Preparation method and device of expanded polytetrafluoroethylene tubular fiber membrane with asymmetric structure

Abstract

The invention provides a method and a device for preparing an expanded polytetrafluoroethylene tubular fiber membrane with an asymmetric structure. The method comprises the following steps: S1, mixing polytetrafluoroethylene dispersion resin and lubricating oil, curing and compacting to obtain a hollow blank; s2, the hollow blank is placed in an extrusion material cavity formed between an extrusion machine core rod and an extrusion machine main body in a spaced mode to be subjected to asymmetric temperature treatment, a polytetrafluoroethylene blank is obtained, the outer side wall of the extrusion machine main body is wrapped with a heating ring, and core rod circulating refrigerating fluid is introduced into the extrusion machine core rod; s3, the polytetrafluoroethylene blank is extruded from the extrusion material cavity to obtain the polytetrafluoroethylene pipe, regular grooves are formed in the outer surface of the core rod transition section, and a coating is arranged on the inner surface of the die sleeve; s4, the polytetrafluoroethylene pipe is sequentially subjected to degreasing, annealing, stretching and heat setting treatment, then the expanded polytetrafluoroethylene tubular fiber membrane of the asymmetric structure is obtained, the structure of an extruder is optimized, and the expanded polytetrafluoroethylene tubular fiber membrane of the asymmetric structure with the inner wall pore diameter smaller than the outer wall pore diameter can be obtained through continuous production.

Description

Technical Field

[0001] This invention relates to the field of fiber membrane processing, and in particular to a method and apparatus for preparing an asymmetric expanded polytetrafluoroethylene tubular fiber membrane. Background Technology

[0002] Currently, expanded polytetrafluoroethylene tubular fiber membranes are mainly prepared by uniaxial stretching. The specific process involves mixing polytetrafluoroethylene dispersion resin and lubricant, followed by curing, pressing, extrusion, degreasing, stretching, heat setting, and finally, product preparation.

[0003] Since PTFE tubular fiber membranes are typically extruded through an annular die, a velocity gradient exists in the material flow within the annular channel. According to fluid mechanics principles, in pressure-driven pipe flow (such as extrusion), the outer wall of the die is in a high shear rate zone; while the inner wall, adjacent to the mandrel surface, experiences a lower average shear rate due to the mandrel's typically smaller diameter and larger radius of curvature. The extrusion aid (lubricant) coats the fine PTFE particles. Under high shear, the particles are stretched, slipped, partially untangled, and oriented along the flow direction (extrusion direction). Because the outer wall is in a high-shear zone with stronger shear force, the PTFE particles / primary fibrils exhibit higher orientation, tighter arrangement, and more regularity. The inner wall is in a low-shear zone with weaker shear force, resulting in lower orientation of the PTFE particles / primary fibrils and a relatively loose and disordered arrangement. During the subsequent longitudinal unidirectional stretching process, the material is stretched along the extrusion direction. Because the outer wall has a highly oriented and dense initial structure, the space for further slippage and extension of molecular chains or protofibers during stretching is relatively small. Stretching mainly leads to the refinement and elongation of existing pores, or the generation of smaller and more uniform micropores, resulting in smaller pore sizes. On the other hand, the inner wall has a low orientation and loose structure. During stretching, weak points are more easily pulled apart, forming larger pores. This results in the phenomenon that the pores on the inner wall are larger than those on the outer wall. In other words, most polytetrafluoroethylene tubular fiber membranes in the existing technology form a structure with larger pores on the inner wall after unidirectional stretching.

[0004] However, when PTFE tubular fiber membranes are used in artificial blood vessels, the larger pore size of the inner wall compared to the outer wall fails to meet practical application requirements. Specifically, in artificial blood vessels, to ensure the growth of outer wall tissue cells, a dense inner wall and sparse outer wall are needed to reduce the activation of platelets by blood flow shear forces, thus significantly reducing platelet adhesion. Furthermore, a dense inner wall and sparse outer wall provides higher hardness, stronger rigidity, better wear resistance, and better dimensional stability. Similarly, when PTFE tubular fiber membranes are used in precision filtration applications, internal pressure cross-flow components are often employed. The "small inner wall and large outer wall" structure also reduces contaminant clogging of the membrane pores, improving filtration efficiency and service life.

