A melt-drawing preparation method of aramid pulp embedded PVDF hollow fiber microfiltration membrane

Abstract

The application discloses a kind of aramid pulp embedded type PVDF hollow fiber microfiltration membrane melt-stretching preparation method, with polyvinylidene fluoride (PVDF) as matrix phase, using two soluble polymers and insoluble polymer as composite pore forming agent, and doping aramid pulp as dispersed phase, titanium dioxide as additive, by melt spinning method to obtain nascent hollow fiber membrane;Then, the nascent membrane is post-treated, the nascent membrane is soaked in clean water, the composite pore forming agent is dissolved out, and the dissolution hole is formed, so as to form a stable multiple pore structure.The method does not add any organic solvent and etching liquid, uses composite pore forming agent and stretches the process after aramid pulp cooperation to obtain hollow fiber membrane, avoids the discharge of organic wastewater in the process of PVDF spinning membrane, and the mechanical property of hollow fiber membrane is good, and the pure water flux is relatively high.

Description

Technical Field

[0001] This invention belongs to the field of hollow fiber membrane technology, specifically relating to a melt-stretching preparation method for an aramid pulp-embedded PVDF hollow fiber microfiltration membrane. Background Technology

[0002] Membrane separation technology has seen widespread application in water treatment due to its green, environmentally friendly, and efficient characteristics. PVDF, with its excellent mechanical strength, oxidation resistance, and chemical corrosion resistance, has become the most popular membrane material and is widely used in the preparation of microfiltration and ultrafiltration membranes. However, PVDF is soluble in many organic solvents at room temperature or low temperatures, therefore, non-solvent-induced phase separation (NIPS) or thermally induced phase separation (TIPS) methods are commonly used to prepare PVDF hollow fiber membranes. Various solvents or diluents, such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), and dioctyl phthalate (DOP), are typically used in the preparation process, generating large amounts of difficult-to-recover industrial wastewater and wasting water resources. Currently, some researchers are attempting to use low-toxicity or even non-toxic organic solvents and diluents to achieve a green membrane preparation process. However, these methods can only reduce the harm of wastewater to human health and the environment during membrane preparation; they cannot completely solve the problem of wastewater generation and recycling.

[0003] Therefore, designing a green membrane fabrication process is crucial in this context. Compared to NIPS and TIPS processes, melt spinning and stretching (MS-S) technology is a relatively green membrane preparation process. The melt spinning-stretching method involves extruding a polymer melt through a spinneret under high-temperature shear, followed by cooling and solidification. Post-stretching then separates the lamellar structures in the nascent hollow fiber membrane, which are arranged parallel to the extrusion direction, to form pores. However, the porosity and pore connectivity of membranes obtained through this method are lower than those prepared by the NIPS method, resulting in lower water flux in the hollow fiber porous membrane, and its performance needs further improvement.

[0004] To address the aforementioned issues, researchers are dedicated to finding a green, pollution-free, and stable method for preparing PVDF hollow fiber membranes with relatively high pure water flux, which can reduce or even eliminate pollution problems during membrane preparation while ensuring good physicochemical properties of the membrane. Summary of the Invention

[0005] One objective of this invention is to provide a melt-stretch preparation method for aramid pulp-embedded PVDF hollow fiber microfiltration membranes, in order to solve the problem that existing membrane preparation methods cannot simultaneously achieve good water flux and high strength of the membrane.

[0006] Another objective of this invention is to provide a PVDF hollow fiber membrane with relatively high pure water flux prepared by the above method, so as to solve the problems of poor mechanical properties, low membrane flux, and instability of hollow fiber membranes prepared by the prior art.

[0007] Therefore, the present invention adopts the following technical solution:

[0008] A melt-stretching method for preparing an aramid pulp-embedded PVDF hollow fiber microfiltration membrane includes the following steps:

[0009] (1) Material mixing: PVDF (polyvinylidene fluoride) is used as the matrix phase, soluble inorganic substances and two soluble polymers are used as composite pore-forming agents, aramid pulp is used as the dispersed phase, and titanium dioxide is used as an additive. The materials are mixed evenly in proportion using a high-speed mixer to obtain spinning raw materials and a uniformly mixed material.

