Polyvinylidene fluoride blend film and preparation method thereof

Abstract

The present invention relates to a polyvinylidene fluoride blended membrane and a preparation method thereof, and belongs to the technical field of membrane materials. The polyvinylidene fluoride blended membrane preparation method of the present invention adopts a solution crystallization-polymer diffusion method to prepare the polyvinylidene fluoride blended membrane, and a β-nucleating agent is also dispersed in the solvent of the solution crystallization-polymer diffusion method, and the β-nucleating agent is an aromatic phosphate salt; the addition amount of the β-nucleating agent is 0.5‰ to 5‰ of the mass of PVDF. The polyvinylidene fluoride prepared by the method of the present invention overcomes the shortcomings of the prior art, and the blended membrane has a high BSA retention rate.

Description

Technical Field

[0001] The invention relates to a polyvinylidene fluoride blended film and a preparation method thereof, belonging to the technical field of membrane materials. Background Art

[0002] Membrane separation technology is widely used, including water pollution treatment, separation of polluted gases, fuel recovery, drug production and purification, etc. PVDF membrane is widely used in the field of membrane separation technology due to its excellent heat resistance and chemical resistance. The preparation methods of membrane include freeze drying, directional stretching, melt extrusion, etc.

[0003] Solution crystallization-polymer diffusion (CCD) method is based on the combination of freeze drying and casting, and has developed into a unique technology for preparing porous materials, and is applied to the preparation of catalyst support structures, solid oxide fuel cells and gas and liquid separation membranes. The CCD method achieves the effect of solvent crystallization by rapidly freezing the casting liquid in the mold to freeze the polymer chain, and then extracts it in an ice water bath to achieve solvent exchange and finally form a membrane. The membrane prepared by the CCD method has a small pore size and a narrow pore distribution, but a very large water flux.

[0004] Liu Zhenhao, Zhao Zinian, Wang Kun, et al. Preparation and properties of PVDF / LiCl ultrafiltration membrane by solution crystallization-polymer diffusion method [J]. Engineering Plastics Application, 2021, 49(6): 5. Based on the solution crystallization-polymer diffusion (CCD) method, anhydrous lithium chloride (LiCl) was used as a porogen and hydrophilic modifier, and N, N-dimethylacetamide was used as a solvent to prepare PVDF / LiCl ultrafiltration membrane by a blending method. The cross-sectional structure of the PVDF / LiCl ultrafiltration membrane was characterized by scanning electron microscopy. The analysis showed that there was a good interconnected structure inside the ultrafiltration membrane, and a macroporous structure and a finger-like pore structure were generated. The contact angle and film formation kinetics test results showed that when the mass fraction of LiCl was 2%, the ultrafiltration membrane had the best hydrophilicity and the fastest film formation rate. The results of water flux and retention rate test showed that with the increase of LiCl content, the ultrafiltration membrane had a sharp increase in water flux and a small decrease in retention rate. The comprehensive performance was best when the LiCl mass fraction was 1%, with a water flux of 1190.48L / (m 2 h), the interception rate was 83.21%, and the flux recovery rate reached 84.46%. The maximum interception rate was 87.23% when 0.5% LiCl was added. If LiCl was not added, the interception rate was 80.64%. The interception rate needs to be further improved. Summary of the invention

[0005] The first object of the present invention is to provide a novel method for preparing a polyvinylidene fluoride blend membrane, wherein the polyvinylidene fluoride blend membrane prepared by the method has a high rejection rate.

[0006] In order to achieve the first purpose of the present invention, the polyvinylidene fluoride blend membrane preparation method adopts a solution crystallization-polymer diffusion method to prepare the polyvinylidene fluoride blend membrane, and a β-nucleating agent is also dispersed in the solvent of the solution crystallization-polymer diffusion method, and the β-nucleating agent is an aromatic phosphate salt; the addition amount of the β-nucleating agent is 0.5‰ to 5‰ of the mass of PVDF.

[0007] In a specific embodiment, the aryl phosphate salt is at least one of TMP-1, TMP-3, TMP-5 or TMP-6.

