Hydrophobic polyvinylidene fluoride gas microporous filter membrane, and preparation method and application thereof

Abstract

The application discloses a hydrophobic PVDF gas microporous filter membrane and a preparation method and application thereof. The membrane material is composed of PVDF, no pore-forming agent is added in the membrane preparation process, and no hydrophilic grafting layer or hydrophilic coating layer is arranged on the surface of the membrane; an organic good solvent and pure water are mixed to form a coagulation bath system, and high-connection low-curved pore networks are constructed through dry-wet twice heat setting. The obtained filter membrane has a bubble point pore size of 0.35-0.50 microns, a thickness of 50-100 microns, a porosity of 70-80%, a total crystallinity of 55-70%, a gas flux of 17-25 under a pressure difference (Delta P) of 100 mbar, a water contact angle of greater than or equal to 110 degrees, a surface energy of less than or equal to 35 dyn / cm, and the bubble point and the flux are stable after 50 kGy gamma irradiation and pass the ASTM F838 verification, and the filter membrane is suitable for biological process gas sterilization filtration.

Description

Technical Field

[0001] This invention relates to filtration membrane technology, and in particular to a hydrophobic polyvinylidene fluoride gas sterilization filtration membrane with high hydrophobicity, high gas flux and resistance to γ-irradiation, as well as its preparation method and application, which is suitable for gas sterilization filtration in bioprocesses. Background Technology

[0002] The bioprocessing and pharmaceutical industries involve numerous gas sterilization filtration processes, primarily using polymer membranes. Polytetrafluoroethylene (PTFE) is widely used due to its excellent hydrophobicity and extremely high gas flux. However, due to material limitations, PTFE membranes cannot withstand gamma-ray sterilization. For processes requiring gamma-ray sterilization, polyethersulfone (PES) and polyvinylidene fluoride (PVDF) are commonly used gas sterilization filtration membranes. PES gas sterilization filtration membranes, due to their slightly higher surface energy and polarity, tend to adsorb polar substances from the gas over prolonged use, eventually becoming wetted by vapor and clogging, thus requiring additional surface hydrophobic modification. PVDF gas sterilization filtration membranes, with their low surface energy and high hydrophobicity, are more suitable for processes requiring long-term sterilization protection, such as bioreactors.

[0003] The hydrophobicity and gas flux of PVDF gas sterilization filter membranes are crucial to their performance. Existing casting methods for PVDF filter membranes are mainly divided into two categories: pore-forming methods relying on pore-forming agents and pore-forming methods without pore-forming agents. Taking CN107174969A as an example, the pore-forming agent method discloses the formulation of PVDF with an organic solvent and the addition of pore-forming agents such as polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), or LiCl, followed by phase inversion to obtain a composite porous membrane; its water flux index (25℃, 1 bar) can reach approximately 480 L·m. -2 ·h -1 This indicates that adding pore-forming agents is beneficial for improving pore connectivity and flux. However, hydrophilic pore-forming additives such as PVP / PEG tend to remain on the pore surface, which increases the hydrophilicity of the membrane surface and weakens its intrinsic hydrophobicity. Furthermore, PVP is more sensitive to free radicals (such as γ-irradiation), thus limiting its long-term stability and anti-wetting properties in gas sterilization scenarios, often requiring subsequent hydrophobic treatment. Taking CN101569837A as an example, the pore-forming agent-free method discloses the use of a binary composite diluent composed of a high-temperature solvent and a non-solvent to dissolve PVDF, followed by cooling and phase separation, and extraction of the diluent to form a film, without introducing polymeric pore-forming additives such as PVP / PEG. However, compared to PTFE membranes that form high porosity and low tortuosity microporous channels through biaxial stretching, the "sponge-like" microporous structure of PVDF has a higher pressure drop and more tortuous channels on the gas side, and the actual gas flux is usually lower than that of PTFE. Summary of the Invention

