PVP (Polyvinyl Pyrrolidone) / lignin blend membrane as well as preparation method and application thereof

Abstract

The invention discloses a PVP (Polyvinyl Pyrrolidone) / lignin blend membrane and a preparation method and application thereof, the PVP / lignin blend membrane is obtained by dealkalized lignin and a polyvinylpyrrolidone modified polyvinylidene fluoride membrane with the molecular weight of 10K-40K, amide carbonyl in PVP molecules can form stable hydrogen-bond interaction with hydroxyl of lignin, and the lignin agglomeration phenomenon is effectively inhibited. The hydrogen bond strength is regulated and controlled by changing the molecular weight of PVP, and the optimal interfacial compatibility and pore structure optimization effect are obtained. The obtained PVP / lignin blended membrane shows excellent separating capacity and anti-pollution performance, and a new thought is provided for design of a bio-based high-performance ultrafiltration membrane.

Description

Technical Field

[0001] This invention belongs to the field of ultrafiltration membrane preparation technology, specifically relating to a PVP / lignin blend membrane, its preparation method, and its application. Background Technology

[0002] With the acceleration of modernization, water scarcity and water pollution problems are becoming increasingly serious. Ultrafiltration (UF) membrane separation technology is a highly efficient, energy-saving, and environmentally friendly separation method that can retain macromolecules and colloidal particles at room temperature, making it important in the field of water treatment. To improve the membrane's resistance to fouling, methods typically include enhancing the membrane surface's hydrophilicity, modifying it with nanomaterials or natural polymers, and optimizing operating conditions to reduce pollutant adsorption and accumulation. These strategies not only extend the membrane's lifespan but also improve separation efficiency, making the application of ultrafiltration membranes in water treatment, food, and pharmaceutical fields more reliable. However, these methods all use petroleum-based materials, which pose significant environmental hazards.

[0003] Lignin is a natural, renewable, and biodegradable polymer, and the second most abundant biopolymer on Earth after cellulose. Due to its rich content of hydrophilic functional groups such as hydroxyl and ether bonds in its molecular structure, lignin shows broad application potential in membrane material modification and functionalization research. Yong et al. improved the hydrophilicity and antifouling properties of polyvinyl chloride (PVC) ultrafiltration membranes by introducing lignin into them, obtaining PVC / lignin ultrafiltration membranes through a phase inversion strategy. The hydrophilicity of the membrane was significantly enhanced, with the water contact angle decreasing from 106.73° to 41.53°. In particular, the PVC / lignin ultrafiltration membrane exhibited excellent performance, achieving an oil rejection rate of 97.36% and an oily wastewater permeate flux of 156.55 Lm−2h−1, almost 2.5 times that of the pure membrane. Therefore, introducing lignin into ultrafiltration membranes can significantly improve membrane performance.

[0004] However, lignin readily aggregates through hydrogen bonding in neutral or acidic aqueous solutions. To achieve efficient utilization of lignin in membrane materials, it requires regulation through chemical modification, physical blending, nano-sizing, and morphology control. Wang et al. prepared PES / LNPs blend membranes by introducing lignin nanoparticles (LNPs) into a polyethersulfone (PES) matrix to improve the membrane's hydrophilicity and antifouling properties. Their study employed a phase inversion method for membrane fabrication and systematically analyzed the effects of lignin nanoparticle content on membrane structure and performance. The results showed that the addition of an appropriate amount of LNPs significantly improved the membrane surface hydrophilicity, with the water contact angle decreasing from 81.2° to 59.4°, indicating enhanced surface wettability. Simultaneously, the pure water flux increased from 68.5 Lm. -2 h -1 Increased to 153.7 Lm -2 h -1The efficiency was increased by approximately 2.2 times, and the BSA retention rate of the membrane remained above approximately 96%, demonstrating excellent antifouling properties. This indicates that lignin nano-sizing can significantly reduce the aggregation of lignin particles.

[0005] Porous membranes can be prepared using phase inversion processes with appropriate polymer / solvent / non-solvent systems. Alternatively, adding additives to the casting solution can increase the membrane porosity. PVP is one of the most commonly used additives in membrane preparation and is generally reported as a good pore-forming agent. Cao et al. modified the structure of a polyethersulfone ultrafiltration membrane using a dual PVP pore-forming agent to improve its permeability and separation performance. Under optimal conditions, the prepared membrane exhibited a porosity of 563 μm. -2 h -1 The high throughput and 99% blue dextran rejection rate demonstrate the good potential of PVP in pore-forming agents.