[0010] (2) Melt spinning: The material obtained in step (1) is fed into a twin-screw extruder for melt granulation, then mixed and heated by the twin-screw extruder at high temperature, and the spinning melt is quantitatively extruded through a hollow spinneret. Air is introduced into the hollow spinneret, and the spinning melt is solidified in an air bath to obtain a nascent hollow fiber membrane.

[0011] (3) Post-processing: After the nascent hollow fiber membrane is dried in air, it is then soaked in water at 70°C for 24 hours to dissolve the soluble inorganic substances and two soluble polymers. It is then dried in an oven and preheated for 2-4 hours, and then hot-stretched to a certain multiple at a certain rate to obtain a stretched hollow fiber membrane. The preheating temperature and the hot stretching temperature are the same, resulting in a PVDF hollow fiber membrane with a relatively high pure water flux.

[0012] Preferably, in step (1), the soluble inorganic substance is at least one of sodium chloride, calcium chloride, or magnesium chloride.

[0013] Preferably, in step (1), the soluble polymer is at least two of polyethylene oxide, polyethylene glycol, polyacrylamide, or polyvinylpyrrolidone.

[0014] Preferably, in step (1), the aramid pulp fiber has a diameter of 7-15 μm and a length of 0.5-2.5 mm.

[0015] Preferably, in step (1), the titanium dioxide is rod-shaped TiO2 with a length of 130-150 nm and a diameter of 20-30 nm.

[0016] Preferably, the PVDF matrix phase has a mass fraction of 40–65 wt%, the soluble inorganic matter has a mass fraction of 15–30 wt%, the soluble polymer has a mass fraction of 15–30 wt%, the aramid pulp has a mass fraction of 0.5–2 wt%, the titanium dioxide has a mass fraction of 0–3 wt%, and the sum of the mass fractions of all components is 100 wt%.

[0017] Preferably, in step (2), the melt temperature is 220–250°C.

[0018] Preferably, the rate of thermal stretching in step (3) is 10 to 20 mm / min.

[0019] Preferably, the thermal stretching ratio in step (3) is 100-200%.

[0020] Preferably, the preheating temperature and hot stretching temperature in step (3) are 90 to 120°C.

[0021] In step (3), the stretched hollow fiber membrane has a multi-pore structure, including circular micropores formed by the dissolution of soluble inorganic substances, vertical continuous macropores formed by two soluble organic substances wrapping inorganic substances during the melting process, and vertical continuous micropores formed by the dissolution of two soluble organic substances. In addition, due to the addition of aramid pulp, interfacial pores can be formed along the stretching direction during the hot stretching process.

[0022] An aramid pulp-embedded PVDF hollow fiber microfiltration membrane was prepared using the above method. This membrane has a multi-pore structure, comprising circular micropores formed by the dissolution of soluble inorganic substances, vertically continuous macropores formed by two soluble organic substances encapsulating inorganic substances during melting, and vertically continuous micropores formed by the dissolution of two soluble organic substances. Furthermore, the addition of aramid pulp allows for the formation of interfacial pores along the stretching direction during thermal stretching. The membrane has a pure water flux of 500–3000 L / m³. 2 The average pore size of the multi-porous structure ranges from 0.4 to 2 μm, the tensile strength of the membrane is 25 to 80 MPa, the water contact angle of the membrane is less than 100°, and the SiO2 rejection rate is greater than 80%.

[0023] The beneficial effects of this invention are as follows: This invention employs a combination of melt spinning and post-stretching to prepare PVDF hollow fiber membranes with high pure water flux and multiple pores, doped with aramid pulp. From the perspective of the film-forming process, this invention uses aramid pulp doping and selects soluble organic matter and two soluble polymers as composite pore-forming agents. No organic solvents or etching solutions are added during the preparation process. The hollow fiber membrane is obtained through dissolution pore-forming and post-stretching processes, avoiding the discharge of organic wastewater during PVDF spinning and membrane production. This method is stable, feasible, green, and environmentally friendly, with no environmental pollution.

