Asymmetric polypropylene hollow fiber oxygenation membrane as well as preparation method and application thereof

Abstract

The invention provides an asymmetric polypropylene hollow fiber oxygenation membrane as well as a preparation method and application thereof. The outer surface of the oxygenation membrane comprises a plurality of first surface fibers; in the circumferential direction of the membrane, the SEM average distance between adjacent first surface fibers is 10-120nm; in addition, under the combined action of proper crystallinity, uniform bubble point and porosity of the whole membrane, excellent oxygenation performance of the oxygenation membrane is realized; meanwhile, the oxygenated membrane is prepared from a high-molecular-weight polypropylene raw material, so that the membrane has good mechanical properties; under the combined action of regulating and controlling the molecular weight of the polypropylene raw material and the crystallinity of the whole membrane, the oxygenation membrane has a certain selection effect, the gas separation factor alpha (CO2 / O2) is greater than 1.3, and effective separation of oxygen and carbon dioxide is more favorably realized; the device is particularly suitable for blood oxygenation in cardiopulmonary surgery and / or organ transplantation; in addition, the invention also provides a preparation method of the hollow fiber membrane, and the preparation method is quick, effective, simple to operate and suitable for large-scale popularization.

Description

An asymmetric polypropylene hollow fiber oxygen membrane, its preparation method and application Technical Field

[0001] This invention relates to the field of membrane materials technology, and more specifically to an asymmetric polypropylene hollow fiber oxygenation membrane, its preparation method, and its application. Background Technology

[0002] An oxygenation membrane, also known as a membrane lung, is the core component of an extracorporeal membrane oxygenation (ECMO) system, primarily responsible for oxygenating the blood. It mimics the gas exchange function of the human lungs, removing carbon dioxide from the patient's blood and replenishing it with oxygen, thus providing continuous extracorporeal respiratory and circulatory support for patients with severe cardiopulmonary failure.

[0003] The working principle of an oxygenation membrane is to drain the patient's venous blood outside the body and utilize the concentration gradient of oxygen and carbon dioxide across the membrane. Through diffusion, carbon dioxide in the blood enters the membrane lumen and is carried away along with oxygen, while oxygen enters the blood, thus achieving blood oxygenation. The selection and design of the oxygenation membrane material are crucial to the efficiency and safety of ECMO. For example, Chinese Patent CN1622850A – a polyolefin membrane with an integral asymmetric structure and its preparation method (applied by Menbrane Ltd.) – describes a polyolefin membrane (the polyolefin can be poly(4-methyl-1-pentene) or polypropylene) prepared by a thermally induced liquid-liquid phase separation method. This membrane has a sponge-like, open-pore microporous support structure and a relatively dense separation layer with a porosity of 30-75% by volume. The support layer has no macropores but contains isotropic pores. Furthermore, the membrane has at least one separation layer with a maximum number of pores <100 on at least one surface of the support layer. This membrane exhibits excellent plasma permeation time and is particularly suitable for use as a blood oxygenation membrane.

[0004] With the rapid development of science and technology and the economy, people have higher requirements for oxygenation membranes, hoping that they will have higher oxygenation performance. This is because in scenarios such as cardiopulmonary surgery and organ transplantation, if the oxygenation membrane has higher oxygenation performance, it can achieve rapid exchange of oxygen and carbon dioxide in the blood, thereby ensuring the normal operation of various organs, further reducing secondary harm to patients during surgery, and ensuring patient health. However, in general, in order to improve the oxygenation performance of oxygenation membranes, those skilled in the art often improve the gas mass transfer rate. To improve the gas mass transfer rate, it is necessary to increase the porosity of the oxygenation membrane. On the one hand, it is difficult to increase the porosity of oxygenation membranes (the porosity of oxygenation membranes cannot be increased indefinitely, as it is affected by factors such as raw materials and processes). On the other hand, increasing the porosity can easily lead to a significant decrease in the mechanical properties of the oxygenation membrane, making the oxygenation membrane unsuitable for practical applications. Therefore, how to prepare an oxygenation membrane with both high oxygenation performance and high mechanical properties is currently one of the hot research topics. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide an asymmetric polypropylene hollow fiber oxygenation membrane, its preparation method, and its application. The outer surface of the polypropylene oxygenation membrane has pores, and the membrane as a whole, under the combined effect of appropriate crystallinity, uniform bubble point, and porosity, achieves excellent oxygenation performance. Furthermore, the use of high molecular weight polypropylene raw materials to prepare the oxygenation membrane results in good mechanical properties.

[0006] To achieve the above objectives, the present invention provides the following technical solution: an asymmetric polypropylene hollow fiber oxygenation membrane, comprising a main body, one side of which is an inner surface facing the inner cavity, and the other side of which is an outer surface; the main body has non-directional tortuous pathways within it; the outer surface includes a plurality of first surface fibers for forming a porous structure; in the circumferential direction of the oxygenation membrane, the average SEM spacing between adjacent first surface fibers is 10-120 nm; the DSC crystallinity of the oxygenation membrane is 30%-60%.

[0007] The polymer constituting the oxygenation membrane is polypropylene with a weight-average molecular weight of 500,000 to 800,000.

[0008] The oxygenated membrane has a porosity of 20%-60%, a uniform bubble point of IPA of 0.6-1.0 MPa, and a thickness of 30-80 μm.

[0009] Currently, those skilled in the art desire polypropylene oxygen membranes to possess excellent mechanical properties. This is because oxygen membranes generally need to be woven into oxygen membrane fabric before use. If their tensile strength and elongation at break are low, it will greatly increase the difficulty of weaving (for example, filament breakage may occur during the weaving process). At the same time, the weaving process may reduce the oxygenation performance and durability of the oxygen membrane. Furthermore, in actual use, the oxygen membrane needs to withstand pressure changes in the circulation system, so it needs sufficient mechanical properties to ensure that it does not rupture under high pressure (the magnitude of internal and external burst pressure reflects the membrane material's ability to resist membrane filament damage caused by internal and external pressure differences).

[0010] To ensure the oxygenated membrane of this invention possesses excellent mechanical properties, the molecular weight of the polypropylene raw material is first controlled. Research has shown that the molecular weight of the raw material significantly affects the mechanical strength of the film; generally, the higher the molecular weight, the greater the mechanical strength of the membrane. However, excessively high molecular weight polymers greatly increase the viscosity of the casting solution, which may lead to poor flow performance during membrane formation, affecting membrane uniformity and pore structure formation, resulting in excessively low porosity. Simultaneously, it affects the crystallinity of the membrane (the molecular weight of the polymer raw material and the overall crystallinity of the membrane are mutually influential), thereby impacting the mechanical properties of the oxygenated membrane. Regarding oxygenation performance (in the prior art, those skilled in the art generally choose polypropylene raw materials with relatively low molecular weight, typically 200,000-400,000 in weight average molecular weight. This is because polypropylene with relatively low molecular weight is easier to form into films, resulting in more uniform membrane pores and higher integrity of membrane fibers, which helps ensure that the membrane fibers have suitable mechanical and oxygenation performance); however, this invention ultimately selects polypropylene raw materials with higher molecular weight. By controlling the weight average molecular weight of the polypropylene raw materials to 500,000-800,000, it is beneficial to improve the mechanical properties of the membrane and also to ensure that the membrane as a whole has suitable porosity and crystallinity, thus guaranteeing oxygenation performance;

[0011] Meanwhile, membrane crystallinity is one of the important factors affecting the mechanical properties of membrane materials. Those skilled in the art generally desire polypropylene oxygen membranes to have high crystallinity, even the higher the better, because generally, higher crystallinity results in higher mechanical strength of the membrane fibers. However, further research has found that excessively high crystallinity can significantly reduce the oxygenation performance of the oxygen membrane, leading to insufficient oxygenation performance and failing to meet the requirements of practical applications. This is because excessively high crystallinity means that there are more ordered molecular chain regions in the membrane, which can easily hinder the diffusion of gas molecules, thereby reducing the gas mass transfer rate of the oxygen membrane. Simultaneously, the crystalline regions... High crystallinity can lead to reduced membrane porosity (i.e., excessively high crystallinity often results in a lower overall membrane porosity), reducing the channels for gas molecules to pass through the membrane and further affecting gas exchange efficiency, thus reducing the membrane's oxygenation capacity. Therefore, in this invention, while using high molecular weight polypropylene raw materials, we do not want the membrane to be too crystallinity. Through research, we control the DSC crystallinity of the membrane fibers to 30%-60%. This appropriate crystallinity ensures that the membrane has good mechanical properties (such as tensile strength and elongation at break) without affecting gas diffusion, which is conducive to obtaining a higher mass transfer rate and ensuring oxygenation performance.

[0012] Furthermore, by adjusting the IPA bubble point of the oxygenated membrane to a uniform range of 0.6-1.0 MPa, we demonstrated that the overall pore size of the oxygenated membrane is relatively small, while the overall porosity is 20%-60% (which can be 25%, 40%, or 50%), further indicating that the overall number of pores in the oxygenated membrane is relatively large. That is, although the overall pores of the membrane fibers are small, the number of pores is large. At the same time, by controlling the membrane fiber thickness to 30-80 μm, a suitable thickness is achieved, ensuring the mechanical properties of the membrane fibers. In other words, based on the use of high molecular weight polypropylene raw materials and a certain degree of crystallinity in the membrane fibers, by further adjusting the bubble point, porosity, and thickness of the oxygenated membrane, we ensured that the oxygenated membrane has excellent mechanical properties, high tensile strength, and high pressure resistance on both the inner and outer surfaces.

[0013] To achieve superior oxygenation capacity and rapid gas exchange of oxygen and carbon dioxide in the oxygenation membrane of this invention, the pore structure on the outer surface of the membrane is first controlled. This involves creating several first surface fibers (fibers of a certain length and thickness) on the outer surface. These first surface fibers are relatively uniformly distributed on the outer surface of the membrane, forming corresponding pores between adjacent fibers. This results in numerous pores on the outer surface of the membrane. The presence of these pores facilitates the rapid permeation of gases such as oxygen and carbon dioxide, significantly improving the gas mass transfer rate and contributing to high oxygenation performance. This is distinctly different from a dense outer surface (where pores are almost nonexistent in a 50,000x electron microscope image). Further research revealed that the average SEM spacing between adjacent first surface fibers needs to be controlled at 10-120 nm (in the circumferential direction of the oxygenation membrane). This is because our research showed that even if the average SEM spacing between the first surface fibers is further increased (i.e., the pore size on the outer surface is increased), the oxygenation performance of the membrane fibers does not improve. Further improvements, however, actually increase the spacing between the first surface fibers, leading to a significant decrease in the compressive strength of the outer surface and a substantial reduction in the overall tensile strength of the membrane. Simultaneously, the membrane fibers' durability deteriorates, resulting in excessively low plasma permeation time. Furthermore, we discovered that the molecular weight of the polypropylene (PP) raw material also affects the gas mass transfer performance of the membrane. This is likely because different molecular weights influence the interaction forces between polymer chains, altering gas diffusion behavior within the membrane and thus affecting the gas mass transfer rate. This invention, through the synergistic effect of a higher molecular weight polypropylene raw material and appropriate crystallinity (based on a suitable spacing between the first surface fibers on the outer surface), not only improves the overall mechanical strength of the membrane but also facilitates higher oxygenation performance. Furthermore, by further controlling the uniform bubble point size, porosity, and thickness of the polypropylene oxygenation membrane, the synergistic effect of these characteristics ensures that the oxygenation membrane of this invention possesses excellent oxygenation capacity, thereby enabling rapid exchange of oxygen and carbon dioxide in the blood, ensuring the normal functioning of various organs, and guaranteeing that surgery will not cause secondary harm to the patient.