[0005] In order to obtain this asymmetric PTFE tubular fiber membrane, patent CN117654312A prepared expanded polytetrafluoroethylene tube blanks by uniaxial stretching, and then extruded the tube blanks to obtain fiber membranes with inner wall pores smaller than outer wall pores. However, this process is difficult to carry out continuous production.

[0006] There is an urgent need for new preparation methods to solve this problem, and to provide an asymmetric expanded polytetrafluoroethylene tubular fiber membrane with small inner pores and large outer hollow structure that can be continuously produced. Summary of the Invention

[0007] The purpose of this invention is to provide a method and apparatus for preparing an asymmetric expanded polytetrafluoroethylene tubular fiber membrane, and to optimize the structure of the extruder so as to continuously produce an asymmetric expanded polytetrafluoroethylene tubular fiber membrane with an inner wall pore diameter smaller than the outer wall pore diameter.

[0008] To achieve the above objectives, firstly, this technical solution provides an apparatus for preparing an asymmetric structure expanded polytetrafluoroethylene tubular fiber membrane, comprising: The extruder body 10 is surrounded by a heating coil 11 on its outer side wall, and the extruder body 10 includes a material cavity body 12 and a die sleeve 13. The opening of the die sleeve 13 at the end near the material cavity body 12 is larger than the opening of the end of the die sleeve 13 away from the material cavity body 12. An extruder mandrel 20 is disposed inside the extruder body 10, wherein the extruder mandrel 20 and the extruder body 10 are spaced apart to form an extrusion chamber 100. The extrusion chamber 100 is composed of a first chamber 101 corresponding to the chamber body 12 and a second chamber 102 corresponding to the die sleeve 13. The extruder mandrel 20 is filled with mandrel circulating coolant 30.

[0009] Unlike traditional extruders with annular dies, this extruder features a mandrel 20 with a circulating coolant 30 inside, which reduces the material temperature in the inner wall region of the extrusion chamber 100. A heating coil 11 surrounds the outer wall of the extruder body 10, increasing the material temperature in the outer wall region of the extrusion chamber 100. Considering fluid dynamics, low temperatures increase the viscosity of PTFE material. Under the same extrusion pressure, the high-viscosity material on the inner wall is more easily forced to generate a higher shear rate, compensating for the low shear rate defect on the inner wall caused by traditional small-diameter mandrels. This improves the orientation and compactness of the PTFE particles / primary fibrils on the inner wall, laying the foundation for subsequent stretching to form small pores, thus creating an asymmetric structure where the inner wall pore diameter is smaller than the outer wall pore diameter.

[0010] In some embodiments, the die sleeve 13 includes an extrusion transition section 131 and an extrusion outlet section 132 connected to each other, wherein the opening area of ​​the extrusion transition section 131 decreases sequentially from the material cavity body 12 to the extrusion outlet section 132, one end of the extrusion transition section 131 is connected to the material cavity body 12, and the other end is connected to the extrusion outlet section 132.

[0011] In some embodiments, both the material chamber body 12 and the extrusion outlet section 132 are designed as cylindrical shapes with uniform opening areas.

[0012] In some embodiments, the shape of the extruder mandrel 20 matches the shape of the extruder body 10, and the extruder mandrel 20 and the extruder body 10 are spaced apart. When the material is squeezed from the extrusion chamber 100 to the extrusion outlet section 132, the pressure gradually increases. The material on the outer wall has low viscosity and good fluidity, and the shear rate is moderately reduced. The material on the inner wall is further compressed and sheared due to the contraction of the cavity, ultimately achieving an inner wall shear rate > outer wall shear rate, breaking the traditional shear distribution of high outer and low inner.

