Experimental equipment: a Tianjin Roots particle counter KB-3; preparation of the experiment: the experimental set-up was assembled as in fig. 12, ensuring the set-up was clean, and the set-up was rinsed with ultra-pure water; and a filter membrane with the diameter of 47mm is taken and arranged in the butterfly filter, so that the air tightness of the assembled filter is ensured to be good.

The experimental steps are as follows:

the challenge was poured into a tank, the butterfly filter was vented, pressurized to 10kPa, and a clean bottle was used to take the butterfly downstream filtrate.

The number of particles in the filtrate and stock solutions was measured using a particle counter.

Intercepting efficiency:

in the formula:

eta-type-interception efficiency,%;

n ₀ -number of particles in stock solution, average of 5 sets of counts;

n ₁ -number of particles in filtrate, average of 5 groups of counts, one.

After testing, the retaining efficiency of the colloidal gold of 20nm of the examples 1-10 is not lower than 99.99%.

The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention. It should be noted that modifications and embellishments within the scope of the invention may occur to those skilled in the art without departing from the principle of the invention, and are considered to be within the scope of the invention.

Claims

1. An asymmetric cellulose-based filter membrane for removing viruses, comprising a body having a non-directional tortuous path therein, one side surface of the body being a first outer surface and the other side surface of the body being a second outer surface, wherein: the second outer surface has an average pore size of 15-40 nm;

the average pore size of the first outer surface is at least 4 times greater than the average pore size of the second outer surface;

2. An asymmetric cellulose-based filter membrane for virus removal according to claim 1, wherein:

the average pore diameter variation gradient of the pollutant containing layer is at least 3 nm/mu m larger than that of the interception layer;

3. An asymmetric cellulose-based filter membrane for virus removal according to claim 1, wherein: the first outer surface comprises a plurality of strip-shaped continuous first fibers, and round-hole-shaped first holes are formed between adjacent continuous first fibers in a surrounding manner; the average diameter of the first fiber is 100-250 nm;

the average pore diameter of the first outer surface is 200-600 nm; the first holes have a hole area ratio of 5-25% on the first outer surface.

4. An asymmetric cellulose-based filter membrane for virus removal according to claim 1, wherein:

the average pore diameter variation gradient of the cellulose filter membrane is 2-7nm/1 mu m;

5. An asymmetric cellulose-based filter membrane for virus removal according to claim 1, wherein: the cellulose filter membrane has a PMI average pore diameter of 15-40nm, a thickness of 70-120 mu m and a porosity of 25-55%.

6. An asymmetric cellulose-based filter membrane for virus removal according to claim 1, wherein: the average pore diameter of the pollutant carrying layer is 80-300nm, and the porosity is 35-70%;

the thickness of the stain containing layer accounts for 70-90% of the thickness of the film; the average pore diameter variation gradient of the pollutant carrying layer is 3-9 nm/mu m.

7. The asymmetric cellulose-based filter membrane for virus removal according to claim 6, wherein:

the average pore diameter of the area of the pollutant containing layer close to the first outer surface is larger than that of the area of the pollutant containing layer close to the second outer surface;

8. An asymmetric cellulose-based filter membrane for virus removal according to claim 1 or 6, wherein: the sewage containing layer also comprises a leather layer area, and one side of the leather layer area comprises a first outer surface;

the thickness of the skin region is 1-15 μm, the porosity of the skin region is 10-55%,

and the average pore diameter of the area on one side close to the first outer surface in the skin layer area is smaller than the average pore diameter of the area on one side close to the interception layer in the skin layer area.

9. An asymmetric cellulose-based filter membrane for virus removal according to claim 1, wherein: the average pore diameter of the interception layer is 20-40nm, the porosity is 10-45%, and the thickness of the interception layer is 5-25 μm; the average pore diameter variation gradient of the interception layer is 0-3nm/1 mu m.