[0014] The oxygenation membrane of this invention is made of polypropylene, a non-polar material that is easy to process, low in cost, and possesses good chemical stability and biocompatibility. (The oxygenation mechanism of polypropylene (PP) differs significantly from that of poly(4-methyl-1-pentene) oxygenation (PMP), therefore, PP oxygenation membranes and PMP oxygenation membranes are fundamentally incomparable and cannot be compared.) In this invention, by adjusting the spacing of the first fibers on the outer surface of the polypropylene oxygenation membrane to a suitable interval, and simultaneously achieving suitable crystallinity, uniform bubble point, and porosity throughout the membrane, excellent oxygenation properties are achieved in this oxygenation membrane. In terms of performance, the oxygenation membrane, made from high-molecular-weight polypropylene raw materials, maintains good mechanical properties through synergistic effects, truly achieving a balance between high oxygenation performance and high mechanical properties. Furthermore, we know that polypropylene is a non-polar polymer material with no selectivity. However, this invention, by controlling the molecular weight of the polypropylene raw material and the overall crystallinity of the membrane, surprisingly achieves a certain selectivity in the polypropylene oxygenation membrane, namely a gas separation factor α (CO2 / O2) greater than 1.3. This facilitates the effective separation of oxygen and carbon dioxide, thereby further improving oxygenation performance.

[0015] In this invention, the non-directional tortuous pathways refer to randomly oriented groove structures and / or discretely distributed pore structures, and each non-directional tortuous pathway is interconnected; and the fibers forming the porous membrane structure are continuous. It can be understood that "continuous" means that essentially all the fibers are interconnected as a whole and are formed integrally without the need for additional adhesives or the like to connect them. Unless torn by external force, the network of fibers cannot be separated from each other. That is, the oxygenated membrane of this invention is a single-layer membrane structure, rather than a composite membrane structure.

[0016] The DSC crystallinity of the oxygen membrane in this invention refers to the crystallinity of the oxygen membrane obtained by differential scanning calorimetry.

[0017] Weight-average molecular weight is the statistical average molecular weight based on mass, obtained by averaging over a unit weight. It can be measured by GPC (gel permeation chromatography).

[0018] The SEM average spacing between adjacent first surface fibers on the outer surface of the oxygenation membrane can be characterized by scanning electron microscopy, followed by measurement and calculation using computer software (such as Matlab, NIS-Elements, etc.) or manually. During membrane fabrication, in the direction perpendicular to the membrane thickness (planar if the membrane is a flat sheet, perpendicular to the radius if it's a hollow fiber membrane), the spacing between adjacent first surface fibers is generally uniform and consistent. Therefore, the spacing between adjacent first surface fibers in a specific region of the corresponding plane can reflect the overall spacing between adjacent first surface fibers on that plane. In actual measurement, the outer surface of the membrane can be characterized using a microscope to obtain the corresponding SEM image. Since the spacing between adjacent first surface fibers on the outer surface is generally uniform, a certain area, such as 100 μm, is selected. 2 (10μm x 10μm), 1μm 2 (1μm x 1μm), the specific area size depends on the actual situation. Then, the spacing between adjacent first surface fibers on this area is measured using appropriate computer software or manually. Several tests are performed (preferably more than 10 times, the specific number depends on the situation), and the average value is taken to obtain the SEM average spacing between adjacent first surface fibers on the outer surface. Of course, those skilled in the art can also obtain the above parameters through other measurement methods. The above measurement methods are for reference only. (The SEM average length and SEM average width of the first surface fibers on the outer surface of the oxygen membrane can also be obtained by referring to this method).

[0019] Bubble point is an important performance characteristic of membranes, and its level significantly affects the application range of the membrane. The testing methods for bubble point are well-known in the art; for example, the procedures for these tests are explained in detail in ASTM F316-70 and ANS / ASTM F316-70 (re-approved in 1976), which are incorporated herein by reference. The test solution used in this invention is IPA (isopropanol). The bubble point is divided into the bubble initiation point and the uniform bubble point. When the membrane fiber begins to bubble, the pressure at this point is recorded as the bubble initiation point. When the entire membrane fiber exhibits uniform bubble formation, the pressure at this point is recorded as the IPA uniform bubble point. The uniform bubble point reflects the overall pore size of the membrane; generally, a larger uniform bubble point indicates a smaller overall pore size. In this invention, the oxygenation membrane has a suitable IPA uniform bubble point, thus demonstrating that the oxygenation membrane has a suitable pore size.

[0020] The thickness of the oxygenated membrane of the present invention can be obtained by characterizing the morphology of the membrane structure using a scanning electron microscope, and then by measuring it using computer software (such as Matlab, NIS-Elements, etc.) or manually. Commonly used porosity testing methods include mercury intrusion porosimetry, density method and wet-dry membrane weighing method, etc. Of course, those skilled in the art can also obtain the above parameters by other measurement methods. The above measurement methods are for reference only.

[0021] As a further improvement of the present invention, infrared absorption spectroscopy tests were performed on the inner and outer surfaces of the oxygenation membrane using the ATR method at a wavenumber of 988 cm⁻¹. -1 -1008cm -1 The first peak is located at a wavenumber of 1450 cm⁻¹. -1 -1470cm -1 A second peak exists at the location of the first peak, and the ratio of the peak area of ​​the first peak to the peak area of ​​the second peak is the mechanical coefficient X of the oxygenation film; wherein the mechanical coefficient of the inner surface of the oxygenation film is X. 内 The mechanical coefficient of the outer surface of the oxygen film is X. 外 The X 外 The initial water contact angle of the outer surface is 0.03-0.12; and / or the initial water contact angle of the outer surface is 100°-135°; and / or the porosity of the outer surface is 0.1%-8%.

[0022] The outer surface is the area of ​​the oxygenation membrane that directly contacts the external blood, therefore, its characteristics can significantly affect various properties of the oxygenation membrane. Simultaneously, factors such as the crystallization state of the porous membrane also influence the gas mass transfer rate and pore structure, thus affecting the oxygenation performance and mechanical properties of the oxygenation membrane. Studies have found that polypropylene exhibits certain characteristics at 998 cm⁻¹ in its infrared spectrum. -1 Near the location (at a wave number of 988cm) -1 -1008cm -1 The position of the oxygen membrane (1460 cm⁻¹) exhibits a crystallization absorption peak, and its value is influenced by various factors such as the crystallization state of polypropylene, the type of crystal form, and the pore size of the membrane. Furthermore, the magnitude of this value affects the mechanical strength of the inner and outer surfaces of the oxygen membrane, as well as the overall mechanical strength of the oxygen membrane. -1 Nearby (1450cm) -1 -1470cm -1 The vibration of the position of the PP is independent of the spatial conformation of the PP and is only related to the characteristic vibrational frequency of the group. It can be used as an internal standard peak to eliminate operational interference. Therefore, this invention controls the mechanical coefficient X of the inner and outer surfaces (the reason for the ratio is that research has found that only 998 cm⁻¹ is used). -1The size of the absorption peak near the location of the crystallization can vary greatly, failing to accurately represent the various properties of the oxygenation membrane. This affects the pressure resistance of both the inner and outer surfaces, further impacting the overall mechanical and oxygenation properties of the membrane, and also affecting the durability of the membrane fibers. Furthermore, this invention adjusts the mechanical coefficient X of the outer surface of the oxygenation membrane... 外 It is 0.03-0.12, because when X 外 When the temperature is too high or too low, it generally means that the crystallinity of the outer surface of the oxygenation membrane is too high or too low, and the membrane pores are too large or too small. This is either detrimental to the pressure resistance and durability of the outer surface of the oxygenation membrane, or it is not conducive to the rapid permeation of gas through the outer surface to achieve rapid gas exchange, thus hindering the achievement of high oxygenation performance; while when X 外 Within a suitable range, it is beneficial to ensure that the outer surface of the membrane has good pressure resistance, thereby ensuring that the membrane as a whole has a high internal burst pressure (bursting from the outside to the inside), while also enabling the oxygenation membrane to have good oxygenation capacity and a high plasma permeation time.

[0023] Meanwhile, the pore area ratio of the outer surface (the ratio of the pore area of ​​the outer surface to the total area of ​​the outer surface) also affects the gas exchange efficiency of the oxygenation membrane. A higher pore area ratio means more gas exchange area, which can improve oxygenation efficiency. However, if the pore area ratio of the outer surface is too high, it may significantly reduce the plasma permeation time of the membrane fibers and also reduce the mechanical strength of the membrane (especially the pressure resistance of the outer surface is easily reduced). In this invention, the oxygenation performance of the oxygenation membrane is further improved by the synergistic effect of the appropriate spacing between adjacent first surface fibers and the pore area ratio of the outer surface, while having little impact on the membrane fiber tolerance (the plasma permeation time remains basically unchanged) and ensuring the mechanical strength of the membrane fibers.

[0024] The size of the water contact angle depends on the properties of the material itself and the properties of the material surface. In this invention, the initial water contact angle of the oxygenation membrane is 100°-135°, preferably 103°-125° (generally, a larger water contact angle indicates better hydrophobicity of the material), which means that the outer surface of the oxygenation membrane of this invention has good hydrophobicity, thus having better tolerance and service life. Generally, in order to ensure the plasma permeation time of the membrane fibers, we want the initial water contact angle of the membrane to be as large as possible. However, further research has found that an excessively large initial water contact angle can easily lead to platelet adhesion and blood deposition, reduce the blood compatibility of the oxygenation membrane, increase the risk of thrombosis, and increase the non-specific adsorption of proteins, thereby increasing the possibility of inflammatory and immune responses. Therefore, we do not want the initial water contact angle of the outer surface to be too large. In this invention, the initial water contact angle of the outer surface, the porosity, and the mechanical coefficient X are used to determine the optimal water contact angle. 外Under the combined control, on the one hand, the outer surface of the membrane fiber has good mechanical strength, and on the other hand, the membrane fiber as a whole has good biocompatibility and tolerance, resulting in a long service life and no secondary harm to patients. It also further improves oxygenation performance and facilitates rapid gas exchange.

[0025] The porosity of the outer surface can be determined by first characterizing the morphology of the outer surface using a scanning electron microscope, then measuring it using computer software (such as Matlab, NIS-Elements, etc.) or manually, and performing corresponding calculations; by selecting a certain area, for example, 1 μm 2 (1μm x 1μm) or 25μm 2 (5μm x 5μm), the specific area size depends on the actual situation. Then, use appropriate computer software or manual measurement to find the area of ​​all holes on this area, then calculate and sum them, and then divide by the corresponding area to obtain the porosity of the surface (measure multiple times and take the average value, preferably more than 3 times); of course, those skilled in the art can also obtain the above parameters through other measurement methods. The above measurement methods are for reference only (the porosity of the inner surface of the oxygenation film can also be obtained by referring to this method).

