A polytetrafluoroethylene hollow fiber janus membrane and a method of making the same

Abstract

The application discloses a polytetrafluoroethylene hollow fiber Janus membrane and a preparation method thereof, and comprises the following steps: filling hydrophilic material and hydrophobic material into a mold of a concentric double-layer embryo after maturation to perform a pressing process, and then performing extrusion, degreasing, stretching and sintering to obtain the polytetrafluoroethylene hollow fiber Janus membrane. Unlike a conventional method which needs to use a post-processing process, the application can realize one-step preparation of the polytetrafluoroethylene hollow fiber Janus membrane with one side being hydrophilic and the other side being hydrophobic, the preparation method is simple and easy to implement, the thickness ratio of the hydrophilic layer and the hydrophobic layer in the Janus membrane can be controlled by adjusting the thickness of the hydrophilic material and the hydrophobic material in the concentric double-layer blank, and the hydrophilic layer and the hydrophobic layer are well combined; no complicated post-processing is needed, the cost is relatively low, and no harmful waste liquid is generated, and no environmental pollution and other problems occur.

Description

Technical Field

[0001] This application belongs to the field of membrane separation, specifically relating to a polytetrafluoroethylene hollow fiber Janus membrane and its preparation method. Background Technology

[0002] Membrane separation technology, with its functions of separation, concentration, purification, and refining, as well as its high efficiency, energy saving, environmental protection, molecular-level filtration, and simple and easy-to-control filtration process, has been widely used in food, medicine, biology, environmental protection, chemical industry, metallurgy, energy, petroleum, water treatment and other fields, generating huge economic and social benefits and becoming one of the most important means in separation science today.

[0003] Janus membranes have attracted widespread attention due to their unique and superior properties endowed by their asymmetric structure or chemical composition, becoming a new direction in the field of membrane materials and membrane research. Janus membranes are separation membranes with different properties on both sides, mainly including two categories: hydrophilic / hydrophobic and positively / negatively charged. Among them, hydrophilic / hydrophobic membranes can effectively reduce energy consumption in separation processes involving two-phase interfaces and have good application prospects in processes such as oil-water separation, bubbling, emulsification, and demulsification.

[0004] Polytetrafluoroethylene (PTFE) possesses outstanding chemical stability, excellent hydrophobicity, and mechanical properties, making it a focus of research in the field of membrane separation due to its significant contribution to the development of hydrophilic / hydrophobic Janus membranes. Current technologies typically involve first preparing hydrophobic PTFE hollow fiber microporous membranes, then achieving hydrophilicity on one side through post-processing. This approach suffers from lengthy and cumbersome preparation processes. Summary of the Invention

[0005] The traditional PTFE hollow fiber membrane preparation process includes batching, curing, pressing, extrusion, degreasing, stretching, and sintering, resulting in a conventional membrane that is hydrophobic both inside and out. If a one-step method could be used to prepare hydrophilic / hydrophobic PTFE hollow fiber Janus membranes, the membrane fabrication process could be significantly simplified, making it more practical. This one-step method refers to avoiding the post-processing techniques previously reported in the literature (i.e., first preparing a hydrophobic membrane and then modifying one side to be hydrophilic, i.e., two steps). During the membrane fabrication process, the hydrophilic and hydrophobic materials are directly formed into a concentric double-layer preform during the pressing step. After conventional subsequent steps, a Janus membrane with one hydrophobic side and one hydrophilic side is obtained, requiring no post-processing.

[0006] Based on the above technical background, this application discloses a method for preparing a hydrophilic / hydrophobic polytetrafluoroethylene (PTFE) hollow fiber Janus membrane. By pressing concentric bilayer preforms, the hydrophilic and hydrophobic PTFE materials are effectively combined, thus obtaining a PTFE hollow fiber Janus membrane with one hydrophilic side and the other hydrophobic side in a one-step process. The preparation method of this application is simple and easy to implement, and has good application value.

[0007] According to one aspect of this application, a method for preparing a polytetrafluoroethylene hollow fiber Janus membrane is provided, comprising the following steps:

[0008] The hydrophilic and hydrophobic materials are respectively filled into a mold of a concentric double-layer preform for pressing, and then extruded, degreased, stretched and sintered to obtain the polytetrafluoroethylene hollow fiber Janus membrane.

[0009] The mold for the concentric double-layered blank includes a cylindrical material cylinder;

[0010] The material cylinder is provided with a central rod at its center;

[0011] The material cylinder is also equipped with a partition;

[0012] The partition is concentric with the material cylinder;

[0013] The height of the partition is at least equal to the height of the material cylinder;

[0014] Cavities are formed between the inner wall of the barrel and the partition, and between the partition and the central rod.