[0024] From the prepared hollow fiber membrane structure, this invention employs a composite pore-forming agent and doped aramid pulp, resulting in the composite pore-forming agent dissolving and leaving multiple uniform macropores on the fiber membrane. The combination of the composite pore-forming agent provides favorable conditions for subsequent multi-pore formation. In the post-stretching process, the aramid pulp, with its numerous fibrillated fibers embedded in the PVDF matrix, increases the size of the PVDF interface pores along the stretching direction during the stretching process. This is significantly different from traditional particle-based pore-forming methods, enhancing the continuity between membrane pores and the pore density per unit area. Simultaneously, the rigidity of the aramid pulp ensures the strength of the hollow fiber membrane. The addition of rod-shaped TiO2 promotes the formation of the β-crystal structure in the PVDF hollow fiber membrane, enhancing elasticity and extending the membrane's service life.

[0025] The aramid pulp-embedded PVDF hollow fiber microfiltration membrane of this invention has a multi-pore structure with a pore size range of 0.4–2 μm, and the high-strength, high-flux PVDF hollow fiber membrane doped with aramid pulp has a pure water flux of 500–3000 L / m³. 2 •h, fracture strength is 25-80 MPa, water contact angle is less than 100°, and SiO2 retention rate is >80%. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below, wherein:

[0027] Figure 1 This is a scanning electron microscope image of the outer surface of the PVDF hollow fiber membrane prepared in Example 1.

[0028] Figure 2 The image shows a cross-sectional electron microscope image of the PVDF hollow fiber membrane prepared in Example 1. Detailed Implementation

[0029] To make the above-mentioned objectives, 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 specific examples.

[0030] Example 1:

[0031] A melt-stretching method for preparing an aramid pulp-embedded PVDF hollow fiber microfiltration membrane includes the following steps:

[0032] (1) Material mixing: PVDF is used as the matrix phase, soluble inorganic matter (MgCl2) and two soluble polymers (PAM, PVP) are used as composite pore-forming agents, and aramid pulp is used as the dispersed phase. The materials are mixed evenly using a high-speed mixer according to the following mass fractions: PVDF (Solvay 6010), MgCl2, PAM (polyacrylamide, average molecular weight 1 million), PVP (polyvinylpyrrolidone, average molecular weight 58,000), and aramid pulp 1F538. The resulting spinning raw material is a uniformly mixed material.

[0033] (2) Melt spinning: The material obtained in step (1) is fed into a twin-screw extruder (SHJ-20, Jiangsu Qijie Machinery Co., Ltd.) for melt granulation, and after blending, it is heated at high temperature by the twin screw and quantitatively extruded into a spinning melt (approximately 2.6 mm in diameter) through a hollow spinneret assembly (spinneret diameter 2.85 mm). The temperature of each zone of the twin screw is: zone 1 160℃, zone 2 180℃, zone 3 220℃, zone 4 220℃, zone 5 230℃, zone 6 230℃, zone 7 230℃, zone 8 230℃, and zone 9 230℃. Air is introduced into the hollow spinneret assembly, and the spinning melt is solidified in the air bath to obtain a nascent hollow fiber membrane (membrane thickness 0.35 mm).

[0034] (3) Post-treatment: After the nascent hollow fiber membrane is dried in air, it is then soaked in water at 70°C for 24 hours to dissolve the soluble inorganic substances and two soluble polymers. After drying in an oven at 90°C and preheating for 2-4 hours, it is stretched at 110°C to an elongation of 100% (based on the length of the nascent hollow fiber membrane, the elongation is 100% when stretched to twice the length of the nascent hollow fiber membrane). The stretching rate is 10 mm / min to obtain the stretched hollow fiber membrane, which is a PVDF hollow fiber membrane with a relatively high pure water flux.

[0035] The pure water flux of the PVDF hollow fiber membrane was tested at 0.1 MPa and the measured flux was 1850 L / m³. 2 The pore size of the hollow fiber membrane was measured to be 1.03 μm; the tensile strength of the PVDF hollow fiber membrane obtained at a clamping distance of 10 cm and a tensile speed of 10 mm / min was 69.7 MPa; the water contact angle of the PVDF hollow fiber membrane surface measured using a contact angle meter was 98.1°; the water contact angle of the PVDF hollow fiber membrane against SiO2 (0.1 g·L⁻¹) was tested at room temperature and operating pressure of 0.1 MPa.-1 The retention rate of the suspension (800nm) was 98.8%.