[0013] In some embodiments, the heating coil 11 is wound around the outer wall of the extruder body 10 to heat the extruder body 10, which is heated to 30°C to 50°C. A circulating coolant is introduced into the extruder mandrel 20 to cool it, and the temperature of the circulating coolant is -50°C to -20°C. It should be noted that in this embodiment, the side of the extrusion chamber 100 closest to the extruder body 10 is defined as the outer wall of the extrusion chamber 100, and the side of the extrusion chamber 100 closest to the extruder mandrel 20 is defined as the inner wall of the extrusion chamber 100.

[0014] In some embodiments, the outer surface of the extrusion transition section 131 of the extruder mandrel 20 corresponding to the die sleeve 13 is provided with regular microgrooves, wherein the depth of the microgrooves is 50~100 micrometers. The advantage of this design is that it can increase the material shear rate of the inner wall of the extrusion chamber 100. Figure 2 As shown, the outer surface of the extrusion transition section 131 of the die sleeve 13 of the extruder mandrel 20 is recessed inward to form a microgroove.

[0015] In some embodiments, the inner surface of the extrusion transition section 131 of the extruder body 10 corresponding to the die sleeve 13 is provided with a carbon coating. The advantage of this design is that it can reduce the material shear rate of the outer wall of the extrusion chamber 100.

[0016] It should be noted that this solution optimizes and improves the extruder in the preparation process of asymmetric expanded polytetrafluoroethylene tubular fiber membranes. Other preparation equipment, such as preform presses, annealing equipment, stretching equipment, and heat setting equipment, are all conventional equipment and will not be described again.

[0017] Secondly, this solution provides a method for preparing an asymmetric structure expanded polytetrafluoroethylene tubular fiber membrane, including: S1: Mix polytetrafluoroethylene dispersion resin and lubricating oil, and then cure and press to obtain a hollow blank; S2: The hollow preform is placed in the first material chamber 101, which is formed by the extruder mandrel 20 and the extruder body 10 at intervals, and asymmetric temperature treatment is performed to obtain polytetrafluoroethylene preform. The outer wall of the extruder body 10 is wrapped with a heating ring 11, and the extruder mandrel 20 is filled with mandrel circulating coolant 300. S3: Extruding the polytetrafluoroethylene (PTFE) preform from the extrusion chamber 100 yields a PTFE tube. S4: Polytetrafluoroethylene tubular material is degreased, annealed, stretched and heat-set sequentially to obtain an asymmetric expanded polytetrafluoroethylene tubular fiber membrane.

[0018] In step S1, the mass ratio of polytetrafluoroethylene dispersion resin to lubricating oil is 100:18 ~ 100:25, the pressing pressure is 1.0 ~ 2.5t, and the holding time is 100 ~ 300s.

[0019] In step S2, the extruder body 10 includes a material cavity body 12 and a die sleeve 13. The extrusion material cavity 100 is composed of a first material cavity 101 corresponding to the material cavity body 10 and a second material cavity 102 corresponding to the die sleeve 13. In step S2, the hollow preform is placed in the first material cavity 101, and in step S3, the polytetrafluoroethylene preform is extruded from the second material cavity 102. In step S2, the hollow blank is placed in the first material cavity 101, and the mold sleeve 13 and the material cavity body 12 are pressed together by hydraulic pressure.

[0020] Specifically, since the die sleeve 13 includes an extrusion transition section 131 and an extrusion outlet section 132 connected to each other, and the opening area of ​​the extrusion transition section 131 decreases sequentially from the material cavity body 12 to the extrusion outlet section 132, the hollow billet is squeezed when it is extruded from the first material cavity 101 to the second material cavity 102.

[0021] It should be noted that the shape and size of the hollow billet match the shape of the first material cavity 101, so that when the hollow billet is placed in the first material cavity 101, the outer wall of the hollow billet contacts the outer wall of the first material cavity 101, and the inner wall of the hollow billet contacts the inner wall of the first material cavity 101. During the asymmetric temperature processing, the PTFE billet is extruded from the second material cavity 102 of the extruder body 10 to obtain a PTFE tube, and the hollow billet is extruded from the extrusion outlet section 132 to obtain a PTFE tube.