[0006] However, even though lignin, as a natural polymer modifier, can reduce agglomeration through nano-processing, it still requires complex pretreatment processes, which increases preparation costs and operational difficulties. Furthermore, the use of a single pore-forming agent or modifier makes it difficult to simultaneously achieve the synergistic effect of membrane structure optimization, hydrophilicity enhancement, and antifouling performance enhancement. Some modified membranes suffer from problems such as flux and rejection rate imbalance and insufficient long-term stability, which limits their promotion and application in practical water treatment scenarios. Summary of the Invention

[0007] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0008] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0009] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing a PVP / lignin blend film.

[0010] To solve the above-mentioned technical problems, the present invention provides the following technical solution: including, Alkali-reduced lignin was placed in N,N-dimethylacetamide, dissolved by ultrasonication, and then polyvinylpyrrolidone was added. After ultrasonication again, dried polyvinylidene fluoride was added to obtain the casting solution. In the casting solution, the mass concentration of dealkalized lignin is 0.2~0.8wt%, the mass concentration of polyvinylpyrrolidone is 0.5~1.5wt%, and the mass concentration of polyvinylidene fluoride is 14~16wt%. The casting solution is heated and stirred until completely dissolved. After ultrasonic degassing, the casting solution is cast onto a nonwoven fabric and immersed in pure water to complete the phase transformation, thus obtaining a PVP / lignin membrane.

[0011] In a preferred embodiment of the preparation method of the PVP / lignin blend membrane of the present invention, the molecular weight of the polyvinylpyrrolidone is 10K-40K.

[0012] In a preferred embodiment of the preparation method of the PVP / lignin blend membrane of the present invention, the ultrasonic power of the ultrasonic dissolution is 400~500W and the ultrasonic time is 1~2h.

[0013] In a preferred embodiment of the method for preparing the PVP / lignin blend membrane of the present invention, the ultrasonic power of the second ultrasonication is 400~500W and the ultrasonication time is 1~2h.

[0014] As a preferred embodiment of the preparation method of the PVP / lignin blend membrane of the present invention, the polyvinylidene fluoride is dried under vacuum at 60~70℃ for 12~36h.

[0015] In a preferred embodiment of the preparation method of the PVP / lignin blend membrane of the present invention, the casting solution is heated and stirred at a temperature of 60~80℃ for 8~12h.

[0016] In a preferred embodiment of the method for preparing the PVP / lignin blend membrane of the present invention, the ultrasonic power of the ultrasonic degassing treatment is 400~500W and the ultrasonic time is 1~2h.

[0017] In a preferred embodiment of the preparation method of the PVP / lignin blend membrane of the present invention, the phase transformation is allowed to stand for 10-20 hours.

[0018] Another object of the present invention is to provide a PVP / lignin blend membrane.

[0019] Another object of the present invention is to provide an application of a PVP / lignin blend membrane in water treatment.

[0020] Beneficial effects of this invention: This invention utilizes a blend of lignin and polyvinylpyrrolidone (PVP) to prepare a PVP / lignin ultrafiltration membrane. The amide carbonyl group in the PVP molecule can form stable hydrogen bonds with the hydroxyl groups of lignin, effectively inhibiting lignin aggregation. By adjusting the molecular weight of PVP to regulate the hydrogen bond strength, optimal interfacial compatibility and pore structure optimization were achieved. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1 The surface and cross-sectional morphology of lignin-PVP blend films with different PVP molecular weights in this embodiment are shown by SEM characterization.

[0022] Figure 2 The filtration performance and antifouling ability of different PVP / lignin membranes were tested using BSA solution.

[0023] Figure 3 The infrared spectral characterization results of the membranes obtained with different lignin concentrations in Example 3 and Comparative Example 2 are shown.

[0024] Figure 4 The surface and cross-sectional morphology of lignin-PVP blend films with different lignin concentrations.

[0025] Figure 5 The results of the antifouling performance evaluation of lignin-PVP blend membranes with different lignin concentrations obtained by filtering a 1 g / L BSA solution are presented.

