WO2024012122A1 - 一种高脱气聚烯烃中空纤维膜及其制备方法与应用 - Google Patents

一种高脱气聚烯烃中空纤维膜及其制备方法与应用 Download PDF

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WO2024012122A1
WO2024012122A1 PCT/CN2023/099655 CN2023099655W WO2024012122A1 WO 2024012122 A1 WO2024012122 A1 WO 2024012122A1 CN 2023099655 W CN2023099655 W CN 2023099655W WO 2024012122 A1 WO2024012122 A1 WO 2024012122A1
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hollow fiber
fiber membrane
polyolefin
semi
finished product
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PCT/CN2023/099655
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English (en)
French (fr)
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贾建东
陈梦泽
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杭州科百特过滤器材有限公司
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Publication of WO2024012122A1 publication Critical patent/WO2024012122A1/zh

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/26—Polyalkenes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/22—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by diffusion
    • B01D53/228—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by diffusion characterised by specific membranes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0002—Organic membrane manufacture
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/08—Hollow fibre membranes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/08—Hollow fibre membranes
    • B01D69/087—Details relating to the spinning process

Definitions

  • the present application relates to the field of degassing membrane materials, and in particular to a highly degassing polyolefin hollow fiber membrane and its preparation method and application.
  • polyolefin is a type of polymer material with large output and wide application.
  • Polyolefin has the characteristics of low relative density, chemical resistance, and good water resistance.
  • Polyolefin can be used in films, pipes, plates, various molded products, wires and cables, etc.
  • Degassing membrane is a membrane separation product that removes gases from liquids, such as carbon dioxide, oxygen, and ammonia nitrogen.
  • the main methods for preparing such membranes are stretching pore method and thermal phase separation method.
  • the stretching porogenization method is to make a crystalline polymer into a hollow fiber membrane or film through melt extrusion, and through post-processing, the polymer is biaxially stretched along the extrusion direction to improve the shape, size and porosity of the membrane pores; thermal
  • the induced phase separation method is that some polymer materials cannot be dissolved at room temperature. When the temperature is raised above their melting temperature, they can form a uniform solution with some small molecular compounds (diluents). After cooling, the homogeneous solution will form solid-liquid or liquid-liquid. The phase separates and solidifies, and the microporous material is obtained after removing the (diluent).
  • Patent CN107998903A discloses a method for preparing a polypropylene hollow fiber microporous membrane used in the fields of membrane distillation and membrane degassing.
  • the patent uses polypropylene as raw material and high-grade aliphatic amine ethylene oxide adduct as diluent.
  • a polypropylene hollow fiber microporous membrane was obtained using a thermally induced phase separation method.
  • the hollow fiber microporous membrane prepared by this patent has a penetrating, sponge-like microporous structure cross-section and a surface with micropore distribution.
  • thermotropic phase method to produce a porous hollow fiber membrane with internal and external penetrations.
  • the hollow fiber membrane prepared by the method needs to add diluent, and there must be diluent residue in the final hollow fiber membrane.
  • this part of the residue is prone to dissolution reaction, which is harmful to ultrapure water.
  • the quality of water has a great influence. Therefore, the filter membrane prepared by the above thermotropic phase method is not suitable for use in the field of ultrapure water preparation.
  • the porous hollow fiber membrane with internal and external penetrations has a better degassing effect, the microporous structure with internal and external penetrations easily allows fluid to flow in. Once the fluid flows in, the membrane will lose its ability to separate gas and liquid, and its service life will be low.
  • asymmetric hollow fiber membranes exhibit excellent performance.
  • asymmetric hollow fiber membranes have a dense outer surface (no hole structure can be observed or a very small number of hole structures can be observed) and The porous structure of the support layer and the dense outer surface can effectively prevent fluid from flowing into the hollow fiber membrane and thereby reducing the service life.
  • the current preparation process of asymmetric hollow fiber membranes is not mature. The problem of how to prepare a hollow fiber membrane with high porosity, high deoxidation efficiency, high mechanical strength and long service life has been puzzling researchers.
  • the present invention aims to provide a highly degassed polyolefin hollow fiber membrane and its preparation method and application.
  • the hollow fiber membrane prepared by the present application has high deoxidation efficiency, high tensile strength, and improved
  • the performance of degassed polyolefin hollow fiber membranes extends the service life.
  • a highly degassing polyolefin hollow fiber membrane includes a main body, one side of the main body is an inner surface facing the inner cavity, and the other side is an outer surface.
  • the main body has a non-directional tortuous passage, and the outer surface is Dense surface, the breathable pore area rate of the inner surface is 10%-30%; the average thickness of the hollow fiber membrane is 45-65 ⁇ m, and the ratio of the average outer diameter to the average inner diameter of the hollow fiber membrane is 1.45-1.55 ;
  • the TOC dissolution amount of the hollow fiber membrane does not exceed 3 ⁇ g/L; the deoxidation efficiency of the hollow fiber membrane is greater than 80%.
  • a dense surface means that when photographed by a scanning electron microscope at 30,000 times, the pore area ratio of its outer surface (i.e., hole area: outer surface area) is not greater than 5%, that is, there is an unobservable hole structure or extremely visible holes. Both cases have a small number of hole structures.
  • One side of the main body of the application is the inner surface close to the inner cavity, and the other side is the outer surface.
  • the outer surface is a dense surface with strong hydrophobicity, making it difficult for water molecules to pass through but oxygen can pass through. Oxygen can pass through the hollow fiber membrane. Knudsen diffusion and viscous flow coexist through the membrane pores. When oxygen is close to the dense surface, oxygen penetrates the membrane pores by Knudsen diffusion.
  • the oxygen mass transfer resistance is mainly the collision of oxygen molecules with the membrane pore wall.
  • Oxygen molecules The probability of collision is greatly reduced and passes through the flow channel in a turbulent manner, causing the oxygen transmission rate to gradually decrease; when oxygen is close to the inner surface, oxygen convection occurs and passes through the membrane pores in a viscous flow manner, mainly laminar flow. Passes through the flow channel, and as the membrane pore size gradually increases, the oxygen transmission rate gradually increases.
  • the thickness of the membrane wall of the hollow fiber membrane increases, the ratio of the viscous flow path to the Knudsen diffusion path for oxygen to pass through the membrane pores increases, that is, the oxygen molecules permeate through the membrane in the form of viscous flow.
  • the distance between the membrane holes further increases the oxygen transmission rate, so that the total flow rate of oxygen increases, further increasing the deoxygenation efficiency of the hollow fiber membrane.
  • Knudsen diffusion is when gas diffuses in a porous solid. If the pore diameter is smaller than the mean free path of the gas molecules, the collisions of gas molecules against the pore walls are much more frequent than the collisions between gas molecules. Viscous flow means that the membrane pore diameter is much larger than the mean free path of gas molecules, and the collision probability between gas molecules is much greater than the collision probability between gas molecules and the membrane pore wall.
  • the free path refers to the straight line distance traveled by a molecule between two consecutive collisions with other molecules. For individual molecules, the free path is long or short, but the free path of a large number of molecules has a certain statistical law. The average value of a large number of molecular free paths is called the mean free path.
  • the breathable pore area ratio of the inner surface is 10%-30%. If the breathable pore area ratio is too large, the tensile strength of the hollow fiber membrane will be reduced, thereby reducing its service life; if the breathable pore area ratio is small, the oxygen content will be reduced. circulation channel, thereby reducing the deoxidation efficiency; at the same time, when the membrane wall is thick, the appropriate ventilation hole surface on the inner surface
  • the volume ratio is to provide enough gas circulation area to avoid accumulation of oxygen near the inner surface area, which increases the mass transfer resistance and reduces the deoxygenation efficiency.
  • the thickness of the hollow fiber membrane of this application is 45-65 ⁇ m.
  • a suitable ratio of the average outer diameter to the average inner diameter of the hollow fiber membrane enables the membrane to have a suitable oxygen flow area and a suitable inner cavity volume, so that the oxygen has a suitable amount in the inner cavity.
  • the circulation rate avoid the surface area of the inner surface being reduced due to the hollow fiber membrane being too thick and the inner diameter being small, thereby reducing the oxygen circulation channel, increasing the resistance to oxygen diffusion, and reducing the deoxygenation efficiency; it can also avoid the hollow fiber membrane being too thick and having a small inner diameter.