[0036] The outer surface of the prepared PVDF hollow fiber membrane was scanned by electron microscopy, and the results are as follows: Figure 1 As shown, from Figure 1 It can be seen that the PVDF hollow fiber membrane prepared in this embodiment has a multi-pore structure, including circular micropores formed by the dissolution of soluble inorganic substances, vertical continuous macropores formed by two soluble organic substances wrapping inorganic substances during the melting process, and vertical continuous micropores formed by the dissolution of two soluble organic substances. In addition, due to the addition of aramid pulp, interfacial pores can be formed along the stretching direction during the hot stretching process.

[0037] The cross-section of the prepared PVDF hollow fiber membrane was scanned by electron microscopy, and the results are as follows: Figure 2 As shown, from Figure 2 As can be seen, the pore structure of the hollow fiber membrane cross-section with added aramid pulp is poor. The poor compatibility between PVDF and aramid pulp stems from the fact that PTA molecular chains are rigid and difficult to bend and fold, resulting in a small molecular contact area between PVDF and flexible PVDF molecular chains, making it difficult to form intermolecular forces. Furthermore, aramid fibers do not melt during processing, allowing their surface fuzzy structure to be completely preserved in the nascent membrane. The abundant surface fuzz enhances the continuity between membrane pores, and the highly fibrillated nature of aramid pulp results in a surface rich in fuzz. Therefore, aramid pulp fibers are embedded in the PVDF matrix, forming numerous protruding flocculent structures.

[0038] Example 2:

[0039] A melt-stretching method for preparing an aramid pulp-embedded PVDF hollow fiber microfiltration membrane includes the following steps:

[0040] (1) Material mixing: PVDF is used as the matrix phase, soluble inorganic substances and two soluble polymers are used as composite pore-forming agents, and aramid pulp is used as the dispersed phase. The PVDF (Solvay 6010), 20.0 wt% CaCl2, 13.5 wt% PEO (polyethylene oxide, average molecular weight 1,000,000), 10.0 wt% PEG (polyethylene glycol, average molecular weight 20,000), and 1.0 wt% aramid pulp 1F1710 are mixed evenly using a high-speed mixer to obtain spinning raw materials and a uniformly mixed material.

[0041] (2) Melt spinning: The material obtained in step (1) is fed into a twin-screw extruder (SHJ-20, Jiangsu Qijie Machinery Co., Ltd.) for melt granulation, and after blending, it is heated at high temperature by the twin screw and quantitatively extruded into a spinning melt (diameter of 2.6 mm) through a hollow spinneret assembly (spinneret diameter 2.85 mm). The temperature of each zone of the twin screw is: zone 1 160℃, zone 2 180℃, zone 3 220℃, zone 4 220℃, zone 5 230℃, zone 6 230℃, zone 7 230℃, zone 8 230℃, zone 9 230℃. Air is introduced into the hollow spinneret assembly, and the spinning melt is solidified in the air bath to obtain a nascent hollow fiber membrane (membrane thickness of 0.34 mm).

[0042] (3) Post-processing: After the nascent hollow fiber membrane is dried in air, it is then soaked in water at 70°C for 24 hours to dissolve the soluble inorganic substances and two soluble polymers. It is then dried in an oven at 90°C and preheated for 24 hours. Finally, it is hot-stretched at 100°C to an elongation of 150% (based on the length of the nascent hollow fiber membrane, stretched to 2.5 times the length of the nascent hollow fiber membrane, i.e., an elongation of 150%). The stretching rate is 10 mm / min to obtain the stretched hollow fiber membrane, which is a PVDF hollow fiber membrane with a relatively high pure water flux.

[0043] The pure water flux of the PVDF hollow fiber membrane was tested at 0.1 MPa and the measured flux was 2445 L / m³. 2 The pore size of the hollow fiber membrane was measured to be 1.14 μm; the tensile strength of the PVDF hollow fiber membrane obtained at a clamping distance of 10 cm and a tensile speed of 10 mm / min was 72.4 MPa; the water contact angle of the PVDF hollow fiber membrane surface measured using a contact angle meter was 92.2°; the water contact angle of the PVDF hollow fiber membrane against SiO2 (0.1 g·L⁻¹) was tested at room temperature and an operating pressure of 0.1 MPa. -1 The retention rate of the suspension (800 nm) was 85.3%.