[0026] Figure 6 The results show the separation performance test results of the two filter membranes prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0027] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0028] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0029] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0030] Unless otherwise specified, all raw materials used in this invention are commercially available in the art. The raw materials used in specific embodiments and their actual sources are as follows: Polyvinylidene fluoride (PVDF) was purchased from Solvay, USA; N,N-Dimethylacetamide (DMAC) was purchased from Shanghai Lingfeng. Dealkaline-lignin, polyvinylpyrrolidone (PVP), bovine serum albumin (BSA, Mw=66 kDa), and sodium alginate (SA) with molecular weights (MW) of 10000, 24000, 40000, and 58000 g / mol were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0031] The membrane was characterized in this invention using the following method: The chemical composition of the film was characterized using attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR, Nicolai IS 50); The surface and cross-sectional structure of the membrane were characterized using field emission scanning electron microscopy (FE-SEM, SUPRA 55). The specific process is as follows: The prepared flat sheet membrane is wiped dry and placed in a freezer. Then, the frozen membrane is dried in a freeze dryer for 20 hours. For membrane surface samples, the membrane is cut to an appropriate size and adhered to a conductive adhesive. For membrane cross-section samples, the membrane is ruptured in liquid nitrogen and attached to the sample stage with conductive adhesive. Before characterization, the samples are cleaned with nitrogen and sprayed twice with platinum. The hydrophilicity of the membrane was tested using a water contact angle meter (JC 2000 D1). The freeze-dried membrane sample was cut into small pieces and fixed to a glass slide with double-sided tape, ensuring that the small pieces of membrane adhered smoothly to the tape. During the test, water droplets were dropped onto the membrane surface, with the droplet size set at 0.5 μL, and each sample was tested at least 6 times.

[0032] In this invention, membrane performance is evaluated using the following method: Pure water flux test The pure water flux of the membrane was tested using a cross-flow filtration device at a transmembrane pressure of 1 bar. Before the test, the membrane was pre-pressurized with pure water at 2 bar for 20 min to ensure its stability. The calculation formula is as follows: In the formula, J represents the filtration flux (L m). -2 h -1 ΔG represents the mass of the filtrate (g) within the time interval Δt, and A represents the filtration area (with an effective membrane area of ​​9.616 cm²). 2 ρ represents the density of the filtrate (value is 1 g / mL).

[0033] Retention performance test The membrane's retention of BSA (200 ppm) was tested using a cross-flow system at a transmembrane pressure of 1 bar. The absorbance of BSA at 280 nm was measured using a UV spectrophotometer, and the calculation formula is as follows: In the formula, R represents the retention rate (%), and C p C f The values ​​represent the concentrations (g / L) of BSA in the permeate and the original solution, respectively.

[0034] Anti-pollution performance test Rinse the membrane after BSA retention with deionized water for 1 minute, then clean it by soaking in pure water or photocatalysis for 1 hour, and then perform a pure water test. The formula for calculating flux recovery rate (FRR) is as follows: Reversible pollution rate R r The calculation formula is as follows: Irreversible pollution rate R ir The calculation formula is as follows: In the above formula, J r The pure water flux after soaking or photocatalysis (L / m) 2 h), J w This indicates the pure water flux before BSA removal (L / m³). 2 h), J L This indicates the water flux (L / m) during BSA filtration. 2 h).

[0035] Example 1 This embodiment provides a method for preparing a PVP / lignin blend membrane by blending lignin with polyvinylpyrrolidone, specifically: Dealkali-reduced lignin (DAL) was placed in N,N-dimethylacetamide (DMAC) and sonicated at 500W for 1 hour. Polyvinylpyrrolidone (PVP) with a molecular weight of 40K was then added, and sonication continued at 500W for another hour. Polyvinylidene fluoride (PVDF), dried in a vacuum oven at 60℃ for 24 hours, was then added to obtain the casting solution. The casting solution contained 0.5 wt% DAL, 1 wt% PVP, and 16 wt% PVDF. The casting solution was stirred at 70℃ for 12 hours until completely dissolved, and then ultrasonicated for 1 hour under 500W ultrasonic power to remove bubbles. The casting solution was then cast onto a nonwoven fabric using a 150 μm thick scraper. After being immersed in pure water and left to stand for 15 hours to complete the phase transformation, a PVP / lignin membrane with a thickness of about 145 μm was obtained.

[0036] Comparative Example 1 This comparative example uses a PVDF-based film as a comparison. The difference from Example 1 is that the casting solution contains only PVDF, and DAL and DMAC are omitted. The remaining steps and processes were all the same as in Example 1, and the PVDF base film of this comparative example was obtained.

