Modified PVDF (Polyvinylidene Fluoride) hollow fiber ultrafiltration membrane as well as preparation method and application thereof

Abstract

The invention provides a modified PVDF (Polyvinylidene Fluoride) hollow fiber ultrafiltration membrane as well as a preparation method and application thereof, and the hollow fiber ultrafiltration membrane is mainly prepared from the following raw materials in percentage by mass: 0.5-2.0% of alpha-zirconium phosphate, 14-18% of polyvinylidene fluoride, 4-6% of a pore-foaming agent and 74-81.5% of dimethylacetamide. According to the hollow fiber ultrafiltration membrane, a membrane pore structure with uniform structure and proper porosity is formed by proportioning the raw materials, and the hollow fiber ultrafiltration membrane has good mechanical strength and hydrophilicity.

Description

Technical Field

[0001] This invention relates to the field of filter membrane technology, specifically to a modified PVDF hollow fiber ultrafiltration membrane, its preparation method, and its application. Background Technology

[0002] Polyvinylidene fluoride (PVDF) has become a popular material for preparing hollow fiber ultrafiltration membranes due to its excellent chemical stability, mechanical strength, and film-forming properties, and it is widely used in many fields. Currently, non-solvent-induced phase separation (NIPS) is the mainstream technology for preparing PVDF hollow fiber membranes. Its principle is to form a porous structure by initiating phase separation through solvent-non-solvent exchange between the polymer solution and the coagulation bath.

[0003] However, PVDF membranes prepared by the traditional NIPS method have significant drawbacks. Their pore structure is difficult to control precisely, often resulting in a mixture of finger-like and sponge-like pores. While finger-like pores can increase water flux, they have poor mechanical strength and are prone to collapse and rupture under backwashing and external pressure, affecting membrane lifespan. Sponge-like pores, while ensuring retention rate and mechanical strength, increase membrane filtration resistance and result in lower initial flux. This contradiction between flux and strength becomes the key constraint on improving PVDF membrane performance.

[0004] To improve membrane performance, existing technologies often employ the addition of porogens or modifiers. While organic porogens (such as polyvinylpyrrolidone and polyethylene glycol) can increase membrane porosity, as water-soluble polymers, they gradually dissolve during long-term use, leading to irreversible changes in the membrane pore structure, performance degradation, and potential secondary pollution. Inorganic nanoparticles (such as titanium dioxide and silica nanoparticles) can enhance membrane hydrophilicity and antifouling properties, but they tend to aggregate in the polymer matrix, making uniform dispersion difficult. This results in defects within the membrane, creating mechanically weak points, and it is difficult to actively and effectively control the thermodynamic and kinetic processes of phase separation to form an ideal gradient pore structure.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The primary objective of this invention is to provide a modified PVDF hollow fiber ultrafiltration membrane that, through a specific raw material ratio, solves the problems of insufficient hydrophilicity, easy fouling, and difficulty in balancing mechanical strength and filtration performance in traditional PVDF ultrafiltration membranes. This membrane combines good hydrophilicity, fouling resistance, mechanical stability, and high-efficiency retention and filtration performance to meet the needs of water treatment and extend the membrane's service life.

[0007] The second objective of this invention is to provide a method for preparing the above-mentioned modified PVDF hollow fiber ultrafiltration membrane. This method is simple to operate, operates under mild conditions, and will not cause harm to the environment, thus achieving a green and environmentally friendly production process.

[0008] To achieve the above-mentioned objectives of this invention, the following technical solution is adopted: A modified PVDF hollow fiber ultrafiltration membrane is mainly made from the following raw materials by mass percentage: 0.5-2.0% zirconium α-phosphate, 14-18% polyvinylidene fluoride, 4-6% pore-forming agent, and 74-81.5% dimethylacetamide.

[0009] Preferably, by mass percentage: 0.8-1.5% zirconium α-phosphate, 15-17% polyvinylidene fluoride, 4.5-5.5% porogen, and 76-79% dimethylacetamide.

[0010] Preferably, by mass percentage: 1.0% zirconium α-phosphate, 16% polyvinylidene fluoride, 5% porogen, and 78% dimethylacetamide.