[0004] This invention aims to solve the long-standing problem of the "three difficulties" in balancing high throughput, stable retention, and adaptability to irradiation sterilization in microporous membranes for gas sterilization. It provides a hydrophobic polyvinylidene fluoride (PVDF) gas microporous filtration membrane, its preparation method, and its applications. The core concept is to utilize a PVDF casting system containing organic solvents and non-organic solvents, without adding pore-forming agents or hydrophilic grafting layers and coatings on the membrane surface. This is achieved through a sequential process of "coagulation bath composed of organic solvents and pure water → water bath cleaning and preliminary heat setting → final drying and heat setting." This allows for windowed control of phase separation rhythm and crystallization behavior to construct a highly interconnected, low-torsion endogenous hydrophobic pore network. Thus, under the structural constraints of a bubble point pore size of 0.35–0.50 μm and a thickness of 50–100 μm, the filtration membrane meets the bacterial retention requirements of ASTM F838. Furthermore, when the porosity is matched to 70–80% and a pure PVDF hydrophobic interface is maintained (water contact angle ≥110°, surface energy ≤35), the membrane can achieve high connectivity and low tortuosity. At dyn / cm, the reduced viscous loss due to improved channel connectivity and lower tortuosity achieves 17–25 L·h under ΔP = 100 mbar conditions. -1 ·cm -2 The stable gas flux is achieved; after morphology locking with a crystallinity of 55-70%, the bubble point, gas flux and hydrophobicity do not change significantly after 50 kGy γ irradiation, thus achieving simultaneous improvement and long-term stability of high flux, strong interception and radiation resistance.

[0005] According to a first aspect of the present invention, a hydrophobic polyvinylidene fluoride gas microporous filtration membrane is provided. The filter membrane is made of PVDF, and no pore-forming agent is added during the membrane fabrication process, and there is no hydrophilic grafting layer or hydrophilic coating layer on the membrane surface. The filter membrane is used for gas sterilization filtration and meets the bacterial rejection standard of ASTM F838. The filter membrane has the following combination of structural and performance parameters: The bubble point pore size is 0.35–0.50 μm; The thickness is 50–100 μm.

[0006] In some technical solutions, the bubble point pore size of the filter membrane is 0.38–0.47 μm.

[0007] In some technical solutions, the thickness of the filter membrane is 60-80 μm.

[0008] In some technical solutions, the porosity of the filter membrane is 70-80%, and the gas flux per unit area of ​​the filter membrane under a pressure difference ΔP = 100 mbar is 17-25 L·h. -1 ·cm -2 .

[0009] In some technical solutions, the total crystallinity of the filter membrane is 55-70%, the water contact angle of the filter membrane is ≥110°, and the surface energy is ≤35 dyn / cm.

[0010] In some technical solutions, the bubble point pore size change rate of the filter membrane after 50 kGy γ irradiation is within ±2%, the gas flux per unit area change rate is within ±10%, and the water contact angle change rate is within ±3%. Furthermore, the filter membrane still meets the bacterial rejection standard of ASTM F838 after irradiation.

[0011] According to a second aspect of the present invention, a method for preparing a hydrophobic polyvinylidene fluoride gas microporous filter membrane as described above is further provided, comprising the following steps: A casting solution is prepared, wherein the casting solution comprises polyvinylidene fluoride resin, a good organic solvent, and a non-organic solvent; The casting solution is coated onto the surface of a substrate to form a casting layer, and the casting layer together with the substrate is immersed in a coagulation bath containing the same organic solvent as the casting solution and pure water, so that the casting layer coagulates to form a solid film. The obtained solid film was placed in a cleaning tank and a heat setting tank in sequence for cleaning and preliminary setting. The cleaned and pre-shaped solid membrane is peeled off from the substrate and dried to achieve secondary shaping, resulting in a hydrophobic polyvinylidene fluoride gas microporous filter membrane.

[0012] In some technical solutions, the casting solution meets one or more of the following conditions: The number-average molecular weight of the polyvinylidene fluoride resin is 700 kDa to 1000 kDa; The organic solvent is selected from one or more of N-methylpyrrolidone, dimethylformamide, dimethylacetamide, and dimethyl sulfoxide; The organic non-solvent is selected from one or more of methyl acetoacetate, ethyl acetoacetate, and propyl acetoacetate. Based on 100 parts by weight, the weight percentages of each component are as follows: 12-18 parts of polyvinylidene fluoride resin, 60-75 parts of organic good solvent, and 10-25 parts of organic non-solvent. The mixing temperature of each component is 35–55°C, and the mixing time is 8–24 hours; The coating thickness is 150–300 μm.

[0013] In some technical solutions, the mass fraction of the organic solvent in the coagulation bath is 45-60%, the curing temperature is 10-30℃, and the curing time is 3-8 min.

