Mixed cellulose microfiltration membrane resistant to cobalt 60-gamma radiation sterilization and preparation method

Abstract

The invention provides a mixed cellulose microfiltration membrane resistant to cobalt 60-gamma radiation sterilization and a preparation method thereof, the preparation method comprises the following steps: (1) preparing a mixed cellulose membrane casting solution: mixing and dissolving nitrocellulose, cellulose acetate, a non-solvent, a hydrophilic additive and a solvent to prepare a mixed solution, the mass ratio of the nitrocellulose to the cellulose acetate being 6-11; a hindered phenol antioxidant is added to the mixed solution and fully stirred to be uniform, a mixed cellulose casting film solution is obtained, and the hindered phenol antioxidant is a compound with substituent groups on one side or two sides of hydroxyl on a benzene ring; and (2) preparing the mixed cellulose microfiltration membrane capable of resisting cobalt 60-gamma radiation sterilization, namely, the mixed cellulose microfiltration membrane can resist high-dose (25KGy-100KGy) cobalt 60-gamma radiation sterilization, and the integrity of the filter membrane can be kept before and after radiation sterilization and is not influenced by the effect after radiation degradation.

Description

Technical Field

[0001] The present invention relates to the preparation and application fields of separation membrane materials, and particularly relates to a mixed cellulose microfiltration membrane resistant to cobalt 60-γ radiation sterilization and a preparation method thereof. Background Art

[0002] Microbial detection plays an indispensable role in aspects such as maintaining human health, ensuring food safety, protecting the environment, and promoting economic development. The membrane filtration method for microbial detection is an internationally recognized standard microbial test method, which is recognized by pharmacopoeias of countries such as AOAC, the United States, Europe, and Japan, and organizations such as FDA and EPA, and is widely used in fields such as environmental monitoring, food and beverage industry, cosmetics, pharmaceutical industry quality control, and electronics industry.

[0003] The membrane filtration method generally should use a closed membrane filter, select the filter membrane material according to the characteristics of the test sample and its solvent. The pore size of the filter membrane for sterility testing should not be greater than 0.45 μm, and the diameter of the filter membrane is about 50 mm. If filter membranes of other sizes are used, the volumes of the dilution solution and the rinsing solution should be adjusted and re-verified. When in use, the integrity of the filter membrane before and after filtration should be ensured. Among them, the mixed cellulose microfiltration membrane has the characteristics of uniform pore size, high porosity, good hydrophilicity, a pore structure suitable for microbial interception and growth, no medium shedding, thin texture, small resistance, fast filtration speed, low cost, etc., and is widely used in the microbial detection industry.

[0004] In addition, the sterility test method needs to be carried out under aseptic conditions, that is, the test environment must meet the requirements of sterility testing. The whole inspection process should strictly abide by aseptic operation to prevent microbial contamination, and the measures to prevent contamination shall not affect the detection of microorganisms in the test sample. This requires that the filter membrane for aseptic detection has asepticity. The main sterilization methods for the filter membrane include radiation sterilization, ethylene oxide sterilization, moist heat sterilization, etc.

[0005] The method of using ethylene oxide sterilization has the disadvantage of a long cycle. The entire sterilization cycle usually takes 24 to 48 hours, and ventilation treatment is also required after sterilization to ensure that the ethylene oxide residue is reduced to a safe level. And ethylene oxide has potential toxicity, and strict control of operating conditions is required. In contrast, irradiation sterilization mainly uses X-rays, γ-rays, and electron beams to kill microorganisms. It has strong penetration and can be directly used for finished product packaging. Its principle is mainly that the energy of irradiation is greater than the molecular bond energy, which can ionize molecules, break bonds, denature proteins and enzymes, and damage DNA and RNA in microbial cells, thereby losing the ability to synthesize proteins and causing cell death. Commonly used is cobalt 60-γ ray sterilization. During the sterilization process, the temperature hardly changes, the rays can reach directly inside the instrument, and the sterilized products can be used directly.

[0006] Compared with ethylene oxide sterilization, irradiation sterilization has the advantages of thorough sterilization, safe operation, and no residue. However, cobalt 60-γ rays have a certain destructive effect on polymer materials. For example, polymer materials may age or become brittle. During the aseptic detection process, to ensure the sterility of the filter membrane, a relatively high dose (generally 25 KGy to 100 KGy) is often used for sterilization, which is more likely to cause damage to the filter membrane material.