[0026] The initial water contact angle of the outer surface of the oxygenated membrane in this invention was measured and obtained by Krüger Scientific Instruments (Shanghai) Co., Ltd. using a K100 surface tension meter and the Williams dynamic contact angle method. In the initial water contact angle test, it is necessary to use tools such as glass slides to flatten the oxygenated membrane filaments and form a thin sheet before the water contact angle of the outer surface is tested.

[0027] As a further improvement of the present invention, the X 内 Not greater than 0.4; X 内 / X 外 The porosity of the oxygenated membrane is 25%-55%, and the uniform bubble point of IPA is 0.7-0.95 MPa.

[0028] Generally, those skilled in the art would prefer a dense outer surface (to ensure plasma permeation time) and a large pore size on the inner surface with a high pore area ratio (to ensure gas mass transfer rate, as the gas mass transfer rate affects oxygenation performance to some extent; a low gas mass transfer rate leads to low oxygenation performance). This could result in low overall mechanical strength of the membrane fibers, or even local defects. Meanwhile, since the oxygenation membrane of this invention is generally prepared by a thermally induced phase method, the crystallization of the inner and outer surfaces generally has a significant impact on the pore size (pore area ratio and pore diameter) of the inner and outer surfaces (i.e., in the prior art, the crystallization of the inner and outer surfaces of existing oxygenation membranes differs greatly). However, in this invention, since pores of a certain diameter already exist on the outer surface, the pore diameter on the inner surface does not need to be very large (it can be relatively small), and the number of pores does not need to be excessive (the pore area ratio can be relatively small). That is, the crystallization of the inner and outer surfaces is less different. By further controlling the crystallization and pore size of the inner and outer surfaces, X... 内 / X 外 The value ranges from 1.1 to 3.8, while X... 内 The ratio is no greater than 0.4, which ensures that both the inner and outer surfaces have suitable opening and crystallization conditions, thus facilitating the transport of oxygen and carbon dioxide in the membrane and achieving a better gas exchange balance. At the same time, it can further improve the overall toughness of the membrane fibers, so that the oxygenation membrane has higher internal and external burst pressures. Meanwhile, under the combined effect of a suitable ratio of inner and outer surface mechanical coefficients, a certain overall porosity, and a certain uniform bubble point of IPA, the membrane fibers are further guaranteed to have excellent oxygenation performance and good mechanical properties.

[0029] As a further improvement of the present invention, the average length of the first surface fiber in SEM is 100-900 nm and the average width in SEM is 20-300 nm.

[0030] The length direction of the first surface fiber is consistent with the length direction of the oxygen film, and the width direction of the first surface fiber is consistent with the circumferential direction of the oxygen film.

[0031] In this invention, pores exist on the outer surface, formed by the first surface fibers. Therefore, certain characteristics of the first surface fibers influence the various properties of the membrane. Research has shown that when the length of the first surface fibers is too large, the pores on the outer surface tend to be larger, thus reducing the plasma permeation time of the membrane fibers. Conversely, when the length of the first surface fibers is too small, the pores on the outer surface tend to be smaller, and the mass transfer rates of various gases do not significantly improve. Simultaneously, the thickness of the first surface fibers affects the overall plasma permeation time and biocompatibility of the membrane fibers. Generally, thicker first surface fibers may result in a more robust oxygenation membrane with better resistance to plasma permeation. The invention improves the anti-plasma leakage performance of the oxygenation membrane while maintaining excellent gas permeability, resulting in good overall oxygenation performance. Furthermore, it enhances the biocompatibility of the PP oxygenation membrane, reducing the likelihood of plasma permeation during oxygenation and preventing secondary harm to patients during surgery. The finer first surface fibers provide a smoother outer surface, reducing the adsorption and activation of blood components, thus lowering the risk of inflammation and thrombosis. Based on a suitable spacing between adjacent first surface fibers on the outer surface, the length and width of the first surface fibers are further simultaneously controlled. This combined effect further improves the anti-plasma leakage performance of the oxygenation membrane while maintaining excellent gas permeability. The PP oxygenation membrane also exhibits good biocompatibility, making it less prone to thrombosis during oxygenation and preventing secondary harm to patients during surgery.

[0032] As a further improvement of the present invention, the inner surface includes a plurality of second surface fibers for forming a porous structure; in the circumferential direction of the oxygen membrane, the average SEM spacing between adjacent second surface fibers is 50-300 nm; the ratio of the average SEM length of the second surface fiber to the SEM width of the second surface fiber is 2.5-20.

[0033] In addition to controlling the characteristics of the first surface fibers on the outer surface, we also further controlled the second surface fibers (fiber structures of a certain length and thickness) on the inner surface. These second surface fibers are relatively uniformly distributed on the inner surface of the membrane, and corresponding pores are formed between adjacent second surface fibers, resulting in several pores on the inner surface of the membrane. The presence of these pores ensures that the membrane as a whole has a high porosity, which is conducive to the rapid permeation of gases such as oxygen and carbon dioxide, thus helping the membrane to obtain high oxygenation performance. The study found that by controlling the average SEM spacing between adjacent second surface fibers to 50-300 nm (in the circumferential direction of the oxygenation membrane), it is beneficial to ensure the gas mass transfer rate, while also ensuring the pressure resistance of the inner surface and the stability of the membrane pores. At the same time, we also found that even if the average SEM spacing between the second surface fibers is further increased (which can be regarded as further increasing the pore size on the inner surface), the oxygenation performance of the membrane fibers is not further improved. On the contrary, the pressure resistance of the inner surface will be significantly reduced, resulting in a decrease in the overall mechanical strength of the membrane fibers.

[0034] Meanwhile, we found that, based on a suitable spacing between adjacent second surface fibers on the inner surface, it is preferable to further adjust the length-to-width ratio of the second surface fibers so that, within a relatively suitable range, the stability of the pores on the inner surface of the membrane can be further guaranteed. Under long-term operation, the pores on the inner surface are not prone to deformation or collapse, resulting in long-term efficient oxygenation.

[0035] As a further improvement of the present invention, the pore area ratio of the inner surface is 2%-20%; the pore area ratio of the inner surface is greater than that of the outer surface, and the difference between the two is not greater than 15%; and / or, the ratio of the average SEM spacing between adjacent second surface fibers to the average SEM spacing between adjacent first surface fibers is 2-18:1.

[0036] Since the outer surface is in direct contact with blood, it needs to be relatively dense (with a low pore area ratio). To ensure oxygenation performance, we want the inner surface to have a relatively large pore area ratio, but not too large (too large a pore area ratio can lead to low compressive strength of the inner surface). Research has shown that the pore area ratio of the inner surface is controlled between 2% and 20%, which helps the membrane fibers to have a larger gas exchange surface area, further improving the gas exchange efficiency of the oxygenation membrane. However, unlike existing technologies (where the outer surface has almost no pores, i.e., the pore area ratio is almost 0, resulting in a large difference between the pore area ratios of the inner and outer surfaces), the pore area ratios of the inner and outer surfaces in this invention will not differ too much, with a difference of no more than 15% (obtained directly by subtracting the outer surface pore area ratio from the inner surface pore area ratio). This helps to ensure the overall mechanical strength of the membrane fibers (high tensile strength and elongation at break), while also providing high durability and stability, and high industrial applicability. Furthermore, by adjusting the ratio of the spacing between adjacent fibers on the inner and outer surfaces (which to some extent reflects the ratio of the membrane pore size on the inner and outer surfaces) and the appropriate pore area ratio on the inner and outer surfaces, the durability of the membrane fibers can be further improved, enabling them to maintain various performance characteristics during long-term use; at the same time, the gas mass transfer rate of the membrane can be adjusted to ensure oxygenation performance.

[0037] As a further improvement of the present invention, the main body cross section includes a plurality of cross-sectional fibers for forming a porous structure, and the SEM average diameter of the cross-sectional fibers is 25-135 nm;

[0038] And / or, the ratio of the IPA bubbling point to the uniform bubbling point of the oxygenation membrane is 0.7-0.96:1.

[0039] The cross-sectional fiber has a significant impact on various properties of the membrane. Generally, thicker cross-sectional fibers are more conducive to ensuring the overall mechanical properties of the membrane, providing better support and structural stability (the membrane pores remain stable under long-term high pressure). However, excessively thick cross-sectional fibers often hinder gas transport, thereby reducing gas exchange efficiency and lowering oxygenation performance. Further research revealed that, based on a certain uniform bubble point and a certain porosity, this invention controls the SEM average diameter of the cross-sectional fibers to 25-135 nm. This allows the membrane fibers to have superior mechanical strength and durability, ensuring better resistance to material fatigue caused by pressure and time, and maintaining the stability of various properties over a long period. At the same time, it has little impact on the oxygenation performance of the membrane fibers, which still exhibit excellent oxygenation performance.

[0040] The bubble point of a membrane primarily reflects the maximum pore size within the membrane (when the pressure reaches this critical value, gas will escape from the membrane pores, forming bubbles). If the bubble point is too small, it indicates that the maximum pore size inside the membrane is very large. This will affect the overall plasma permeation time of the membrane, increasing the risk of plasma permeation. Furthermore, it may indicate defects in certain areas of the membrane, affecting its mechanical properties (e.g., increased filament breakage during weaving). The ratio between the bubble point and the uniform bubble point further indicates the pore size distribution of the membrane. The pore size distribution affects the diffusion path of gas molecules, the mass transfer area, and the flow pattern within the pores (the transfer mechanism of gas molecules may differ in different pore sizes). The gas mass transfer rate is significantly affected, thus influencing oxygenation performance. This invention features a suitable pore size distribution, ensuring appropriate porosity for the membrane fibers and relatively ideal mass transfer between oxygen and carbon dioxide. This facilitates carbon dioxide removal and allows oxygen to more easily and quickly pass through the membrane into the bloodstream. Furthermore, an excessively large pore size distribution indicates significant differences in pore size within the membrane, which can easily affect the durability of the membrane fibers. This invention, with its specific fiber cross-section and a suitable ratio of IPA bubble point to IPA uniform bubble point, ensures that the membrane fibers possess high oxygenation membrane performance while also exhibiting good durability and stability, guaranteeing the stability of the membrane pores under prolonged high-pressure operation.

[0041] In this invention, the SEM average diameter of the cross-sectional fibers can be obtained by first characterizing the morphology of the outer surface of the membrane using a scanning electron microscope, and then measuring and calculating it using computer software (such as Matlab, NIS-Elements, etc.) or manually. Specifically, the cross-section of the oxygen membrane is first characterized using SEM to obtain the corresponding SEM image. Since the width of the fibers on the cross-section of the oxygen membrane is roughly uniform, a certain area is selected, for example, 100 μm. 2 (10μm x 10μm) or 1μm 2(1μm x 1μm), the specific area depends on the actual situation. Then, use computer software or manual measurement to determine the diameter of the cross-sectional fiber in that area. Perform several tests (preferably more than 10 times, the specific number depends on the situation), take the average value, and thus obtain the SEM average diameter of the cross-sectional fiber.