[0022] In some embodiments, the heating coil 11 is wound around the outer wall of the extruder body 10 to heat the extruder body 10, which is heated to 30°C to 50°C. A circulating coolant is introduced into the extruder mandrel 20 to cool it, and the temperature of the circulating coolant is -50°C to -20°C. It should be noted that in this embodiment, the side of the extrusion chamber 100 closest to the extruder body 10 is defined as the outer wall of the extrusion chamber 100, and the side of the extrusion chamber 100 closest to the extruder mandrel 20 is defined as the inner wall of the extrusion chamber 100.

[0023] In some embodiments, the outer surface of the extrusion transition section 131 of the extruder mandrel 20 corresponding to the die sleeve 13 is provided with regular microgrooves, wherein the depth of the microgrooves is 50~100 micrometers. The advantage of this design is that it can increase the material shear rate of the inner wall of the extrusion chamber 100.

[0024] In some embodiments, the inner surface of the extrusion transition section 131 of the extruder body 10 corresponding to the die sleeve 13 is provided with a carbon coating. The advantage of this design is that it can reduce the material shear rate of the outer wall of the extrusion chamber 100.

[0025] In step S4, the degreasing temperature is 160℃ ~ 220℃, the annealing temperature is 230℃ ~ 280℃, the stretching temperature is 250℃ ~ 320℃, and the setting temperature is 330℃ ~ 360℃.

[0026] It should be noted that because the outer wall temperature of the extrusion chamber 100 is higher than that of the inner wall, the inner wall of the hollow billet near the extrusion chamber 100 is rapidly cooled during the extrusion process. The PTFE molecular chains do not have enough time to align properly, resulting in smaller and less perfect crystals with lower overall crystallinity. This low-crystallinity region is more prone to plastic deformation and pore expansion during subsequent stretching. Furthermore, the subsequent annealing process causes secondary crystallization in the low-crystallinity region (inner wall), significantly increasing its crystallinity and making it harder. Meanwhile, the outer wall, which cools more slowly and has higher crystallinity, undergoes relatively less change. Thus, during stretching, the high-crystallinity inner wall is more difficult to stretch, resulting in smaller pores, while the low-crystallinity outer wall is easier to stretch, resulting in larger pores.

[0027] Compared with existing technologies, this technical solution has the following characteristics and beneficial effects: This solution optimizes the extruder structure by integrating asymmetric temperature treatment within the extruder body and mandrel. The hollow preform is directly extruded from the extrusion chamber into a tube, allowing for seamless integration with subsequent conventional processes such as degreasing, annealing, and stretching. This enables continuous production throughout the entire process, significantly improving efficiency and reducing material loss and time costs caused by process interruptions, making it more suitable for industrial mass production. Furthermore, precise temperature control (outer wall 30℃~50℃, inner wall -50℃~-20℃) ensures a gradual increase in pressure and a stable shear rate distribution during extrusion, avoiding the uneven orifice diameter problem caused by abrupt shear changes in traditional annular dies.

[0028] Furthermore, the extruder mandrel in this design employs a hollow circulating cooling system, circulating a low-temperature coolant (lowering the mandrel temperature to -50℃ to -20℃). This rapidly reduces the temperature of the PTFE material in the inner wall region of the extrusion chamber through heat conduction. During extrusion, the low temperature causes a sharp decrease in the molecular chain movement rate of the inner wall material, preventing it from forming a regular arrangement before initial shaping. This results in a microstructure with small crystal size, poor crystal region integrity, and low overall crystallinity. This low-crystallinity structure features loosely intertwined molecular chains and weak intermolecular forces, providing ample "deformable space" for structural control in subsequent processes. The addition of a heating ring on the outer wall (maintaining the extruder body temperature at 30℃ to 50℃) ensures that the PTFE material in the outer wall region of the chamber is in a suitable high-temperature flow state. Under high-temperature conditions, the molecular chains of the outer wall material move actively, allowing for sufficient regular arrangement and forming a microstructure with large crystal size, high crystal region integrity, and high overall crystallinity. This high-crystallinity structure has tightly intertwined molecular chains and strong intermolecular forces, resulting in higher structural stability and less susceptibility to significant deformation during subsequent processing. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the extruder used to prepare the asymmetric expanded polytetrafluoroethylene tubular fiber membrane according to this scheme.