[0037] Comparative Example 2 The difference between this comparative example and Example 1 is that DAL in the casting solution is omitted, and the casting solution contains only PVP and PVDF with a molecular weight of 40K. The remaining steps and processes were all performed according to Example 1 to obtain the PVP film of this comparative example, which was denoted as PVP40.

[0038] Comparative Example 3 The difference between this comparative example and Example 1 is that PVP in the casting solution is omitted, and the casting solution contains only DAL and PVDF. The remaining steps and processes were all performed in accordance with Example 1 to obtain the lignin film of this comparative example.

[0039] Example 2 The difference between this embodiment and Example 1 is that the molecular weight of the raw material polyvinylpyrrolidone was adjusted to 10K, 24K, 40K, and 58K, respectively. The remaining steps and processes were the same as in Example 1. PVP / lignin films prepared with polyvinylpyrrolidone of different molecular weights were obtained in this embodiment and were denoted as 0.5L-PVP10, 0.5L-PVP24, 0.5L-PVP40, and 0.5L-PVP58, respectively.

[0040] Figure 1 The images show the surface and cross-sectional morphology of PVP / lignin films prepared with different PVP molecular weights in this embodiment, characterized by SEM. Figure 1 Images (a) to (d) show the surface morphology of the films at different PVP molecular weights. Figure 1Figures (e) to (h) show the cross-sectional morphology of membranes with different PVP molecular weights. Surfacely, the membrane with 10K PVP is relatively dense with small pores and uneven pore distribution, indicating a weaker hydrophilic agent effect, resulting in more closed pores on the membrane surface. At 40K molecular weight, the surface pores are significantly larger and more uniform, forming a typical porous structure, which is beneficial for increasing water flux. As the molecular weight continues to increase, although the membrane remains relatively porous, local pore collapse occurs, potentially affecting water flow stability. Cross-sectionally, when the added PVP molecular weight is small, the finger pores are small and the channels are short, resulting in lower flux. When the PVP molecular weight is large, although the pores are larger, local collapse and uneven support layers lead to increased resistance in the water flow channels and decreased flux.

[0041] Figure 2 The filtration performance and antifouling ability of PVP / lignin membranes prepared with different PVP molecular weights were tested using BSA solution. Figure 2 (a) shows the change in membrane flux over time. Figure 2 (b) Flux and rejection rate of bovine serum albumin solution treated with PVP membranes of different molecular weights. Figure 2 (c) represents the ratio of reversible to irreversible fouling resistance of these membranes. Figure 2 (d) represents the water contact angle of PVP membranes with different molecular weights.

[0042] The results showed that in the pure water flux test, as the molecular weight of PVP increased from 10K to 58K, the pure water flux increased from 68 Lm. -2 h -1 Increased to 135 Lm -2 h -1 The flux reached its maximum at a molecular weight of 40K. The significant increase in pure water flux was due to the addition of high molecular weight PVP, which increased the area of ​​the finger pores, thereby improving permeability. In the filtration of BSA solution, the flux increased from 27 L / m³ to [value missing] as the molecular weight of PVP increased. -2 h -1 Increased to 61 L m -2 h -1 The rejection rate increased from 85% to 95%, with the highest rejection rate at a molecular weight of 40K. This is because the addition of PVP enhances antifouling properties; when the PVP molecular weight reaches 58K, the membrane pores enlarge, allowing BSA to pass through more easily. After soaking in deionized water for 1 hour, the pure water flux of all membranes recovered to some extent. Compared to the base membrane, the membrane with added PVP exhibited a higher FRR because the hydrophilic PVP forms a hydration layer on the membrane surface, reducing the adhesion of irreversible contaminants. By comparing the performance of membranes with different molecular weights, it was found that the membrane with added PVP at a molecular weight of 40K performed best, with higher flux and rejection rates than membranes with other molecular weights.

[0043] Example 3 The difference between this embodiment and Embodiment 1 is that the mass concentration of DAL in the casting solution was adjusted to 0.2wt%, 0.5wt%, and 0.8wt%, respectively. The remaining steps and processes were all the same as in Example 1, and composite membranes prepared with different lignin concentrations in this example were obtained, which were denoted as 0.2L-PVP40, 0.5L-PVP40, and 0.8L-PVP40, respectively.