[0008] In a specific embodiment, the method comprises:

[0009] a. PVDF, polyvinyl pyrrolidone and β-nucleating agent were vacuum dried at 65-75°C for 12-24 hours;

[0010] b. evenly dispersing the dried β-nucleating agent into the solvent;

[0011] c. After drying, PVDF, polyvinyl pyrrolidone, polyethylene glycol, and polyoxypropylene-polyoxyethylene copolymer are added to a solvent in which a β-nucleating agent is uniformly dispersed to form a homogeneous casting solution, and degassing is performed;

[0012] d. The casting solution is evenly distributed on the substrate, and after heat preservation treatment at -80°C to -20°C, it is then placed in a 0-25°C treatment to obtain a polyvinylidene fluoride blended membrane; preferably, the polyvinylidene fluoride blended membrane is obtained by immersing it in an ice-water mixture.

[0013] The casting liquid is evenly distributed on the substrate, and the -80℃~-20℃ insulation treatment can be: pre-cooling the substrate to -80℃~-20℃, then evenly distributing the casting liquid on the substrate, and insulation treatment at -80℃~-20℃; or first evenly distributing the casting liquid on the substrate, and then placing the casting liquid and the substrate in an environment of -80℃~-20℃ for insulation treatment.

[0014] In a specific embodiment, the substrate provides support and can be a smooth aluminum plate, stainless steel plate or glass plate. We put the plate into a refrigerator first, and after heat preservation treatment at -80℃ to -20℃, take it out and evenly distribute the casting liquid on the substrate. After a period of 5s to 5min, soak it in an ice-water mixture (0℃ treatment) to obtain a polyvinylidene fluoride blended membrane.

[0015] In a specific embodiment, the uniform dispersion in step b includes dispersion using ultrasound, and the power of the ultrasound is preferably 50 to 300 W, and the time is 0.5 to 5 hours.

[0016] In a specific embodiment, the mass ratio of PVDF: solvent: polyvinyl pyrrolidone: polyethylene glycol: polyoxypropylene polyoxyethylene copolymer in step c is: 15-25: 65-85: 5-10: 1-10: 1-5.

[0017] In a specific embodiment, the solvent is at least one of dimethyl sulfoxide, N,N-dimethylacetamide or N-methylpyrrolidone; the degree of polymerization of the polyethylene glycol is preferably 400-20000; the model of the polyvinyl pyrrolidone is preferably K30 or K25.

[0018] In a specific embodiment, the polyoxypropylene polyoxyethylene copolymer is at least one of P123, polyether L65, polyether F124, polyether F127, polyether F188, and polyether L68; preferably, the polyoxypropylene polyoxyethylene copolymer is P123.

[0019] The polyoxypropylene polyoxyethylene copolymer is CAS 106392-12-5 of P123.

[0020] In a specific embodiment, the method of forming a homogeneous casting solution in step c comprises stirring for 10 to 15 hours at 65 to 75° C.; the degassing in step c is preferably vacuum degassing, and the stirring speed is preferably 200 to 1500 rpm.

[0021] In a specific embodiment, the insulation time at -80°C to -20°C in step d is 3s to 5min; the treatment time at 0°C is 0.5 to 24h.

[0022] A second object of the present invention is to provide a novel polyvinylidene fluoride blend membrane having a high BSA rejection rate.

[0023] To achieve the second object of the present invention, the polyvinylidene fluoride blend membrane is prepared by the above method, and the BSA rejection rate of the polyvinylidene fluoride blend membrane is preferably above 91.8%, and more preferably above 97%.

[0024] Beneficial effects:

[0025] The polyvinylidene fluoride prepared by the method of the present invention overcomes the shortcomings of the prior art, the blended membrane has a high BSA retention rate, the polyvinylidene fluoride blended membrane has good hydrophilicity, and the permeability and anti-pollution properties are also very excellent. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Electron microscopic image of the membrane cross section of the product of Example 2;

[0027] Figure 2 Electron microscopic image of the membrane surface of the product of Example 2;

[0028] Figure 3 Electron microscope image of the membrane cross section of the product of Comparative Example 1;

[0029] Figure 4 Electron microscopic image of the membrane surface of the product of Comparative Example 1. DETAILED DESCRIPTION

[0030] In order to achieve the first purpose of the present invention, the polyvinylidene fluoride blend membrane preparation method adopts a solution crystallization-polymer diffusion method to prepare the polyvinylidene fluoride blend membrane, and a β-nucleating agent is also dispersed in the solvent of the solution crystallization-polymer diffusion method, and the β-nucleating agent is an aromatic phosphate salt; the addition amount of the β-nucleating agent is 0.5‰ to 5‰ of the mass of PVDF.