[0042] As a further improvement of the present invention, in the film thickness direction from the outer surface to the inner surface, the average pore size of the main body first decreases and then increases; the main body includes a pore region, the nearest average distance from the pore region to the outer surface is less than the nearest average distance from the pore region to the inner surface, and the nearest average distance from the pore region to the outer surface is 0.2-3 μm; the porosity of the oxygenated membrane is 30%-50%.

[0043] As is known from existing technology, those skilled in the art generally expect the outer surface (regardless of whether there are pores on the outer surface; if the outer surface is dense, it is equivalent to the outer surface membrane pore diameter being 0) to be the region with the smallest membrane pore diameter on the oxygenation membrane. This is because the outer surface of the oxygenation membrane is the region in the oxygenation membrane that is in direct contact with external blood. If its pore diameter is not the smallest, then the tolerance of the oxygenation membrane (i.e., plasma permeation time) will easily be very poor, failing to meet the needs of practical applications. However, continuous research has revealed that the pore diameter of the outer surface membrane of the oxygenation membrane does not necessarily have to be the smallest. In some oxygenation membranes prepared by this invention, in the membrane thickness direction from the outer surface to the inner surface, the overall pore diameter of the oxygenation membrane can first decrease and then increase. That is, there is a region with a very small pore diameter on the main body of the oxygenation membrane, which we call the pore region (this region can be considered as the region with the smallest pore diameter in the main body of the membrane). This pore region does not include the outer surface, but only needs to be located on the outer surface. The oxygenation membrane is located close to the surface. Since blood is directly located on the outside of the membrane, the distance between the pores and the outer surface cannot be too far. Research has optimized the closest average distance (the average distance from the side of the pore closest to the outer surface to the outer surface) to be 0.2-3 μm. This allows the oxygenation membrane to significantly improve its oxygenation performance while maintaining a good plasma permeation time (unlike existing membrane fibers where plasma permeation time rapidly decreases once oxygenation performance is improved). Furthermore, although the outer surface is not the area with the smallest pore size inside the oxygenation membrane, by controlling the presence of pores near the outer surface, the overall porosity of the oxygenation membrane, and the synergistic effect of uniform bubble points in the IPA, the oxygenation membrane achieves high oxygenation performance while also maintaining a good plasma permeation time and high tolerance. Simultaneously, the oxygenation membrane exhibits high mechanical properties, meeting various practical requirements and demonstrating high industrial applicability.

[0044] Since the oxygenated membrane of this invention is integrally formed without undergoing processes such as "composite bonding", by observing the main structure of the membrane (e.g., cross-sectional SEM image), it can be seen that the average pore size of the main body gradually changes with the thickness (without abrupt changes). Furthermore, in the membrane thickness direction from the outer surface to the inner surface, the membrane pore size first decreases and then increases. It should be noted that such pore size change is from the perspective of the membrane as a whole, rather than judging from just a specific location.

[0045] Since the pore size of the oxygenation membrane of this invention gradually decreases and then gradually increases with thickness (from the outer surface to the inner surface), there must exist a relatively dense pore region. The determination of this pore region is achieved by first characterizing the membrane cross-section using a scanning electron microscope to obtain a 10,000x magnification electron microscope image of the membrane cross-section; then, taking the outer surface as X0, ten baseline lines (straight lines) perpendicular to the membrane thickness direction are drawn at intervals of 0.5 μm and recorded as X1, X2…X8, X… 9 and X10, each baseline is 10 μm long; for example, taking X5 as an example, measure the pore size of the membrane located on this baseline (preferably more than 5 pores, the specific number depends on the situation), and then take the average value, which is △X5. Then, there must be at least one minimum value from △X1 to △X10, for example, △X5 is the minimum value; then, taking the position of X5 as Y0, draw 5 baselines (straight lines) perpendicular to the membrane thickness direction every 0.2 μm in the direction towards the inner and outer surfaces, and record them as Y. +1 -Y +5 Y -1 To Y -5 (Where the values ​​are +1 to +5 towards the outer surface and -1 to -5 towards the inner surface. However, depending on the actual situation of the SEM image, 6 baselines can be set towards the outer surface and only 4 towards the inner surface. The total number of baselines can also exceed 10, depending on the specific circumstances.) Each baseline is 10 μm long. Measure the pore diameter of the membrane pores located on this baseline (preferably 5 or more pores, the specific number depending on the situation), and then take the average value. Select several baselines whose difference from the average pore diameter of Y0 is no greater than 20% as qualified baselines. Finally, the qualified baseline closest to the outer surface and the qualified baseline closest to the inner surface are the small pore area (assuming the measured average pore diameter at Y0 is 200 nm, then any baseline with an average pore diameter no greater than 240 nm is a qualified baseline, such as Y3, Y2, Y1, Y...). -1 Y -2 These baselines are considered acceptable baselines. Therefore, the acceptable baseline closest to the outer surface is Y3, and the acceptable baseline closest to the inner surface is Y... -2 Therefore, the location of the small hole region can be considered as Y3-Y -2(The thickness of the small hole area is the Y3 baseline and Y...) -2 The distance between the baselines), and the shortest average distance from the pore area to the outer surface is the distance between the outer surface and the Y3 baseline (the average distance is used because theoretically the membrane pore size cannot be absolutely uniform), and the shortest average distance from the pore area to the inner surface is the distance between the inner surface and the Y3 baseline. -2 The distance between baselines.

[0046] As a further improvement of the present invention, the thickness of the pore region is 0.2-2 μm, and the ratio of the thickness of the pore region to the overall thickness of the membrane is 0.4%-5%.

[0047] When the pore structure of the oxygenation membrane first decreases and then increases (in the membrane thickness direction from the outer surface to the inner surface), the micropore region within the membrane can be considered the area with the smallest pore size in the membrane body. Further research revealed that both the absolute and relative thickness of the micropore region affect the overall membrane pore size (uniform bubble point size) and porosity, thus impacting the oxygenation performance and tolerance of the oxygenation membrane. When the absolute and relative thickness of the micropore region is too large, it will reduce local porosity and affect the overall porosity, potentially increasing the resistance to gas (such as oxygen and carbon dioxide) flow, thereby affecting oxygenation efficiency (even if the overall porosity of the membrane fibers remains relatively constant, excessive absolute thickness of the micropore region can still easily reduce oxygenation performance). Furthermore, it will... If the overall pore size of the membrane is too small, it will affect oxygenation performance and hinder the effective exchange of oxygen and carbon dioxide. In addition, if the pore area is too thick, it may increase the rigidity of the membrane, affecting its flexibility, greatly increasing the difficulty of membrane processing, and reducing its industrial applicability. When the absolute and relative thickness of the pore area is too small, it may lead to the pore size of the membrane fibers being too large, affecting the membrane fibers' tolerance and reducing the plasma permeation time. On the other hand, the synergistic effect of the pore area with appropriate absolute and relative thickness is as follows: First, the moderate thickness of the pore area can provide sufficient support (the pore area is equivalent to a reinforcing layer), enhancing the membrane's pressure resistance and tensile strength. Second, it allows the membrane fibers to have a longer plasma permeation time. In addition, it can also ensure the effective exchange of oxygen and carbon dioxide, meeting the needs of clinical applications.

[0048] As a further improvement of the present invention, the plasma permeation time of the oxygenation membrane is not less than 12 hours, preferably not less than 18 hours, and more preferably not less than 24 hours; the O2 mass transfer rate of the oxygenation membrane is not less than 15 ml / (cm²). 2 *min*bar), and the gas separation factor α(CO2 / O2) is not less than 1.3;

[0049] At 1.6m 2When oxygenating blood at a flow rate of 5 L / min, the oxygen saturation of the blood is not less than 99%, and the oxygen partial pressure is not less than 150 mmHg; the tensile strength of the oxygenating membrane is not less than 200 cN, and the elongation at break is not less than 500%; the internal burst pressure of the oxygenating membrane is not less than 2 bar, and the external burst pressure is not less than 3.5 bar.

[0050] The plasma permeation time of the PP oxygenation membrane of this invention is at least 12 hours, preferably at least 18 hours, and more preferably at least 24 hours, indicating that the oxygenation membrane has a long service life. During various cardiopulmonary surgeries and organ transplants, the oxygenation membrane does not need to be replaced, ensuring the normal progress of the surgery and reducing the impact of external factors on the success of the surgery. The oxygenation membrane of this invention has suitable oxygen and carbon dioxide mass transfer rates, allowing CO2 in the blood to be rapidly expelled and oxygen to rapidly enter the blood, achieving ideal gas exchange without affecting the patient's physical and mental health, ensuring the smooth progress of the surgery. Furthermore, the oxygenation membrane of this invention exhibits a certain selectivity, i.e., a gas separation factor α (CO2 / O2) greater than 1.3, which is more conducive to the effective separation of oxygen and carbon dioxide, further improving oxygenation performance and ensuring the oxygenation effect. Furthermore, after oxygenation performance testing, the oxygenation membrane has high oxygenation performance (oxygen saturation not less than 99%, preferably 100%; oxygen partial pressure not less than 150 mmHg, preferably not less than 200 mmHg, more preferably not less than 300 mmHg; the higher the oxygen partial pressure, the better the oxygenation performance), thus enabling the normal operation of various organs during surgery.

[0051] After mechanical strength testing, the tensile strength of the PP oxygen membrane of this invention is not less than 200 cN and the elongation at break is not less than 500%, which shows excellent mechanical properties and high industrial practical value. At the same time, the internal burst pressure (bursting from the outside to the inside) of the oxygen membrane is not less than 2 bar and the external burst pressure (bursting from the inside to the outside) is not less than 3.5 bar, which shows that the pressure resistance of both the inner and outer surfaces of the oxygen membrane is high, and it can resist and withstand the pressure changes in the circulatory system for a long time, and work normally under high pressure for a long time.

[0052] A second aspect of the present invention provides a method for preparing an asymmetric polypropylene hollow fiber oxygen membrane as described above, comprising the following steps:

[0053] Step 1: Heat and melt polypropylene, dissolve it in a solvent system containing compound A and compound B to prepare a homogeneous casting solution; wherein the molecular weight distribution index of polypropylene is 4-9, and the melt index is 0.1-1 g / min@(190℃, 5kg); wherein compound A is the solvent for polypropylene, and compound B is the non-solvent for PP, and the mass fraction of compound A in the solvent system is 55%-80%; the solid content of polypropylene in the casting solution is 30%-50%;

[0054] Step 2: Extrude the casting liquid through a die at a temperature of 175-190℃ to form a molded product with inner and outer surfaces.

[0055] Step 3: Cool the molded product with a coolant to separate the phases. The cooling temperature is 30-50℃ and the cooling time is 80-120ms. The coolant is a solvent system containing compound A and compound B, and the mass fraction of compound A in the solvent system is 10%-45%.

[0056] Step 4: Next, the molded product is subjected to high-temperature flash quenching with quenching liquid. The high-temperature flash quenching temperature is 75-100℃ and the time is 1s-20s. At the same time, it is stretched by 0.5%-2%. After quenching, a green film is obtained. The content of compound B in the quenching liquid is not less than 70%.