[0030] Figure 2 This is a magnified view of a portion of the extruder mandrel.

[0031] Figure 3 This is a structural schematic diagram of the main body of the extruder.

[0032] Figure 4 These are SEM images of the outer and inner surfaces of the membrane in Embodiment 2 of the present invention.

[0033] Figure 5 The images show the SEM images of the outer and inner surfaces of the membrane in Comparative Example 1 of this invention.

[0034] In the diagram: 10-Extruder body, 20-Extruder mandrel, 100-Extrusion chamber, 101-First chamber, 102-Second chamber, 11-Heating coil, 12-Cavity body, 13-Die sleeve, 131-Extrusion transition section, 132-Extrusion outlet section, 30-Mandrel circulating coolant. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0036] Those skilled in the art should understand that, in the disclosure of this invention, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limiting this invention.

[0037] Example 1: 1) Mix polytetrafluoroethylene dispersion resin and lubricating oil at a mass ratio of 100:20, and after curing, press the mixture in a compact press to form a hollow blank. The pressing pressure is 1.5t and the holding time is 200s. 2) The hollow preform is placed into the extruder chamber for asymmetric heating / freezing treatment. The temperature of the circulating coolant in the extruder mandrel is designed to be -20℃, and the outer wall of the extruder chamber is heated to 30℃. 3) The processed polytetrafluoroethylene (PTFE) preform is extruded into PTFE tubing through the extrusion head of an extruder. The outer surface of the mandrel die of the extruder contains a regular microgroove structure (80 micrometers deep), and the inner surface of the die sleeve has a layer of graphene coating. 4) Asymmetric expanded polytetrafluoroethylene tubular fiber membranes are prepared by sequentially degreasing, annealing, stretching and heat setting of polytetrafluoroethylene tubular materials. The degreasing temperature is 160℃, the annealing temperature is 280℃, the stretching temperature is 250℃ and the heat setting temperature is 360℃.

[0038] Example 2: 1) Mix polytetrafluoroethylene dispersion resin and lubricating oil at a mass ratio of 100:20, and after curing, press the mixture in a compact press to form a hollow blank. The pressing pressure is 1.5t and the holding time is 200s. 2) The hollow preform is placed into the extruder chamber for asymmetric heating / freezing treatment. The temperature of the circulating coolant in the extruder mandrel is designed to be -50℃, and the outer wall of the extruder chamber is heated to 50℃. 3) The processed polytetrafluoroethylene (PTFE) preform is extruded into PTFE tubing through the extrusion head of an extruder. The outer surface of the mandrel die of the extruder contains a regular microgroove structure (80 micrometers deep), and the inner surface of the die sleeve has a layer of graphene coating. 4) Asymmetric expanded polytetrafluoroethylene tubular fiber membranes are prepared by sequentially degreasing, annealing, stretching and heat setting of polytetrafluoroethylene tubular materials. The degreasing temperature is 200℃, the annealing temperature is 250℃, the stretching temperature is 300℃ and the heat setting temperature is 350℃.