[0015] The hydrophilic and hydrophobic materials are respectively filled into the mold of the concentric double-layered blank, and the partition needs to be removed before pressing.

[0016] The hydrophilic material includes polytetrafluoroethylene dispersion resin, hydrophilic modifier, and extrusion aid;

[0017] The mass fraction of the polytetrafluoroethylene dispersion resin in the hydrophilic material is 66-82 wt%; the mass fraction of the polytetrafluoroethylene dispersion resin in the hydrophilic material is any value among 66 wt%, 70 wt%, 75 wt%, 80 wt%, and 82 wt%, or any value between two of them.

[0018] The mass fraction of the hydrophilic modifier in the hydrophilic material is 1 to 10 wt%; the mass fraction of the hydrophilic modifier in the hydrophilic material is any value or a range between 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, and 10 wt%.

[0019] The mass fraction of the extrusion aid in the hydrophilic material is 17-25 wt%; the mass fraction of the extrusion aid in the hydrophilic material is any value among 17 wt%, 20 wt%, and 25 wt%, or any value between two of them;

[0020] The hydrophobic material includes polytetrafluoroethylene dispersion resin and extrusion aid;

[0021] The mass fraction of polytetrafluoroethylene dispersion resin in the hydrophobic material is 75-83 wt%; the mass fraction of polytetrafluoroethylene dispersion resin in the hydrophobic material is any value among 75 wt%, 80 wt%, and 83 wt%, or any range between two of them.

[0022] The mass fraction of the extrusion aid in the hydrophobic material is 17-25 wt%; the mass fraction of the extrusion aid in the hydrophobic material is any value among 17 wt%, 20 wt%, and 25 wt%, or any range between two of them;

[0023] The number average molecular weight of the polytetrafluoroethylene dispersion resin is 5 million to 10 million; the number average molecular weight of the polytetrafluoroethylene dispersion resin is any value of 5 million, 6 million, 7 million, 8 million, 9 million, and 10 million or a range between any two.

[0024] The hydrophilic modifier is selected from inorganic nanoparticles and / or inorganic whiskers;

[0025] The extrusion aid is selected from aviation kerosene and / or isoalkanes;

[0026] The inorganic nanoparticles are selected from at least one of graphene oxide nanoparticles, SiO2 nanoparticles, or ZnO nanoparticles.

[0027] The inorganic whiskers are selected from calcium carbonate whiskers;

[0028] The isoalkanes are selected from Isopar G.

[0029] The hydrophilic material and the hydrophobic material are cured;

[0030] The curing temperature is 25 to 60°C; the curing temperature is any value or a range between any two of 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, and 60°C.

[0031] The maturation time is 8 to 60 hours; the maturation time is any value among 8 hours, 10 hours, 15 hours, 20 hours, 25 hours, 30 hours, 35 hours, 40 hours, 45 hours, 50 hours, 55 hours, and 60 hours, or a range between any two.

[0032] Specifically, the technical solution of this application mainly includes the following steps:

[0033] (a) Prepare polytetrafluoroethylene hydrophilic material I and polytetrafluoroethylene hydrophobic material II respectively;

[0034] (b) After being cured, hydrophilic material I and hydrophobic material II are pressed into a concentric double-layered blank, with one layer being hydrophilic material and the other layer being hydrophobic material;

[0035] (c) After extrusion, degreasing, stretching and sintering, a polytetrafluoroethylene hollow fiber Janus membrane with one hydrophilic side and the other hydrophobic side is obtained from the bilayer preform.

[0036] The thickness ratio of the outer layer to the inner layer in the concentric double-layer blank is 0.2 to 5:1.

[0037] According to another aspect of this application, a polytetrafluoroethylene hollow fiber Janus membrane is provided, which is prepared by the above-described preparation method.

[0038] The polytetrafluoroethylene hollow fiber Janus membrane includes a hydrophilic layer on one side and a hydrophobic layer on the other side.

[0039] The thickness ratio of the hydrophobic layer to the hydrophilic layer is 0.2 to 5:1.

[0040] The polytetrafluoroethylene hollow fiber Janus membrane has a hydrophilic side water contact angle of <80° and a hydrophobic side water contact angle of >100°.