[0014] In some technical solutions, the solvents in the cleaning tank and the heat setting tank are both pure water, the temperature of the cleaning tank is 10-30℃ and the time is 3-8 min, and the temperature of the heat setting tank is 60-90℃ and the time is 3-8 min.

[0015] In some technical solutions, the cleaning medium is deionized water, and no surface modifiers or grafted monomers are added between the cleaning tank and the heat setting tank.

[0016] In some technical solutions, the drying process is carried out at a temperature of 110–150 °C for 4–10 h.

[0017] According to a third aspect of the present invention, an application of a hydrophobic polyvinylidene fluoride gas microporous filter membrane is further provided, characterized in that the above-mentioned hydrophobic polyvinylidene fluoride gas microporous filter membrane is used for gas sterilization filtration in a bioprocess.

[0018] The present invention, by employing the above technical solution, has at least the following beneficial effects: 1. This invention achieves the construction of a hydrophobic microporous network by using a PVDF casting system containing organic solvents and organic non-solvents, without adding pore-forming agents or applying hydrophilic grafting layers or hydrophilic coatings to the membrane surface, and in conjunction with a sequential process. This enables the membrane to simultaneously achieve high flux, stable retention, and irradiation compatibility in gas sterilization filtration. Since there are no residual polar pore-forming agents in the system, the chemical environment of the pore walls remains in the intrinsic low surface energy state of PVDF, significantly reducing the probability of liquid bridges and condensation nuclei forming at the micropores, reducing the loss of effective channels caused by microwetting during operation, and thus maintaining the consistency between nominal flux and effective flux for a longer period of time under constant pressure difference conditions.

[0019] 2. This invention first subjectes the cast film to a relatively delayed phase separation in a coagulation bath containing organic solvents and pure water, and then transfers it to a rapid displacement environment with pure water as the medium. This creates a "delayed-rapid" phase separation rhythm that synergizes with crystallization, which is beneficial for obtaining a pore structure with high connectivity, low tortuosity, and relatively round micropores. This structure leads to a reduction in gas viscous flow resistance per unit pressure drop, enabling the membrane to achieve a high gas flux within the bubble point pore size range that meets the bacterial retention threshold.

[0020] 3. This invention controls the overall crystallinity within a suitable window by using a high-temperature water bath for initial shaping, followed by drying and secondary heat setting. The pore wall structure is "locked," avoiding both micropore softening and deformation caused by insufficient crystallization and embrittlement and micropore shrinkage caused by excessive crystallization. This results in two direct effects: first, the bubble point and pore size distribution remain stable during use and storage, improving the reliability of bacterial retention; second, morphological changes after irradiation are suppressed, and the flux and bubble point drift before and after irradiation are reduced, allowing the membrane to maintain functional stability while meeting common irradiation sterilization doses, facilitating direct online use in bioprocessing.

[0021] 4. The coagulation bath and cleaning heat-setting process composed of organic solvents and pure water used in this invention allows the diffusion exchange process between solvents and non-solvents to be controlled in stages. The first stage mainly builds a continuous framework and suppresses finger-shaped cavities. The second stage rapidly replaces and connects the pores and removes solvent residues. The subsequent heat setting uniformly tunes the crystallization and internal stress of the pore walls. This staged control allows the membrane porosity and membrane thickness to be repeatedly obtained within the target range, and the initial pressure drop and flux show good batch consistency.

[0022] 5. In the absence of a hydrophilic layer and pore-forming agent, the chemical composition of the membrane surface and the inner wall of the pores is simple. This interfacial purity improves hydrophobic stability, enabling the membrane to maintain a high flux retention rate and a low wetting failure rate under high humidity gas or humid heat cycling conditions. Attached Figure Description

[0023] Figure 1 This is a cross-sectional electron microscope image of the hydrophobic polyPVDF gas sterilization filter membrane prepared in Example 1 of the present invention; Figure 2 The infrared comparison spectra of the hydrophobic polyPVDF gas sterilization filter membrane prepared in Example 1 of the present invention and the pure PVDF resin raw material are shown. Detailed Implementation

[0024] The present invention will be further described below with reference to embodiments, but this is not intended to limit the present invention in any way. Any modifications or substitutions made based on the technical teachings of the present invention shall fall within the protection scope of the present invention.

