Modified polyvinylidene fluoride dialysis membrane and preparation method thereof

Abstract

The invention discloses a modified polyvinylidene fluoride dialysis membrane and a preparation method thereof, after cellulose nanocrystals are uniformly dispersed, cellulose acetate and polyvinylidene fluoride are added to obtain a membrane casting solution in which the solid content of the cellulose nanocrystals relative to the polyvinylidene fluoride is 3-15wt%, and then the membrane casting solution is coated to obtain the modified polyvinylidene fluoride dialysis membrane. Wherein the addition amount of the cellulose acetate CA is 5-20 wt%, the addition amount of the cellulose nanocrystals CNC is 1-10 wt%, and the mass of the polyvinylidene fluoride is 70-85 wt%. Through the synergistic addition effect of PVDF, CA and CNC, the structure of the PVDF membrane is changed, the MWCO and MWRO of the membrane are improved, the effective aperture and flux are increased, the PVDF membrane with high flux and selectivity is obtained, and finally the dialysis filtration capacity of the PVDF membrane is improved.

Description

Technical Field

[0001] The present invention relates to the field of biofilms, and particularly to a modified polyvinylidene fluoride dialysis membrane and a preparation method thereof. Background Art

[0002] Insufficient removal of organic waste is an important factor leading to diseases in patients undergoing dialysis. Observational studies have found that in terms of improving patient survival, techniques that can increase the clearance rate of middle molecules, such as hemodiafiltration (HDF), have advantages over traditional dialysis (HD). However, traditional dialysis membrane technologies mainly aim at eliminating small molecule toxins such as urea and creatinine, and they show low performance in removing middle molecules and protein-bound uremic toxins (PBUT). Therefore, the development of high-throughput selective dialysis membranes suitable for HDF has important application value.

[0003] Polyvinylidene fluoride (PVDF) has been widely used in scientific research and industrial processes due to its excellent properties, such as good chemical resistance, high thermal stability, high mechanical strength, and excellent film-forming properties. In recent years, PVDF membranes have been applied in the field of hemodialysis due to their characteristics. However, due to the hydrophobicity of its surface and its inherent properties, the flux and selectivity of PVDF membranes are poor, which to a certain extent limits its application in hemodialysis. To solve this problem, in current research, many methods to improve membrane flux have been adopted, including surface modification and blending. However, the surface modification process is complex and the durability is limited. In contrast, blending is simpler in operation and the modification effect is relatively uniform. Blending can improve the properties of the membrane by mixing hydrophilic polymers, natural polymer materials, and inorganic metal compounds. For example, Liu et al. blended polyethylene glycol-multi-walled carbon nanotubes (PMWCNT) with PVDF to prepare ultrafiltration membranes (PMWCNT / PVDF). The PMWCNT / PVDF membrane showed better hydrophilicity and higher pure water flux compared with the pure PVDF membrane. Zheng et al. and Boruah et al. obtained composite membranes by blending cellulose nanocrystals (CNCs) in PVDF respectively. Although these composite membranes all showed larger pore sizes and permeability, their ability to remove middle molecule toxins still needs to be improved. Summary of the Invention

[0004] To solve the above problems, the purpose of the present invention is to provide a modified polyvinylidene fluoride dialysis membrane and a preparation method thereof. This method regulates the polymer membrane structure and effective pore size through CA blending and CNC doping, so as to improve the dialysis filtration effect of the PVDF membrane, enhance the ability to remove middle molecule toxins, and show a high selective clearance property for middle molecule toxins.

[0005] The present invention is achieved by the following technical solutions: A preparation method of a modified polyvinylidene fluoride dialysis membrane. After uniformly dispersing cellulose nanocrystals, cellulose acetate and polyvinylidene fluoride are added to obtain a casting solution with a cellulose nanocrystal content relative to the solid content of polyvinylidene fluoride of 3-15 wt%. Then, the casting solution is coated to obtain the modified polyvinylidene fluoride dialysis membrane, wherein the addition amount of cellulose acetate CA is 5-20 wt%, the addition amount of cellulose nanocrystals CNC is 1-10 wt%, and the mass of polyvinylidene fluoride is 70-85 wt%.