[0057] Step 5: Remove compounds A and B from the generated membrane to obtain the original membrane;

[0058] Step 6: Set the original film at high temperature and stretch it at the same time. The stretching rate is 1.5-10 times that of the stretching rate during high temperature flash quenching to obtain PP hollow fiber oxygen membrane.

[0059] As a further improvement of the present invention, the heating and melting process in step one includes three steps: melting, mixing and metering; wherein the melting temperature is 170-250℃, the mixing temperature is 180-245℃, and the metering temperature is 190-220℃; and / or, the die extrusion temperature is 10-25℃ lower than the metering temperature.

[0060] As a further improvement of the present invention, compound A is at least one of soybean oil, N,N-bis(2-hydroxyethyl) tallow amine, palm seed oil, sesame oil, peanut oil, sunflower seed oil, corn oil, dioctyl phthalate, paraffin oil, dibutyl sebate, dibutyl phthalate, and diisooctyl phthalate.

[0061] Compound B is at least one of diethyl phthalate, glyceryl triacetate, castor oil, dioctyl adipate, glyceryl diacetate, glycerol, and polyethylene glycol 200.

[0062] As a further improvement of the present invention, before cooling and separating the molded article in step three, the molded article is first subjected to preliminary phase separation. The specific steps of preliminary phase separation are as follows: the molded article is subjected to preliminary phase separation in an air section; the preliminary phase separation time is 0.02s-0.1s, and the air section temperature is 70-130℃; and / or, in step four, the quenching liquid is a solvent system of compound A and compound B, and the mass fraction of compound B in the solvent system is 75%-90%.

[0063] As a further improvement of the present invention, the removal of compounds A and B from the raw film in step five specifically refers to extracting the raw film with an extraction solution at a temperature of 60-80°C for 4-12 hours; wherein the extraction solution is any one of isopropanol, ethanol, and acetone; and / or, the high-temperature setting of the original film in step six specifically refers to placing the original film at a temperature of 90-120°C for high-temperature setting for 30-60 minutes, with an elongation rate of 3%-10%.

[0064] This invention prepares asymmetric polypropylene hollow fiber oxygenated membranes using a thermally induced phase separation method. The first step in preparing the oxygenated membrane involves heating and melting polypropylene (PP), dissolving it in a solvent system containing compounds A and B to form a homogeneous casting solution. This process facilitates the production of hollow fiber oxygenated membranes with good integrity and uniformity. One of the innovative aspects of this invention is the discovery of a suitable casting solution formulation, the most crucial element being the selection of a high molecular weight polypropylene raw material. In existing technologies, those skilled in the art generally choose polypropylene raw materials with relatively low molecular weights, and a weight-average molecular weight of... The molecular weight is typically between 200,000 and 400,000. This is because polypropylene with a relatively low molecular weight is easier to form a film, resulting in more uniform pores and higher film integrity. This helps ensure that the film has suitable mechanical and oxygenation properties (those skilled in the art believe that if the molecular weight of the raw material is higher, on the one hand, film formation becomes more difficult, and on the other hand, various defects are easily generated in the film fibers, resulting in poor integrity and a decrease in the overall mechanical strength of the film). After repeated research, this invention selected polypropylene raw materials with a weight-average molecular weight of 500,000 to 800,000, while controlling the molecular weight distribution index of the polypropylene raw material to be 4-9 and the melt flow index to be 0.1-1g. / min@(190℃, 5kg); Due to the high molecular weight of polypropylene raw materials, we hope that the molecular weight distribution of polypropylene raw materials is as wide as possible. We have found that a relatively wide molecular weight distribution makes it easier to form a film, but an excessively wide molecular weight distribution can easily lead to unstable film quality and a decrease in the mechanical strength of the film fibers. The melt index of a polymer is an important parameter for measuring the flow performance of a polymer in the molten state. Materials with a high melt index have good flowability and are easy to mold and process, while materials with a low melt index may have better mechanical strength. This invention selects polypropylene raw materials with appropriate molecular weight, a certain molecular weight distribution, and a certain melt index to form a suitable casting solution formulation. Under suitable process conditions, the oxygenated film fibers obtained will have ideal pore structure and porosity, and at the same time, they will have better mechanical properties. Meanwhile, the solid content of PP is relatively high, at 30%-50%, which makes it easy for the overall film to have a small pore size, ensuring plasma penetration time and mechanical strength, while also having high porosity to ensure oxygenation performance (if the solid content is too low, the overall pore size of the film will be too large, and the uniform bubble point will be too low; if the solid content is too high, the film forming difficulty will be greatly increased, and the porosity will be significantly reduced).

[0065] The solvent system includes compound A and compound B, wherein compound A is a solvent for PP and compound B is a non-solvent for PP; in this invention, a solvent refers to a polymer with a solid content of 25% that can be completely dissolved in the solvent at a temperature 50°C above the polymer's melting point; a non-solvent refers to a polymer with a solid content of 5% that can be completely dissolved in the solvent at a temperature 50°C above the polymer's melting point; more preferably, compound A is at least one of soybean oil, N,N-bis(2-hydroxyethyl) tallow amine, palm seed oil, sesame oil, peanut oil, sunflower seed oil, corn oil, dioctyl phthalate, paraffin oil, dibutyl sebate, dibutyl phthalate, and diisooctyl phthalate; compound B is diethyl phthalate, glyceryl triacetate, castor oil, etc. The solvent system contains at least one of the following: oil and dioctyl adipate, glyceryl diacetate, glycerol, and polyethylene glycol 200; a suitable solvent system that readily forms an ideal casting solution; combined with subsequent phase separation processes, this allows for the formation of the required membrane pore structure and corresponding pore size (with a suitable bubble point) and porosity (high porosity) characteristics of the oxygenated membrane of this invention; preferably, the mass fraction of compound A in the solvent system is 55%-80%, meaning that the solvent content is greater than the non-solvent content, which is more conducive to the uniform dispersion of polypropylene in the solvent system, further ensuring the integrity of the membrane fibers and the uniformity of the membrane pores; of course, if necessary, other substances such as antioxidants, nucleating agents, fillers, and similar substances can also be used as additives.

[0066] Preferably, in the heating and melting process, after the solid polypropylene raw material enters the equipment system from the hopper, it first passes through the screw extruder, then through the metering pump, and finally reaches the spinning box (die assembly), and is extruded from the spinneret. In this process, the melt mainly undergoes melting, mixing, and metering. The melting section is primarily responsible for conveying, pushing, and preheating the raw material. The preheating temperature is above the melting point of the raw material, allowing it to gradually melt and eventually reach a completely molten state. If the temperature in this section is too high, the raw material may decompose; if the temperature is too low, the raw material may not melt completely. The melting temperature of this application is 170-250℃, which allows the raw material to reach a suitable molten state. The mixing section is mainly responsible for mixing, compressing, and pressurizing the raw materials for degassing. All raw materials passing through this section are in a molten state. Excessive temperature in this section can cause the raw materials to decompose, while insufficient temperature results in poor melting and affects fluidity. In this application, the mixing section temperature is 180-245℃. Within this range, the raw materials achieve a suitable molten state, and the mixing, compression, and pressurizing degassing are effectively performed, preventing uneven pore distribution in the prepared membrane. The metering section's main functions are mixing, melting, and conveying, while also providing sufficient pressure to maintain a uniform temperature and stable melt flow rate. Excessive temperature causes the raw materials to decompose, while insufficient temperature results in poor melting. In this application, the metering section temperature is set at 190-220℃, allowing the raw materials to achieve a suitable molten state and a good melt flow rate. Preferably, the die extrusion temperature is 10-25℃ lower than the metering temperature. When polypropylene (PP) is extruded from the die, internal heat conduction occurs, lowering its temperature. During the cooling process, the temperature of the inner and outer surfaces becomes more uniform, ensuring more uniform crystallization and thus ensuring more uniform pore size in the prepared membrane.

[0067] The second step involves forming a molded product with inner and outer surfaces in a die at a temperature higher than the critical delamination temperature using the casting solution; this molded product is a hollow fiber oxygenated membrane. The casting solution is extruded through the central cavity of the hollow fiber die, which serves as the inner core, forming and stabilizing the hollow fiber membrane cavity. During extrusion, the inner core is heated to essentially the same temperature as the polymer solution. The extruded hollow fiber membrane has a surface facing the cavity, i.e., the inner surface, and a surface opposite the cavity, i.e., the outer surface; the outer surface is separated from the inner surface by the hollow fiber membrane wall. In this invention, the inner core used during hollow fiber membrane extrusion is in gaseous form, preferably nitrogen, argon, or other inert gases, to ensure that the pressure inside the hollow fiber membrane cavity remains balanced with the external pressure, thereby stabilizing the hollow fiber membrane cavity.

[0068] The third step is to cool and separate the molded product using a coolant. The selection of the type of coolant, the cooling temperature, and the duration of the cooling time are crucial during the phase separation and curing process. These factors determine whether an oxygenated membrane with ideal structure and performance can be obtained. Furthermore, the various conditions during cooling and phase separation are closely related to the casting solution formulation and subsequent processes, and cannot be chosen arbitrarily. In this invention, the coolant is a solvent system containing compound A and compound B. To ensure that the final oxygenated membrane has small pore sizes, is uniformly distributed, and has a relatively high bubble point, we use a relatively high amount of compound B (non-solvent) in the solvent system. Of course, a certain amount of compound A is also added to control the phase separation rate and ensure the uniformity of the membrane pores. With a suitable casting solution formulation and coolant, and by further controlling the cooling phase separation temperature to 30-50℃ and the cooling phase separation time to 80-120ms, along with a suitable coolant system, we ensured that the overall pore size of the oxygenation membrane was small, resulting in a longer plasma permeation time and higher overall mechanical strength. Furthermore, we were surprised to find that in addition to ensuring small pore size, we could also achieve a relatively large number of pores (i.e., the overall membrane still had high porosity). This ensured that the oxygenation membrane had high oxygenation performance, enabling rapid exchange of oxygen and carbon dioxide.

[0069] Preferably, before cooling and separating the molded product in step three, preliminary phase separation can be performed first. The purpose of preliminary phase separation is to create the "prototype" of pores on the outer surface of the membrane. With proper preliminary phase separation and cooling phase separation working together, it is beneficial to obtain an ideal outer surface, that is, the outer surface has first surface fibers of ideal length and width, and there is a suitable spacing between adjacent first surface fibers; and the outer surface has a suitable mechanical coefficient X. 外 However, it should be noted that the initial phase separation must be extremely short; otherwise, large pores may easily appear on the outer surface, which will affect the plasma permeation time of the membrane fibers and the pressure resistance of the outer surface.