[0025] The following are some of the testing methods used in this application: The crystallinity of the filter membrane was measured by differential scanning calorimetry (DSC), using a DSC3 model from Mettler Toledo Thermal Analysis Instruments Department. The scanning temperature ranged from 20 to 200 °C, and the scanning rate was 5 °C / min. Total crystallinity was measured by calculating the area of ​​the endothermic peak from the 140-180 °C curve; this area represents the enthalpy of fusion of the crystals in the PVDF. Dividing this value by the theoretical enthalpy of fusion of 105 J / g for 100% crystallized PVDF yielded the total crystallinity.

[0026] The porosity of the filter membrane was determined by the gravimetric method. Membrane sheets of the same area were cut, and their thickness was measured using a thickness gauge. The membrane volume was then calculated and multiplied by the density of PVDF, 1.78 g / cm³. 3 The mass M1 is obtained, the actual weight M2 of the membrane is measured, and the porosity is calculated using the following formula: .

[0027] The bubble point pore size was measured using a bubble pressure membrane pore size analyzer, model BSD-PB, manufactured by Beijing Best Instrument Technology Co., Ltd.

[0028] The surface energy of a filter membrane is measured using the critical wetting surface tension method. Specifically, a series of liquids with surface tensions varying from 2 to 4 dynes / cm are applied to its surface, and the absorption or non-absorption of each liquid is observed. The critical wetting surface tension (CWST, in dynes / cm) of a porous medium is defined as the average of the surface tensions of the absorbing liquid and the surface tensions of the nearly non-absorbing liquid. This method is derived from CN1036513A (US4880548A).

[0029] The water contact angle was measured using a Kono SL250 contact angle meter. The sample was placed flat on the sample stage, and 2 μL of ultrapure water was automatically injected to form and release droplets on the sample surface. After the droplets stabilized, the "freeze" button was clicked in the software to capture a static image and the water contact angle was calculated using the Young-Laplace equation fitting method.

[0030] The thickness of the filter membrane was measured using a thickness gauge, model YHT 1271388.

[0031] Gas flux testing method: Cut a 47mm diameter membrane sample and place it in a plastic clamp, locking it securely. Then connect compressed air upstream of the clamp and a flow meter downstream. Use a pressure valve to control the upstream inlet pressure, adjusting the valve to 100mbar while keeping the downstream inlet open. Simultaneously read the flow meter flow rate and convert it to L·h based on the effective filtration area. -1 ·cm -2 Ultimately, the data on gas flux were obtained.

[0032] Unless otherwise specified, the atmosphere used in the preparation process is empty. Unless otherwise specified, the temperature refers to room temperature.

[0033] According to one embodiment of the present invention, a hydrophobic polyvinylidene fluoride gas microporous filter membrane is provided. The membrane material is composed of PVDF, no pore-forming agent is added during the membrane fabrication process, and there is no hydrophilic grafting layer or hydrophilic coating layer on the membrane surface. It is suitable for gas sterilization filtration and is evaluated for bacterial retention according to ASTM F838.

[0034] In practice, the bubble point pore size of the filter membrane is controlled within 0.35–0.50 μm, preferably 0.38–0.47 μm, so that the minimum limiting pore size forms a stable margin above the bacterial penetration critical value of ASTM F838. This margin ensures retention reliability while avoiding the contradiction between increased pressure drop and increased retention risk caused by excessively enlarging the pore size in pursuit of throughput. In conjunction with this, the membrane thickness is set to 50–100 μm, preferably 60–80 μm, to achieve a balance between axial mass transfer path and mechanical support: the thinner membrane shortens the length of convection and diffusion channels, reduces viscous energy consumption per unit pressure difference, and maintains sufficient structural integrity and compressive stability within this thickness window. Thus, while meeting the retention requirements of ASTM F838, it achieves high consistency between nominal throughput and effective throughput and improves the long-term process stability.

[0035] In a preferred embodiment, the porosity of the filter membrane is controlled at 70–80% to increase the proportion of interconnected pores and reduce tortuosity and flow resistance. With this structural combination, the filter membrane achieves 17–25 L / h at ΔP = 100 mbar. -1 ·cm -2 The effective gas flux.