[0039] Example 3: 1) Mix polytetrafluoroethylene dispersion resin and lubricating oil at a mass ratio of 100:25, and after curing, press the mixture in a compact press to form a hollow blank. The pressing pressure is 1.0 t and the holding time is 300s. 2) The hollow preform is placed into the extruder chamber for asymmetric heating / freezing treatment. The temperature of the circulating coolant ④ in the extruder mandrel ③ is -50℃, and the outer wall of the chamber ② is heated to 40℃. 3) The processed polytetrafluoroethylene preform is extruded into polytetrafluoroethylene tubing through the extrusion head of an extruder. The outer surface ⑤ of the mandrel die of the extruder contains a regular microgroove structure (depth 80 micrometers), and the inner surface ⑥ of the die sleeve has a layer of graphene coating. 4) Asymmetric expanded polytetrafluoroethylene tubular fiber membranes are prepared by sequentially degreasing, annealing, stretching and heat setting of polytetrafluoroethylene tubular materials. The degreasing temperature is 220℃, the annealing temperature is 230℃, the stretching temperature is 320℃ and the heat setting temperature is 330℃.

[0040] Example 4 1) Mix polytetrafluoroethylene dispersion resin and lubricating oil at a mass ratio of 100:20, and after curing, press the mixture in a compact press to form a hollow blank. The pressing pressure is 1.5t and the holding time is 200s. 2) The hollow preform is placed into the extruder chamber for asymmetric heating / freezing treatment. The temperature of the circulating coolant in the extruder mandrel is designed to be -50℃, and the outer wall of the extruder chamber is heated to 50℃. 3) The treated polytetrafluoroethylene (PTFE) preform is extruded into PTFE tubing through the extrusion head of an extruder. The outer surface of the mandrel die head of the extruder is smooth, and the inner surface of the die sleeve is uncoated. 4) Asymmetric expanded polytetrafluoroethylene tubular fiber membranes are prepared by sequentially degreasing, annealing, stretching and heat setting of polytetrafluoroethylene tubular materials. The degreasing temperature is 200℃, the annealing temperature is 250℃, the stretching temperature is 300℃ and the heat setting temperature is 350℃.

[0041] Comparative Example 1: 1) Mix polytetrafluoroethylene dispersion resin and lubricating oil at a mass ratio of 100:20, and after curing, press the mixture in a compact press to form a hollow blank. The pressing pressure is 1.5t and the holding time is 200s. 2) The hollow preform is placed into the material chamber of a conventional extruder without temperature control. At the same time, the outer surface of the mandrel die of the extruder is smooth and the inner surface of the die sleeve is uncoated. Extrusion is carried out to form polytetrafluoroethylene pipe. 4) Asymmetric expanded polytetrafluoroethylene tubular fiber membranes are prepared by sequentially degreasing, stretching and heat setting of polytetrafluoroethylene tubular materials. The degreasing temperature is 200℃, the stretching temperature is 300℃ and the heat setting temperature is 350℃.

[0042] Node spacing test method: Randomly select 10 locations on the inner and outer surfaces of the sample, magnify them 1000 times, and randomly measure the node spacing of 5 sets of nodes at this magnification. Calculate the average value of 50 sets of node spacing.

[0043] Table 1. Spacing values ​​of each sample node .

[0044] As can be seen from Table 1, the spacing between nodes on the inner surface of the asymmetric expanded polytetrafluoroethylene tubular fiber membrane prepared in the embodiments of the present invention is smaller than the spacing between nodes on the outer surface. Therefore, it can be seen that this scheme yields an asymmetric expanded polytetrafluoroethylene tubular fiber membrane with an inner wall pore diameter smaller than the outer wall pore diameter.

[0045] from Figure 4 As can be seen from the SEM images of the inner and outer surfaces in Embodiment 2 of the present invention, Figure 5 For comparative example 1, SEM images of the inner and outer surfaces are shown. Figure 4 and Figure 5 It can be seen that the pores on the inner surface of the prepared asymmetric polytetrafluoroethylene tubular fiber membrane are smaller than those on the outer surface.