  • the fiber membrane is thinner, which reduces its tensile strength and thus its service life.
  • This application has a suitable breathable hole area ratio, membrane wall thickness and the ratio of the average outer diameter to the average inner diameter of the hollow fiber membrane, so as to increase the channels for oxygen circulation while ensuring strong tensile strength.
  • the outer surface of this application is a dense surface with low porosity and strong hydrophobicity, it prevents ultrapure water from entering the membrane through the holes on the surface, that is, the contact area between ultrapure water and the outer surface is very small, thereby reducing the hollow The dissolution amount of organic matter in the fiber membrane.
  • the dissolution amount of TOC does not exceed 3 ⁇ g/L, and preferably the dissolution amount does not exceed 0.5 ⁇ g/L; in addition, the surface pores are prevented from being blocked by the dissolved TOC, so that oxygen can pass through better amount, so that the deoxidation effect is good.
  • the hollow fiber membrane of this application has a suitable thickness and a dense outer surface, so that the dissolution amount of TOC is low, and the distance for oxygen molecules to penetrate the membrane pores in a viscous flow manner in the membrane is more suitable, thereby improving the Oxygen transmission rate, while the breathable pore area rate of the inner surface is 10%-30%, and the ratio of the average outer diameter to the average inner diameter of the hollow fiber membrane is 1.45-1.55, so that oxygen has sufficient circulation channels and a suitable inner cavity
  • the flow rate is such that the deoxidation efficiency of the hollow fiber membrane is higher than 80%; at the same time, the hollow fiber membrane is ensured to have sufficient tensile strength.
  • the inner surface has a plurality of elliptical ventilation holes, the long diameter orientation of the ventilation holes is the length direction of the hollow fiber membrane, and the short diameter orientation of the ventilation holes is the circumferential direction of the hollow fiber membrane. direction, the average long diameter of the air permeable pores is 150-300nm, the average short diameter of the air permeable pores is 10-60nm, and the hollowness of the hollow fiber membrane is 35%-55%.
  • the short diameter orientation of this application is the circumferential direction of the hollow fiber membrane.
  • the ratio of the short diameter to the long diameter of the ellipse is the shape ratio. When the shape ratio is closer to 1, both the long diameter and the short diameter of the ellipse need to withstand certain stress.
  • the average long diameter of the vents in this application is 150-300nm, and the average short diameter is 10-60nm, making the structure of the vents more stable. , is not easy to collapse or break, and at the same time increases the circulation of oxygen molecules in the membrane pores, thereby increasing the oxygen transmission rate, making it have better deoxidation efficiency.
  • the hollow fiber membrane of this application has a hollow degree of 35%-55%. It should be noted that the hollow degree is the percentage of the actual effective inner cavity area to the external cross-sectional area, which is calculated through Formula 1:
  • W is the hollowness
  • the unit is %
  • S 1 is the area of the external cross-section
  • the unit is mm 2
  • S 2 is the area of the effective cavity
  • the unit is mm 2 .
  • the hollowness is higher, the effective membrane area will be smaller, resulting in lower porosity. The thinner the membrane, the easier it will be for the fiber to be compressed and difficult to process. At the same time, the tensile strength of the membrane will be reduced, and when the membrane is under pressure, the hollow will easily deform, thus Reducing the performance of the membrane; if the hollowness is small, that is, the effective cavity area is small, the surface area of the inner surface is reduced, the channels for oxygen circulation are reduced, the resistance to oxygen diffusion is increased, and the deoxidation efficiency is reduced.
  • the hollow fiber membrane of this application has a suitable hollowness, so that the membrane has strong tensile strength and better deoxidation efficiency. At the same time, the hollow fiber membrane is resistant to pressure and is not easily deformed.
  • the difference between the maximum thickness and the minimum thickness of the hollow fiber membrane does not exceed 5um, and the difference does not exceed 10% of the average thickness of the hollow fiber membrane; the porosity of the hollow fiber membrane is 30%-50 %, the hollow fiber membrane is 1.5-3.5 times the breathable hole area ratio of the inner surface.
  • the difference between the maximum thickness and the minimum thickness of the hollow fiber membrane in this application does not exceed 5 ⁇ m. It can be seen that the wall thickness of the hollow fiber membrane is relatively uniform. If the difference is too large, the wall thickness of the hollow fiber membrane will be uneven, causing the gas in the hollow fiber membrane to The passage method is chaotic, resulting in an increase in the mass transfer resistance of oxygen in the membrane, which is not conducive to the passage of oxygen, resulting in uneven gas passage throughout the hollow fiber membrane, thereby reducing the deoxidation efficiency, and easily leading to uneven tensile strength throughout the hollow fiber membrane. This further reduces the tensile strength of the hollow fiber membrane.
  • the porosity of the hollow fiber membrane of this application is 30%-50%, allowing more oxygen to pass through the pores in a viscous flow manner, increasing the amount of oxygen passing through, while ensuring the tensile strength of the membrane. If the porosity of the hollow fiber membrane is too large, the tensile strength of the membrane will be easily reduced; if the porosity of the hollow fiber membrane is small, the oxygen passage of the membrane will be reduced, thereby reducing the deoxidation efficiency.
  • the hollow fiber membrane is 1.5-3.5 times the breathable pore area ratio of the inner surface.
  • the porosity of the hollow fiber membrane will be lower, and the oxygen throughput will be lower, thereby reducing the deoxidation efficiency; if the multiple is smaller, the hollow fiber membrane will be hollow.
  • the porosity of the fiber membrane is larger, which reduces the tensile strength of the membrane.
  • the average long diameter of the vent holes is 2-8 times the average short diameter; the difference between the maximum long diameter and the minimum long diameter of the vent holes is 150-350 nm, and the maximum short diameter of the vent holes is 150-350 nm. The difference in minimum short diameter is 10-100nm.
  • the size and uniformity of the ventilation holes in the breathable membrane directly affect the performance of the hollow fiber membrane. If the ratio of the average long diameter to the average short diameter of the ventilation holes is too large, the stress in the axial direction of the ventilation holes (the length direction of the membrane) will be If the ratio of the average long diameter to the average short diameter of the breathable pores is small, the average pore area of the breathable pores will be reduced, thereby reducing the oxygen release rate. The throughput further reduces the deoxidation efficiency. If the difference between the maximum long diameter and the minimum long diameter is large, then The ventilation holes are unevenly distributed in the axial direction of the hollow fiber membrane.
  • the ventilation holes are unevenly distributed in the circumferential direction of the hollow fiber membrane, regardless of the axial distribution of the ventilation holes in the hollow fiber membrane. Uneven or uneven circumferential distribution can easily lead to uneven tensile strength of the hollow fiber membrane and breakage, which in turn affects the performance of the hollow fiber membrane.
  • the size distribution of the ventilation holes is uneven, which reduces the amount of oxygen passing through the membrane. Non-uniformity can easily increase the mass transfer resistance of oxygen in the flow channel, causing the oxygen transmission rate to decrease, thereby reducing the deoxygenation efficiency.
  • the average long diameter of the ventilation holes in this application is 2-8 times the average short diameter; the difference between the maximum long diameter and the minimum long diameter of the ventilation holes is 150-350nm, and the difference between the maximum short diameter and the minimum short diameter of the ventilation holes is 10- 100nm, so that the membrane prepared in this application has relatively uniform breathable pores, so that the membrane has higher deoxidation efficiency and tensile strength.
  • a plurality of the ventilation holes are regularly arranged to form a ventilation area for ventilation; the direction of the length of the ventilation area is consistent with the circumferential direction of the hollow fiber membrane; so The direction of the width of the breathable zone is consistent with the length direction of the hollow fiber membrane; the average length of the breathable zone is 400-1100 nm, and the average length of the breathable zone is greater than the average width of the breathable zone.
  • the hollow fiber membrane has several breathable areas.
  • the average length of the breathable area is greater than the average width of the breathable area.
  • the breathable area is approximately elliptical, and the average length is 400-1100nm.
  • the breathable area is stable and difficult to collapse, which in turn makes the structure of the hollow fiber membrane more stable and difficult to deform. If the average length of the breathable area is too long, it will easily lead to insufficient circumferential support strength of the hollow fiber membrane and lead to deformation or collapse, which will affect the performance of the membrane. If the average length of the breathable area is small, it will easily lead to an increase in the non-hole area, and then Reduce porosity.