[0036] In the preferred embodiment, the total crystallinity of the filter membrane is limited to a window of 55-70% to achieve a morphology lock effect; in terms of interface parameters, the water contact angle is ≥110° or the surface energy is ≤35 dyn / cm, forming a hydrophobic interface feature. The hydrophobicity comes from the low surface energy of pure PVDF and the interface purity without polar residues, demonstrating excellent anti-wetting performance and flux retention.

[0037] In the preferred embodiment, after the sample was subjected to 50 kGy γ irradiation, the bubble point pore size, gas flux per unit area, and water contact angle were re-measured, and their change rates were within ±2%, ±10%, and ±3%, respectively. Furthermore, the filter membrane still met the bacterial rejection standard of ASTM F838 after irradiation, thus satisfying the stability requirements. The mechanism is that the moderate crystallinity formed after heat setting has a morphology-locking effect on the micropore geometry, making it difficult for the chain segment breakage and micro-shrinkage induced by irradiation to be transformed into observable micropore shrinkage or pore closure.

[0038] According to another embodiment of the present invention, a method for preparing a hydrophobic polyvinylidene fluoride gas microporous filter membrane is provided, which mainly includes the following steps: First, a casting solution without pore-forming agents is prepared. The casting solution consists of PVDF resin, a good organic solvent, and an organic non-solvent. The number average molecular weight of the PVDF resin is selected in the range of 700 kDa to 1000 kDa to balance solution viscosity and film strength. The good organic solvent is selected from one or more of N-methylpyrrolidone, dimethylformamide, dimethylacetamide, and dimethyl sulfoxide. The organic non-solvent is selected from one or more of methyl acetoacetate, ethyl acetoacetate, and propyl acetoacetate. The mixture is mixed and homogenized at 35–55 °C for 8–24 hours to obtain a clear and homogeneous system. In the specific design, the casting solution ratio meets the following window: 12–18 parts PVDF, 60–75 parts good organic solvent, and 10–25 parts organic non-solvent, totaling 100 parts. This formulation, on the one hand, pre-establishes phase separation sensitivity through the thermodynamic disturbance of the non-solvent, and on the other hand, avoids extractable residues caused by the introduction of polar pore-forming agents.

[0039] Next, the casting solution is applied to a clean, flat substrate with a wet film thickness of 150–300 μm. The substrate is then immersed in a coagulation bath containing the same organic solvent as the casting solution and pure water until a solid film is formed. The mass fraction of the organic solvent in the coagulation bath is controlled at 45–60%, the bath temperature at 10–30 °C, and the curing time at 3–8 min. This coagulation environment containing the organic solvent initially slows down the solvent-non-solvent exchange rate, triggering delayed phase separation to first form a continuous framework and suppress excessively deep finger-like pores. Subsequently, as the concentration gradient of the organic solvent in the bath phase is flattened, displacement accelerates the formation of short-channel, rounded microporous structures, thus laying the foundation for subsequent highly interconnected, low-torsion pore networks.

[0040] Next, the solid membrane is sequentially placed into a cleaning tank and a heat-setting tank for cleaning and preliminary setting. Both the cleaning tank and the heat-setting tank use deionized water as the cleaning medium, without adding any surface modifiers or hydrophilic graft monomers, to avoid external polar substances forming adsorption sites at the micropores and damaging the hydrophobic interface; the temperature of the cleaning tank is 10-30 ℃ and the time is 3-8 min, the main function of which is to remove solvent / non-solvent residues and maintain the flexibility of the pore walls; the temperature of the heat-setting tank is 60-90 ℃ and the time is 3-8 min, which at the same time plays a setting role in thermally induced crystallization and internal stress release.

[0041] Finally, the cleaned and pre-shaped solid film is peeled off from the substrate and dried to achieve secondary shaping at a temperature of 110–150 °C for 4–10 h. During this stage, controlled crystal phase growth and chain segment rearrangement stabilize the overall crystallinity within the range of 55–70% and "co-lock" with the micropore geometry, thereby maintaining the stability of bubble point and flux during subsequent use and irradiation.