[0007] Therefore, it is very important to develop a mixed cellulose microfiltration membrane that can withstand cobalt 60 radiation sterilization and ensure its integrity before and after radiation sterilization. Summary of the Invention

[0008] The purpose of the present invention is to provide a mixed cellulose microfiltration membrane that can withstand cobalt 60-γ radiation sterilization and a preparation method thereof. The mixed cellulose microfiltration membrane can withstand high-dose (25 KGy to 100 KGy) cobalt 60-γ radiation sterilization, and can maintain the integrity of the filter membrane before and after radiation sterilization and is not affected by the post-radiation degradation effect.

[0009] To achieve the above purpose, the present technical solution provides a preparation method of a mixed cellulose microfiltration membrane that can withstand cobalt 60-γ radiation sterilization, including the following steps:

[0010] (1) Prepare a mixed cellulose casting solution:

[0011] Mix cellulose nitrate, cellulose acetate, a non-solvent, a hydrophilic additive, and a solvent to prepare a mixed solution;

[0012] Add a hindered phenol antioxidant to the mixed solution, and stir well to obtain a mixed cellulose casting solution, where the hindered phenol antioxidant is a compound with substituents on one or both sides of the hydroxyl group on the benzene ring;

[0013] (2) Prepare a mixed cellulose microfiltration membrane that can withstand cobalt 60-γ radiation sterilization:

[0014] Coat the mixed cellulose casting solution into a film and place it in a film-forming space to cure and dry to form a mixed cellulose microfiltration membrane that can withstand cobalt 60 radiation sterilization.

[0015] In some embodiments, since there are a large number of internal stresses in the mixed cellulose microfiltration membrane that can withstand cobalt 60-γ radiation sterilization during the initial film-forming process, in order to eliminate the internal stresses of the mixed cellulose microfiltration membrane that can withstand cobalt 60-γ radiation sterilization, the preparation method of the mixed cellulose microfiltration membrane that can withstand cobalt 60-γ radiation sterilization has an additional step:

[0016] (3) Post-treat the mixed cellulose microfiltration membrane that can withstand cobalt 60-γ radiation sterilization:

[0017] The heat treatment is performed on the mixed cellulose microfiltration membrane resistant to cobalt 60-γ radiation sterilization prepared in step (2).

[0018] According to a large number of studies, after cellulose is irradiated, it can cause the breakage of the main chain molecules, thereby reducing the molecular weight. And radiation also causes a decrease in the crystallinity of cellulose. With the termination of radiation, the degradation of cellulose does not stop immediately, but will continue to degrade within a certain period of time. This phenomenon is called the post-effect of radiation degradation. Of course, with the increase of the radiation dose, the general trend of the post-effect of radiation is increasing.

[0019] However, the cellulose nitrate, which is the raw material of the mixed cellulose microfiltration membrane, also has a post-effect of radiation under the radiation of cobalt 60-γ rays. Some covalent bonds on the surface of the amorphous region and the crystalline region of cellulose are broken to form free radicals, and these free radicals initiate the degradation reaction of cellulose. After the radiation terminates, although the free radicals in the amorphous region basically or even completely disappear, the free radicals on the surface of its crystalline region do not disappear immediately, forming trapped free radicals. These free radicals will continue to act on the cellulose nitrate to cause its degradation. As time goes by, the number of free radicals that can initiate the degradation of cellulose becomes less and less, and the degradation effect on cellulose gradually decreases. Only when the free radicals are completely annihilated does the post-effect of radiation terminate, and this time period is often relatively long, usually lasting from 7 to 30 days. And during the process of cobalt 60-γ ray radiation sterilization of the mixed cellulose microfiltration membrane, it is easier to generate molecules such as H2, other gases and reducing sugars. And these reducing sugars are more likely to combine with the trapped free radicals, resulting in phenomena such as "yellow spots" and "black spots" on the surface of the filter membrane (see the attachment for details) Figure 1 ), seriously affecting the appearance and integrity of the mixed cellulose filter membrane.