[0070] The fourth step is to quench the molded product with a quenching liquid. According to existing technology, precise control of quenching conditions can optimize the pore structure of the oxygen membrane, thereby improving the mechanical properties and gas exchange efficiency of the membrane fibers. As one of the innovations of this invention, due to the use of high-molecular-weight polypropylene raw materials, a high-temperature flash quenching process is adopted during quenching. This involves two aspects: firstly, the quenching temperature is higher than existing technologies, at 75-100℃; secondly, the quenching time is very short, even extremely short, only 1-20 seconds. Simultaneously, the content of non-solvent compound B in the quenching liquid is not less than 70% (preferably, the quenching liquid is a solvent system of compound A and compound B, with the mass fraction of compound B in the solvent system being 75%-90%). Through this quenching process, on the one hand, it is beneficial to further form and fix the required pore structure; on the other hand, quenching can be rapid. The polymer phase formed during phase separation is solidified to prevent structural changes during subsequent processing or use, thereby obtaining the membrane structure required by this invention (ideal fiber structure appearing on the inner and outer surfaces of the membrane); at the same time, it improves the uniformity of membrane pores, which is more conducive to the formation of a uniform pore structure, resulting in suitable uniform bubble point and bubble initiation point of IPA, while the inner and outer surfaces have suitable mechanical coefficients; in addition, it can minimize the stress and small defects in the overall membrane, thereby improving the various mechanical properties of the membrane; furthermore, we found that during high-temperature flash quenching, slight stretching of the molded product at a stretch rate of 0.5%-2% helps the membrane fibers to open up better, opening some previously closed pores, which is more conducive to gas mass transfer, improves oxygenation performance, and further improves the tensile strength of the membrane.

[0071] The fifth step is to remove compounds A and B from the biofilm to obtain the original membrane. This process removes as many solvents and non-solvents as possible to minimize residues and prevent the introduction of other impurities, ensuring the biocompatibility of the polypropylene oxygen membrane and minimizing secondary harm to patients. Preferably, the extraction solvent is any one of isopropanol, ethanol, and acetone, extracted at 60-80℃ for 4-12 hours to ensure maximum removal of solvents and non-solvents from the membrane, reducing internal stress and defects, thereby improving membrane uniformity and mechanical properties.

[0072] Finally, the original membrane is high-temperature set to obtain a polypropylene oxygenated membrane. The PP oxygenated membrane after high-temperature setting exhibits good mechanical strength (high tensile strength and elongation at break), while eliminating internal stress and maintaining good integrity. As one of the inventive aspects of this invention, the original membrane is stretched during high-temperature setting, with a stretching rate of 1.5-10 times that during high-temperature flash quenching. This demonstrates that the stretching rate during high-temperature setting and the stretching rate during high-temperature flash quenching are closely related and inseparable. Through this stretching treatment during high-temperature setting, the membrane pore structure of the oxygenated membrane is further optimized, its permeability and mechanical properties are improved, plasma leakage is reduced, and other properties are modified. The surface properties are improved. Preferably, the high-temperature setting of the present invention specifically refers to setting at a temperature of 90-120℃ for 30-60 minutes with a stretching rate of 3%-10%, thereby fixing the membrane pore structure formed during the preparation of the oxygenation membrane, ensuring the uniformity of the membrane pore structure, and further guaranteeing the overall performance of the membrane. The final polypropylene oxygenation membrane has excellent oxygenation performance, good mechanical strength, and surprisingly exhibits a certain selectivity with a certain gas separation factor α (CO2 / O2), which is more conducive to the effective separation of oxygen and carbon dioxide, further improving the oxygenation performance.

[0073] As a further improvement of the present invention, an application of an asymmetric polypropylene hollow fiber oxygenation membrane is provided, wherein the oxygenation membrane is used for blood oxygenation in cardiopulmonary surgery and / or organ transplantation.

[0074] In cardiopulmonary surgery, oxygenation membranes can provide temporary cardiopulmonary support, ensuring oxygen supply and carbon dioxide removal in the patient's body and maintaining stable vital signs. In organ transplantation, oxygenation membranes can be used to maintain donor organs by providing stable blood circulation and oxygen supply, protecting organs from ischemia and reperfusion injury, while also helping to improve graft quality, reduce post-transplant complications, and improve patient survival rate and quality of life. The oxygenation membrane of this invention has excellent oxygenation performance, can rapidly increase blood oxygen partial pressure and blood oxygen saturation, and also has a good plasma penetration time, making it particularly suitable for use in cardiopulmonary surgery and / or organ transplantation.

[0075] The beneficial effects of this invention are as follows: The outer surface of the polypropylene oxygenation membrane provided by this invention includes a plurality of first surface fibers for forming a porous structure; the average SEM spacing between adjacent first surface fibers in the circumferential direction of the oxygenation membrane is 10-120 nm; and the membrane as a whole, under the combined effect of suitable crystallinity, uniform bubble point, and porosity, achieves excellent oxygenation performance; simultaneously, the oxygenation membrane, made from high molecular weight polypropylene raw materials, exhibits good mechanical properties; and by controlling the molecular weight of the polypropylene raw materials and the overall crystallinity of the membrane, this invention achieves a certain selectivity in the polypropylene oxygenation membrane, with a gas separation factor α (CO2 / O2) greater than 1.3, which is more conducive to the effective separation of oxygen and carbon dioxide, thereby further improving the oxygenation performance. Furthermore, this invention also provides a method for preparing this oxygenation membrane, which is rapid, effective, simple to operate, and suitable for large-scale promotion. Attached Figure Description

[0076] Figure 1 is a scanning electron microscope (SEM) schematic diagram of the outer surface of the polypropylene oxygenated film obtained in Example 3, where the magnification is 5000×.

[0077] Figure 2 is a scanning electron microscope (SEM) schematic diagram of the inner surface of the polypropylene oxygen membrane prepared in Example 3, where the magnification is 5000×.

[0078] Figure 3 is a scanning electron microscope (SEM) schematic diagram of the cross-section of the polypropylene oxygenated film prepared in Example 2, near the outer surface, with a magnification of 5000×.

[0079] Figure 4 is a scanning electron microscope (SEM) schematic diagram of the cross-section of the PP oxygen membrane prepared in Example 2 near the inner surface, where the magnification is 5000×.

[0080] Figure 5 is a schematic diagram of the testing device for oxygen saturation and oxygen partial pressure in the oxygenation membrane. Detailed Implementation

[0081] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0082] Example 1: A method for preparing an asymmetric polypropylene hollow fiber oxygen membrane, comprising the following steps:

[0083] Step 1: Heat and melt polypropylene, dissolve it in a solvent system containing compound A and compound B to prepare a homogeneous casting solution; wherein the molecular weight distribution index of polypropylene is 5 and the melt index is 0.8 g / min.

[0084] (190℃, 5kg); wherein compound A is sesame oil, compound B is diethyl phthalate, and the mass fraction of compound A in the solvent system is 60%; the solid content of polypropylene in the casting solution is 30%; the heating and melting process includes three steps: melting, mixing and metering; wherein the melting temperature is 180℃, the mixing temperature is 200℃, and the metering temperature is 195℃;

[0085] Step 2: The casting liquid is extruded through a die at a temperature of 175°C to form a molded product with an inner and outer surface;

[0086] Step 3: First, the molded product undergoes preliminary phase separation in an air section for 0.08 s at an air temperature of 110°C. Then, the molded product is cooled and separated using a coolant at 45°C for 110 ms. The coolant is a solvent system containing compound A (sesame oil) and compound B (diethyl phthalate), with compound A comprising 38% by mass.

[0087] Step 4: Next, the molded product is subjected to high-temperature flash quenching treatment with a quenching solution at a temperature of 95℃ for 5 seconds, while being stretched by 1.8%. After quenching, a green film is obtained. The quenching solution is a solvent system containing compound A (sesame oil) and compound B (diethyl phthalate), with compound B having a mass fraction of 90%. Step 5: The green film is extracted with an extraction solution at a temperature of 75℃ for 6 hours to remove compounds A and B, obtaining the original film. The extraction solution is isopropanol.

[0088] Step 6: Place the original film at a temperature of 110℃ for high-temperature setting for 40 minutes, with an elongation rate of 8%, to obtain a polypropylene hollow fiber oxygenated film.

[0089] Example 2: A method for preparing an asymmetric polypropylene hollow fiber oxygen membrane, comprising the following steps:

[0090] Step 1: Heat and melt polypropylene, dissolve it in a solvent system containing compound A and compound B to prepare a homogeneous casting solution; wherein the molecular weight distribution index of polypropylene is 6 and the melt index is 0.6 g / min.

[0091] (190℃, 5kg); wherein compound A is soybean oil, compound B is castor oil, and the mass fraction of compound A in the solvent system is 65%; the solid content of polypropylene in the casting solution is 35%; the heating and melting process includes three steps: melting, mixing and metering; wherein the melting temperature is 190℃, the mixing temperature is 210℃, and the metering temperature is 205℃.

[0092] Step 2: The casting liquid is extruded through a die at a temperature of 180℃ to form a molded product with an inner and outer surface;

[0093] Step 3: First, the molded product undergoes preliminary phase separation in an air section for 0.06 s at an air temperature of 100°C. Then, the molded product is cooled and separated using a coolant at 40°C for 100 ms. The coolant is a solvent system containing compound A (soybean oil) and compound B (castor oil), with compound A comprising 30% by mass.

[0094] Step 4: Next, the molded product is subjected to high-temperature flash quenching with quenching liquid at a temperature of 90°C for 8 seconds, while being stretched by 1.5%. After quenching, a green film is obtained. The quenching liquid is a solvent system containing compound A (soybean oil) and compound B (castor oil), with compound B having a mass fraction of 85%.

[0095] Step 5: Extract the raw membrane with an extraction solution at 70℃ for 8 hours to remove compounds A and B and obtain the original membrane; the extraction solution is isopropanol.

[0096] Step 6: Place the original film at a temperature of 105℃ for high-temperature setting for 45 minutes, with an elongation rate of 6%, to obtain a polypropylene hollow fiber oxygen membrane.

[0097] Example 3: A method for preparing an asymmetric polypropylene hollow fiber oxygen membrane, comprising the following steps:

[0098] Step 1: Heat and melt polypropylene, dissolving it in a solvent system containing compound A and compound B to prepare a homogeneous casting solution; wherein the molecular weight distribution index of polypropylene is 7, and the melt index is 0.5 g / min.

[0099] (190℃, 5kg); wherein compound A is dioctyl phthalate, compound B is glyceryl diacetate, and the mass fraction of compound A in the solvent system is 70%; the solid content of polypropylene in the casting solution is 40%; the heating and melting process includes three steps: melting, mixing and metering; wherein the melting temperature is 195℃, the mixing temperature is 215℃, and the metering temperature is 210℃;

[0100] Step 2: The casting liquid is extruded through a die at a temperature of 185℃ to form a molded product with an inner and outer surface;

[0101] Step 3: First, the molded product undergoes preliminary phase separation in an air section for 0.05 s at a temperature of 95°C. Then, the molded product is cooled and separated using a coolant at a temperature of 35°C for 95 ms. The coolant is a solvent system containing compound A (dioctyl phthalate) and compound B (glyceryl diacetate), with compound A comprising 25% by mass.

[0102] Step 4: Next, the molded product is subjected to high-temperature flash quenching treatment with quenching liquid. The high-temperature flash quenching temperature is 85℃ and the time is 12s. At the same time, it is stretched by 1.2%. After quenching, a green film is obtained. The quenching liquid is a solvent system containing compound A dioctyl phthalate and compound B diglyceride. The mass fraction of compound B in the solvent system is 75%.