[0006] The weight-average molecular weight of polyvinylidene fluoride is 700-800 kDa.

[0007] The addition amount of cellulose acetate CA is 15 wt%, the addition amount of cellulose nanocrystals CNC is 1-10 wt%, and the mass of polyvinylidene fluoride is 75-84 wt%.

[0008] The addition amount of cellulose acetate CA is 15 wt%, the addition amount of cellulose nanocrystals CNC is 5-10 wt%, and the mass of polyvinylidene fluoride is 75-80 wt%. It can be seen from the examples that the addition of this range of ratios makes the performance of the PVDF membrane more excellent.

[0009] After uniformly dispersing the cellulose nanocrystals, the cellulose nanocrystals need to be ultrasonically treated for 20-40 min.

[0010] The molecular weight cut-off value is 870-2561 kDa, the starting molecular weight retention value is 8-12 kDa, and the average effective pore size is 7.6-18 nm.

[0011] The clearance rate of middle molecule toxins is 31.5-52.3%.

[0012] The molecular weight cut-off value (MWCO) and the starting molecular weight retention value (MWRO) are key parameters for controlling the quality of hemodialysis membranes. The former is used to maintain selectivity for proteins, while the latter is used to control the removal efficiency of middle molecules. A higher MWRO value will increase the removal of uremic toxins.

[0013] In the present invention, by adding cellulose acetate (CA) and cellulose nanocrystals (CNCs), the structure of the PVDF membrane and MWCO, MWRO, such as the effective pore size of the membrane, are adjusted. It achieves a high flux and a high molecular weight retention level, and significantly improves the clearance rate of middle molecule toxins, showing a high selective clearance property for middle molecule toxins. The prepared modified PVDF membrane can not only improve the clearance of uremic toxins, but also minimize protein loss.

[0014] Compared with the prior art, the present invention has the following advantages and beneficial effects: Through the synergistic addition of PVDF, CA, and CNC, the structure of the PVDF membrane is changed, the MWCO and MWRO of the membrane are improved, the effective pore size and flux are increased, a high-flux and selective PVDF membrane is obtained, and finally the diafiltration ability of the PVDF membrane is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, form a part of this application, and do not limit the embodiments of the present invention. In the drawings: Figure 1 are the appearance photos of the PVDF membrane of Comparative Example 1 and the modified PVDF membranes of Examples 6, 7, and 8 of the present invention.

[0016] Figure 2 are the scanning electron microscope photos of the PVDF membrane of Comparative Example 1 and the modified PVDF membrane of Example 3 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and the drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and do not limit the present invention.

[0018] The diafiltration ability of the membrane before and after modification is characterized by MWCO, effective pore size, and pure water flux; β2-microglobulin is a medium molecule toxin that needs to be removed from the blood of patients with renal failure. In the research, lysozyme in synthetic human plasma is commonly used to replace β2-microglobulin for dialysis to evaluate the removal ability of the membrane for medium molecule solutes. Here, MWRO and lysozyme clearance rate are used to characterize the removal ability of the membrane for medium molecule toxins before and after modification. In the implementation, the weight average molecular weight of polyvinylidene fluoride is 700 - 800 kDa. EXAMPLES

[0019] (1) 0.125 grams of CNCs were uniformly dispersed in 85 grams of DMAc by ultrasonic treatment for 30 minutes, and then 2.5 grams of CA and 12.5 grams of PVDF were added to obtain a casting solution with a CNC solid content of 1 wt% relative to PVDF.

[0020] (2) The casting solution was slowly poured onto a clean glass plate of an automatic film coater, and the solution was coated on the glass plate with a 0.5 mm thick gap knife at a coating speed of 20 cm / min. Finally, the coated membrane was quickly immersed in deionized water at room temperature to obtain membrane sample 1 by non-solvent induced phase separation method.