[0044] Compared to Example 1, Example 2 increased the aramid pulp content to 1.0 wt%. With the increase in aramid pulp content, the cross-sectional surface pores of the membrane increased in size and pore structure. Furthermore, the increased aramid pulp content promoted the increase of surface-extended flocculent structures and the formation of interfacial pores. Therefore, the membrane pore size increased from 1.03 μm to 1.14 μm, and the flux also increased from 1850 L / m³. 2 h increased to 2445 L / m 2 Meanwhile, with the increase of aramid pulp content, the tensile strength of the hollow fiber membrane improved from 69.7 MPa to 72.4 MPa. Compared with Example 1, the water contact angle of the membrane decreased. When the aramid pulp content was 1.0 wt%, the SiO2 rejection rate was 85.3%.

[0045] Example 3:

[0046] A melt-stretching method for preparing an aramid pulp-embedded PVDF hollow fiber microfiltration membrane includes the following steps:

[0047] (1) Material mixing: PVDF is used as the matrix phase, soluble inorganic substances and two soluble polymers are used as composite pore-forming agents, and aramid pulp is used as the dispersed phase. The PVDF (Solvay 6010), NaCl, PAM 1000000, PVP 58000, and aramid pulp 1F538 are mixed evenly in proportion using a high-speed mixer to obtain spinning raw materials and a uniformly mixed material.

[0048] (2) Melt spinning: The material obtained in step (1) is fed into a twin-screw extruder (SHJ-20, Jiangsu Qijie Machinery Co., Ltd.) for melt granulation, and after blending, it is heated at high temperature by the twin screw and quantitatively extruded into a spinning melt (diameter of 2.6 mm) through a hollow spinneret assembly (spinneret diameter 2.85 mm). The temperature of each zone of the twin screw is: zone 1 160℃, zone 2 180℃, zone 3 220℃, zone 4 220℃, zone 5 230℃, zone 6 230℃, zone 7 230℃, zone 8 230℃, zone 9 230℃. Air is introduced into the hollow spinneret assembly, and the spinning melt is solidified in the air bath to obtain a nascent hollow fiber membrane (membrane thickness of 0.36 mm).

[0049] (3) Post-processing: After the nascent hollow fiber membrane is dried in air, it is then soaked in water at 70°C for 24 hours to dissolve the soluble inorganic substances and two soluble polymers. It is then dried in an oven at 90°C and preheated for 2-4 hours. Finally, it is hot-stretched at 110°C to an elongation of 100% (based on the length of the nascent hollow fiber membrane) at a stretching rate of 10 mm / min to obtain the stretched hollow fiber membrane, thus obtaining a PVDF hollow fiber membrane with relatively high pure water flux.

[0050] The pure water flux of the PVDF hollow fiber membrane was tested at 0.1 MPa and the measured flux was 2730 L / m³. 2 The pore size of the hollow fiber membrane was measured to be 1.21 μm; the tensile strength of the PVDF hollow fiber membrane obtained at a clamping distance of 10 cm and a tensile speed of 10 mm / min was 75.7 MPa; the water contact angle of the PVDF hollow fiber membrane surface measured using a contact angle meter was 88.3°; the water contact angle of the PVDF hollow fiber membrane against SiO2 (0.1 g·L⁻¹) was tested at room temperature and operating pressure of 0.1 MPa. -1The retention rate of the suspension (800 nm) was 95.2%.

[0051] Compared to Example 2, Example 3 increased the aramid pulp content to 1.5 wt%. With the increase in aramid pulp content, the cross-sectional surface pores of the membrane increased in size and pore structure. Furthermore, the increased aramid pulp content promoted the increase of surface-extended flocculent structures and the formation of interfacial pores. Therefore, the membrane pore size increased from 1.14 μm to 1.21 μm, and the flux also increased from 2445 L / m³. 2 h increased to 2730 L / m 2 Meanwhile, with the increase of aramid pulp content, the tensile strength of the hollow fiber membrane improved from 72.4 MPa to 75.7 MPa. Compared with Example 2, the water contact angle of the membrane decreased from 92.2° to 88.3°, and the SiO2 rejection rate increased from 85.3% to 95.2%.