[0020] The research team of this application is committed to solving these problems existing in the mixed cellulose microfiltration membrane under cobalt-60 γ-ray radiation. The research team of this application found that under the radiation of cobalt-60 γ-rays, the local degradation of the mixed cellulose microfiltration membrane is essentially a process of a series of free radical chain reactions. That is, under the action of γ-rays, the chemical bonds of organic molecules are broken to generate active free radicals, and these free radicals can initiate a series of free radical chain reactions, resulting in fundamental changes in the local structure and properties of cellulose. The research team of this application surprisingly found that during the preparation of the mixed cellulose microfiltration membrane, adding compounds such as hindered phenol antioxidants and their derivatives to the casting solution system can prevent the progress of the chain reaction. Due to the spatial hindrance of —OH, the H atom of the hindered phenol antioxidant is easily detached from the molecule and combines with peroxyl radicals (ROO·), alkyl radicals (RO·), hydroxyl radicals (·OH), etc. to make them lose their activity, thereby eliminating the free radicals generated during the radiation sterilization process and preventing the progress of the chain reaction, so as to ensure that cellulose is not affected by the post-effect of radiation degradation. Based on this discovery, the research team of this application developed a preparation method for the mixed cellulose microfiltration membrane resistant to cobalt-60 radiation sterilization.

[0021] In step (1), the hindered phenol antioxidant is selected from one or more combinations of 2,6-di-tert-butyl-4-methylphenol, bis(3,5-di-tert-butyl-4-hydroxyphenyl) sulfide, and pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate]. Taking 2,6-di-tert-butyl-4-methylphenol as an example, the steric hindrance of its two tert-butyl groups makes the H atom more likely to react with free radicals, effectively blocking the free radical chain reaction, preventing the mixed cellulose microfiltration membrane from being degraded by free radicals during radiation sterilization, and ensuring the stability of the structure and performance of the filter membrane.

[0022] In addition, these hindered phenol antioxidants selected in this solution are widely sourced and low-cost, suitable for large-scale industrial production. When preparing the casting solution of the mixed cellulose microfiltration membrane, they can be evenly dispersed in the system, are well compatible with other components, and will not affect the stability of the casting solution and the subsequent film-forming process, ensuring the smooth progress of the industrial production process and facilitating the large-scale preparation of the mixed cellulose microfiltration membrane resistant to cobalt-60 radiation sterilization.

[0023] Moreover, different application scenarios have different requirements for the performance of microfiltration membranes. Appropriate hindered phenol antioxidants or their combinations can be selected according to actual needs. For example, in scenarios with high requirements for the flexibility of the filter membrane, when 2,6-di-tert-butyl-4-methylphenol is used alone, while capturing free radicals, it has little impact on the flexibility of the filter membrane; in microbial detection with high requirements for chemical corrosion resistance, pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] can, due to its own structural characteristics, protect the filter membrane from radiation damage while enhancing the chemical corrosion resistance of the filter membrane, ensuring the service performance of the filter membrane in complex detection environments.

[0024] In step (1), the mass concentration of the hindered phenol antioxidant in the mixed cellulose casting solution is 0.05% - 0.3%. The research team of this application found that when the mass concentration of the hindered phenol antioxidant is lower than 0.05%, these free radicals cannot be fully captured and neutralized, and it is difficult to effectively prevent the free radical chain reaction. This will lead to continuous degradation of cellulose, causing problems such as a decrease in the strength of the filter membrane, changes in pore size, and the appearance of "yellow spots" and "black spots" on the surface, and it is impossible to ensure the integrity and performance stability of the filter membrane before and after radiation sterilization; while when the mass concentration of the hindered phenol antioxidant exceeds 0.3%, too much antioxidant may disrupt the phase equilibrium of the casting solution. During the film-forming process, it will interfere with the phase transformation of the casting solution, affecting key properties such as the pore size distribution, porosity, and hydrophilicity of the microfiltration membrane.

[0025] In some embodiments, the mass concentration of the hindered phenol antioxidant in the mixed cellulose casting solution is 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, and 0.3%.

[0026] In step (1), the solvent is selected from one or a combination of ethyl acetate, methyl acetate, and acetone.

[0027] In step (1), the non-solvent is selected from one or a combination of methanol, ethanol, n-propanol, isopropanol, n-butanol, and isobutanol.

[0028] In step (1), the hydrophilic additive is selected from one or a combination of propylene glycol, butylene glycol, and glycerol.