[0011] Preferably, the porogen is any one of PVP-K30, PVP-K17, PVP-K90, PEG2000, PEG400, PEG600, PEG800, and PEG1000.

[0012] Among the aforementioned raw materials, each component plays a unique and synergistic role. Polyvinylidene fluoride (PVDF), as the film-forming matrix material, provides the structural framework and basic mechanical strength of the membrane; pore-forming agents (such as PVP or PEG series) are extracted during phase separation to form the initial pore structure, which is crucial for pore formation; dimethylacetamide (DMAC), as a solvent, ensures that all components are fully dissolved and form a uniform and stable spinning solution, providing a foundation for the phase separation process; α-zirconium phosphate (α-ZrP) nanosheets, as a functional additive, not only guide the formation of a continuous sponge-like pore structure through their surface P-OH groups, but also regulate phase separation kinetics, promote the formation of gradient pores, and synergistically enhance the membrane's permeability, flux, and mechanical stability in conjunction with the pore-forming agents.

[0013] In this invention, α-zirconium phosphate (α-ZrP), as a key functional additive, plays multiple regulatory roles in the membrane formation process and is the core of achieving high-performance PVDF hollow fiber ultrafiltration membranes. First, the P-OH groups abundant on the surface of α-ZrP have strong hydrophilicity, serving as nucleation sites for "water channels" during phase separation. This guides the directional migration and distribution of water molecules within the membrane, promoting the formation of a well-connected, sponge-like pore structure, rather than the large pores or finger-like pores easily generated in traditional non-solvent-induced phase separation (NIPS). Second, α-ZrP accumulates at the phase separation interface, effectively slowing down the mass transfer rate between the solvent dimethylacetamide and the non-solvent, inducing a "delayed phase separation" effect. This delay is beneficial for forming a gradient pore structure with gradually decreasing pore size from the outer to the inner surface of the membrane, enhancing the membrane's mechanical stability and optimizing its separation performance. Furthermore, there is a synergistic effect between α-ZrP and traditional pore-forming agents: pore-forming agents are mainly responsible for inducing pore formation, while α-ZrP regulates the morphology, connectivity and distribution of pores. The combination of the two achieves a "1+1>2" effect, which not only significantly improves the membrane flux and rejection rate, but also enhances its long-term operational stability.

[0014] The present invention also provides a method for preparing the above-mentioned modified PVDF hollow fiber ultrafiltration membrane, comprising the following steps: Polyvinylidene fluoride, a pore-forming agent, and zirconium α-phosphate were added together to a solvent containing dimethylacetamide, heated and stirred until completely dissolved, and then degassed under vacuum to obtain a homogeneous spinning solution. The spinning solution is injected into the spinning nozzle and extruded through the spinneret into the coagulation bath to complete phase separation and solidification, thereby obtaining a nascent hollow fiber membrane. The nascent hollow fiber membrane is soaked and washed, then subjected to pore preservation treatment and dried to obtain the final product.

[0015] Preferably, the temperature is controlled at 60-65°C during the heating and stirring process until completely dissolved.

[0016] Preferably, when the spinning solution is extruded through the spinneret, the spinning speed is controlled to be 1.5-2.5 m / min.

[0017] Preferably, the coagulation bath is composed of dimethylacetamide and pure water in a volume ratio of 85:15, and the temperature of the coagulation bath is controlled at 30-35°C.

[0018] Through the meticulously designed preparation steps described above in this invention, the efficient preparation of modified PVDF hollow fiber ultrafiltration membranes is achieved. This invention also provides an application of a modified PVDF hollow fiber ultrafiltration membrane in water treatment.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention overcomes the challenge of balancing flux and strength in traditional PVDF ultrafiltration membranes. By innovatively introducing α-zirconium phosphate nanosheets, the mechanical properties of the membrane are significantly enhanced while maintaining high porosity, solving the problem that conventional additives struggle to achieve both porous structure and mechanical strength. Simultaneously, the synergistic effect of functional components—organic porogen constructing the basic pore structure, and α-zirconium phosphate precisely controlling the pore morphology and distribution—is achieved. These two elements complement each other, enabling the membrane to possess both an ideal three-dimensional pore structure and excellent physical properties. This results in a high-performance ultrafiltration membrane that combines high water flux, excellent mechanical strength, and good stability.