  • the average length of the breathable zone is greater than the average width of the breathable zone in order to maintain the overall tensile strength of the hollow fiber membrane and avoid a reduction in the tensile strength of the hollow fiber membrane in the length direction.
  • the distance between two adjacent breathable areas is distance is the first distance, and the average length of the first distance is 100-350nm; the distance between two adjacent air permeable areas in the circumferential direction of the hollow fiber membrane is the second distance, and the average length of the second distance is 100 -300nm; the average length of the first distance is 2-3 times the average length of the second distance; the average spacing between adjacent ventilation holes in the length direction of the ventilation area is 20-70nm; the The ventilation hole area ratio of the ventilation zone is 25%-70%, and the ventilation hole area ratio of the ventilation zone is 20%-50% higher than the ventilation hole area ratio of the inner surface.
  • the air-permeable area has a high air-permeable hole area ratio.
  • the distance between two adjacent air-permeable areas in the length direction of the hollow fiber membrane is the first distance.
  • the distance between the two adjacent air-permeable areas in the circumferential direction of the hollow fiber membrane is the second distance. .
  • the appropriate size of the first distance and the second distance has a supporting effect on the air-permeable area, and avoids the air-permeable area having a higher air-permeable hole area ratio (reducing the tensile strength of the hollow fiber membrane) when the hollow fiber membrane is under pressure.
  • the stress borne by the ventilation holes is concentrated in the long diameter, that is, the stress borne by the breathable area is concentrated in the width direction of the breathable area, and the stress borne by the hollow fiber membrane is concentrated in the length direction, so the average length of the first distance
  • the size should be relatively large to provide adequate support.
  • the size of the average length of the first distance in this application is 2-3 times the size of the average length of the second distance. If the multiple is larger, the porosity of the hollow fiber membrane will be reduced. If the multiple is smaller, the porosity of the hollow fiber membrane will be reduced when the hollow fiber membrane is under pressure. , the supporting force of the first distance of the hollow fiber membrane is insufficient, which can easily lead to collapse or breakage in the width direction of the breathable area.
  • the breathable area is the main area for gas transmission on the inner surface
  • the average length of the third spacing is 20-70nm, and the average length of the third spacing is within a certain
  • the degree reflects the number of holes on the inner surface. When the average length of the third spacing is too large, the number of holes in a certain area of the inner surface will be smaller. Fewer holes will inevitably affect the degassing efficiency and at the same time make the gas permeable.
  • the resistance to the passage is greatly increased, and the pressure loss during the degassing process is greatly increased; and when the average length of the third spacing is small, more holes will appear in a certain area of the inner surface (that is, in this area, the hole surface If the volume ratio is too high and the solid area ratio is too low), then this must be a big flaw. When external forces act on it, it can easily cause the holes to collapse, making it impossible for the degassing membrane to continue degassing. Short service life.
  • the hole area ratio in the breathable area of this application is relatively high, so that the membrane fiber can have a higher degassing rate; however, the hole area ratio in the breathable area cannot be too high, otherwise there is a risk of hole collapse and the service life will be too short;
  • the hole area ratio in the breathable area is 30-70%, and the hole area ratio in the breathable area is 20-50% higher than the overall hole area ratio on the inner surface. Such a hole area ratio further ensures that the hollow fiber membrane has a high degassing rate and strong dimensional stability.
  • the outer surface also has a number of silver-like cracks, the width of the cracks is not greater than 20nm; the surface energy of the outer surface is 15-40mN/m.
  • the outer surface of the present application also has a number of silver-like cracks, which increase the gas passage on the outer surface, thereby increasing the deoxidation efficiency. If the crack width is large, when the hollow fiber membrane is under high pressure, it is easy to cause liquid to enter the membrane through the cracks, thereby reducing the service life of the membrane. Therefore, the crack width in this application is not greater than 20nm, which can increase the oxygen on the outer surface. The permeability ensures that liquid does not enter the membrane.
  • surface energy is a measure of the disruption of chemical bonds between molecules when creating the surface of a substance. If the surface energy of the outer surface is too large, the surface tension of the outer surface will be large, which will reduce the barrier property of the outer surface to liquid. When the outer surface of the hollow fiber membrane carries a large pressure, it will easily cause liquid to enter the membrane through the outer surface. Inside, the breathable membrane loses its gas-liquid separation function. If the surface energy is small, the surface tension on the outer surface will be too small, which will reduce the gas permeability and thus reduce the deoxidation efficiency.
  • the surface energy of the outer surface of this application is 15-40mN/m, so that it has appropriate barrier properties, ensuring a high gas throughput, and at the same time effectively blocking liquid from entering the membrane through the outer surface.
  • the main body of the hollow fiber membrane has a cortical area and a porous area along the membrane thickness direction, with a continuous fiber transition between the cortical area and the porous area; one side of the cortical area is the outer surface, and the porous area is One side of the hole area is the inner surface; the thickness of the cortex area is 0.5-4 ⁇ m, the thickness of the cortex area accounts for 1%-8% of the thickness of the hollow fiber membrane, and the porosity of the cortex area is not higher than 10% .
  • the thickness of the cortical area in this application is 0.5-4 ⁇ m. If the cortical area is thinner, the tensile strength of the film will be reduced. If the cortical area is thicker, the oxygen permeability will be reduced, and at the same time, the Knudsen diffusion distance of oxygen in the film will be extended, increasing The mass transfer resistance of oxygen reduces the oxygen transmission rate, thereby reducing the deoxygenation efficiency.
  • the thickness of the skin layer of this application accounts for 1%-8% of the thickness of the hollow fiber membrane, so that the hollow fiber membrane has higher deoxidation efficiency and tensile strength; if it is less than 1%-8%, the oxygen permeability of the hollow fiber membrane will be reduced. This will further reduce the deoxidation efficiency; if it is greater than 1%-8%, the tensile strength of the hollow fiber membrane will be reduced.
  • the average pore diameter of the porous region changes in a gradient from the area close to the inner surface to the area close to the outer surface; the average pore diameter of the porous area changes gradient is 1.5-3nm/ ⁇ m, and the porous area
  • the porosity of the zone is 40%-70%, and the fiber diameter of the porous zone is 60-300 nm.
  • the porous area changes in a gradient, and the average pore size change gradient is 1.5-3nm/ ⁇ m. It can be seen that the average pore size change gradient is relatively gentle, allowing oxygen to diffuse at a higher diffusion rate in the membrane. If the gradient of the average pore size change is large, the diffusion mode of oxygen in the membrane changes from Knudsen diffusion to viscous flow. During the mutation process, oxygen consumes a large amount of kinetic energy, thereby reducing the gas transmission rate.
  • the fiber diameter of the porous area of this application is 60-300nm, so that the porous area has appropriate tensile strength and porosity.
  • the porosity of the porous area of this application is 40%-70%, so that oxygen has a relatively high capacity in the hollow fiber membrane. Multiple flow channels ensure the passage of oxygen.
  • step S2 Pre-crystallization.
  • the semi-molded product obtained in step S1 is cooled and pre-crystallized in an air-cooling manner to obtain a pre-crystallized semi-finished product;
  • step S2 Air-cooling crystallization.
  • the pre-crystallized semi-finished product obtained in step S2 is subjected to secondary cooling and crystallization by blowing cooling, and is rolled up to obtain the cooled semi-finished product;
  • step S4 Annealing and shaping, the cooled semi-finished product obtained in step S3 is heat-set, and the heat-set semi-finished product is obtained after cooling;
  • the heat-set semi-finished product obtained in step S4 is subjected to the first cold drawing process.
  • the rate of the first cold drawing is 10-25%/min.
  • the rate of the first cold drawing is
  • the stretching ratio is 15%-25%, and a cold-drawn semi-finished product is obtained; a second cold-drawing process is performed on it, and the rate of the second cold-drawing is 15-30%/min.
  • the stretching ratio is 5%-20% to obtain a secondary cold-drawn semi-finished product;
  • step S6 Hot drawing and hole expansion.
  • the cold drawn semi-finished product obtained in step S5 is hot drawn and hole expanded to obtain the hot drawn semi-finished product;
  • Heat setting perform a secondary heat setting treatment on the heat-drawn semi-finished product obtained in step S6, and obtain a hollow fiber membrane after cooling.
  • the polyolefin is melted and extruded, and the cavity-forming fluid is introduced at the same time to form an unshaped semi-finished product.