10. An asymmetric cellulose-based filter membrane for virus removal according to claim 1 or 9, wherein:

an average pore size within the trapping layer is substantially constant with thickness in a direction of a film thickness from the first outer surface to the second outer surface;

or the average pore diameter in the trapping layer becomes smaller along with the continuous gradient of the thickness;

or the average pore diameter in the trapping layer is firstly reduced and then increased along with the thickness.

11. An asymmetric cellulose-based filter membrane for virus removal according to claim 1, wherein: the ratio of the average pore size of the fouling layer to the average pore size of the rejection layer is 2.5-9.5: 1;

the thickness of the soil-containing layer is at least 35 μm greater than the thickness of the retention layer.

12. An asymmetric cellulose-based filter membrane for virus removal according to claim 1, wherein: the pollutant carrying layer comprises prefilter fibers forming a porous structure, and the prefilter fibers are in a strip-shaped structure; the interception layer comprises separation fibers forming a porous structure, and the separation fibers are in a strip-shaped structure; one side of the prefiltration fiber close to the interception layer is connected with one side of the separation fiber close to the pollutant containing layer; the pre-filter fibers have an average diameter of 40-100 nm; the mean diameter of the separation fiber is 20-90 nm.

13. An asymmetric cellulose-based filter membrane for virus removal according to claim 1, wherein:

the film forming material of the cellulose filter membrane is cellulose polymer with acetyl of which the mass percentage is 0-40%.

14. An asymmetric cellulose-based filter membrane for virus removal according to claim 1 or 13, wherein:

the cellulose filter membrane is made of at least one of cellulose nitrate, cellulose acetate and regenerated cellulose.

15. An asymmetric cellulose-based filter membrane for virus removal according to claim 1, wherein: the first water contact angle of the cellulose filter membrane is 25-70 degrees; the cellulose filter membrane has the tensile strength of 6-15MPa and the elongation at break of 5-40 percent;

the flux of the cellulose filter membrane is more than 300L h ^-1 *m ^-2 @30 psi; the LRV of the cellulose filter membrane to virus impurities is not less than 4; the protein yield of the cellulose filter membrane is not lower than 98%;

at a pressure of 30psiUsing 0.4g/L IVIG solution as test solution, the initial flux of the filter membrane is 300-1000L h-1 m-2@30psi, and the load of the filter membrane is not lower than 300L/m ² 。

16. The method for preparing an asymmetric cellulose-based filter membrane for virus removal according to any one of claims 1 to 15, comprising the steps of:

s1: preparing a casting solution, and casting the casting solution on a carrier to form a liquid film; the casting solution comprises the following substances in parts by weight: 10-30 parts of a film-forming polymer; 15-40 parts of a first organic solvent; 30-75 parts of a pore-forming agent; the film-forming polymer is a cellulose polymer;

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

the pore-forming agent is a non-solvent substance with the surface tension lower than 35dyne/cm, and the substance can be mutually dissolved with the coagulating bath;

17. The method for preparing an asymmetric cellulose filter membrane for virus removal as claimed in claim 16, wherein the temperature of the casting solution is 15-40 ℃;

the pore-forming agent is any one of formamide, ethanol, 1-propanol, isopropanol, n-butanol, 1-pentanol, 2-pentanol and diethylamine.

18. The method for preparing an asymmetric cellulose filter membrane for removing viruses as claimed in claim 16, wherein the pre-phase separation is performed by immersing the liquid membrane in a pre-phase separation liquid for 2-10s before immersing the liquid membrane in a coagulating bath for phase separation and solidification; wherein the pre-split phase liquid comprises a second organic solvent and a non-solvent, and the content of the non-solvent is 0-30%;

the second organic solvent is mutually soluble with the first organic solvent; the second organic solvent is acetone or dioxane

At least one of dimethylacetamide, N-methylpyrrolidone, acetic acid, propionic acid, butyric acid, and valeric acid; the non-solvent is water or ethanol.

19. The method for preparing an asymmetric cellulose filter membrane for removing viruses as claimed in claim 16, wherein the membrane is hydrolyzed in sodium hydroxide solution at 20-40 ℃ for 15-45 min; and (4) drying after hydrolysis to form a solid film.