[0029] In some embodiments, the total proportion of nitrocellulose and cellulose acetate in the mass concentration of the mixed cellulose casting solution is 7 - 15%, the non-solvent accounts for 10 - 40% of the mass concentration of the mixed cellulose casting solution, the hydrophilic additive accounts for 1 - 5% of the mass concentration of the mixed cellulose casting solution, the solvent accounts for 40 - 80% of the mass concentration of the mixed cellulose casting solution, and the sum of the mass concentrations of each component in the mixed cellulose casting solution is 100%, where the mass ratio of nitrocellulose to cellulose acetate is 6 - 11.

[0030] In step (2), the mixed cellulose casting solution obtained in step (1) is coated into a film with a doctor blade gap of 300-700 μm using an automatic film coater, and then placed in a film-forming space for curing and drying to form a mixed cellulose microfiltration membrane resistant to cobalt-60 radiation sterilization.

[0031] In the film-forming space, the phase inversion process of the casting solution is controlled by controllable film-forming conditions (such as temperature control, humidity control, and film-forming time).

[0032] Preferably, in step (2), the film-forming temperature is controlled within the range of 15-30 °C, the film-forming humidity is controlled within the range of 60-95% RH, and the film-forming time is controlled within the range of 2-4 h.

[0033] Preferably, in step (3), the temperature of the post-treatment is controlled within the range of 40-50 °C; the humidity is controlled within the range of 20-40% RH; and the post-treatment time is controlled within the range of 8-12 h.

[0034] This solution also provides a mixed cellulose microfiltration membrane resistant to cobalt-60 γ-radiation sterilization prepared according to the above preparation method of the mixed cellulose microfiltration membrane resistant to cobalt-60-γ radiation sterilization, which does not produce "yellow spots" and "black dots" under cobalt-60-γ radiation.

[0035] Compared with the prior art, this technical solution has the following characteristics and beneficial effects:

[0036] The present invention specifically prepares a mixed cellulose filter membrane used in the microbial detection industry. The prepared mixed microfiltration membrane has excellent tolerance to cobalt-60 γ-ray radiation, can effectively eliminate the post-radiation effect, ensure the integrity and performance stability of the filter membrane before and after radiation sterilization, meet the strict asepticity and performance requirements of the microbial detection industry for the filter membrane, and improve the reliability of the detection results.

[0037] The raw materials selected in the present invention, such as nitrocellulose, cellulose acetate, various solvents, non-solvents, hydrophilic additives, and hindered phenol antioxidants, etc., are widely sourced and easily obtainable. Especially the hindered phenol antioxidants not only have a low cost, but also can be evenly dispersed in the casting solution system during large-scale industrial production, are well compatible with other components, do not affect the stability of the casting solution and the subsequent film-forming process, reduce the production cost, and improve the production efficiency.

[0038] The entire preparation process is simple in operation and concise in steps. The process parameters of each step are clear and easy to control, making it suitable for large-scale industrial production. From raw material preparation, casting solution preparation, film formation to post-treatment, each link has operability and repeatability, providing a strong guarantee for large-scale production of high-quality mixed cellulose microfiltration membranes resistant to cobalt-60-γ radiation sterilization. Description of the Drawings

[0039] Figure 1 The "yellow spots" and "black spots" phenomena generated on the surface of the mixed cellulose microfiltration membrane after radiation sterilization.

[0040] Figure 2 The "yellow spots" and "black spots" phenomena generated on the mixed cellulose microfiltration membrane in Comparative Example 1 after radiation sterilization. Specific embodiments

[0041] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0042] Example 1:

[0043] (1) Take 1 part of cellulose acetate and 8 parts of cellulose nitrate, add them to 55 parts of methyl acetate, then add 15 parts of ethanol non-solvent, 15 parts of n-butanol non-solvent, and 2 parts of the hydrophilic agent glycerol. Stir at 20 - 30 °C for 8 - 12 hours until fully dissolved to obtain a mixed solution. Finally, add 0.1 part of pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and finally obtain a mixed cellulose casting solution.

[0044] (2) Use an automatic film coater to coat the mixed cellulose casting solution obtained in step (1) into a film on a glass plate with a 550 μm doctor blade gap, and control the film-forming process conditions: the temperature is 25 - 30 °C, the humidity is 70 - 80% RH, and form for 3 h under this condition to obtain a mixed cellulose microfiltration membrane.

[0045] (3) Put the mixed cellulose microfiltration membrane obtained in step (2) into a constant temperature and humidity drying oven for heat treatment. The heat treatment process conditions are: the temperature is 50 °C, the humidity is 30% RH, and the treatment time is 8 h. Finally, obtain a mixed cellulose microfiltration membrane that can withstand cobalt 60-γ ray radiation sterilization and has stable dimensions.