[0021] The MWCO of Membrane 1 is 870 kDa, the MWRO is 8 kDa, the average effective pore size is 7.6 nm, the lysozyme clearance rate is 31.5%, and the pure water flux is 347 L / (m 2 ·h·bar).

[0022] The modified Membrane 1 has a larger average effective pore size and flux, and also has a higher clearance rate for medium molecular toxins. Example

[0023] (1) 0.375 g of CNCs was uniformly dispersed in 85 g of DMAc by ultrasonic treatment for 30 min, and then 2.5 g of CA and 12.5 g of PVDF were added to obtain a casting solution with a CNC solid content of 3 wt% relative to PVDF.

[0024] (2) The casting solution was slowly poured onto a clean glass plate of an automatic film coater, and the solution was coated on the glass plate with a 0.5 mm thick blade, and the film coating speed was 20 cm / min. Finally, the coated film was quickly immersed in deionized water at room temperature to obtain Membrane Sample 2 by non-solvent induced phase separation.

[0025] The MWCO of Membrane 2 is 924 kDa, the MWRO is 11 kDa, the average effective pore size is 16.4 nm, the lysozyme clearance rate is 40.4%, and the pure water flux is 406 L / (m 2 ·h·bar).

[0026] For the modified Membrane 2, the average effective pore size and flux increased significantly with the increase in the addition amount of CNCs, and the clearance rate for medium molecular toxins also increased significantly. Example

[0027] (1) 0.625 g of CNCs was uniformly dispersed in 85 g of DMAc by ultrasonic treatment for 30 min, and then 2.5 g of CA and 12.5 g of PVDF were added to obtain a casting solution with a CNC solid content of 5 wt% relative to PVDF.

[0028] (2) The casting solution was slowly poured onto a clean glass plate of an automatic film coater, and the solution was coated on the glass plate with a 0.5 mm thick blade, and the film coating speed was 20 cm / min. Finally, the coated film was quickly immersed in deionized water at room temperature to obtain Membrane Sample 3 by non-solvent induced phase separation.

[0029] The MWCO of Membrane 3 is 2375 kDa, the MWRO is 12 kDa, the average effective pore size is 17.4 nm, the lysozyme clearance rate is 50.5%, and the pure water flux is 453 L / (m 2 ·h·bar).

[0030] For the modified membrane 3, the average effective pore size and flux further increase with the increase in the addition amount of CNC, and the clearance rate of medium molecular toxins also further improves. Example

[0031] (1) 1.25 g of CNCs was uniformly dispersed in 85 g of DMAc by ultrasonic treatment for 30 min, and then 2.5 g of CA and 12.5 g of PVDF were added to obtain a casting solution with a CNC solid content of 10 wt% relative to PVDF.

[0032] (2) The casting solution was slowly poured onto a clean glass plate of an automatic film coater, and the solution was coated on the glass plate with a 0.5 mm thick gap knife, and the film coating speed was 20 cm / min. Finally, the coated film was quickly immersed in deionized water at room temperature, and membrane sample 4 was obtained by non-solvent induced phase separation method.

[0033] The MWCO of membrane 4 is 2561 kDa, the MWRO is 13 kDa, the average effective pore size is 18.0 nm, the lysozyme clearance rate is 52.3%, and the pure water flux is 475 L / (m 2 ·h·bar).

[0034] For the modified membrane 4, the average effective pore size and flux do not increase proportionally with the increase in the addition amount of CNC, and the improvement of the clearance rate of medium molecular toxins also slows down. Comparative Example 1 (1) 15 g of PVDF was uniformly dispersed in 85 g of DMAc by ultrasonic treatment for 30 min to obtain a pure PVDF casting solution with a solid content of 15 wt%.

[0035] (2) The casting solution was slowly poured onto a clean glass plate of an automatic film coater, and the solution was coated on the glass plate with a 0.5 mm thick gap knife, and the film coating speed was 20 cm / min. Finally, the coated film was quickly immersed in deionized water at room temperature, and membrane sample 5 was obtained by non-solvent induced phase separation method.