[0103] Step 5: Extract the membrane with an extraction solution at 65℃ for 10 hours to remove compounds A and B and obtain the original membrane; the extraction solution is acetone.

[0104] Step 6: Place the original film at a temperature of 100℃ for high-temperature setting for 50 minutes, with an elongation rate of 5%, to obtain a polypropylene hollow fiber oxygen membrane.

[0105] Example 4: A method for preparing an asymmetric polypropylene hollow fiber oxygen membrane, comprising the following steps:

[0106] Step 1: Heat and melt polypropylene, dissolve it in a solvent system containing compound A and compound B to prepare a homogeneous casting solution; wherein the molecular weight distribution index of polypropylene is 8 and the melt index is 0.3 g / min.

[0107] (190℃, 5kg); wherein compound A is paraffin oil, compound B is dioctyl adipate, and the mass fraction of compound A in the solvent system is 75%; the solid content of polypropylene in the casting solution is 45%; the heating and melting process includes three steps: melting, mixing and metering; wherein the melting temperature is 205℃, the mixing temperature is 225℃, and the metering temperature is 215℃;

[0108] Step 2: The casting liquid is extruded through a die at a temperature of 190℃ to form a molded product with an inner and outer surface;

[0109] Step 3: First, the molded product undergoes preliminary phase separation in an air section for 0.03 s at a temperature of 90 ℃. Then, the molded product is cooled and separated using a coolant at a temperature of 30 ℃ for 85 ms. The coolant is a solvent system containing compound A (paraffin oil) and compound B (dioctyl adipate), with compound A comprising 20% ​​by mass.

[0110] Step 4: Next, the molded product is subjected to high-temperature flash quenching treatment with quenching liquid. The high-temperature flash quenching temperature is 80℃ and the time is 18s. At the same time, it is stretched by 0.9%. After quenching, a green film is obtained. The quenching liquid is a solvent system containing compound A paraffin oil and compound B dioctyl adipate. The mass fraction of compound B in the solvent system is 75%.

[0111] Step 5: Extract the membrane with an extraction solution at 60℃ for 12 hours to remove compounds A and B, and obtain the original membrane; the extraction solution is ethanol.

[0112] Step 6: Place the original film at a temperature of 95℃ for high-temperature setting for 55 minutes, with an elongation rate of 4%, to obtain a polypropylene hollow fiber oxygen membrane.

[0113] Structural and performance tests were performed on the samples.

[0114] 1. Structural characterization: The morphology of the main membrane structure of each sample was characterized using a scanning electron microscope (Hitachi S-5500), and the required data were obtained; the specific results are shown in the table below:

[0115] Table 1 - External Surface Characteristics:

[0116]

[0117]

[0118] Table 2 - Overall characteristics of the oxygenation membrane

[0119]

[0120] Table 3 - Characteristics of the pore area and overall characteristics of the oxygenation film

[0121]

[0122] Table 4 - Internal Surface Characteristics

[0123]

[0124] The ratio of the average length to the width of the second surface fibers on the inner surface of the polypropylene oxygenation membranes prepared in Examples 1-4 is within the range of 2.5-20, ensuring the stability of the membrane pores on the inner surface. Furthermore, as shown in Tables 1-4, the polypropylene oxygenation membranes prepared in Examples 1-4 all have ideal membrane pore structures, which helps the oxygenation membranes to have excellent mechanical strength and oxygenation performance, as well as good plasma permeation time.

[0125] Comparative Example 1

[0126] The procedure was carried out in accordance with Example 2, except that the raw material used was polypropylene with a weight-average molecular weight of 200,000, while the other conditions remained unchanged. The resulting polypropylene oxygenated membrane had low mechanical strength, low tensile strength and low elongation at break due to the low molecular weight of the raw material, and was not industrially applicable.

[0127] Comparative Example 2

[0128] The experiment was conducted in accordance with Example 2, except that the raw material used was polypropylene with a weight average molecular weight of 950,000, while the other conditions remained the same. The study found that due to the excessively high molecular weight of the raw material used, it was impossible to form a uniform casting solution, let alone a film.

[0129] Comparative Example 3

[0130] The procedure was carried out in accordance with Example 2, except that preliminary phase separation was not performed in step three; and in step five, the quenching temperature was 120°C (too high quenching temperature), the time was 60s (too long time), and the elongation rate was 5% (too high elongation rate); all other conditions remained unchanged; the outer surface of the final polypropylene oxygen membrane also contained several first surface fibers for forming a porous structure; in the circumferential direction of the oxygen membrane, the average SEM spacing between adjacent first surface fibers was 180nm, and the DSC crystallinity of the oxygen membrane was 15%; thus, the plasma permeation time of the oxygen membrane was too short and the mechanical strength was too low.

[0131] Comparative Example 4

[0132] The procedure was carried out in accordance with Example 2, except that preliminary phase separation was not performed in step three; in step five, the quenching temperature was 60°C (too low) and the time was 0.5s (too short), and no stretching was performed, while the other conditions remained unchanged; the final polypropylene oxygen film also contained several first surface fibers for forming a porous structure on its outer surface; in the circumferential direction of the oxygen film, the average SEM spacing between adjacent first surface fibers was 5nm, and the DSC crystallinity of the oxygen film was 70%, resulting in poor oxygenation performance of the oxygen film.

[0133] Comparative Example 5

[0134] The procedure was carried out in accordance with Example 2, except that the solid content of polypropylene in the casting solution in step 1 was 20%; no preliminary phase separation was performed in step 3; and the molded product was cooled and phase separated using a coolant at a temperature of 60°C for 200 ms; the coolant was a solvent system containing compound A and compound B, with compound A having a mass fraction of 50%; all other conditions remained unchanged.

[0135] In the final PP hollow fiber oxygenation membrane, the uniform bubble point of the IPA was 0.45 MPa, which was too small, indicating that the overall pore size of the oxygenation membrane was too large; and the porosity was 63%, which resulted in a short plasma permeation time and low mechanical strength of the oxygenation membrane.

[0136] Comparative Example 6

[0137] The procedure was carried out in accordance with Example 2, except that the solid content of polypropylene in the casting solution in step one was 55%; in step three, no preliminary phase separation was performed, and the molded product was cooled and phase separated using a coolant at a temperature of 22°C for 60 ms; the coolant was a solvent system containing compound A and compound B, with compound A comprising 5% by mass; all other conditions remained unchanged.

[0138] The final polypropylene oxygenated membrane had a uniform bubble point of 1.12 MPa, which was too high, indicating that the overall pore size of the membrane was too small. At the same time, the overall porosity was only 10%, which was too low, indicating that the number of membrane pores was too small. This resulted in poor oxygenation performance of the membrane.

[0139] Example 5

[0140] The procedure was carried out in accordance with Example 2, except that the melting temperature in step one was 165°C, the mixing temperature was 175°C, and the metering temperature was 195°C; no preliminary phase separation was performed in step three; the quenching liquid in step four was a solvent system containing compound A (soybean oil) and compound B (castor oil), with compound B having a mass fraction of 98%; and the original film was high-temperature shaped in step six with a stretching rate of 2%; all other conditions remained unchanged.

[0141] In the final polypropylene oxygenated membrane, the pore size changes gradually from the outer surface to the inner surface in the thickness direction, and gradually increases. That is, there is no small pore area. Therefore, it is impossible to achieve a balance between oxygenation performance, mechanical strength and plasma permeation time.

[0142] Example 6

[0143] The procedure was carried out in accordance with Example 2, except that in step two, the casting liquid was extruded under a die at a temperature of 200°C (the die extrusion temperature was 5°C lower than the metering temperature); in step three, no preliminary phase separation was performed; in step four, the quenching liquid was a solvent system containing compound A (soybean oil) and compound B (castor oil), with compound B having a mass fraction of 72% in the solvent system; the other conditions remained unchanged.

[0144] In the final polypropylene oxygenated membrane, the pore size first decreases and then increases in the thickness direction from the outer surface to the inner surface, and there is a small pore region. However, the closest average distance from the small pore region to the outer surface is 3.5 μm. The porosity of the oxygenated membrane is 53%. Compared with Example 2, Example 6 has lower tolerance and shorter plasma permeation time. At the same time, the overall tensile strength of the membrane is lower, and the compressive strength of the outer surface is slightly lower.

[0145] Example 7

[0146] The process was carried out in accordance with Example 2, except that the heating and melting process in step one included three steps: melting, mixing, and metering; the melting temperature was 170°C, the mixing temperature was 190°C, and the metering temperature was 185°C; in step two, the casting liquid was extruded under a die at a temperature of 180°C (the die extrusion temperature was 5°C lower than the metering temperature); no preliminary phase separation was performed in step three; and in step six, the original film was high-temperature shaped with an elongation rate of 13%; all other conditions remained unchanged.

[0147] In the final polypropylene oxygenated film, the outer surface mechanical coefficient X 外 The initial water contact angle of the outer surface was 100°, and the porosity of the outer surface was 8.3%. Further testing revealed that compared to Example 2, the overall tensile strength of the oxygenation membrane in Example 7 was lower, and the compressive strength of the outer surface was worse. At the same time, the oxygenation membrane had poor tolerance and a shorter plasma permeation time.

[0148] Example 8

[0149] The procedure was carried out in accordance with Example 2, except that preliminary phase separation was not performed in step three; in step four, the quenching solution was a solvent system containing compound A (soybean oil) and compound B (castor oil), with compound B having a mass fraction of 70%; in step five, the removal of compounds A and B from the raw film specifically refers to extracting the raw film with an extraction solution at 50°C for 3 hours; in step six, the high-temperature setting of the original film specifically refers to placing the original film at 80°C for 20 minutes for high-temperature setting; all other conditions remained unchanged.

[0150] The final polypropylene oxygenated membrane had an X-internal / X-external ratio of 4, a porosity of 58%, and a uniform IPA bubble point of 0.65 MPa. The membrane pores were relatively large, and the non-uniformity was also increased. Further testing revealed that compared to Example 2, the oxygenated membrane of Example 7 had lower overall tensile strength and poorer compressive strength on the outer surface. At the same time, the oxygenated membrane had poorer tolerance and a shorter plasma permeation time.

[0151] II: Performance Testing

[0152] 1. Gas mass transfer rate tests were conducted on the PP oxygen membranes prepared in Examples 1 to 8. The testing method was as follows: Under conditions of 25°C, 1 bar pressure, and a membrane sample area of ​​0.1 square meters, one side of the membrane sample was subjected to the test gas (oxygen, carbon dioxide, anesthetic gas); the test gas was supplied into the inner cavity of the hollow fiber membrane; the volumetric flow rate of the gas permeating through the membrane wall was measured using a flow meter (KOFLOC / 4800, Japan); the test was performed three times from inside the membrane to outside, and three times from outside the membrane to inside, and the average value was taken. This average value is the gas mass transfer rate of the membrane. Gas mass transfer rate unit: ml / (cm²) 2 *min*bar)

[0153] 2. To determine the plasma leakage time of the sample, a phospholipid solution (1.5g lecithin dissolved in 500ml physiological saline solution) at 37℃ was used at a rate of 6L / (min*m). 2 A pressure of 1.0 bar is applied to the surface of the membrane sample. Air is then allowed to flow along the other side of the membrane sample, and the air that has flowed through the membrane sample passes through a cold trap. The weight of the liquid that accumulates in the cold trap is measured as a function of time. The time at which a significant increase in weight occurs, i.e., the time at which the liquid first significantly accumulates in the cold trap, is defined as the plasma leakage time.