[0046] Example 2:

[0047] (1) Take 0.8 part of cellulose acetate and 9 parts of cellulose nitrate, add them to 52 parts of acetone, then add 25 parts of ethanol non-solvent, 10 parts of n-propanol non-solvent, and 1 part of the hydrophilic agent propylene glycol. Stir at 20 - 30 °C for 8 - 12 hours until fully dissolved to obtain a mixed solution. Finally, add 0.3 part of pentaerythritol tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and finally obtain a mixed cellulose casting solution.

[0048] (2) Use an automatic film coater to coat the mixed cellulose casting solution obtained in step (1) on a glass plate with a blade gap of 550 μm to form a film. Control the film-forming process conditions: the temperature is 25 - 30 °C, the humidity is 70 - 80% RH, and form for 4 h under these conditions. A mixed cellulose microfiltration membrane is obtained.

[0049] (3) Put the anti-wrinkle mixed cellulose microfiltration membrane obtained in step (2) into a constant temperature and humidity drying oven for heat treatment. The heat treatment process conditions are: the temperature is 50 °C, the humidity is 30% RH, and the treatment time is 12 h. Finally, a mixed cellulose microfiltration membrane that can withstand cobalt 60 - γ ray radiation sterilization and has stable dimensions is obtained.

[0050] Comparative Example 1:

[0051] (1) Take 1 part of cellulose acetate and 8 parts of cellulose nitrate, add them to 55 parts of methyl acetate, then add 15 parts of ethanol non-solvent, 15 parts of n-butanol non-solvent, and 2 parts of hydrophilic agent glycerol. Stir at 20 - 30 °C for 8 - 12 hours until fully dissolved to obtain a mixed cellulose casting solution.

[0052] (2) Use an automatic film coater to coat the polyethersulfone casting solution obtained in step (1) on a glass plate with a blade gap of 550 μm to form a film. Control the film-forming process conditions: the temperature is 25 - 30 °C, the humidity is 70 - 80% RH, and form for 3 h under these conditions. A mixed cellulose microfiltration membrane is obtained.

[0053] (3) Put the mixed cellulose microfiltration membrane obtained in step (2) into a constant temperature and humidity drying oven for heat treatment. The heat treatment process conditions are the same as those in Example 1: the temperature is 50 °C, the humidity is 30% RH, and the treatment time is 8 h.

[0054] In Comparative Example 1 compared with Example 1, the hindered phenol antioxidant - pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] was not added.

[0055] Cut 150 A4-sized membrane sheets from the mixed cellulose filtration membranes obtained in Comparative Example 1 and Example 1 respectively, and perform cobalt 60 - γ ray radiation sterilization (sterilization dose is 100 kGy) under the same conditions. After radiation sterilization, observe whether there are phenomena such as "yellow spots" and "black dots" on the mixed fiber filtration membrane, and continuously observe for 2 months, and count whether the number of "yellow spots" and "black dots" increases, so as to evaluate the influence of the hindered phenol antioxidant on the post-radiation effect of the mixed cellulose filtration membrane. The specific data is as follows in Table 1:

[0056] Table 1 Data table of the ratio of the number of "yellow spots" and "black dots"

[0057]

[0058] It can be clearly seen from the above table that, compared with Comparative Example 1 and Example 1, after the mixed cellulose filter membrane is sterilized by cobalt 60-γ ray radiation, the number of abnormal points on the membrane surface is relatively large (for examples, see Figure 2 , the left figure is the "yellow spot" picture on the membrane surface of Comparative Example 1, and the right figure is the "black spot" picture on the membrane surface of Comparative Example 1), and with the passage of time, its post-radiation effect is more obvious, and the number of abnormal points keeps increasing until it stabilizes after 30 to 60 days. However, the number of abnormal points in Example 1 is 0, and no abnormal points appear with the increase of the observation time. This shows that the implementation effect of the present invention is obvious and effective.