[0042] The filter membrane of this embodiment, obtained through the above process, has the following combination of structure and performance: bubble point pore size of 0.35–0.50 μm to ensure the bacterial rejection threshold of ASTM F838; membrane thickness of 50–100 μm to balance mechanical support and pressure drop; porosity of 70–80% to increase the number of effective channels and reduce viscous resistance; and overall crystallinity of 55–70% to achieve morphological stability and radiation resistance. The gas flux per unit area at ΔP = 100 mbar is 17–25 L·h. -1 ·cm -2 Within the target zone, the hydrophobic interface characteristics of a water contact angle ≥110° and surface energy ≤35 dyn / cm indicate that the inner wall of the pore maintains a pure PVDF chemical environment and raises the local condensation threshold, reducing liquid bridging and wetting failure during high-humidity gas operation. In the specific design, the membrane was subjected to 50 kGy γ irradiation in both unassembled and assembled states, and its performance was retested. The changes in bubble point, flux, and contact angle were not significant, and it continued to meet ASTM F838. This stability comes from the microporous structure shaped by "delayed-rapid phase separation," which makes it difficult for irradiation-induced chain segment breakage and micro-shrinkage to accumulate to the micropore scale.

[0043] This embodiment achieves a comprehensive effect of "high throughput, strong retention, radiation resistance, and anti-wetting" through the synergistic use of pure PVDF, no pore-forming agent, and sequential process.

[0044] According to another embodiment of the present invention, an application of a hydrophobic polyvinylidene fluoride gas microporous filter membrane is provided. The hydrophobic polyvinylidene fluoride gas microporous filter membrane or the hydrophobic polyvinylidene fluoride gas microporous filter membrane prepared by the above preparation method is used for gas sterilization filtration in bioprocesses.

[0045] In practice, the membrane is assembled into a pleated filter element for gas sterilization filtration in biological processes; under aseptic ventilation conditions, it is continuously operated and verified with ΔP = 100 mbar, and the gas flux per unit area is consistent with the membrane test and the bacterial retention meets ASTM F838.

[0046] The following description is based on embodiments of the present invention.

[0047] Example 1 1) A casting solution was prepared by dissolving PVDF resin with a molecular weight of 820 kDa in a mixed solvent of dimethylacetamide and ethyl acetoacetate. The casting solution had the following composition: 16 parts PVDF resin, 70 parts dimethylacetamide and 14 parts ethyl acetoacetate. The mixing temperature of the casting solution was 40-45°C and the mixing time was 12-18 hours. 2) The casting solution is coated onto a PET film (Mylar) substrate with a coating thickness of 200 μm, and then immersed in a coagulation bath to solidify and form a solid film. The temperature of the coagulation bath is 20-25℃ and the curing time is 5 min. The coagulation bath contains 55% dimethylacetamide by weight and the remainder is pure water. 3) The obtained solid membrane was placed in the cleaning tank and the heat setting tank in sequence for cleaning and preliminary setting. Both the cleaning tank and the heat setting tank contained pure water. The temperature of the cleaning tank was 20-25 ℃ and the time was 5 min. The temperature of the heat setting tank was 75-85 ℃ and the time was 5 min. 4) The cleaned and pre-shaped solid membrane is peeled off from the substrate and dried to achieve secondary shaping, thus obtaining a hydrophobic polyPVDF gas sterilization filter membrane; the drying temperature is 120-140 ℃ and the time is 8h.

[0048] Example 2 Example 2 differs from Example 1 in that the casting solution consists of 16 parts PVDF resin, 70 parts dimethylformamide, and 14 parts methyl acetoacetate. The coagulation bath contains 55% by weight of dimethylformamide.

[0049] Example 3 The difference between Example 3 and Example 1 is that the casting solution consists of 17 parts PVDF resin, 70 parts dimethylacetamide and 13 parts ethyl acetoacetate, and the coating thickness is 150 μm.

[0050] Example 4 The difference between Example 4 and Example 1 is that the mixing temperature of the casting solution is 35-40°C, the coating thickness is 170 μm, and the drying temperature is 140-150°C.

[0051] Example 5 The difference between Example 5 and Example 1 is that the casting solution has the following composition: 15 parts PVDF resin, 71 parts dimethylacetamide and 14 parts ethyl acetoacetate. The mixing temperature of the casting solution is 45-50°C and the coating thickness is 300 μm.

[0052] The hydrophobic polyvinylidene fluoride filter membranes prepared in Examples 1-5 were tested according to the aforementioned experimental methods, and their performance is shown in Table 1.

[0053]

[0054] Figure 1 The image shows a cross-sectional electron microscope image of the hydrophobic polyPVDF gas sterilization filter membrane prepared in Example 1, which shows that the pore size is uniform.