[0020] In terms of preparation, the raw materials used in this invention are readily available, and the preparation process requires no special equipment or complex procedures. A high-performance separation membrane can be obtained simply through a reasonable formulation and spinning process. This simple and efficient preparation method significantly reduces production costs. Detailed Implementation

[0021] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0022] Example 1 The modified PVDF hollow fiber ultrafiltration membrane preparation process in this embodiment is carried out according to the following steps: Weigh out 320 g of PVDF resin powder, 100 g of PVP-K30, 20 g of α-zirconium phosphate nanosheets and 1560 g of DMAC; The weighed α-zirconium phosphate nanosheets and a portion of DMAC were placed in a mixing container. Under constant temperature of 60°C, the mixture was mechanically stirred at 300 rpm until completely dissolved, ensuring the α-zirconium phosphate nanosheets were fully dispersed in the DMAC to form a homogeneous and stable milky white dispersion with a solid content of 1.5 wt%. This dispersion was sealed and stored for later use. The prepared α-zirconium phosphate dispersion, along with weighed PVDF resin powder and PVP-K30 material, were added all at once to a mixing tank equipped with heating and mechanical stirring. The mixture was stirred continuously at a constant temperature of 60°C for 10 hours until the PVDF resin powder was completely dissolved, resulting in a homogeneous, transparent, and viscous spinning solution. Heating was then stopped, and the spinning solution underwent vacuum degassing for 6 hours to remove air bubbles trapped during stirring, thus obtaining a homogeneous spinning solution. Using a spinning device, the pretreated homogeneous spinning solution is uniformly coated onto the fiber liner through a spinning nozzle at a spinning speed of 2 m / min, ensuring the formation of a uniform film on the surface of the fiber liner; the spun-coated fiber liner is then subjected to phase separation and solidification in a coagulation bath at 35°C (water / DMAC=85 / 15 vol%), ensuring the formation of a stable nascent hollow fiber membrane structure; The nascent hollow fiber membrane is guided through a pure water bath for thorough immersion and washing to preserve its pores; subsequently, the membrane is air-dried at room temperature to obtain the final product.

[0023] Example 2 The modified PVDF hollow fiber ultrafiltration membrane preparation process in this embodiment is carried out according to the following steps: Weigh out 320 g of PVDF resin powder, 100 g of PVP-K30, 30 g of α-zirconium phosphate nanosheets and 1550 g of DMAC; The weighed α-zirconium phosphate nanosheets and a portion of DMAC were placed in a mixing container. Under constant temperature of 60°C, the mixture was mechanically stirred at 300 rpm until completely dissolved, ensuring the α-zirconium phosphate nanosheets were fully dispersed in the DMAC to form a homogeneous and stable milky white dispersion with a solid content of 1.5 wt%. This dispersion was sealed and stored for later use. The prepared α-zirconium phosphate dispersion, along with weighed PVDF resin powder and PVP-K30 material, were added all at once to a mixing tank equipped with heating and mechanical stirring. The mixture was stirred continuously at a constant temperature of 60°C for 10 hours until the PVDF resin powder was completely dissolved, resulting in a homogeneous, transparent, and viscous spinning solution. Heating was then stopped, and the spinning solution underwent vacuum degassing for 6 hours to remove air bubbles trapped during stirring, thus obtaining a homogeneous spinning solution. Using a spinning device, the pretreated homogeneous spinning solution is uniformly coated onto the fiber liner through a spinning nozzle at a spinning speed of 2 m / min, ensuring the formation of a uniform film on the surface of the fiber liner; the spun-coated fiber liner is then subjected to phase separation and solidification in a coagulation bath at 35°C (water / DMAC=85 / 15 vol%), ensuring the formation of a stable nascent hollow fiber membrane structure; The nascent hollow fiber membrane is guided through a pure water bath for thorough immersion and washing to preserve its pores; subsequently, the membrane is air-dried at room temperature to obtain the final product.