[0031] In a specific embodiment, the aryl phosphate salt is at least one of TMP-1, TMP-3, TMP-5 or TMP-6.

[0032] In a specific embodiment, the method comprises:

[0033] a. PVDF, polyvinyl pyrrolidone and β-nucleating agent were vacuum dried at 65-75°C for 12-24 hours;

[0034] b. evenly dispersing the dried β-nucleating agent into the solvent;

[0035] c. After drying, PVDF, polyvinyl pyrrolidone, polyethylene glycol, and polyoxypropylene-polyoxyethylene copolymer are added to a solvent in which a β-nucleating agent is uniformly dispersed to form a homogeneous casting solution, and degassing is performed;

[0036] d. The casting solution is evenly distributed on the substrate, and after heat preservation treatment at -80°C to -20°C, it is placed in 0-25°C to obtain a polyvinylidene fluoride blended membrane; preferably, it is immersed in an ice-water mixture to obtain a polyvinylidene fluoride blended membrane.

[0037] The casting liquid is evenly distributed on the substrate, and the -80℃~-20℃ insulation treatment can be: pre-cooling the substrate to -80℃~-20℃, then evenly distributing the casting liquid on the substrate, and insulation treatment at -80℃~-20℃; or first evenly distributing the casting liquid on the substrate, and then placing the casting liquid and the substrate in an environment of -80℃~-20℃ for insulation treatment.

[0038] In a specific embodiment, the substrate provides support and can be a smooth aluminum plate, stainless steel plate or glass plate. We put the plate into a refrigerator first, and after heat preservation treatment at -80℃ to -20℃, take it out and evenly distribute the casting liquid on the substrate. After a period of 5s to 5min, soak it in an ice-water mixture (0℃ treatment) to obtain a polyvinylidene fluoride blended membrane.

[0039] In a specific embodiment, the uniform dispersion in step b includes dispersion using ultrasound, and the power of the ultrasound is preferably 50 to 300 W, and the time is 0.5 to 5 hours.

[0040] In a specific embodiment, the mass ratio of PVDF: solvent: polyvinyl pyrrolidone: polyethylene glycol: polyoxypropylene polyoxyethylene copolymer in step c is: 15-25: 65-85: 5-10: 1-10: 1-5.

[0041] In a specific embodiment, the solvent is at least one of dimethyl sulfoxide, N,N-dimethylacetamide (DMAc) or N-methylpyrrolidone (NMP); the degree of polymerization of the polyethylene glycol is preferably 400 to 20,000; and the model of the polyvinyl pyrrolidone is preferably K30 or K25.

[0042] In a specific embodiment, the polyoxypropylene polyoxyethylene copolymer is at least one of P123, polyether L65, polyether F124, polyether F127, polyether F188, and polyether L68; preferably, the polyoxypropylene polyoxyethylene copolymer is P123. The polyoxypropylene polyoxyethylene copolymer is CAS 106392-12-5 of P123.

[0043] In a specific embodiment, the method of forming a homogeneous casting solution in step c comprises stirring for 10 to 15 hours at 65 to 75° C.; the degassing in step c is preferably vacuum degassing, and the stirring speed is preferably 200 to 1500 rpm.

[0044] In a specific embodiment, the insulation time at -80°C to -20°C in step d is 3s to 5min; the treatment time at 0°C is 0.5 to 24h.

[0045] To achieve the second object of the present invention, the polyvinylidene fluoride blend membrane is prepared by the above method, and the BSA rejection rate of the polyvinylidene fluoride blend membrane is preferably above 91.8%, and more preferably above 97%.

[0046] The specific implementation modes of the present invention are further described below in conjunction with embodiments, but the present invention is not limited to the scope of the embodiments.

[0047] Example 1

[0048] Take each component according to the mass fraction of raw materials in Table 1.