[0046] Those skilled in the art should understand that the technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0047] The above embodiments are merely illustrative of several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A method for preparing an asymmetric structure expanded polytetrafluoroethylene tubular fiber membrane, characterized in that, include: S1: Mix polytetrafluoroethylene dispersion resin and lubricating oil, and then cure and press to obtain a hollow blank; S2: The hollow preform is placed in the extrusion chamber (100) formed between the extruder mandrel (20) and the extruder body (10) for asymmetric temperature treatment to obtain polytetrafluoroethylene preform, wherein the outer wall of the extruder body (10) is wrapped with a heating ring (11), and the extruder mandrel (20) is filled with mandrel circulating coolant (30). S3: Polytetrafluoroethylene (PTFE) preform is extruded from the extrusion chamber (100) to obtain PTFE tubing; S4: Polytetrafluoroethylene tubular material is degreased, annealed, stretched and heat-set sequentially to obtain an asymmetric expanded polytetrafluoroethylene tubular fiber membrane.

2. The method for preparing the asymmetric structure expanded polytetrafluoroethylene tubular fiber membrane according to claim 1, characterized in that, In step S1, the mass ratio of polytetrafluoroethylene dispersion resin to lubricating oil is 100:18 ~ 100:25, the pressing pressure is 1.0 ~ 2.5t, and the holding time is 100 ~ 300s.

3. The method for preparing the asymmetric structure expanded polytetrafluoroethylene tubular fiber membrane according to claim 1, characterized in that, The extruder body (10) includes a material cavity body (12) and a die sleeve (13). The extrusion material cavity (100) is composed of a first material cavity (101) corresponding to the material cavity body (10) and a second material cavity (102) corresponding to the die sleeve (13). In step S2, the hollow preform is placed in the first material cavity (101), and in step S3, the polytetrafluoroethylene preform is extruded from the second material cavity (102).

4. The method for preparing the asymmetric structure expanded polytetrafluoroethylene tubular fiber membrane according to claim 1, characterized in that, The extruder body (10) is heated to 30℃~50℃, and the temperature of the circulating coolant (300) is -50℃ ~ -20℃.

5. The method for preparing the asymmetric expanded polytetrafluoroethylene tubular fiber membrane according to claim 1, characterized in that, The outer surface of the extrusion transition section (131) of the extruder mandrel (20) corresponding to the die sleeve (13) is provided with regular microgrooves, wherein the depth of the microgrooves is 50~100 micrometers.

6. The method for preparing the asymmetric structure expanded polytetrafluoroethylene tubular fiber membrane according to claim 1, characterized in that, The inner surface of the extrusion transition section (131) of the extruder body (10) corresponding to the die sleeve (13) is provided with a carbon coating.

7. The method for preparing the asymmetric expanded polytetrafluoroethylene tubular fiber membrane according to claim 1, characterized in that, In step S4, the degreasing temperature is 160℃ ~ 220℃, the annealing temperature is 230℃ ~ 280℃, the stretching temperature is 250℃ ~ 320℃, and the setting temperature is 330℃ ~ 360℃.

8. The method for preparing the asymmetric expanded polytetrafluoroethylene tubular fiber membrane according to claim 1, characterized in that, Asymmetric expanded polytetrafluoroethylene tubular fiber membranes are used for artificial blood vessels.

9. An apparatus for preparing an asymmetric expanded polytetrafluoroethylene tubular fiber membrane, characterized in that, include: The extruder body (10) has a heating coil (11) wrapped around its outer side wall, and the extruder body (10) includes a material cavity body (12) and a die sleeve (13). The opening of the die sleeve (13) at the end near the material cavity body (12) is larger than the opening of the die sleeve (13) at the end away from the material cavity body (12). An extruder mandrel (20) is disposed inside the extruder body (10), wherein the extruder mandrel (20) and the extruder body (10) are spaced apart to form an extrusion chamber (100), the extrusion chamber (100) is composed of a first chamber (101) corresponding to the chamber body (12) and a second chamber (102) corresponding to the die sleeve (13), and the extruder mandrel (20) is filled with mandrel circulating coolant (30).

10. The apparatus for preparing asymmetric expanded polytetrafluoroethylene tubular fiber membrane according to claim 9, characterized in that, include: Heating coil (11) is wrapped around the outer wall of extruder body (10) to heat extruder body (10). Extruder body (10) is heated to 30℃~50℃, and the temperature of circulating coolant is -50℃~-20℃.

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