[0024] Example 3 The modified PVDF hollow fiber ultrafiltration membrane preparation process in this embodiment is carried out according to the following steps: Weigh out 360 g of PVDF resin powder, 80 g of PVP-K17, 10 g of α-zirconium phosphate nanosheets and 1580 g of DMAC; The weighed α-zirconium phosphate nanosheets and a portion of DMAC were placed in a mixing container. Under constant temperature of 60°C, the mixture was mechanically stirred at 300 rpm until completely dissolved, ensuring the α-zirconium phosphate nanosheets were fully dispersed in the DMAC to form a homogeneous and stable milky white dispersion with a solid content of 1.5 wt%. This dispersion was sealed and stored for later use. The prepared α-zirconium phosphate dispersion, along with weighed PVDF resin powder and PVP-K17 material, were added all at once to a mixing tank equipped with heating and mechanical stirring. The mixture was stirred continuously at a constant temperature of 65°C for 10 hours until the PVDF resin powder was completely dissolved, resulting in a homogeneous, transparent, and viscous spinning solution. Heating was then stopped, and the spinning solution underwent vacuum degassing for 6 hours to remove air bubbles trapped during stirring, thus obtaining a homogeneous spinning solution. Using a spinning device, the pretreated homogeneous spinning solution is uniformly coated onto the fiber liner through a spinning nozzle at a spinning speed of 1.5 m / min, ensuring the formation of a uniform film on the surface of the fiber liner. The spun-coated fiber liner is then subjected to phase separation and solidification in a coagulation bath at 30°C (water / DMAC=85 / 15 vol%), ensuring the formation of a stable nascent hollow fiber membrane structure. The nascent hollow fiber membrane is guided through a pure water bath for thorough immersion and washing to preserve its pores; subsequently, the membrane is air-dried at room temperature to obtain the final product.

[0025] Example 4 The modified PVDF hollow fiber ultrafiltration membrane preparation process in this embodiment is carried out according to the following steps: Weigh out 340 g of PVDF resin powder, 120 g of PVP-K90, 25 g of α-zirconium phosphate nanosheets and 1520 g of DMAC; The weighed α-zirconium phosphate nanosheets and a portion of DMAC were placed in a mixing container. Under constant temperature of 60°C, the mixture was mechanically stirred at 300 rpm until completely dissolved, ensuring the α-zirconium phosphate nanosheets were fully dispersed in the DMAC to form a homogeneous and stable milky white dispersion with a solid content of 1.5 wt%. This dispersion was sealed and stored for later use. The prepared α-zirconium phosphate dispersion, along with weighed PVDF resin powder and PVP-K90 material, were added all at once to a mixing tank equipped with heating and mechanical stirring. The mixture was stirred continuously at a constant temperature of 63°C for 10 hours until the PVDF resin powder was completely dissolved, resulting in a homogeneous, transparent, and viscous spinning solution. Heating was then stopped, and the spinning solution underwent vacuum degassing for 6 hours to remove air bubbles trapped during stirring, thus obtaining a homogeneous spinning solution. Using a spinning device, the pretreated homogeneous spinning solution is uniformly coated onto the fiber liner through a spinning nozzle at a spinning speed of 2.5 m / min, ensuring the formation of a uniform film on the surface of the fiber liner. The spun-coated fiber liner is then subjected to phase separation and solidification in a coagulation bath at 33°C (water / DMAC=85 / 15 vol%), ensuring the formation of a stable nascent hollow fiber membrane structure. The nascent hollow fiber membrane is guided through a pure water bath for thorough immersion and washing to preserve its pores; subsequently, the membrane is air-dried at room temperature to obtain the final product.