[0041] The advantages of this application are:

[0042] Compared to the current method of first preparing hydrophobic polytetrafluoroethylene hollow fiber microporous membranes and then achieving hydrophilicity on one side of the polytetrafluoroethylene microporous membrane through post-processing, this application can achieve a one-step preparation of polytetrafluoroethylene hollow fiber Janus membranes with one side hydrophilic and the other side hydrophobic. The advantages include: the preparation method is simple and easy to implement; the thickness ratio of the hydrophilic / hydrophobic layer in the Janus membrane can be controlled by adjusting the thickness of the hydrophilic / hydrophobic material in the concentric bilayer preform; and the hydrophilic and hydrophobic layers are well bonded; no complicated post-processing is required, resulting in lower costs; and no harmful waste liquid or environmental pollution is generated. Attached Figure Description

[0043] Figure 1 A schematic diagram illustrating the preparation of a concentric circular double-layered blank;

[0044] Figure 2 A schematic diagram of the concentric double-layered blank obtained;

[0045] Figure 3 Photograph of the hydrophobic side water contact angle of the polytetrafluoroethylene hollow fiber Janus membrane obtained in Example 3;

[0046] Figure 4 This is a photograph of the hydrophilic side water contact angle of the polytetrafluoroethylene hollow fiber Janus membrane obtained in Example 3. Detailed Implementation

[0047] The present application will be further described below with reference to specific embodiments. However, it should be understood that various modifications and variations can be made without departing from the scope of the present application as defined by the appended claims. The detailed description and drawings should be considered illustrative only and not restrictive, and any such modifications and variations shall fall within the scope of the present application described herein. Furthermore, the background art is intended to illustrate the current state of research and development and significance of the present technology, and is not intended to limit the present application or its application field.

[0048] Example 1

[0049] Polytetrafluoroethylene (PTFE) dispersion resin (number average molecular weight 8 million), isoparaffin Isopar G, and graphene oxide nanoparticles were formulated at mass fractions of 72%, 5%, and 23%, respectively, to form PTFE hydrophilic material I; PTFE dispersion resin (number average molecular weight 8 million) and isoparaffin Isopar G were formulated at mass fractions of 77% and 23%, respectively, to form PTFE hydrophilic material II; after curing at 30°C for 48 hours, the hydrophilic material I and hydrophobic material II were pressed into concentric bilayer preforms in a pre-pressing device, with the outer side being hydrophobic and the inner side being hydrophilic, and the thickness ratio being 1:1; the bilayer preforms were extruded, degreased at 200°C, stretched 3 times at 200°C, and sintered at 360°C for 3 minutes to obtain a PTFE hollow fiber Janus membrane with a hydrophobic outer side and a hydrophilic inner side; the water contact angle on the hydrophilic side was 56°, and the water contact angle on the hydrophobic side was 116°.

[0050] Figure 1 A schematic diagram illustrating the preparation of a concentric circular double-layered blank;

[0051] Figure 2 A schematic diagram of the concentric double-layered blank obtained.

[0052] Example 2

[0053] Polytetrafluoroethylene (PTFE) dispersion resin (number average molecular weight 5 million), isoparaffin Isopar G, and SiO2 nanoparticles were formulated at mass fractions of 76%, 3%, and 21%, respectively, to form PTFE hydrophilic material I; PTFE dispersion resin (number average molecular weight 5 million) and isoparaffin Isopar G were formulated at mass fractions of 79% and 21%, respectively, to form PTFE hydrophilic material II; after curing at 50°C for 12 hours, the hydrophilic material I and hydrophobic material II were pressed into concentric bilayer preforms in a pre-pressing device, with the outer side being hydrophobic and the inner side being hydrophilic, and the thickness ratio being 0.2:1; after extrusion, degreasing at 200°C, stretching by 3 times at 200°C, and sintering at 360°C for 3 minutes, a PTFE hollow fiber Janus membrane with a hydrophobic outer side and a hydrophilic inner side was obtained; the water contact angle on the hydrophilic side was 72°, and the water contact angle on the hydrophobic side was 108°.

[0054] Example 3

[0055] Polytetrafluoroethylene (PTFE) dispersion resin (number average molecular weight 10 million), aviation kerosene, and ZnO nanoparticles were formulated into PTFE hydrophilic material I at mass fractions of 66%, 10%, and 24%, respectively. PTFE dispersion resin (number average molecular weight 10 million) and aviation kerosene were formulated into PTFE hydrophilic material II at mass fractions of 76% and 24%, respectively. After curing at 40°C for 24 hours, hydrophilic material I and hydrophobic material II were pressed into concentric bilayer preforms in a pre-pressing device, with the outer layer being hydrophilic and the inner layer being hydrophobic, with a thickness ratio of 4:1. The bilayer preforms were extruded, degreased at 200°C, stretched 3 times at 200°C, and sintered at 360°C for 3 minutes to obtain a PTFE hollow fiber Janus membrane with a hydrophilic outer side and a hydrophobic inner side. The water contact angle on the hydrophilic side was 42°, and the water contact angle on the hydrophobic side was 102°.