[0036] The MWCO of membrane 5 is 65 kDa, the MWRO is 0.6 kDa, the average effective pore size is 5.5 nm, the lysozyme clearance rate is 7.9%, and the pure water flux is 67 L / (m 2 ·h·bar).

[0037] The pure PVDF membrane 5 has a dense structure, small average effective pore size and flux, and low clearance rate of medium molecular toxins. Comparative Example 2 (1) 0.71 g of CA and 14.29 g of PVDF were uniformly dispersed in 85 g of DMAc by ultrasonic treatment for 30 min to obtain a casting solution with a CA solid content of 5 wt% relative to PVDF.

[0038] (2) The casting solution was slowly poured onto a clean glass plate of an automatic film coater, and the solution was coated on the glass plate with a 0.5 mm thick blade. The film coating speed was 20 cm / min. Finally, the coated film was quickly immersed in deionized water at room temperature to obtain membrane sample 6 by non-solvent induced phase separation method.

[0039] Membrane 6 had an MWCO of 189 kDa, an MWRO of 2 kDa, an average effective pore size of 5.8 nm, a lysozyme clearance rate of 21.4%, and a pure water flux of 103 L / (m 2 ·h·bar).

[0040] After blending with CA, the surface of membrane 6 became wrinkled. The average effective pore size and flux increased compared to the pure PVDF membrane, and the clearance rate of medium molecular toxins also increased. Comparative Example 3 (1) 1.36 g of CA and 13.64 g of PVDF were uniformly dispersed in 85 g of DMAc by ultrasonic treatment for 30 min to obtain a casting solution with a CA solid content of 10 wt% relative to PVDF.

[0041] (2) The casting solution was slowly poured onto a clean glass plate of an automatic film coater, and the solution was coated on the glass plate with a 0.5 mm thick blade. The film coating speed was 20 cm / min. Finally, the coated film was quickly immersed in deionized water at room temperature to obtain membrane sample 7 by non-solvent induced phase separation method.

[0042] Membrane 7 had an MWCO of 376 kDa, an MWRO of 3 kDa, an average effective pore size of 6.3 nm, a lysozyme clearance rate of 26.7%, and a pure water flux of 128 L / (m 2 ·h·bar).

[0043] After blending with CA, the surface of membrane 7 became wrinkled. The average effective pore size and flux increased with the increase of CA content, and the clearance rate of medium molecular toxins also increased. Comparative Example 4 (1) 1.96 g of CA and 13.04 g of PVDF were uniformly dispersed in 85 g of DMAc by ultrasonic treatment for 30 min to obtain a casting solution with a CA solid content of 15 wt% relative to PVDF.

[0044] (2) Slowly pour the casting solution onto a clean glass plate of an automatic film coater, and apply the solution onto the glass plate with a 0.5 mm thick blade. The film coating speed is 20 cm / min. Finally, quickly immerse the coated film in deionized water at room temperature to obtain membrane sample 8 through non-solvent induced phase separation method.

[0045] The MWCO of membrane 8 is 510 kDa, the MWRO is 5 kDa, the average effective pore size is 6.6 nm, the lysozyme clearance rate is 30.8%, and the pure water flux is 155 L / (m 2 ·h·bar).

[0046] After blending with CA, the surface of membrane 8 becomes flat again. The average effective pore size and flux increase slightly with the increase of CA content, and the clearance rate of medium molecular toxins also increases slowly. Comparative Example 5 (1) Uniformly disperse 0.15 g of CNC and 14.85 g of PVDF in 85 g of DMAc by ultrasonic treatment for 30 min to obtain a casting solution with a solid content of 1 wt% of CNC relative to PVDF.

[0047] (2) Slowly pour the casting solution onto a clean glass plate of an automatic film coater, and apply the solution onto the glass plate with a 0.5 mm thick blade. The film coating speed is 20 cm / min. Finally, quickly immerse the coated film in deionized water at room temperature to obtain membrane sample 9 through non-solvent induced phase separation method.