  • the introduction of the cavity-forming fluid can effectively avoid concave deformation of the semi-finished product; the semi-finished product is then air-cooled. It is initially shaped to form a pre-crystallized semi-finished product.
  • the pre-crystallized semi-finished product is cooled and crystallized by blowing cooling, with appropriate cooling temperature, cooling length and wind speed, so that it can crystallize and have appropriate crystallinity. At the same time, it can be rolled up after reaching the appropriate winding temperature to obtain the cooled product.
  • Semi-finished product is melted and extruded, and the cavity-forming fluid is introduced at the same time to form an unshaped semi-finished product.
  • the introduction of the cavity-forming fluid can effectively avoid concave deformation of the semi-finished product; the semi-finished product is then air-cooled. It is initially shaped to form a pre-c
  • the cooled semi-finished product is annealed in order to eliminate internal defects.
  • Two cold drawing treatments are performed. Although the rate of the two cold drawings is relatively close to the draw ratio, the second cold drawing is performed on the basis of the first cold drawing. That is, the two cold drawing methods are actually cold drawing. The process in which the pulling rate continues to become faster and the stretching ratio continues to increase. If one cold drawing is used, the tensile stress is likely to be too large, and different lamellae (there are easy-to-pull lamellae and hard-to-pull lamellae) have different stretching degrees, resulting in uneven pore sizes or structural collapse of the prepared membrane. This application Two cold drawings are used.
  • the tensile stress produced by the stretching rate and draw ratio in the first cold drawing is small, so that the easily stretched lamellae are pulled apart first.
  • the stretching rate and draw ratio of the second cold drawing are The stretching ratio is based on the first cold drawing, so as to generate a large tensile stress to pull apart the difficult-to-pull lamellae, and further allow the molecular chains to have enough time to relax, so as to solve the problem that the microfiber laces are easy to be pulled apart. Problems such as pull-off and uneven lamellar pull-out sizes can be solved to make the pore size of the prepared membrane more uniform and have higher porosity. At the same time, the stress distribution of the two stretchings is more uniform, making the membrane wall of the prepared membrane more uniform.
  • This application uses two cold drawings, first stretching with a small stress for the first time, and then increasing the tensile stress for the second stretching, so that the prepared film has a suitable thickness and the polyolefin has a suitable degree of orientation. This further increases the crystallinity of the film and makes the film wall thickness more uniform.
  • the larger the melt index value the better the processing fluidity of the material, making the melt flow rate more uniform, resulting in thicker film wall thickness, and vice versa.
  • the melt index is small, the obstacles to the arrangement of molecular chains increase, the molecular chains diffuse, and the activation energy required for the crystal phase structure increases, resulting in a decrease in the ability to arrange the molecular chains in a regular manner, thereby reducing the crystallinity.
  • the melt index is too large, the plasticity of the material becomes poor and it is difficult to form.
  • the appropriate melt index of this application enables the prepared hollow fiber membrane to have a suitable thickness, make the polyolefin have a higher crystallinity, increase the porosity of the hollow fiber membrane, and increase the penetration of oxygen molecules in the membrane in a viscous flow manner.
  • the distance between membrane holes; at the same time, it has good processing fluidity, making the membrane wall thickness more uniform, improving raw material processing efficiency, and reducing energy consumption and production costs.
  • the cavity-forming fluid in this application is preferably nitrogen with a suitable flow rate. If the nitrogen flow rate is too high, the inner surface of the semi-finished product will be stressed too much, which will easily cause the inner surface of the semi-finished product to be damaged.
  • the regularity is reduced and the uniformity of the membrane wall is reduced; if the nitrogen flow rate is small, the support force required for the semi-finished product to form the inner cavity cannot be achieved, and the surface of the semi-finished product may easily collapse.
  • the appropriate flow rate of nitrogen can make the membrane wall thickness of the prepared membrane more uniform.
  • the thickness of the semi-finished product extruded from the die is 1.8-2.2mm. If the thickness of the semi-finished product is too thick, the film prepared by two cold drawings will be thicker and uneven; if the thickness of the semi-finished product is thin, the film prepared by two stretching will be thinner. Reduce tensile strength.
  • rapid cold drawing is used to draw holes to obtain cold drawn semi-finished products.
  • the holes formed will rebound and shrink, reducing the average pore diameter and increasing the thickness. Therefore, the cold-drawn semi-finished product is subjected to hot-drawing hole expansion processing to make it have a suitable average pore diameter, resulting in a suitable Gas throughput.
  • heat setting treatment is performed to shape the pores and film thickness formed at the appropriate temperature and time.
  • the main function of cold drawing is to pull apart the lamellae and form the initial microfiber lace structure, while the main function of hot drawing is to expand the micropores generated during the cold drawing stage, increase the separation of lamellae and make the microfiber laces The structure is more stable.
  • the die extrusion temperature is (Tm+10)-(Tm+70)°C
  • the melting point of the polyolefin is Tm
  • the die aspect ratio is 2-5
  • the molecular weight of the polyolefin is 60,000-100,000, and the molecular weight distribution index of the polyolefin is 1-5.
  • the die extrusion temperature is 10-40°C above the melting point of the polyolefin, preferably 15-38°C above the melting point of the polyolefin.
  • the flow viscosity of the polymer melt is significantly affected by temperature. Generally, the viscosity increases with the temperature. high and low. When the extrusion temperature of the die is too low, the viscosity of the polyolefin increases, increasing the resistance of the extrusion die, making the polyolefin extrusion volume unstable, resulting in unstable film thickness, and at the same time, the stress on the melt is reduced.
  • the die aspect ratio is the ratio of the effective length of the screw to the diameter of the screw.
  • the length-to-diameter ratio is small, the free volume of the extruder decreases, and the outlet expansion effect is greater, so that the macromolecules are less affected by the shear force in the pore channel, the less regular structure is formed, the crystallinity is reduced, and the film preparation process is
  • the reduction in the number of holes reduces the porosity of the membrane; at the same time, it cannot effectively solve the pore expansion phenomenon produced during the spinning process, which in turn affects the thickness of the membrane and the mechanical properties of the prepared membrane.
  • orifice expansion also known as the Barras effect
  • the phenomenon of orifice expansion means that when a polymer fluid is extruded from a small hole, capillary tube or slit, the diameter or thickness of the extrudate will be significantly larger than the size of the orifice.
  • the aspect ratio is too large, the pressure exerted by the screw is too large, which affects the performance of the membrane.
  • the appropriate aspect ratio of the die in this application enables the film to have appropriate crystallinity and uniform film wall thickness.
  • the rapid crystallization of low molecular weight components limits the growth of crystal nuclei, resulting in a reduction in the size of the crystal nuclei, making the formed pores smaller, thereby reducing the gas throughput. If the molecular weight distribution becomes narrower, the interaction between high and low molecular weight components decreases and the components crystallize at similar speeds, which is conducive to the generation of crystal nuclei and makes the distribution of crystal nuclei more uniform, thereby making the pore distribution of the prepared hollow fiber membrane more uniform. Uniform, thus having suitable porosity and greater mechanical properties, resulting in suitable gas passage volume and greater tensile strength.
  • the polyolefin in this application has a suitable molecular weight, with a molecular weight of 60,000-100,000, and a narrow molecular weight distribution of 1-5, which makes the distribution of crystal nuclei in the process of preparing hollow fiber membranes tend to be uniform.
  • the pore distribution of the prepared membrane is relatively uniform, and the membrane has appropriate porosity and greater mechanical properties, appropriate gas throughput and greater tensile strength.
  • step S1 when the polyolefin is PP, the isotacticity of the PP is greater than 99%, the crystallinity is 45%-75%, and the melt index is 2-5g/min @ (190°C , 5kg); or, when the polyolefin is PE, the PE is mLLDPE, the density of the mLLDPE is 0.91-0.93g/cm 3 , the molecular weight distribution index is 2-2.5, and the degree of branching is 0.1-0.4; or , when the polyolefin is PMP, the Vicat softening point of the PMP is 160-170°C.
  • the polyolefin of the present application is preferably PP, and the isotacticity of PP is greater than 99%.
  • isotacticity refers to the percentage of isotactic and syndiotactic polymers in all polymer molecules in the polymer. The larger the isotacticity, the better the symmetry of PP, and it has no branching or very few branches. Polymers with few or small side groups and large intermolecular forces tend to be closer to each other, making them easier to crystallize and thus have better crystallinity in the process of preparing hollow fibers.