[0044] Figure 3 The infrared spectral characterization results of the membranes obtained with different lignin concentrations in Example 3 and Comparative Example 2 are as follows. It can be seen that the characteristic peaks of the membrane changed significantly with the addition of lignin. (3400 cm⁻¹) -1 The peak at 1660 cm⁻¹ can be attributed to the -OH stretching vibration of lignin. With increasing lignin concentration, the -OH peak gradually strengthens and becomes broader, indicating that the introduced lignin -OH forms a stronger hydrogen bond with the C=O of PVP. -1 The enhanced C=O stretching vibration peak of PVP, along with a slight redshift, also indicates the interaction between lignin and PVP. (1590 cm⁻¹) -1 The vibration of the aromatic ring skeleton increased with the increase of lignin content, which proved the effective introduction of lignin. The results show that the addition of lignin not only successfully incorporated it into the membrane material in terms of chemical structure, but also strengthened the interaction with PVP through hydrogen bonding.

[0045] The surface and cross-sectional morphology of composite films prepared with different lignin concentrations were studied by SEM characterization, such as... Figure 4 As shown, Figure 4 Images (a) to (d) show the surface morphology of the film at different lignin concentrations. Figure 4 Images (e) to (h) show the cross-sectional morphology of the membranes at different lignin concentrations. Superficially, the hydrogen bonding between lignin and PVP improves the uniformity of the casting solution, accelerates the phase transformation rate, and makes the membrane surface more uniform. With increasing lignin concentration, the membrane pore size gradually increases. Cross-sections of both the lignin-free and blended membranes exhibit typical asymmetric ultrafiltration membrane structures, including a skin layer, finger-like pores, and sponge-like pores. With increasing lignin concentration, the finger-like pores increase in size, while the sponge-like pores decrease. This phenomenon is mainly attributed to the abundance of phenolic hydroxyl groups in lignin, which can attract water molecules through hydrogen bonds, enabling faster water diffusion. Therefore, larger finger-like pores can be generated.

[0046] The antifouling performance of the membrane was evaluated by filtering a 1 g / L BSA solution, and the results are as follows: Figure 5 As shown, Figure 5 (a) shows the change in membrane flux over time. Figure 5 (b) Flux and rejection rate of membranes with different DL concentrations when treating bovine serum albumin solution. Figure 5 (c) represents the ratio of reversible to irreversible pollution resistance at different DL concentrations. Figure 5 (d) represents the water contact angle of films with different lignin concentrations; from Figure 5 As can be seen, compared with the untreated base membrane (Comparative Example 1), both the pure water flux and BSA flux increase with increasing lignin concentration. This is because the water contact angle of the membrane decreases with the addition of lignin. Simultaneously, the addition of lignin forms a synergistic network with PVP, creating a hydrophilic layer on the membrane surface, increasing hydrophilicity. Regarding BSA retention, the retention rate is high at low concentrations and decreases at high concentrations. The retention rate reaches its highest value at 0.5 wt%, and then decreases as the concentration increases to 0.8 wt%. This is because the finger pores enlarge with increasing lignin concentration, leading to a decrease in retention rate. Calculations show that the blended membrane exhibits a slightly higher total recovery rate compared to the base membrane. The highest total recovery rate (74.4%) is achieved at a lignin concentration of 0.5 wt%, indicating the highest reversible fouling resistance and the lowest irreversible fouling resistance. This is because the C=O of PVP forms hydrogen bonds with the –OH group of lignin, and can form a stable hydration layer with water molecules on the membrane surface, effectively reducing the adsorption and clogging of pollutants, allowing the membrane to recover a high flux after cleaning. At the same time, the hydrogen bonding between PVP and lignin improves their compatibility and structural stability, preventing lignin loss during use and further enhancing the membrane's antifouling performance.

[0047] To evaluate the practical application capability of the PVP / lignin membrane, separation performance was tested using 1 g / L BSA and 0.2 g / L SA to simulate food processing wastewater. Performance tests were conducted on two filtration membranes prepared in Comparative Example 1 and Comparative Example 2. First, the pure water flux of the membrane was tested, followed by filtration with a mixed solution of BSA and SA for 60 min. After filtration, the membrane was rinsed with pure water for 3 min to remove adsorbed contaminants, repeated 5 times.