[0026] Example 5 The modified PVDF hollow fiber ultrafiltration membrane preparation process in this embodiment is carried out according to the following steps: Weigh out 280 g of PVDF resin powder, 110 g of PEG400, 16 g of α-zirconium phosphate nanosheets and 1630 g of DMAC; The weighed α-zirconium phosphate nanosheets and a portion of DMAC were placed in a mixing container. Under constant temperature of 60°C, the mixture was mechanically stirred at 300 rpm until completely dissolved, ensuring the α-zirconium phosphate nanosheets were fully dispersed in the DMAC to form a homogeneous and stable milky white dispersion with a solid content of 1.5 wt%. This dispersion was sealed and stored for later use. The prepared α-zirconium phosphate dispersion, along with weighed PVDF resin powder and PEG400 material, were added all at once to a mixing tank equipped with heating and mechanical stirring. The mixture was stirred continuously at a constant temperature of 60°C for 10 hours until the PVDF resin powder was completely dissolved, resulting in a homogeneous, transparent, and viscous spinning solution. Heating was then stopped, and the spinning solution underwent vacuum degassing for 6 hours to remove air bubbles trapped during stirring, thus obtaining a homogeneous spinning solution. Using a spinning device, the pretreated homogeneous spinning solution is uniformly coated onto the fiber liner through a spinning nozzle at a spinning speed of 2 m / min, ensuring the formation of a uniform film on the surface of the fiber liner; the spun-coated fiber liner is then subjected to phase separation and solidification in a coagulation bath at 35°C (water / DMAC=85 / 15 vol%), ensuring the formation of a stable nascent hollow fiber membrane structure; The nascent hollow fiber membrane is guided through a pure water bath for thorough immersion and washing to preserve its pores; subsequently, the membrane is air-dried at room temperature to obtain the final product.

[0027] Example 6 The modified PVDF hollow fiber ultrafiltration membrane preparation process in this embodiment is carried out according to the following steps: Weigh out 300 g of PVDF resin powder, 90 g of PEG800, 40 g of α-zirconium phosphate nanosheets and 1480 g of DMAC; The weighed α-zirconium phosphate nanosheets and a portion of DMAC were placed in a mixing container. Under constant temperature of 60°C, the mixture was mechanically stirred at 300 rpm until completely dissolved, ensuring the α-zirconium phosphate nanosheets were fully dispersed in the DMAC to form a homogeneous and stable milky white dispersion with a solid content of 1.5 wt%. This dispersion was sealed and stored for later use. The prepared α-zirconium phosphate dispersion, along with weighed PVDF resin powder and PEG800 material, were added all at once to a mixing tank equipped with heating and mechanical stirring. The mixture was stirred continuously at a constant temperature of 63°C for 10 hours until the PVDF resin powder was completely dissolved, resulting in a homogeneous, transparent, and viscous spinning solution. Heating was then stopped, and the spinning solution underwent vacuum degassing for 6 hours to remove air bubbles trapped during stirring, thus obtaining a homogeneous spinning solution. Using a spinning device, the pretreated homogeneous spinning solution is uniformly coated onto the fiber liner through a spinning nozzle at a spinning speed of 2 m / min, ensuring the formation of a uniform film on the surface of the fiber liner; the spun-coated fiber liner is then subjected to phase separation and solidification in a coagulation bath at 30°C (water / DMAC=85 / 15 vol%), ensuring the formation of a stable nascent hollow fiber membrane structure; The nascent hollow fiber membrane is guided through a pure water bath for thorough immersion and washing to preserve its pores; subsequently, the membrane is air-dried at room temperature to obtain the final product.

[0028] Comparative Example 1 The preparation steps of the modified PVDF hollow fiber ultrafiltration membrane are basically the same as those in Example 1, except that α-zirconium phosphate nanosheets are not added.

[0029] Comparative Example 2 The preparation steps of the modified PVDF hollow fiber ultrafiltration membrane are basically the same as those in Example 1, except that an equal amount of TiO2 nanoparticles are used to replace the α-zirconium phosphate nanosheets.

[0030] Comparative Example 3 The preparation steps of the modified PVDF hollow fiber ultrafiltration membrane are basically the same as those in Example 1, except that the amount of α-zirconium phosphate nanosheets added is changed to 10%.

[0031] Experimental Example 1 The modified PVDF hollow fiber ultrafiltration membranes prepared in each example and comparative example were subjected to certain performance tests. PVDF hollow fiber ultrafiltration membrane samples prepared in Example 1, Example 2, and Comparative Example 1 were cut into membrane modules of effective length. A 5 g / L aqueous solution of polyethylene oxide with a molecular weight of 100,000 was prepared as the feed liquid. The test results are shown in Table 1.