  • the PP of this application has suitable crystallization degree and melt index, so that PP has good processing fluidity to improve raw material processing efficiency, reduce energy consumption and production costs, and at the same time make the thickness of the prepared film more uniform, thereby making the pores formed in the film more uniform to allow oxygen to pass through the film
  • the permeability rate of the holes is relatively uniform and has good gas throughput.
  • the polyolefin in this application is PE, it is preferably mLLDPE with a relatively regular molecular chain structure.
  • branching degree of mLLDPE is higher, the short branches in the mLLDPE molecular chain have more steric hindrance for molecular movement and orderly arrangement. The larger it is, the lower the crystallinity.
  • the mLLDPE of this application has a suitable degree of branching, giving it a greater degree of crystallinity.
  • the molecular weight distribution of mLLDPE is narrow, the intermolecular force is larger, which is beneficial to its molecules. The stacking of chain secrets makes the movement speeds of each chain segment closer and improves its crystallinity.
  • the mLLDPE of this application has a suitable molecular weight distribution index, making it have greater crystallinity.
  • the density of the mLLDPE of the present application is 0.91-0.93g/cm 3 , where the density is determined by the concentration of the comonomer in the polyolefin chain.
  • the comonomer concentration controls the number of short chain branches (the length of which depends on the comonomer type) and thus the resin density.
  • the lack of long branches in mLLDPE prevents the polymer from becoming tangled and preventing the formation of pores with excessively large pore sizes.
  • the hollow fiber membrane prepared by mLLDPE in the present application has higher crystallinity, uniform pore size distribution and smaller average pore size.
  • the hollow fiber membrane has higher porosity, increasing the channels for oxygen to circulate in the membrane, so as to improve the oxygen flow in the membrane.
  • the internal permeation speed improves the deoxidation efficiency while ensuring the mechanical strength.
  • the degree of branching refers to the density of branch points in the polymer chain or the segment length between adjacent branches or the relative molecular weight of the segments.
  • the Vicat softening point of PMP is 160-170°C, which makes the hollow fiber membrane have good dimensional stability and small thermal deformation when heated, that is, it has good heat resistance and deformation resistance, high rigidity, and good modulus. high.
  • step S2 the air cooling temperature is 110-220°C lower than the die extrusion temperature, and the air cooling distance is 30-1000 mm.
  • the extrusion temperature of the die head is higher than the melting point of the polyolefin so as not to affect the regularity of the surface and avoid crystallization at too low a temperature, which will affect the crystallinity in subsequent steps, so that the polyolefin is extruded in a molten state to form a semi-molded product.
  • the products are cooled by air cooling, and the semi-molded products are shaped. When the temperature of air cooling is too low, the semi-molded product will directly form crystals during the setting process, which will lead to uneven crystallization and uneven pore size in the membrane, thereby reducing the oxygen transmission rate in the membrane. When the air-cooling temperature is too high, the semi-finished product will not be fully shaped.
  • the surface will easily be dented, making the film wall thickness uneven, thereby affecting the performance of the film.
  • the air cooling distance of semi-finished products is too long, and the molten material is susceptible to The influence of external factors causes jitter, and the thickness of the membrane also changes accordingly, resulting in poor uniformity of membrane wall thickness; the short air cooling distance of the semi-finished product results in insufficient shaping, resulting in uniform differences in the membrane wall of the prepared membrane.
  • This application adopts appropriate air cooling temperature and air cooling distance so that no crystals are formed during the air cooling process, the shape is complete, and the film wall thickness of the prepared film is avoided to be uneven.
  • the air-cooling length of the pre-crystallized semi-finished product is 4-8m; the air-cooling temperature is 40-70°C; the air flow speed during the air-cooled crystallization process is 30-60m/min.
  • the air-cooling temperature when the air-cooling temperature is too high, the outer surface cannot be cooled quickly, and a dense surface cannot be formed. It is easy for the liquid to penetrate the hollow fiber membrane, causing the liquid to lose the degassing effect.
  • the air cooling temperature is too low, the area rapidly cooled along the membrane thickness direction increases, thereby increasing the thickness of the skin layer, resulting in a reduction in the gas throughput of the hollow fiber membrane.
  • This application has a suitable air-cooling temperature, so that the hollow fiber membrane prepared by this application not only has a larger gas throughput, but also has a higher mechanical strength.
  • the suitable cooling temperature of this application causes the outer surface to cool rapidly, so that the outer surface forms a dense surface and has a cortical area, but the inner surface is still in a high temperature state.
  • the blowing air cools it to a suitable length, so that the inner surface temperature can be increased within a reasonable length range.
  • the temperature can be lowered to the rewinding temperature to save process costs.
  • the relative speed of the air flow and the pre-crystallized semi-finished product is 30-60m/min. If the relative speed is too fast, the outer surface will easily collapse, making the film wall uniformity poor; if the relative speed is too slow, the cooling speed will be too high. If it is too slow, a dense surface cannot be formed on the outer surface, thus affecting the performance of the membrane.
  • the appropriate relative speed of this application enables the outer surface of the membrane to form a dense surface with appropriate gas throughput and mechanical properties.
  • step S5 the temperature of the first cold drawing is 25-72°C higher than the glass transition temperature of the polyolefin, and the temperature of the second cold drawing is higher than the glass transition temperature of the polyolefin.
  • the temperature is 35-80°C higher.
  • Each cold drawing temperature in this application is higher than the glass transition temperature of polyolefin.
  • the cold drawing temperature is higher, Agglomeration easily occurs between adjacent crystal nuclei, resulting in uneven pore sizes and uneven pore distribution in the hollow fiber membrane.
  • the cold drawing temperature is low, the fibers between adjacent crystal nuclei lack elasticity when the temperature is low, and it is easy to occur. fracture, thereby affecting the performance of the membrane, reducing the mechanical strength, and affecting the degassing effect of the membrane.
  • the first cold drawing is mainly to pull apart the easy-to-stretch lamellae first, so the temperature of the first cold drawing should not be too high to avoid uneven stretching of the lamellae; the second cold drawing temperature is higher than that of the first cold drawing.
  • the secondary cold drawing temperature is higher to pull apart the difficult-to-pull lamellae, and at the same time to avoid the second cold drawing temperature being too high, resulting in uneven pore sizes and uneven pore distribution in the hollow fiber membrane.
  • the application has a suitable first cold drawing temperature and a second cold drawing temperature, so that the prepared hollow fiber membrane has a suitable average pore size, uniform hole distribution, and strong tensile strength, thereby making the hollow fiber membrane Has good gas throughput.
  • the hot drawing temperature in step S6 is at least 60-103°C higher than the temperature of the first cold drawing in step S5; the hot drawing speed is 10% of the first cold drawing speed. -30%; the hot drawing is 2-7 times the stretching ratio of the first cold drawing.
  • the fiber When the temperature of hot drawing is high, due to the occurrence of heat-induced crystallization and tensile stress-induced crystallization, the fiber is rapidly crystallized, resulting in the failure of the macromolecular chain segments to be fully stretched along the stretching direction. At the same time, the polymer molecular chains are Fracture has occurred, so that the hole expansion effect cannot be achieved and the tensile strength of the hollow fiber membrane is reduced.
  • the hot drawing temperature is low, it cannot reach the temperature at which the polymer macromolecule segments can move freely, causing the semi-finished product to have lower elasticity, resulting in insufficient stretching, or fiber breakage during the stretching process, so that the hole expansion cannot be achieved. Effect.
  • the hot drawing adopts a multi-stage, slow stretching and hole expansion method, preferably 5 times of hot drawing; and the preferred hot drawing speed is 10% of the first cold drawing speed, and rapid cold drawing is performed at a suitable speed, that is It can avoid tensile fractures caused by excessive speed, and can quickly break the crystal nuclei so that the sizes of the holes formed are more uniform.
  • This application has a suitable hot drawing temperature, and the hot drawing temperature is at least 60-60- higher than the first cold drawing temperature. 103°C, it can achieve the ideal effect of stretching and expanding holes, and at the same time it has greater tensile strength and greater Gas throughput and filtration effect are good.
  • the so-called hot drawing rate is based on the determination of the cold drawing rate, and the hot drawing rate is characterized by the ratio of the cold drawing rate
  • the tensile stress has sufficient time. Acting on each area, at this time, the molecular chains of the lamellae and the molecular chains at the boundary between the lamellae and the amorphous zone have enough time to relax and be pulled out, thereby converting some of the lamellae into microfiber ties, and the microfiber system Too much band structure and too little lamellar structure lead to the deterioration of the microporous structure.