[0048] The MWCO of membrane 9 is 70 kDa, the MWRO is 0.8 kDa, the average effective pore size is 5.7 nm, the lysozyme clearance rate is 8.1%, and the pure water flux is 75 L / (m 2 ·h·bar).

[0049] For membrane 9 blended with CNC, the average effective pore size and flux increase slightly, and the clearance rate of medium molecular toxins increases slightly. Comparative Example 6 (1) Uniformly disperse 0.75 g of CNC and 14.25 g of PVDF in 85 g of DMAc by ultrasonic treatment for 30 min to obtain a casting solution with a solid content of 5 wt% of CNC relative to PVDF.

[0050] (2) Slowly pour the casting solution onto a clean glass plate of an automatic film coater, and apply the solution onto the glass plate with a 0.5 mm thick blade. The film coating speed is 20 cm / min. Finally, quickly immerse the coated film in deionized water at room temperature to obtain membrane sample 10 through non-solvent induced phase separation method.

[0051] The MWCO of membrane 10 is 150 kDa, the MWRO is 1.7 kDa, the average effective pore size is 6.0 nm, the lysozyme clearance rate is 12%, and the pure water flux is 110 L / (m 2 ·h·bar).

[0052] For membrane 10 blended with CNC, the average effective pore size and flux increase with the increase of CNC addition amount, and the clearance rate of medium molecular toxins also improves. Comparative Example 7 (1) 1.36 g of CNC and 13.64 g of PVDF were uniformly dispersed in 85 g of DMAc by ultrasonic treatment for 30 min to obtain a casting solution with a solid content of 10 wt% of CNC relative to PVDF.

[0053] (2) The casting solution was slowly poured onto a clean glass plate of an automatic film coater, and the solution was coated on the glass plate with a 0.5 mm thick blade, and the film coating speed was 20 cm / min. Finally, the coated film was quickly immersed in deionized water at room temperature to obtain membrane sample 11 by non-solvent induced phase separation method.

[0054] The MWCO of membrane 11 is 160 kDa, the MWRO is 1.9 kDa, the average effective pore size is 6.2 nm, the lysozyme clearance rate is 14%, and the pure water flux is 115 L / (m 2 ·h·bar).

[0055] For membrane 11 blended with CNC, the average effective pore size and flux did not increase significantly with the further increase of CNC addition amount, and the clearance rate of medium molecular toxins did not improve significantly either.

[0056] Table 1 Performance indicators of modified polyvinylidene fluoride dialysis membrane Experiment Membrane CA addition amount / % CNC addition amount / % MWCO / kDa MWRO / kDa Average effective pore size / nm Lysozyme clearance rate / % <![CDATA[Water flux / L / (m 2 ·h·bar)]]> Example 1 1 15 1 870 8 7.6 31.5 347 Example 2 2 15 3 924 11 16.4 40.4 406 Example 3 3 15 5 2375 12 17.4 50.5 453 Example 4 4 15 10 2561 13 18.0 52.3 475 Comparative Example 1 5 0 0 65 0.6 5.5 7.9 67 Comparative Example 2 6 5 0 189 2 5.8 21.4 103 Comparative Example 3 7 10 0 376 3 6.3 26.7 128 Comparative Example 4 8 15 0 510 5 6.6 30.8 155 Comparative Example 5 9 0 1 70 0.8 5.7 8.1 75 Comparative Example 6 10 0 5 150 1.7 6.0 12 110 Comparative Example 7 11 0 10 160 1.9 6.2 14 115 It can be seen from Comparative Example 1 that the flux of the pure PVDF membrane and the diafiltration ability for medium molecular toxins are poor; it can be seen from Comparative Examples 2-4 and Comparative Examples 5-7 that although blending with CA or adding CNC alone can improve the diafiltration performance of the PVDF membrane, the effect of CNC is not obvious. However, the synergistic regulation effect of using CA blending and CNC doping is better. As shown in Examples 1-4, both the MWCO and MWRO of the modified PVDF membrane increase significantly, and its flux and the removal efficiency of medium molecular toxins increase significantly.