[0056] Figure 3 Photograph of the hydrophobic side water contact angle of the polytetrafluoroethylene hollow fiber Janus membrane obtained in Example 3;

[0057] Figure 4 This is a photograph of the hydrophilic side water contact angle of the polytetrafluoroethylene hollow fiber Janus membrane obtained in Example 3.

[0058] Example 4

[0059] Polytetrafluoroethylene (PTFE) dispersion resin (number average molecular weight 6 million), aviation kerosene, and calcium carbonate whiskers were formulated into PTFE hydrophilic material I at mass fractions of 73%, 4%, and 23%, respectively. PTFE dispersion resin (number average molecular weight 6 million) and aviation kerosene were formulated into PTFE hydrophilic material II at mass fractions of 77% and 23%, respectively. After curing at 25°C for 60 hours, hydrophilic material I and hydrophobic material II were pressed into concentric bilayer preforms in a pre-pressing device, with the outer layer being hydrophilic and the inner layer being hydrophobic, with a thickness ratio of 0.5:1. The bilayer preforms were extruded, degreased at 200°C, stretched 3 times at 200°C, and sintered at 360°C for 3 minutes to obtain a PTFE hollow fiber Janus membrane with a hydrophilic outer side and a hydrophobic inner side. The water contact angle on the hydrophilic side was 54°, and the water contact angle on the hydrophobic side was 106°.

[0060] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing a polytetrafluoroethylene hollow fiber Janus membrane, characterized in that, Includes the following steps: The hydrophilic and hydrophobic materials are respectively filled into a mold of a concentric double-layer preform for pressing, and then extruded, degreased, stretched and sintered to obtain the polytetrafluoroethylene hollow fiber Janus membrane.

2. The preparation method according to claim 1, characterized in that, The hydrophilic material includes polytetrafluoroethylene dispersion resin, hydrophilic modifier, and extrusion aid; The mass fraction of the polytetrafluoroethylene dispersion resin in the hydrophilic material is 66~82wt%; The mass fraction of the hydrophilic modifier in the hydrophilic material is 1~10wt%; The mass fraction of the extrusion aid in the hydrophilic material is 17~25wt%.

3. The preparation method according to claim 1, characterized in that, The hydrophobic material includes polytetrafluoroethylene dispersion resin and extrusion aid; The mass fraction of polytetrafluoroethylene dispersion resin in the hydrophobic material is 75-83 wt%. The mass fraction of the extrusion aid in the hydrophobic material is 17~25wt%.

4. The preparation method according to claim 2 or 3, characterized in that, The number average molecular weight of the polytetrafluoroethylene dispersion resin is 5 million to 10 million. The hydrophilic modifier is selected from inorganic nanoparticles and / or inorganic whiskers; The extrusion aid is selected from aviation kerosene and / or isoalkanes.

5. The preparation method according to claim 4, characterized in that, The inorganic nanoparticles are selected from at least one of graphene oxide nanoparticles, SiO2 nanoparticles, or ZnO nanoparticles. The inorganic whiskers are selected from calcium carbonate whiskers; The isoalkanes are selected from Isopar G.

6. The preparation method according to claim 1, characterized in that, The hydrophilic material and the hydrophobic material are cured; The ripening temperature is 25~60℃; The ripening time is 8 to 60 hours.

7. A polytetrafluoroethylene hollow fiber Janus membrane, characterized in that, Prepared by the preparation method according to any one of claims 1 to 6.

8. The polytetrafluoroethylene hollow fiber Janus membrane according to claim 7, characterized in that, The polytetrafluoroethylene hollow fiber Janus membrane includes a hydrophilic layer on one side and a hydrophobic layer on the other side.

9. The polytetrafluoroethylene hollow fiber Janus membrane according to claim 7, characterized in that, The thickness ratio of the hydrophobic layer to the hydrophilic layer is 0.2~5:

1.

10. The polytetrafluoroethylene hollow fiber Janus membrane according to claim 7, characterized in that, The hydrophilic side water contact angle of the polytetrafluoroethylene hollow fiber Janus membrane is <80°. Hydrophobic side water contact angle >100° .

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