  • the thermal drawing rate is too high, the tensile stress distribution is uneven and the molecular chains with a long relaxation time have no time to transform.
  • the molecular chains with a short relaxation time transform into a microfiber tie structure, and the lamellae and amorphous
  • the molecular chains at the zone boundaries are easily stretched too much, thereby blocking the resulting micropore structure, causing the micropores to close and the micropore structure to deteriorate.
  • the thermal stretching in this application has a suitable stretching rate, so that the hollow fiber membrane has more lamellar structure during the preparation process, so that it has a larger porosity, thereby increasing the gas throughput and at the same time increasing Gas transmission rate.
  • Stretch ratio refers to the ratio of the fiber length after stretching to the length before stretching.
  • the stretching ratio is high. Excessive tensile stress destroys the original ordered crystal regions of the fiber and reduces the crystallinity of the fiber.
  • the stretching ratio is low, the expected membrane thickness and pore size cannot be achieved.
  • the stretching ratio of the hot drawing in this application is 2-7 times the stretching ratio of the first cold drawing, so that the prepared hollow fiber membrane has appropriate membrane thickness and pore size, and does not affect the crystallization during the preparation process of the hollow fiber membrane. Spend.
  • step S4 the annealing and shaping reduces the temperature to 75-150°C, and the annealing and shaping time is 20-50 minutes.
  • the heat setting temperature is 5-30°C higher than the annealing temperature; the heat setting time is 0.5-3min.
  • the above definition can make the inner layer of the fiber have higher crystallinity, good crystal regularity and orientation after annealing and shaping. Therefore, when stretching into pores, a good pore structure can be obtained. During heat setting, the residual stress existing in the inner layer of the fiber can be well eliminated, thereby making the fiber and the microporous structure on the fiber highly stable.
  • a specific annealing setting temperature can reduce the crystallinity, crystal orientation and regularity of the dense surface, thereby reducing the possibility of microporous structures on the dense surface during the stretching and pore-forming process, while during heat setting At this time, higher temperature can not only eliminate defects on the dense surface, but also promote the crystallization behavior of the dense surface, increase the crystallinity of the dense surface, and thus improve the mechanical properties of the dense surface.
  • the various process parameters of annealing and heat setting are also interrelated. This is because the crystallinity, crystal form, regularity, etc. of the fiber after annealing and setting have a great impact on the microporous structure of the fiber. Different lamella thicknesses, different microfiber tie sizes, etc. require different heat setting process parameters.
  • the highly degassing polyolefin hollow fiber membrane described in any one of the above, where the polyolefin is PP, and the hollow fiber membrane is used to remove oxygen from ultrapure water.
  • the hollow fiber membrane The oxygen permeability rate is 15-30L/(min ⁇ bar ⁇ m 2 ), the tensile strength of the hollow fiber membrane is not less than 150CN, and the elongation at break of the hollow fiber membrane is 30%-150%.
  • the hollow fiber membrane made of polyolefin in this application is mainly used to remove oxygen from ultrapure water. It has a fast permeability rate, which can reach 15-30L/(min ⁇ bar ⁇ m 2 ); and it also has strong tensile strength. The strength is not less than 150CN; and the breaking length is 30%-150%, so that the prepared hollow fiber membrane has a higher oxygen transmission rate, thereby making its deoxidation efficiency higher than 80%, and at the same time making it have better of tensile strength.
  • the hollow fiber membrane provided by this application has a more suitable thickness, the wall thickness of the membrane is more uniform, and at the same time has greater crystallinity and higher porosity to increase the
  • the flow channel of oxygen in the membrane increases the permeation rate of oxygen in the membrane, thereby making the hollow fiber membrane have greater deoxidation efficiency and ensuring that the hollow fiber membrane has greater tensile strength.
  • Figure 1 is a scanning electron microscope (SEM) image of the inner surface of the hollow fiber membrane prepared in Example 4, where the magnification is 10000 ⁇ ;
  • Figure 2 is a scanning electron microscope (SEM) image of the inner surface of the hollow fiber membrane prepared in Example 4, where the magnification is 20000 ⁇ ;
  • Figure 3 is a scanning electron microscope (SEM) image of the outer surface of the hollow fiber membrane prepared in Example 4, where the magnification is 20000 ⁇ ;
  • Figure 4 is a schematic diagram of the device used for the deoxygenation efficiency test of this application.
  • the raw materials and equipment used to prepare the hollow fiber membrane can be purchased through commercial channels.
  • a scanning electron microscope model S-5500 provided by Hitachi was used to characterize the structural morphology of the filter membrane.
  • Embodiment 1 provides a method for preparing a hollow fiber membrane for degassing. The specific steps are as follows:
  • Pre-crystallization Use air cooling to cool and pre-crystallize the semi-molded product obtained in step S1 to obtain a pre-crystallized semi-finished product; the air cooling temperature is 100°C, and the air-cooling distance of the semi-finished product is 500 mm.
  • step S3 Air-cooling crystallization.
  • the pre-crystallized semi-finished product obtained in step S2 is subjected to secondary cooling and crystallization by blowing cooling, and is rolled up to obtain a cooled semi-finished product.
  • the cooling length of the pre-crystallized semi-finished product is 4.5m; the air-cooling temperature is 65 °C; the air flow speed during the air-cooled crystallization process is 55m/min.
  • step S4 Annealing and shaping.
  • the cooled semi-finished product obtained in step S3 is heat-set. After cooling, the heat-set semi-finished product is obtained; annealing and shaping reduces the temperature to 90°C, and the annealing and shaping time is 48 minutes.
  • the heat-set semi-finished product obtained in step S4 is subjected to the first cold drawing process.
  • the rate of the first cold drawing is 15%/min, and the stretching ratio of the first cold drawing is 25%.
  • the temperature of the first cold drawing is 30°C
  • the temperature of the second cold drawing is 20°C.
  • step S6 Hot-drawing and hole-expanding.
  • the cold-drawn semi-finished product obtained in step S5 is hot-drawn and hole-expanded to obtain a hot-drawn semi-finished product.
  • the hot-drawing temperature is 100°C.
  • the hot-drawing speed is 15% of the first cold-drawing speed.
  • the draw ratio is 6.5 times the draw ratio of the first cold drawing.
  • Heat setting perform a secondary heat setting treatment on the heat-drawn semi-finished product obtained in step S6, and obtain a hollow fiber membrane after cooling; the heat setting temperature is 100°C; the heat setting time is 2 minutes.
  • Embodiment 2 provides a method for preparing a hollow fiber membrane for degassing. The specific steps are as follows:
  • Pre-crystallization Use air cooling to cool and pre-crystallize the semi-molded product obtained in step S1 to obtain a pre-crystallized semi-finished product; the air cooling temperature is 30°C, and the air-cooling distance of the semi-finished product is 850 mm.
  • step S3 Air-cooling crystallization.
  • the pre-crystallized semi-finished product obtained in step S2 is subjected to secondary cooling and crystallization by blowing air cooling, and is rolled up to obtain a cooled semi-finished product.
  • the cooling length of the pre-crystallized semi-finished product is 7.5m; the air-cooling temperature is 45 °C; the air flow speed during the air-cooled crystallization process is 35m/min.
  • step S4 Annealing and shaping.
  • the cooled semi-finished product obtained in step S3 is heat-set. After cooling, the heat-set semi-finished product is obtained; annealing and shaping reduces the temperature by 135°C, and the annealing and shaping time is 25 minutes.
  • the heat-set semi-finished product obtained in step S4 is subjected to the first cold drawing process.
  • the first cold drawing rate is 23%/min, and the first cold drawing stretch ratio is 18%.
  • the temperature of the first cold drawing is 10°C
  • the temperature of the second cold drawing is 50°C.
  • step S6 Hot-drawing and hole-expanding.
  • the cold-drawn semi-finished product obtained in step S5 is hot-drawn and hole-expanded to obtain a hot-drawn semi-finished product;
  • the hot-drawing temperature is 95°C;
  • the hot-drawing speed is 25% of the first cold-drawing speed;
  • the draw ratio is 2.5 times the draw ratio of the first cold drawing.