[0052] Example 4:

[0053] A melt-stretching method for preparing an aramid pulp-embedded PVDF hollow fiber microfiltration membrane includes the following steps:

[0054] (1) Material mixing: PVDF is used as the matrix phase, soluble inorganic substances and two soluble polymers are used as composite pore-forming agents, aramid pulp is used as the dispersed phase, and titanium dioxide is used as an additive. The materials are mixed evenly using a high-speed mixer according to the following mass fractions: PVDF (Soval 6010), 23.0 wt% CaCl2, 11.0 wt% PEO 1000000, 8.0 wt% PEG 20000, 1.5 wt% aramid pulp 1F1710 and 2.0 wt% rod-shaped TiO2 (length 130-150 nm, diameter 20-30 nm). The resulting spinning raw material is a uniformly mixed material.

[0055] (2) Melt spinning: The material obtained in step (1) is fed into a twin-screw extruder (SHJ-20, Jiangsu Qijie Machinery Co., Ltd.) for melt granulation, and after blending, it is heated at high temperature by the twin screw and quantitatively extruded into a spinning melt (diameter of 2.6 mm) through a hollow spinneret assembly (spinneret diameter 2.85 mm). The temperature of each zone of the twin screw is: zone 1 160℃, zone 2 180℃, zone 3 220℃, zone 4 220℃, zone 5 230℃, zone 6 230℃, zone 7 230℃, zone 8 230℃, zone 9 230℃. Air is introduced into the hollow spinneret assembly, and the spun body is cured in the air bath to obtain a nascent hollow fiber membrane (membrane thickness of 0.35 mm).

[0056] (3) Post-processing: After the nascent hollow fiber membrane is dried in air, it is then soaked in water at 70°C for 24 hours to dissolve the soluble inorganic substances and two soluble polymers. It is then dried in an oven at 90°C and preheated for 24 hours. Finally, it is hot-stretched at 110°C to an elongation of 100% (based on the length of the nascent hollow fiber membrane) at a stretching rate of 10 mm / min to obtain the stretched hollow fiber membrane, thus obtaining a PVDF hollow fiber membrane with a relatively high pure water flux.

[0057] The pure water flux of the PVDF hollow fiber membrane was tested at 0.1 MPa and the measured flux was 2935 L / m³. 2 The pore size of the hollow fiber membrane was measured to be 1.35 μm; the tensile strength of the PVDF hollow fiber membrane obtained at a clamping distance of 10 cm and a tensile speed of 10 mm / min was 78.8 MPa; the water contact angle of the PVDF hollow fiber membrane surface measured using a contact angle meter was 87.2°; the water contact angle of the PVDF hollow fiber membrane against SiO2 (0.1 g·L⁻¹) was tested at room temperature and operating pressure of 0.1 MPa. -1 The retention rate of the suspension (800nm) was 97.8%.

[0058] Compared to Example 3, Example 4 added 2.0 wt% rod-shaped TiO2. The pores formed by the rod-shaped TiO2 are vertical pores, consistent with the stretching direction, so the pore size increases. The membrane pore size increases from 1.21 μm to 1.35 μm, and the flux also increases from 2730 L / m³. 2 h increased to 2935 L / m 2 The tensile strength of the hollow fiber membrane increased from 75.7 MPa to 78.8 MPa. Compared with Example 3, the water contact angle of the membrane decreased from 88.3° to 87.2°, and the SiO2 rejection rate increased from 95.2% to 97.8%.

[0059] Example 5:

[0060] A melt-stretching method for preparing an aramid pulp-embedded PVDF hollow fiber microfiltration membrane includes the following steps:

[0061] (1) Material mixing: PVDF is used as the matrix phase, soluble inorganic substances and two soluble polymers are used as composite pore-forming agents, aramid pulp is used as the dispersed phase, and titanium dioxide is used as an additive. The materials are mixed evenly using a high-speed mixer according to the following mass fractions: PVDF (Soval 6010), 22.0 wt% MgCl2, 11.0 wt% PEO 1000000, 8.0 wt% PEG 20000, 1.5 wt% aramid pulp 1F1710 and 3.0 wt% rod-shaped TiO2. The resulting spinning raw material is a uniformly mixed material.

[0062] (2) Melt spinning: The material obtained in step (1) is fed into a twin-screw extruder (SHJ-20, Jiangsu Qijie Machinery Co., Ltd.) for melt granulation, and after blending, it is heated at high temperature by the twin screw and quantitatively extruded into a spinning melt (diameter of 2.6 mm) through a hollow spinneret assembly (spinneret diameter 2.85 mm). The temperature of each zone of the twin screw is: zone 1 160℃, zone 2 180℃, zone 3 220℃, zone 4 220℃, zone 5 230℃, zone 6 230℃, zone 7 230℃, zone 8 230℃, zone 9 230℃. Air is introduced into the hollow spinneret assembly, and the spun body is cured in the air bath to obtain a nascent hollow fiber membrane (membrane thickness of 0.35 mm).