[0055] Figure 2The infrared contrast spectrum of the hydrophobic PVDF gas sterilization filter membrane prepared in Example 1 and the pure PVDF resin raw material is shown. It can be seen that, except for 1235 cm⁻¹, the other characteristic peaks completely overlap and there are no other impurity peaks. The extra small peak at 1235 cm⁻¹ on the hydrophobic membrane is the characteristic peak of beta crystallization of PVDF, which is consistent with the characteristic of a significant increase in the proportion of beta crystallization during the film formation process.

[0056] The hydrophobic polyvinylidene fluoride filter membranes prepared in Examples 1-5 were subjected to 50 kGy gamma irradiation and re-tested. The data are shown in Table 2.

[0057]

[0058] As can be seen from the data in Table 2, the gas filter membranes prepared in Examples 1-5 did not show significant performance changes after 50 kGy gamma irradiation.

[0059] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the casting solution consists of 20 parts of PVDF resin, 67 parts of dimethylacetamide and 13 parts of ethyl acetoacetate, and the initial setting temperature of the solid film in the heat setting bath is 50-60 °C.

[0060] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the coagulation bath contains 40% by weight of dimethylacetamide, and the initial setting temperature of the solid film in the heat setting bath is 90-95 °C.

[0061] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the coagulation bath includes 75% by weight of dimethylacetamide, and the temperature of the pre-shaped solid film peeled off from the substrate and the drying treatment is 90-100°C for 8 hours.

[0062] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that the molecular weight of PVDF is 600 kDa. The casting solution consists of 15 parts PVDF resin, 65 parts dimethylacetamide, and 20 parts ethyl acetoacetate.

[0063] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that the casting solution consists of 15 parts PVDF resin, 75 parts dimethylacetamide, and 10 parts ethyl acetoacetate. The coagulation bath contains 40% by weight of dimethylacetamide.

[0064] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is that the coating thickness is 120 μm. The initial setting temperature of the solid film in the heat setting bath is 50-60 °C.

[0065] Comparative Example 8 The difference between Comparative Example 8 and Example 1 is that the curing time in the coagulation bath is 2 minutes. The cleaning and preliminary setting times are both 2 minutes.

[0066] Comparative Example 9 The difference between Comparative Example 9 and Example 1 is that the casting solution has the following composition: 16 parts PVDF resin, 70 parts dimethylacetamide and 14 parts ethanol.

[0067] Comparative Example 10 The difference between Comparative Example 10 and Example 1 is that the casting solution has the following composition: 16 parts PVDF resin, 70 parts dimethylacetamide and 14 parts ethyl acetate.

[0068] Following the aforementioned experimental method, the hydrophobic polyvinylidene fluoride filter membranes prepared in Comparative Examples 1-6 and 8-10 were tested, and their performance is shown in Table 3.

[0069]

[0070] As can be seen from Table 3, neither Comparative Examples 1-6 nor Comparative Examples 8-10 could prepare gas filter membranes that meet the synergistic constraints of the bubble point pore size and membrane thickness parameters of this application and satisfy the bacterial rejection standard of ASTM F838.

[0071] The above is a further detailed description of the present invention and should not be considered as a limitation on the specific implementation of the present invention. For those skilled in the art, simple deductions or substitutions without departing from the concept of the present invention are all within the protection scope of the present invention.