[0049] Table 1 Raw materials by weight in Examples 1-3 and Comparative Example 1

[0050] Ingredients PVDF DMSO PVP PEG 400 Polyoxypropylene polyoxyethylene copolymer β-nucleating agent Example 1 20％ 73％ 1％ 5％ 1％ 1‰ Example 2 15％ 78％ 5％ 1％ 1％ 1‰ Example 3 15％ 78％ 1％ 5％ 1％ 1‰ Comparative Example 1 15％ 78％ 5％ 1％ 1％ 0‰

[0051] Then proceed as follows:

[0052] The degree of polymerization of the polyethylene glycol in Example 1 is 400, the model of the polyvinyl pyrrolidone is K30, and the polyoxypropylene polyoxyethylene copolymer is P123.

[0053] 1) PVDF, polyvinyl pyrrolidone and β-nucleating agent TMP-5 were vacuum dried at 65°C for 12 hours respectively;

[0054] 2) adding the dried β-nucleating agent to dimethyl sulfoxide (DMSO), and then uniformly dispersing the β-nucleating agent in the dimethyl sulfoxide by ultrasonic treatment at a power of 100 W for 0.5 h;

[0055] 3) Then, the dried PVDF, polyvinyl pyrrolidone, polyethylene glycol (PEG) and polyoxypropylene polyoxyethylene copolymer are added to the dimethyl sulfoxide in which the β-nucleating agent is evenly dispersed, and the mixture is stirred for 10 hours at 65° C. to form a homogeneous casting solution, and vacuum degassing is performed.

[0056] 4) The degassed homogeneous casting solution was scraped onto the surface of the stainless steel plate by a flat film scraper, and then quickly placed on another stainless steel plate kept warm at -40°C. After 5 seconds, it was placed in an ice-water mixture to prepare a polyvinylidene fluoride (PVDF) blended membrane.

[0057] The properties of the prepared polyvinylidene fluoride blend membrane are shown in Table 2.

[0058] Table 2 Test results of membrane properties of Examples 1-3 and Comparative Example 1

[0059] Test results BAS retention rate Water flux Example 1 97.20％ 205L / h Example 2 97.20％ 422L / h Example 3 91.80％ 345L / h Comparative Example 1 77.80％ 547L / h

[0060] Example 2

[0061] Take each component according to the mass fraction of the raw materials in Table 1, and then carry out the following steps:

[0062] The degree of polymerization of the polyethylene glycol in Example 2 is 400, the model of the polyvinyl pyrrolidone is K30, and the polyoxypropylene polyoxyethylene copolymer is P123.

[0063] 1) PVDF, polyvinyl pyrrolidone and β-nucleating agent TMP-5 were vacuum dried at 75°C for 24 hours respectively;

[0064] 2) adding the dried β-nucleating agent to dimethyl sulfoxide (DMSO), and then performing ultrasound at a power of 200 W for 2 h to uniformly disperse the β-nucleating agent in the dimethyl sulfoxide;

[0065] 3) Then, the dried PVDF, polyvinyl pyrrolidone, polyethylene glycol (PEG) and polyoxypropylene polyoxyethylene copolymer are added to the dimethyl sulfoxide in which the β-nucleating agent is evenly dispersed, and the mixture is stirred for 15 hours at 75° C. to form a homogeneous casting solution, and vacuum degassing is performed.

[0066] 4) The degassed homogeneous casting solution was scraped onto the surface of the stainless steel plate by a flat film scraper, and then quickly placed on another stainless steel plate kept warm at -40°C. After 10 seconds, it was placed in an ice-water mixture to prepare a polyvinylidene fluoride (PVDF) blended membrane.

[0067] The properties of the prepared polyvinylidene fluoride blend membrane are shown in Table 2 and the SEM images are shown in Figure 1 and 2 ,Depend on Figure 1 and 2 It can be seen that the membrane structure is regular and the membrane surface is flat.

[0068] Example 3

[0069] Take each component according to the mass fraction of the raw materials in Table 1, and then carry out the following steps:

[0070] The degree of polymerization of the polyethylene glycol in Example 1 is 2000, the model of the polyvinyl pyrrolidone is K25, and the polyoxypropylene polyoxyethylene copolymer is P123.

[0071] 1) PVDF, polyvinyl pyrrolidone and β-nucleating agent TMP-5 were vacuum dried at 75°C for 12 hours respectively;

[0072] 2) adding the dried β-nucleating agent to dimethyl sulfoxide (DMSO), and then uniformly dispersing the β-nucleating agent in the dimethyl sulfoxide by ultrasonic treatment at a power of 100 W for 0.5 h;

[0073] 3) Then, the dried PVDF, polyvinyl pyrrolidone, polyethylene glycol (PEG) and polyoxypropylene polyoxyethylene copolymer are added to the dimethyl sulfoxide in which the β-nucleating agent is evenly dispersed, and the mixture is stirred for 10 hours at 65° C. to form a homogeneous casting solution, and vacuum degassing is performed.