[0063] (3) Post-processing: After the nascent hollow fiber membrane is dried in air, it is then soaked in water at 70°C for 24 hours to dissolve the soluble inorganic substances and two soluble polymers. It is then dried in an oven at 90°C and preheated for 2-4 hours. Finally, it is hot-stretched at 100°C to an elongation of 150% (based on the length of the nascent hollow fiber membrane) at a stretching rate of 10 mm / min to obtain the stretched hollow fiber membrane, thus obtaining a PVDF hollow fiber membrane with relatively high pure water flux.

[0064] The pure water flux of the PVDF hollow fiber membrane was tested at 0.1 MPa and the measured flux was 1920 L / m³. 2 The pore size of the hollow fiber membrane was measured to be 1.05 μm; the tensile strength of the PVDF hollow fiber membrane obtained at a clamping distance of 10 cm and a tensile speed of 10 mm / min was 79.5 MPa; the water contact angle of the PVDF hollow fiber membrane surface measured using a contact angle meter was 86.6°; the water contact angle of the PVDF hollow fiber membrane against SiO2 (0.1 g·L⁻¹) was tested at room temperature and operating pressure of 0.1 MPa. -1 The retention rate of the suspension (800nm) was 98.3%.

[0065] Compared to Example 4, Example 5 added 3.0 wt% rod-shaped TiO2, reducing the membrane pore size from 1.35 μm to 1.05 μm and increasing the flux from 2935 L / m³. 2 h decreased to 1920 L / m 2 The tensile strength of the hollow fiber membrane increased from 78.8 MPa to 79.5 MPa, the water contact angle decreased from 87.2° to 86.6°, and the SiO2 rejection rate increased from 97.8% to 98.3%. Excessive rod-shaped TiO2 content is detrimental to the pure water flux of the membrane.

[0066] Compare with Example 1:

[0067] The preparation method is the same as in Example 1, except that the material ratio in step (1) is: 54.5 wt% PVDF6010, 18.0 wt% MgCl2, 12.5 wt% PAM1000000, 10.0 wt% PVP58000 and 5.0 wt% aramid pulp 1F538.

[0068] The pure water flux of the PVDF hollow fiber membrane was tested at 0.1 MPa and the measured flux was 975 L / m³. 2 The pore size of the hollow fiber membrane was measured to be 0.52 μm; the tensile strength of the PVDF hollow fiber membrane obtained at a clamping distance of 10 cm and a tensile speed of 10 mm / min was 100.6 MPa; the water contact angle of the PVDF hollow fiber membrane surface measured using a contact angle meter was 70.5°; the water contact angle of the PVDF hollow fiber membrane against SiO2 (0.1 g·L⁻¹) was tested at room temperature and an operating pressure of 0.1 MPa. -1 The retention rate of the suspension (800nm) was 70.8%.

[0069] Compared to Implementation 1, the addition of 5.0 wt% aramid pulp 1F538 increased the membrane pore size from 1.03 μm to 1.05 μm, and the flux also increased from 1850 L / m³. 2 h increased to 1920 L / m 2 The tensile strength of the membrane increased from 69.7 MPa to 74.3 MPa. The water contact angle of the membrane decreased from 98.1° to 70.5°, and the SiO2 rejection rate decreased from 98.8% to 70.8%. This indicates that adding excessive aramid pulp does not significantly improve the membrane's permeability, but it does significantly reduce its rejection performance.

[0070] Compare with Example 2:

[0071] The preparation method is the same as in Example 2, except that the material ratio in step (1) is: 55.5 wt% PVDF (Sowe 6010), 20.0 wt% CaCl2, 13.5 wt% PEO1000000, 10.0 wt% PEG20000, and 1.0 wt% aramid short fiber 1414.