[0048] The results are as follows Figure 6 As shown, Figure 6 (a) shows the change of membrane flux over time for the two types of membranes. Figure 6 (b) represents the ratio of reversible to irreversible fouling resistance for the two membranes. Figure 6 (c) The flux and rejection rate of the PVDF-based membrane used in Comparative Example 1 when treating a mixed solution of BSA and SA. Figure 6 (d) represents the flux and rejection rate of the PVP / lignin membrane used in Example 1 to treat a mixed solution of BSA and SA.

[0049] from Figure 6It can be seen that the initial pure water flux of the 0.5L-PVP40 membrane is 118 L / m³. -2 h -1 The initial filtration flux was approximately 60 L / m. -2 h -1 After rinsing with pure water, it returned to 95 L m. -2 h -1 Approximately. The initial pure water flux of the PVDF membrane is 50 L / m³. -2 h -1 The initial filtration flux was approximately 34 Lm. -2 h -1 After rinsing with pure water, it returned to 39 L m. -2 h -1 Around 100%. In filtering a mixed solution of BSA and SA, the water flux gradually decreased, and the flux of the PVDF membrane was significantly lower than that of 0.5L-PVP40, with a lower recovery rate. This is because the addition of PVP and lignin allows them to form a hydrophilic coating on the membrane surface through hydrogen bonding, effectively reducing the adsorption of pollutants. Figure 6 As shown in (c) and 6(d), the TOC rejection rate of 0.5L-PVP40 was around 95% for five cycles, which showed better rejection performance than PVDF membrane.

[0050] In summary, this invention utilizes a blend of lignin and polyvinylpyrrolidone (PVP) to prepare a PVP / lignin ultrafiltration membrane. The amide carbonyl group in the PVP molecule can form stable hydrogen bonds with the hydroxyl groups of lignin, effectively inhibiting lignin aggregation. By adjusting the molecular weight of PVP to regulate the hydrogen bond strength, optimal interfacial compatibility and pore structure optimization were achieved. Experimental results show that the membrane exhibits the best overall performance when it contains 1 wt% PVP with a molecular weight of 40 K and 0.5 wt% lignin, achieving a BSA solution rejection rate as high as 94.5% and a flux recovery rate (FRR) of 71%, demonstrating excellent separation capability and antifouling performance. This provides a new approach for the design of bio-based high-performance ultrafiltration membranes.

[0051] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a PVP / lignin blend membrane, characterized in that: include, Alkali-reduced lignin was placed in N,N-dimethylacetamide, dissolved by ultrasonication, and then polyvinylpyrrolidone was added. After ultrasonication again, dried polyvinylidene fluoride was added to obtain the casting solution. In the casting solution, the mass concentration of dealkalized lignin is 0.2~0.8wt%, the mass concentration of polyvinylpyrrolidone is 0.5~1.5wt%, and the mass concentration of polyvinylidene fluoride is 14~16wt%. The casting solution is heated and stirred until completely dissolved. After ultrasonic degassing, the casting solution is cast onto a nonwoven fabric and immersed in pure water to complete the phase transformation, thus obtaining a PVP / lignin membrane.

2. The method for preparing the PVP / lignin blend membrane as described in claim 1, characterized in that: The molecular weight of the polyvinylpyrrolidone is 10K-40K.

3. The method for preparing the PVP / lignin blend membrane as described in claim 1, characterized in that: The ultrasonic power for ultrasonic dissolution is 400~500W, and the ultrasonic time is 1~2h.

4. The method for preparing the PVP / lignin blend membrane as described in claim 2, characterized in that: The ultrasonic power of the second ultrasonic treatment is 400~500W, and the ultrasonic time is 1~2h.

5. The method for preparing the PVP / lignin blend membrane as described in claim 2, characterized in that: The polyvinylidene fluoride was dried under vacuum at 60-70°C for 12-36 hours.

6. The method for preparing the PVP / lignin blend membrane as described in claim 1, characterized in that: The casting solution is heated and stirred at a temperature of 60~80℃ for 8~12 hours.

7. The method for preparing the PVP / lignin blend membrane as described in claim 1, characterized in that: The ultrasonic power for the ultrasonic degassing treatment is 400~500W, and the ultrasonic time is 1~2h.

8. The method for preparing the PVP / lignin blend membrane as described in claim 1, characterized in that: The phase transformation is allowed to stand for 10-20 hours.

9. The PVP / lignin blend membrane prepared by any one of the preparation methods described in claims 1 to 8.

10. The application of the PVP / lignin blend membrane as described in claim 9 in water treatment.

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