[0074] 4) The degassed homogeneous casting solution was scraped onto the surface of the stainless steel plate by a flat film scraper, and then quickly placed on another stainless steel plate kept warm at -40°C. After 10 seconds, it was placed in an ice-water mixture to prepare a polyvinylidene fluoride (PVDF) blended membrane.

[0075] The properties of the prepared polyvinylidene fluoride blend membrane are shown in Table 2.

[0076] Comparative Example 1

[0077] Take each component according to the mass fraction of the raw materials in Table 1, and then carry out the following steps:

[0078] The degree of polymerization of the polyethylene glycol in Example 1 is 400, the model of the polyvinyl pyrrolidone is K30, and the polyoxypropylene polyoxyethylene copolymer is P123.

[0079] 1) PVDF and polyvinyl pyrrolidone were vacuum dried at 65°C for 12 hours respectively;

[0080] 2) Dimethyl sulfoxide (DMSO) was ultrasonicated at a power of 100 W for 0.5 h;

[0081] 3) Then, the dried PVDF, polyvinyl pyrrolidone, polyethylene glycol (PEG) and polyoxypropylene-polyoxyethylene copolymer are added into dimethyl sulfoxide, stirred for 10 hours at 65° C. to form a homogeneous casting solution, and vacuum degassing is performed.

[0082] 4) The degassed homogeneous casting solution was scraped onto the surface of the stainless steel plate by a flat film scraper, and then quickly placed on another stainless steel plate kept warm at -40°C. After 10 seconds, it was placed in an ice-water mixture to prepare a polyvinylidene fluoride (PVDF) blended membrane.

[0083] The properties of the prepared polyvinylidene fluoride blend membrane are shown in Table 2 and the SEM images are shown in Figure 3 and 4 ,compared to Figure 1 and 2 , Figure 3 and 4 The membrane structure is relatively disordered.

Claims

1. A method for preparing a polyvinylidene fluoride blended membrane, wherein the method adopts a solution crystallization-polymer diffusion method to prepare a polyvinylidene fluoride blended membrane, characterized in that: The solvent of the solution crystallization-polymer diffusion method also disperses a β-nucleating agent, and the β-nucleating agent is an aromatic phosphate salt; the added amount of the β-nucleating agent is 1‰ of the mass of PVDF; The aryl phosphate salt is TMP-5; The method comprises: a. PVDF, polyvinyl pyrrolidone and β-nucleating agent were vacuum dried at 75 ° C for 24 hours; b. The dried β-nucleating agent is uniformly dispersed in the solvent; the uniform dispersion in step b comprises dispersing using ultrasound, the power of the ultrasound is 200W, and the time is 2h; c. Add the dried PVDF, polyvinyl pyrrolidone, polyethylene glycol, and polyoxypropylene polyoxyethylene copolymer to a solvent uniformly dispersed with a β-nucleating agent to form a homogeneous casting solution, and degassing; the mass ratio of PVDF: solvent: polyvinyl pyrrolidone: polyethylene glycol: polyoxypropylene polyoxyethylene copolymer in step c is 15:78:5:1:1; the degree of polymerization of the polyethylene glycol is 400; the model of the polyvinyl pyrrolidone is K30; the solvent is dimethyl sulfoxide; the polyoxypropylene polyoxyethylene copolymer is P123; the method for forming a homogeneous casting solution in step c includes stirring at 65°C for 10 hours; the degassing in step c is vacuum degassing, and the stirring speed is 200-1500rpm; d. The casting solution is evenly distributed on the substrate, kept at -40°C for 5 seconds, and then immersed in an ice-water mixture to obtain a polyvinylidene fluoride blended membrane.

2. A polyvinylidene fluoride blend film, characterized in that: The polyvinylidene fluoride blend membrane is prepared by the method according to claim 1, and the polyvinylidene fluoride blend membrane has a BSA rejection rate of 97.2% and a water flux of 422 L / h.

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