[0059] The above embodiments only express several implementation manners of the present application, and the description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several deformations and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A method for preparing a mixed cellulose microfiltration membrane resistant to cobalt 60-γ radiation sterilization, characterized in that: The following steps are involved: (1) Preparation of mixed cellulose casting solution: Mixing cellulose nitrate with cellulose acetate, a non-solvent, a hydrophilic additive and a solvent to prepare a mixed solution, wherein the mass ratio of the cellulose nitrate to the cellulose acetate is 6 to 11; Adding a hindered phenol antioxidant to the mixed solution, stirring the mixture to obtain a mixed cellulose casting solution, wherein the hindered phenol antioxidant is a compound having a substituent on one or both sides of the hydroxyl group on the benzene ring; (2) Preparation of mixed cellulose microfiltration membranes resistant to cobalt 60-γ radiation sterilization: The mixed cellulose casting liquid is coated into a film and placed in a film-forming space to solidify and dry to form a mixed cellulose microfiltration membrane that can withstand cobalt 60-γ radiation sterilization.

2. The method for preparing a mixed cellulose microfiltration membrane resistant to cobalt 60-γ radiation sterilization according to claim 1, characterized in that: The following steps are also included: (3) Post-treatment resistant cobalt 60-γ radiation sterilization mixed cellulose microfiltration membrane: The mixed cellulose microfiltration membrane prepared in step (2) and resistant to cobalt 60-γ radiation sterilization is subjected to heat treatment.

3. The method for preparing a mixed cellulose microfiltration membrane resistant to cobalt 60-γ radiation sterilization according to claim 1, characterized in that: The hindered phenol antioxidant is selected from one or a combination of two or more of 2,6-di-tert-butyl-4-methylphenol, bis(3,5-di-tert-butyl-4-hydroxyphenyl) sulfide, and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate.

4. The method for preparing a mixed cellulose microfiltration membrane resistant to cobalt 60-γ radiation sterilization according to claim 1, characterized in that: The mass concentration of the hindered phenol antioxidant in the mixed cellulose casting solution is 0.05% to 0.3%.

5. The method for preparing a mixed cellulose microfiltration membrane resistant to cobalt 60-γ radiation sterilization according to claim 1, characterized in that: The solvent is selected from one or a combination of ethyl acetate, methyl acetate, and acetone; the non-solvent is selected from one or a combination of methanol, ethanol, n-propanol, isopropanol, n-butanol, and isobutanol; the hydrophilic additive is selected from one or a combination of propylene glycol, butylene glycol, and glycerol.

6. The method for preparing a mixed cellulose microfiltration membrane resistant to cobalt 60-γ radiation sterilization according to claim 1, characterized in that: The total ratio of cellulose nitrate and cellulose acetate accounts for 7-15% of the mass concentration of the mixed cellulose casting solution, the non-solvent accounts for 10-40% of the mass concentration of the mixed cellulose casting solution, the hydrophilic additive accounts for 1-5% of the mass concentration of the mixed cellulose casting solution, the solvent accounts for 40-80% of the mass concentration of the mixed cellulose casting solution, the total mass concentration of each component in the mixed cellulose casting solution is 100%, and the mass ratio of cellulose nitrate to cellulose acetate is 6-11.

7. The method for preparing a mixed cellulose microfiltration membrane resistant to cobalt 60-γ radiation sterilization according to claim 1, characterized in that: The mixed cellulose casting liquid is coated into a film at a scraper gap of 300-700 μm using an automatic coating machine, and is placed in a film-forming space for curing and drying to obtain a mixed cellulose microfiltration membrane that can withstand cobalt 60 radiation sterilization.

8. The method for preparing a mixed cellulose microfiltration membrane resistant to cobalt 60-γ radiation sterilization according to claim 1, characterized in that: The film forming temperature is controlled within the range of 15 to 30° C., the film forming humidity is controlled within the range of 60 to 95% RH, and the film forming time is controlled within the range of 2 to 4 hours.

9. The method for preparing a mixed cellulose microfiltration membrane resistant to cobalt 60-γ radiation sterilization according to claim 1, characterized in that: The post-processing temperature is controlled within the range of 40 to 50° C.; the humidity is controlled within the range of 20 to 40% RH; and the post-processing time is controlled within the range of 8 to 12 hours.

10. A mixed cellulose microfiltration membrane resistant to cobalt 60-γ radiation sterilization, characterized in that: The mixed cellulose microfiltration membrane resistant to cobalt 60-γ radiation sterilization is prepared according to the method for preparing the mixed cellulose microfiltration membrane resistant to cobalt 60-γ radiation sterilization according to any one of claims 1 to 9.

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