  • Embodiment 3 provides a method for preparing a hollow fiber membrane for degassing. The specific steps are as follows:
  • pre-crystallization use air cooling to cool and pre-crystallize the semi-molded product obtained in step S1 to obtain a pre-crystallized semi-finished product;
  • the air cooling temperature is 30°C, and the air cooling distance of the semi-finished product is 1500mm.
  • step S3 Air-cooling crystallization.
  • the pre-crystallized semi-finished product obtained in step S2 is subjected to secondary cooling and crystallization by blowing air cooling, and is rolled up to obtain a cooled semi-finished product.
  • the cooling length of the pre-crystallized semi-finished product is 6m; the air-cooling temperature is 55°C. ;
  • the air flow speed during the air-cooled crystallization process is 40m/min.
  • step S4 Annealing and shaping.
  • the cooled semi-finished product obtained in step S3 is heat-set. After cooling, the heat-set semi-finished product is obtained; annealing and shaping reduces the temperature to 100°C, and the annealing and shaping time is 35 minutes.
  • the heat-set semi-finished product obtained in step S4 is subjected to the first cold drawing process.
  • the first cold drawing rate is 18%/min, and the first cold drawing stretch ratio is 20%.
  • the first cold-drawn semi-finished product is obtained;
  • the second cold-drawing treatment is carried out, the second cold-drawing rate is 25%/min, and the second cold-drawing draw ratio is 10%, and the second cold-drawn semi-finished product is obtained.
  • the temperature of the first cold drawing is -5°C
  • the temperature of the second cold drawing is 8°C.
  • step S6 Hot-drawing and hole-expanding.
  • the cold-drawn semi-finished product obtained in step S5 is hot-drawn and hole-expanded to obtain a hot-drawn semi-finished product.
  • the hot-drawing temperature is 75°C.
  • the hot-drawing speed is 10% of the first cold-drawing speed. It is 4.5 times the stretching ratio of the first cold drawing.
  • Heat setting perform a secondary heat setting treatment on the heat-drawn semi-finished product obtained in step S6, and obtain a hollow fiber membrane after cooling.
  • the heat setting temperature is 110°C higher than the annealing temperature; the heat setting time is 1 minute.
  • Embodiment 4 provides a method for preparing a hollow fiber membrane for degassing. The specific steps are as follows:
  • Pre-crystallization Use air cooling to cool and pre-crystallize the semi-molded product obtained in step S1 to obtain a pre-crystallized semi-finished product; the air cooling temperature is 60°C, and the air-cooling distance of the semi-finished product is 600 mm.
  • step S3 Air-cooled crystallization.
  • the pre-crystallized semi-finished product obtained in step S2 is subjected to secondary cooling and crystallization by blowing air cooling, and is rolled up to obtain a cooled semi-finished product.
  • the cooling length of the pre-crystallized semi-finished product is 5m; the air-cooling temperature is 50°C. ;
  • the air flow speed during the air-cooled crystallization process is 50m/min.
  • step S4 Annealing and shaping.
  • the cooled semi-finished product obtained in step S3 is heat-set. After cooling, the heat-set semi-finished product is obtained; annealing and shaping reduces the temperature to 110°C, and the annealing and shaping time is 40 minutes.
  • step S5 Two times of cold drawing to create holes.
  • the heat-set semi-finished product obtained in step S4 is subjected to the first cold drawing process.
  • the rate of the first cold drawing is 12%/min, and the stretching ratio of the first cold drawing is 23%.
  • the first cold-drawn semi-finished product is obtained;
  • the second cold-drawing treatment is carried out, the second cold-drawing rate is 28%/min, and the second cold-drawing draw ratio is 7%, and the second cold-drawn semi-finished product is obtained.
  • the temperature of the first cold drawing is 50°C
  • the temperature of the second cold drawing is 30°C.
  • step S6 Hot-drawing and hole-expanding.
  • the cold-drawn semi-finished product obtained in step S5 is hot-drawn and hole-expanded to obtain a hot-drawn semi-finished product.
  • the hot-drawing temperature is 110°C.
  • the hot-drawing speed is 20% of the first cold-drawing speed.
  • the draw ratio is 5 times the draw ratio of the first cold drawing.
  • step S7 Heat setting.
  • the heat-drawn semi-finished product obtained in step S6 is subjected to a secondary heat-setting process. After cooling, a hollow fiber membrane is obtained.
  • the heat-setting temperature is 130°C; the heat-setting time is 2.5 minutes.
  • Embodiment 5 provides a method for preparing a hollow fiber membrane for degassing. The specific steps are as follows:
  • Pre-crystallization Use air cooling to cool and pre-crystallize the semi-molded product obtained in step S1 to obtain a pre-crystallized semi-finished product; the air cooling temperature is 50°C, and the air-cooling distance of the semi-finished product is 200 mm.
  • the pre-crystallized semi-finished product obtained in step S2 is subjected to secondary cooling and crystallization by blowing cooling, and is rolled up to obtain a cooled semi-finished product.
  • the cooling length of the pre-crystallized semi-finished product is 5.5m; the air-cooling temperature is 60 °C; the air flow speed during the air-cooled crystallization process is 45m/min.
  • step S4 Annealing and shaping.
  • the cooled semi-finished product obtained in step S3 is heat-set. After cooling, the heat-set semi-finished product is obtained; annealing and shaping reduces the temperature to 145°C, and the annealing and shaping time is 30 minutes.
  • the heat-set semi-finished product obtained in step S4 is subjected to the first cold drawing process.
  • the rate of the first cold drawing is 20%/min, and the stretching ratio of the first cold drawing is 15%.
  • step S6 Hot-drawing and hole-expanding.
  • the cold-drawn semi-finished product obtained in step S5 is hot-drawn and hole-expanded to obtain a hot-drawn semi-finished product.
  • the hot-drawing temperature is 125°C.
  • the hot-drawing speed is 20% of the first cold-drawing speed.
  • the draw ratio is 3 times the draw ratio of the first cold drawing.
  • Heat setting perform a secondary heat setting treatment on the heat-drawn semi-finished product obtained in step S6, and obtain a hollow fiber membrane after cooling; the heat setting temperature is 170°C; the heat setting time is 1 minute.
  • Embodiment 6 provides a method for preparing a hollow fiber membrane for degassing. The specific steps are as follows:
  • Pre-crystallization Use air cooling to cool and pre-crystallize the semi-molded product obtained in step S1 to obtain a pre-crystallized semi-finished product; the air cooling temperature is 80°C, and the air-cooling distance of the semi-finished product is 900 mm.
  • step S3 Air-cooling crystallization.
  • the pre-crystallized semi-finished product obtained in step S2 is subjected to secondary cooling and crystallization by blowing air cooling, and is rolled up to obtain a cooled semi-finished product.
  • the air-cooling length of the pre-crystallized semi-finished product is 7m; the air-cooling temperature is 70°C. ;
  • the air flow speed during the air-cooled crystallization process is 60m/min.
  • step S4 Annealing and shaping.
  • the cooled semi-finished product obtained in step S3 is heat-set. After cooling, the heat-set semi-finished product is obtained; annealing and shaping reduces the temperature to 80°C, and the annealing and shaping time is 45 minutes.
  • the heat-set semi-finished product obtained in step S4 is subjected to the first cold drawing process.
  • the first cold drawing rate is 10%/min, and the first cold drawing stretch ratio is 21%.
  • step S6 Hot-drawing and hole-expanding.
  • the cold-drawn semi-finished product obtained in step S5 is hot-drawn and hole-expanded to obtain a hot-drawn semi-finished product.
  • the hot-drawing temperature is 105°C.
  • the hot-drawing speed is 23% of the first cold-drawing speed.
  • the draw ratio is 6 times the draw ratio of the first cold drawing.
  • Comparative Example 1 provides a method for preparing a hollow fiber membrane for degassing. The specific steps are as follows:
  • pre-crystallization use air cooling to cool and pre-crystallize the semi-molded product obtained in step S1 to obtain a pre-crystallized semi-finished product;
  • the air cooling temperature is 100°C lower than the die extrusion temperature, and the air-cooling distance of the semi-finished product is 500mm.
  • step S3 Air-cooling crystallization.
  • the pre-crystallized semi-finished product obtained in step S2 is subjected to secondary cooling and crystallization by blowing cooling, and is rolled up to obtain a cooled semi-finished product.
  • the cooling length of the pre-crystallized semi-finished product is 4.5m; the air-cooling temperature is 65 °C; the air flow speed during the air-cooled crystallization process is 55m/min.