[0032] Table 1. Test Results

[0033] Based on the above data, the following conclusions can be drawn: The modified PVDF hollow fiber ultrafiltration membranes prepared in Examples 1-6 of this invention exhibit superior performance in both pure water flux and retention rate compared to Comparative Example 1 (conventional formulation membrane). This means that the technical solution of this invention, by introducing α-zirconium phosphate as a functional additive, successfully achieves a significant improvement in the performance of PVDF ultrafiltration membranes. Experimental data clearly show that when the amount of α-ZrP added is within an appropriate range, the membrane performance is comprehensively optimized. Example 1 demonstrates the best overall performance, achieving a pure water flux of 5.4 LMH / kPa while maintaining a high retention rate of 98.3%. Compared to Comparative Example 1 without any inorganic filler, the examples of this invention show a 42%-63% increase in pure water flux, fully demonstrating the unique role of α-ZrP in improving membrane pore structure and increasing water flux. More importantly, compared to Comparative Example 2 using conventional TiO2 filler, the α-ZrP-modified membrane exhibits superior flux performance at the same addition amount, indicating that the layered structure and surface properties of α-ZrP nanosheets have irreplaceable advantages in regulating membrane pore structure. More importantly, there is a clearly defined optimal range for the amount of α-ZrP added. When the amount added is too low, the performance improvement is limited; while when the amount added is too high (e.g., in Comparative Example 3, the amount added is 200g / 2000g), it leads to a decrease in membrane performance, with the flux dropping to 3.5 LMH / kPa and the retention rate significantly decreasing to 92.0%, which may be due to structural defects caused by nanoparticle aggregation. This invention, by precisely controlling the amount of α-ZrP added, significantly improves the flux performance of the membrane while maintaining a high retention rate, successfully solving the technical problem of traditional PVDF ultrafiltration membranes in balancing flux and retention rate.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A modified PVDF hollow fiber ultrafiltration membrane, characterized in that, It is mainly made from the following raw materials by mass percentage: 0.5-2.0% zirconium α-phosphate, 14-18% polyvinylidene fluoride, 4-6% pore-forming agent, and 74-81.5% dimethylacetamide.

2. The modified PVDF hollow fiber ultrafiltration membrane according to claim 1, characterized in that, By mass percentage: 0.8-1.5% zirconium α-phosphate, 15-17% polyvinylidene fluoride, 4.5-5.5% porogen, and 76-79% dimethylacetamide.

3. The modified PVDF hollow fiber ultrafiltration membrane according to claim 1, characterized in that, By mass percentage: 1.0% zirconium α-phosphate, 16% polyvinylidene fluoride, 5% porogen, and 78% dimethylacetamide.

4. The modified PVDF hollow fiber ultrafiltration membrane according to claim 1, characterized in that, The porogen is any one of PVP-K30, PVP-K17, PVP-K90, PEG2000, PEG400, PEG600, PEG800, and PEG1000.

5. A method for preparing a modified PVDF hollow fiber ultrafiltration membrane as described in any one of claims 1-4, characterized in that, Includes the following steps: Polyvinylidene fluoride, a pore-forming agent, and zirconium α-phosphate were added together to a solvent containing dimethylacetamide, heated and stirred until completely dissolved, and then degassed under vacuum to obtain a homogeneous spinning solution. The spinning solution is injected into the spinning nozzle and extruded through the spinneret into the coagulation bath to complete phase separation and solidification, thereby obtaining a nascent hollow fiber membrane. The nascent hollow fiber membrane is soaked and washed, then subjected to pore preservation treatment and dried to obtain the final product.

6. The method for preparing the modified PVDF hollow fiber ultrafiltration membrane according to claim 5, characterized in that, The temperature is controlled at 60-65℃ during the heating and stirring process until completely dissolved.

7. The method for preparing the modified PVDF hollow fiber ultrafiltration membrane according to claim 5, characterized in that, When the spinning solution is extruded through the spinneret, the spinning speed is controlled to be 1.5-2.5 m / min.

8. The method for preparing the modified PVDF hollow fiber ultrafiltration membrane according to claim 5, characterized in that, The coagulation bath is composed of dimethylacetamide and pure water in a volume ratio of 85:15, and the temperature of the coagulation bath is controlled at 30-35℃.

9. The application of the modified PVDF hollow fiber ultrafiltration membrane prepared by the method according to any one of claims 1-4 or according to any one of claims 5-8 in water treatment.

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