[0154] 3. Based on the ISO-7199 standard, at 1.6m 2 Under oxygenation membrane treatment of blood at a flow rate of 5 L / min, the oxygen saturation and partial pressure of blood (arterial blood) (unit: mmHg) were measured using a blood gas analyzer, as shown in Figure 5; 4. Tensile strength and elongation at break test: Each sample was stretched uniformly at a tensile tester at room temperature (tensile speed 50 mm / min, distance between upper and lower clamps 30 mm) until it broke, and the tensile strength and elongation at break were measured. This was repeated 3 times, and the average value was taken; the average value is the final tensile strength and elongation at break value of the membrane.

[0155] Table 5

[0156]

[0157] Table 6:

[0158] Oxygen saturation of blood samples; oxygen partial pressure / mmHg; tensile strength / cN; elongation at break / %; Example 1: 100 325 31 162 1; Example 2: 100 350 31 76 32; Example 3: 100 31 83 29 62 5; Example 4: 100 30 43 22 60 7; Example 5: 100 185 275 56 3; Example 6: 100 21 22 86 57 1; Example 7: 100 20 72 54 53 1; Example 8: 100 21 92 18 53 4; Comparative Example 1: / / 100 250; Comparative Example 3: / / 120 30 5; Comparative Example 4: 97 118 / / ; Comparative Example 5: / / 143 38 1; Comparative Example 6: 96 101 / / surface

[0159] Further burst pressure tests were conducted on the polypropylene oxygen membranes prepared in Examples 1-8. The results showed that the internal burst pressure of the polypropylene oxygen membranes was not less than 2 bar (from the outside in), and the external burst pressure was not less than 3.5 bar (from the inside out), further demonstrating that the polypropylene oxygen membranes possess good mechanical strength. Meanwhile, as shown in Tables 5 and 6, the polypropylene oxygen membranes prepared by this invention have excellent oxygenation performance, enabling rapid exchange of oxygen and carbon dioxide. Simultaneously, the tensile strength is not less than 200 cN, and the elongation at break is not less than 500%, exhibiting excellent mechanical properties and high industrial practical value. Furthermore, the plasma permeation time of the polypropylene oxygen membranes was all above 12 hours, indicating that the oxygen membranes of this invention have good durability and a long service life.

[0160] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. An asymmetric polypropylene hollow fiber oxygenated membrane, comprising a main body, wherein one side of the main body is an inner surface facing the inner cavity, and the other side of the main body is an outer surface, characterized in that: The main body has non-directional tortuous pathways; the outer surface contains a plurality of first surface fibers for forming a porous structure; in the circumferential direction of the oxygen membrane, the average SEM spacing between adjacent first surface fibers is 10-120 nm; the DSC crystallinity of the oxygen membrane is 30%-60%; the polymer constituting the oxygen membrane is polypropylene with a weight average molecular weight of 500,000-800,000; the porosity of the oxygen membrane is 20%-60%, the uniform bubble point of IPA is 0.6-1.0 MPa, and the thickness is 30-80 μm.

2. The asymmetric polypropylene hollow fiber oxygen membrane according to claim 1, characterized in that: The inner and outer surfaces of the oxygenation membrane were measured by infrared absorption spectroscopy using the ATR method at a wavenumber of 988 cm⁻¹. -1 -1008cm -1 The first peak is located at a wavenumber of 1450 cm⁻¹. -1 -1470cm -1 A second peak exists at the location of the first peak, and the ratio of the peak area of ​​the first peak to the peak area of ​​the second peak is the mechanical coefficient X of the oxygenation film; wherein the mechanical coefficient of the inner surface of the oxygenation film is X. 内 The mechanical coefficient of the outer surface of the oxygen film is X. 外 The X 外 The initial water contact angle of the outer surface is 0.03-0.12; and / or the initial water contact angle of the outer surface is 100°-135°; and / or the porosity of the outer surface is 0.1%-8%.

3. The asymmetric polypropylene hollow fiber oxygen membrane according to claim 2, characterized in that: The X 内 Not greater than 0.4; X 内 / X 外 The porosity of the oxygenated membrane is 25%-55%, and the uniform bubble point of IPA is 0.7-0.95 MPa.

4. The asymmetric polypropylene hollow fiber oxygen membrane according to claim 1, characterized in that: The average length of the first surface fiber in SEM is 100-900 nm, and the average width in SEM is 20-300 nm. The length direction of the first surface fiber is consistent with the length direction of the oxygen film, and the width direction of the first surface fiber is consistent with the circumferential direction of the oxygen film.

5. The asymmetric polypropylene hollow fiber oxygen membrane according to claim 1, characterized in that: The inner surface includes a plurality of second surface fibers for forming a porous structure; In the circumferential direction of the oxygenated membrane, the average SEM spacing between adjacent second surface fibers is 50-300 nm; the ratio of the average SEM length of the second surface fiber to the SEM width of the second surface fiber is 2.5-20.

6. The asymmetric polypropylene hollow fiber oxygen membrane according to claim 5, characterized in that: The pore area ratio of the inner surface is 2%-20%; the pore area ratio of the inner surface is greater than that of the outer surface, and the difference between the two is not greater than 15%; and / or, the ratio of the average SEM spacing between adjacent second surface fibers to the average SEM spacing between adjacent first surface fibers is 2-18:

1.

7. The asymmetric polypropylene hollow fiber oxygen membrane according to claim 1, characterized in that: The main cross-section contains a plurality of cross-sectional fibers for forming a porous structure, and the SEM average diameter of the cross-sectional fibers is 25-135 nm; and / or, the ratio of the IPA bubbling point to the uniform bubbling point of the oxygenated membrane is 0.7-0.96:

1.

8. The asymmetric polypropylene hollow fiber oxygen membrane according to claim 1, characterized in that: In the film thickness direction from the outer surface to the inner surface, the average pore size of the main body first decreases and then increases; the main body includes a pore region, the nearest average distance from the pore region to the outer surface is less than the nearest average distance from the pore region to the inner surface, and the nearest average distance from the pore region to the outer surface is 0.2-3 μm; the porosity of the oxygenated membrane is 30%-50%.

9. The asymmetric polypropylene hollow fiber oxygen membrane according to claim 1, characterized in that: The thickness of the pore region is 0.2-2 μm, and the ratio of the thickness of the pore region to the overall thickness of the membrane is 0.4%-5%.

10. The asymmetric polypropylene hollow fiber oxygen membrane according to claim 1, characterized in that: The plasma permeation time of the oxygenation membrane is not less than 12 hours, preferably not less than 18 hours, and more preferably not less than 24 hours; the O2 mass transfer rate of the oxygenation membrane is not less than 15 ml / (cm²). 2 *min*bar), and the gas separation factor α(CO2 / O2) is not less than 1.3; at 1.6m 2 When oxygenating blood at a flow rate of 5 L / min, the oxygen saturation of the blood is not less than 99%, and the oxygen partial pressure is not less than 150 mmHg; the tensile strength of the oxygenating membrane is not less than 200 cN, and the elongation at break is not less than 500%; the internal burst pressure of the oxygenating membrane is not less than 2 bar, and the external burst pressure is not less than 3.5 bar.

11. A method for preparing an asymmetric polypropylene hollow fiber oxygen membrane according to any one of claims 1-10, characterized in that: The process includes the following steps: Step 1: Melting polypropylene by heating it, dissolving it in a solvent system containing compound A and compound B to prepare a homogeneous casting solution; wherein the molecular weight distribution index of polypropylene is 4-9, and the melt index is 0.1-1 g / min@(190℃, 5kg); wherein compound A is the solvent for polypropylene, and compound B is the non-solvent for PP, and the mass fraction of compound A in the solvent system is 55%-80%; the solid content of polypropylene in the casting solution is 30%-50%; Step 2: Extruding the casting solution under a die at a temperature of 175-190℃ to form a molded product with an inner surface and an outer surface; Step 3: Cooling and separating the molded product with a cooling liquid at a cooling separation temperature of 30- Step 1: Cooling at 50℃ for 80-120ms; the coolant is a solvent system containing compound A and compound B, with compound A comprising 10%-45% by mass. Step 2: The molded product is then subjected to high-temperature flash quenching at 75-100℃ for 1-20s, while being stretched by 0.5%-2%. A green film is obtained after quenching, with compound B comprising no less than 70% in the quenching solution. Step 3: Compounds A and B are removed from the green film to obtain the original film. Step 4: The original film is then high-temperature shaped and stretched, with a stretching rate 1.5-10 times that of the high-temperature flash quenching, to obtain a PP hollow fiber oxygenated film.

12. The method for preparing an asymmetric polypropylene hollow fiber oxygen membrane according to claim 11, characterized in that: The heating and melting process described in step one includes three steps: melting, mixing, and metering; wherein the melting temperature is 170-250℃, the mixing temperature is 180-245℃, and the metering temperature is 190-220℃; and / or, the die extrusion temperature is 10-25℃ lower than the metering temperature.

13. The method for preparing an asymmetric polypropylene hollow fiber oxygen membrane according to claim 11, characterized in that: Compound A is at least one of soybean oil, N,N-bis(2-hydroxyethyl) tallow amine, palm seed oil, sesame oil, peanut oil, sunflower seed oil, corn oil, dioctyl phthalate, paraffin oil, dibutyl sebate, dibutyl phthalate, and diisooctyl phthalate; Compound B is at least one of diethyl phthalate, glyceryl triacetate, castor oil, dioctyl adipate, glyceryl diacetate, glycerol, and polyethylene glycol 200.

14. The method for preparing an asymmetric polypropylene hollow fiber oxygen membrane according to claim 11, characterized in that: Before cooling and separating the molded product in step three, a preliminary phase separation is performed on the molded product. The specific steps for the preliminary phase separation are as follows: the molded product is subjected to preliminary phase separation in an air section; the preliminary phase separation time is 0.02s-0.1s, and the air section temperature is 70-130℃; and / or, in step four, the quenching liquid is a solvent system of compound A and compound B, and the mass fraction of compound B in the solvent system is 75%-90%.

15. The method for preparing an asymmetric polypropylene hollow fiber oxygen membrane according to claim 11, characterized in that: In step five, removing compounds A and B from the raw film specifically refers to extracting the raw film with an extraction solution at a temperature of 60-80℃ for 4-12 hours; wherein the extraction solution is any one of isopropanol, ethanol, and acetone; and / or, in step six, high-temperature setting of the original film specifically refers to placing the original film at a temperature of 90-120℃ for high-temperature setting for 30-60 minutes, with an elongation rate of 3%-10%.

16. The application of an asymmetric polypropylene hollow fiber oxygen membrane according to any one of claims 1-10, characterized in that: The oxygenation membrane is used for blood oxygenation in cardiopulmonary surgery and / or organ transplantation.

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