Claims

1. A hydrophobic polyvinylidene fluoride gas microporous filter membrane, characterized in that: The filter membrane is made of PVDF, and no pore-forming agent is added during the membrane fabrication process, and there is no hydrophilic grafting layer or hydrophilic coating layer on the membrane surface. The filter membrane is used for gas sterilization filtration and meets the bacterial rejection standard of ASTM F838. The filter membrane has the following combination of structural and performance parameters: The bubble point pore size is 0.35–0.50 μm; Thickness is 50–100 μm; With a porosity of 70–80%, the gas flux per unit area under a pressure difference ΔP = 100 mbar is 17–25 L·h. -1 ·cm -2 ; The filter membrane is formed from a casting solution comprising polyvinylidene fluoride resin, a good organic solvent, and an organic non-solvent. The number average molecular weight of the polyvinylidene fluoride resin is 700 kDa to 1000 kDa. The organic non-solvent is selected from one or more of methyl acetoacetate, ethyl acetoacetate, and propyl acetoacetate. Furthermore, based on 100 parts by weight, the casting solution comprises 12 to 18 parts of polyvinylidene fluoride resin, 60 to 75 parts of the good organic solvent, and 10 to 25 parts of the organic non-solvent. The filter membrane is a gas sterilization filter membrane formed through the following process: the casting solution is coated on the surface of the substrate to form a casting layer, and the casting layer together with the substrate is immersed in a coagulation bath to solidify the casting layer to form a solid membrane; the obtained solid membrane is placed in a cleaning tank and a heat setting tank in sequence for cleaning and preliminary setting; the cleaned and preliminarily set solid membrane is peeled off from the substrate and dried to achieve secondary setting; The preliminary shaping involves placing the solidified film in a heat-setting bath with pure water as the solvent at a temperature of 60–90°C for 3–8 minutes. The secondary shaping involves peeling the pre-shaped solid film off the substrate and then drying it at 110–150°C for 4–10 hours.

2. The filter membrane according to claim 1, characterized in that, The bubble point pore size of the filter membrane is 0.38–0.47 μm.

3. The filter membrane according to claim 1, characterized in that, The thickness of the filter membrane is 60–80 μm.

4. The filter membrane according to claim 1, characterized in that, The filter membrane has at least one of the following structural and performance parameters: Total crystallinity 55-70%; Water contact angle ≥110°; Surface energy ≤35 dyn / cm.

5. The filter membrane according to any one of claims 1-4, characterized in that, The filter membrane, after being irradiated with 50 kGy γ, exhibits a bubble point pore size change rate within ±2%, a gas flux per unit area change rate within ±10%, and a water contact angle change rate within ±3%. Furthermore, the filter membrane still meets the bacterial rejection standard of ASTM F838 after irradiation.

6. A method for preparing a hydrophobic polyvinylidene fluoride gas microporous filter membrane according to any one of claims 1 to 5, characterized in that, Includes the following steps: A casting solution is prepared, wherein the casting solution comprises polyvinylidene fluoride resin, a good organic solvent, and a non-organic solvent; The casting solution is coated onto the surface of a substrate to form a casting layer, and the casting layer together with the substrate is immersed in a coagulation bath containing the same organic solvent as the casting solution and pure water, so that the casting layer coagulates to form a solid film. The obtained solid film was placed in a cleaning tank and a heat setting tank in sequence for cleaning and preliminary setting. The cleaned and pre-shaped solid membrane is peeled off from the substrate and dried to achieve secondary shaping, resulting in a hydrophobic polyvinylidene fluoride gas microporous filter membrane.

7. The preparation method according to claim 6, characterized in that, The casting solution meets one or more of the following conditions: The number-average molecular weight of the polyvinylidene fluoride resin is 700 kDa to 1000 kDa; The organic solvent is selected from one or more of N-methylpyrrolidone, dimethylformamide, dimethylacetamide, and dimethyl sulfoxide; The organic non-solvent is selected from one or more of methyl acetoacetate, ethyl acetoacetate, and propyl acetoacetate. Based on 100 parts by weight, the weight percentages of each component are as follows: 12-18 parts of polyvinylidene fluoride resin, 60-75 parts of organic good solvent, and 10-25 parts of organic non-solvent. The mixing temperature of each component is 35–55°C, and the mixing time is 8–24 hours; The coating thickness is 150–300 μm.

8. The preparation method according to claim 6, characterized in that, The coagulation bath contains 45-60% organic solvent by mass, the curing temperature is 10-30℃, and the curing time is 3-8 min.

9. The preparation method according to claim 6, characterized in that, The solvents used in both the cleaning tank and the heat setting tank are pure water. The temperature of the cleaning tank is 10–30 °C and the time is 3–8 min. The temperature of the heat setting tank is 60–90 °C and the time is 3–8 min.

10. The preparation method according to claim 6, characterized in that, The drying process is carried out at a temperature of 110–150°C for 4–10 hours.

11. An application of a hydrophobic polyvinylidene fluoride gas microporous filtration membrane, characterized in that, The hydrophobic polyvinylidene fluoride gas microporous filter membrane according to any one of claims 1 to 5, or the filter membrane prepared by the preparation method according to any one of claims 6 to 10, is used for gas sterilization filtration in bioprocesses.

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