[0057] Figure 1The figure shows the appearance photos of PVDF membranes and modified PVDF membranes 6, 7, and 8. It can be seen from the photos that the surface of the PVDF membrane is smooth and flat. When the CA content is 5% and 10%, the membrane wrinkles, and when it increases to 15%, it returns to being flat again, reflecting the change process of the membrane structure. The interaction between CA, PVDF, and DMAc molecules causes wrinkles to appear on the surface of the PVDF / CA membrane. When the CA content increases to more than 15 wt%, this effect or interaction may reach a certain balance, and the surface of the PVDF / CA membrane becomes smooth and flat again.

[0058] The surfaces and cross-sections of PVDF and PVDF / CA / CNCs membranes were observed and analyzed by SEM, and the results are as Figure 2 shown (including a1-2 surfaces, b1-2 cross-sections, and c1-2 partial enlarged views). From Figure 2 Figure (a1), it can be observed that the pure PVDF membrane is relatively dense, and obvious agglomerations caused by polymer phase separation can be seen on the membrane surface. The spherical nodules on the brittle fracture surface Figure 2 Figure (c1) also indicate the existence of macroscopic polymer-polymer phase separation. This may be related to the fact that PVDF is a hydrophobic semi-crystalline polymer. Shallow pores formed by solvent / nonsolvent exchange below the membrane skin account for about one-fifth of the membrane thickness, as shown in Figure 2 Figure (b1). This may be the reason why the rich polymer phase rapidly vitrifies during the phase inversion membrane formation process, and the expansion of pores towards the bottom of the thin film stops quickly.

[0059] After adding CA and CNCs, the membrane structure becomes completely different. The PVDF / CA / CNCs membrane exhibits a typical asymmetric membrane structure, including a thin dense surface layer, a thick macroporous sublayer, and a spongy structure between the macropores, as shown in Figure 2 Figure (b2) and Figure 2 Figure (c2). A large number of small pores also appear on the skin, as shown in Figure 2 Figure (a2).

[0060] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a modified polyvinylidene fluoride dialysis membrane, characterized in that: After the cellulose nanocrystals are uniformly dispersed, cellulose acetate and polyvinylidene fluoride are added to obtain a casting solution with a solid content of cellulose nanocrystals of 3-10wt% relative to polyvinylidene fluoride, and the casting solution is coated to obtain a modified polyvinylidene fluoride dialysis membrane, wherein the added amount of cellulose acetate CA is 5-20wt%, the added amount of cellulose nanocrystals CNC is 1-10wt%, and the mass of polyvinylidene fluoride is 70-85wt%.

2. The preparation method according to claim 1, characterized in that: The weight average molecular weight of polyvinylidene fluoride is 700-800 kDa.

3. The preparation method according to claim 1, characterized in that: The addition amount of cellulose acetate CA is 15wt%, the addition amount of cellulose nanocrystals CNC is 1-10wt%, and the mass of polyvinylidene fluoride is 75-84wt%.

4. The preparation method according to claim 1, characterized in that: The addition amount of cellulose acetate CA is 15wt%, the addition amount of cellulose nanocrystals CNC is 5-10wt%, and the mass of polyvinylidene fluoride is 75-80wt%.

5. The preparation method according to claim 1, characterized in that: After the cellulose nanocrystals are evenly dispersed, the cellulose nanocrystals need to be ultrasonically treated for 20-40 minutes.

6. The modified polyvinylidene fluoride dialysis membrane obtained by the preparation method according to any one of claims 1 to 4, characterized in that: The molecular weight cut-off value is 870-2561 kDa, the molecular weight retention value is 8-12 kDa, and the average effective pore size is 7.6-18 nm.

7. The modified polyvinylidene fluoride dialysis membrane according to claim 1, characterized in that: The clearance rate of medium-molecular toxins was 31.5-52.3%.

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