[0072] The pure water flux of the PVDF hollow fiber membrane was tested at 0.1 MPa and the measured flux was 830 L / m³. 2The pore size of the hollow fiber membrane was measured to be 0.46 μm; the tensile strength of the PVDF hollow fiber membrane obtained at a clamping distance of 10 cm and a tensile speed of 10 mm / min was 53.5 MPa; the water contact angle of the PVDF hollow fiber membrane surface measured using a contact angle meter was 104.9°; the water contact angle of the PVDF hollow fiber membrane against SiO2 (0.1 g·L⁻¹) was tested at room temperature and an operating pressure of 0.1 MPa. -1 The retention rate of the suspension (800 nm) was 73.2%.

[0073] Compared to Example 2, which added aramid staple fibers, the membrane pore size decreased from 1.14 μm to 0.46 μm, and the flux also increased from 2445 L / m³. 2 h decreased to 830 L / m 2 The tensile strength of the hollow fiber membrane decreased from 72.4 MPa to 53.5 MPa, the water contact angle increased from 92.2° to 104.9°, and the SiO2 rejection rate decreased from 85.3% to 73.2%. This demonstrates that aramid pulp is superior to aramid staple fiber, and aramid pulp can improve the mechanical properties, permeability, and rejection performance of the membrane.

[0074] Compare with Example 3:

[0075] Similar to Example 4, except that the proportion of rod-shaped TiO2 in the material of step (1) of Example 4 is replaced with 5.0 wt%.

[0076] The pure water flux of the PVDF hollow fiber membrane was tested at 0.1 MPa and the measured flux was 1570 L / m³. 2 The pore size of the hollow fiber membrane was measured to be 0.85 μm; the tensile strength of the PVDF hollow fiber membrane obtained at a clamping distance of 10 cm and a tensile speed of 10 mm / min was 82.3 MPa; the water contact angle of the PVDF hollow fiber membrane surface measured using a contact angle meter was 80.5°; the water contact angle of the PVDF hollow fiber membrane against SiO2 (0.1 g·L⁻¹) was tested at room temperature and an operating pressure of 0.1 MPa. -1 The retention rate of the suspension (800nm) was 99.4%.

[0077] Compared to Example 4, the proportion of rod-shaped TiO2 increased to 5.0 wt%, the pore size increased from 1.35 μm to 1.63 μm, and the flux also increased from 2935 L / m³. 2 h decreased to 1570 L / m 2The tensile strength increased from 79.8 MPa to 82.3 MPa, the water contact angle of the membrane decreased from 87.2° to 80.5°, and the SiO2 rejection rate increased from 97.8% to 99.4%. Considering all indicators, a higher content of rod-shaped TiO2 is not necessarily better. Although the tensile strength and SiO2 rejection rate were improved in Control Example 3, the flux was significantly reduced. Considering the water treatment efficiency of the membrane, excessive amounts of rod-shaped TiO2 should not be added.

[0078] 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 melt-stretching method for preparing an aramid pulp-embedded PVDF hollow fiber microfiltration membrane, characterized in that: Step (1) Material mixing: According to the mass fraction, 54.5 wt% PVDF, 23.0 wt% CaCl2, 11.0 wt% PEO 1000000, 8.0 wt% PEG 20000, 1.5 wt% aramid pulp 1F1710 and 2.0 wt% rod-shaped TiO2 are mixed evenly in proportion using a high-speed mixer to obtain spinning raw materials and a uniformly mixed material. Step (2) Melt spinning: The material obtained in step (1) is fed into a twin-screw extruder for melt granulation, blended, and then heated at high temperature by the twin screw. The melt is then quantitatively extruded through a hollow spinneret. The temperatures of each zone of the twin screw are: Zone 1 160 ℃, Zone 2 180 ℃, Zone 3 220 ℃, Zone 4 220 ℃, Zone 5 230 ℃, Zone 6 230 ℃, Zone 7 230 ℃, Zone 8 230 ℃, and Zone 9 230 ℃. Air is introduced into the hollow spinneret. After the melt is solidified in the air bath, a nascent hollow fiber membrane with a thickness of 0.35 mm is obtained. Step (3) Post-processing: After the nascent hollow fiber membrane is dried in air, it is soaked in water at 70 ℃ for 24 h, dried in an oven at 90 ℃ and preheated for 2~4 h, and then hot-stretched at 110 ℃ to an elongation of 100% and a stretching rate of 10 mm / min to obtain an aramid pulp embedded PVDF hollow fiber microfiltration membrane.

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