  • step S4 Annealing and shaping.
  • the cooled semi-finished product obtained in step S3 is heat-set. After cooling, the heat-set semi-finished product is obtained; annealing and shaping reduces the temperature to 90°C, and the annealing and shaping time is 48 minutes.
  • step S5 Two times of cold drawing to create holes.
  • the heat-set semi-finished product obtained in step S4 is subjected to the first cold drawing process.
  • the first cold drawing rate is 15%/min, and the stretching ratio of the first cold drawing is 25%.
  • the first cold-drawn semi-finished product is obtained;
  • the second cold-drawing process is carried out, the rate of the second cold-drawing is 20%/min, and the stretching ratio of the second cold-drawing is 10%, and the second cold-drawn semi-finished product is obtained, wherein , the temperature of the first cold drawing is 30°C, and the temperature of the second cold drawing is 20°C.
  • step S6 Hot-drawing and hole-expanding.
  • the cold-drawn semi-finished product obtained in step S5 is hot-drawn and hole-expanded to obtain a hot-drawn semi-finished product.
  • the hot-drawing temperature is 100°C.
  • the hot-drawing speed is 15% of the first cold-drawing speed.
  • the draw ratio is 6.5 times the draw ratio of the first cold drawing.
  • Heat setting perform a secondary heat setting treatment on the heat-drawn semi-finished product obtained in step S6, and obtain a hollow fiber membrane after cooling; the heat setting temperature is 100°C; the heat setting time is 2 minutes.
  • Comparative Example 1 under the same conditions as other step parameters of Example 1, the PP melt index, die extrusion The thickness and nitrogen flow rate increase the thickness of the hollow fiber membrane and reduce the uniformity of the membrane wall.
  • Comparative Example 2 provides a method for preparing a hollow fiber membrane for degassing. The specific steps are as follows:
  • pre-crystallization use air cooling to cool and pre-crystallize the semi-molded product obtained in step S1 to obtain a pre-crystallized semi-finished product;
  • the air cooling temperature is 100°C lower than the die extrusion temperature, and the air-cooling distance of the semi-finished product is 500mm.
  • step S3 Air-cooling crystallization.
  • the pre-crystallized semi-finished product obtained in step S2 is subjected to secondary cooling and crystallization by blowing cooling, and is rolled up to obtain a cooled semi-finished product.
  • the cooling length of the pre-crystallized semi-finished product is 4.5m; the air-cooling temperature is 65 °C; the air flow speed during the air-cooled crystallization process is 55m/min.
  • step S4 Annealing and shaping.
  • the cooled semi-finished product obtained in step S3 is heat-set. After cooling, the heat-set semi-finished product is obtained; annealing and shaping reduces the temperature to 90°C, and the annealing and shaping time is 48 minutes.
  • the heat-set semi-finished product obtained in step S4 is subjected to the first cold drawing process.
  • the rate of the first cold drawing is 35%/min, and the stretching ratio of the first cold drawing is 10%.
  • the temperature of the first cold drawing is 40°C
  • the temperature of the second cold drawing is 30°C.
  • step S6 Hot-drawing and hole-expanding.
  • the cold-drawn semi-finished product obtained in step S5 is hot-drawn and hole-expanded to obtain a hot-drawn semi-finished product.
  • the hot-drawing temperature is 100°C.
  • the hot-drawing speed is 15% of the first cold-drawing speed.
  • the draw ratio is 6.5 times the draw ratio of the first cold drawing.
  • Heat setting perform a secondary heat setting treatment on the heat-drawn semi-finished product obtained in step S6, and obtain a hollow fiber membrane after cooling; the heat setting temperature is 100°C; the heat setting time is 2 minutes.
  • the hollow fiber membranes obtained in each example and the comparative example were characterized by morphological morphology of the longitudinal section, inner surface and outer surface, the thickness and average pore diameter of each layer in the main body were measured, and the average fiber diameter and porosity of the hollow fiber membrane were measured. and the measurement of the hollowness, as well as the test of the area ratio of the inner surface ventilation holes and the ventilation area.
  • the measurement data are shown in Tables 1-4, and the morphological characterization results of Example 4 are shown in Figures 1-3.
  • the wall thickness uniformity refers to measuring the membrane wall thickness of the hollow fiber membranes prepared in each example or comparative example. Each hollow fiber membrane is cut into 4 sections, and the wall thickness is measured once for each section. The interval between each measurement is 20cm. Among them, the maximum value of the wall thickness recorded is dmax, and the minimum value of the wall thickness recorded is dmin. The average wall thickness ⁇ d is calculated based on the wall thickness measured four times, and the wall thickness uniformity is calculated according to the following formula:
  • the wall thickness uniformity is not more than 5%.
  • the tensile properties of the hollow fiber membranes obtained in each example were tested, and a tensile testing machine was used for tensile strength testing.
  • Figure 4 is a schematic diagram of the device for the deoxygenation efficiency test.
  • the hollow fiber membranes prepared in each of the examples or comparative examples were used as raw materials to assemble a module with a membrane area of 0.1mm2 , and the module was used as a sample to detect the gas flux.
  • Gas with a pressure of 0.1MPa is introduced at the inlet of the component.
  • the gases are oxygen and carbon dioxide respectively.
  • the outlet of the component is connected to the flow meter to record the gas flux of the component in unit time.
  • the hollow fiber membranes prepared in each of the examples or comparative examples as raw materials to assemble a module with a membrane area of 0.65mm2 , and connect the dissolved oxygen meter, water channel and module for testing.
  • the waterway is used to transport the degassed liquid
  • the components are used to degas the degassed liquid
  • the dissolved oxygen meter is used to detect the oxygen content of the degassed liquid after the degassing treatment.
  • the degassing liquid flows out of the outside of the membrane, the degassing liquid is deionized water, and the temperature of the degassing liquid is 25°C.
  • the inside of the membrane is vacuum swept.
  • Step 1 Detect the initial oxygen content of the degassing liquid, pump the degassing liquid into the waterway, turn off the vacuum equipment at this time, so that the inside of the membrane is at normal pressure, and the degassing liquid passes through the component (without degassing) and then passes through the dissolved oxygen instrument, and keep the flow rate of degassing liquid into the dissolved oxygen instrument at about 1.8GLH.
  • Real-time observation of the dissolved oxygen display on the dissolved oxygen meter After the dissolved oxygen meter indication has stabilized (the change in the dissolved oxygen meter indication is less than 1% within 5 minutes), read the dissolved oxygen amount indication O on the dissolved oxygen meter.
  • Step 2 Detect the final oxygen content of the degassed liquid after degassing.
  • step 1 On the basis of step 1, turn on the vacuum equipment to vacuum sweep the inner layer of the membrane to degas the degassed liquid. Maintain the vacuum during vacuum sweep.
  • the degree indication is -0.094MPa (50torr).
  • Read Take the dissolved oxygen reading on the dissolved oxygen meter and read O. Calculate deoxidation efficiency according to the following formula:
  • the oxygen permeability rate of the hollow fiber membrane obtained in each example was tested.
  • one side of the membrane sample is exposed to the gas to be measured (oxygen, carbon dioxide); supply the gas to be measured into the inner cavity of the hollow fiber membrane;
  • a flowmeter Japanese KOFLOC/4800 to measure the volume flow rate of the gas passing through the sample membrane wall; test it three times from the inside of the membrane to the outside of the membrane, and also test three times from the outside of the membrane to the inside of the membrane, and then take the average value.
  • the average value is is the gas permeation rate of the membrane.
  • Gas permeation rate unit L/(min ⁇ bar ⁇ m 2 ).

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Abstract

一种高脱气聚烯烃中空纤维膜及其制备方法和用于脱除超纯水中氧气的用途，聚烯烃中空纤维膜包括主体，其一侧为朝向内腔的内表面，另一侧为外表面，主体内具有非定向曲折通路，外表面为致密表面，内表面的透气孔面积率为10％-30％；中空纤维膜的平均厚度为45-65μm，平均外径与平均内径之比为1.45-1.55；中空纤维膜TOC溶出量不超过3μg/L，脱氧效率大于80％。制备方法包括以下步骤：S1、纺丝；S2、预结晶；S3、风冷结晶；S4、退火定型；S5、两次冷拉致孔；S6、热拉扩孔；S7、热定型。

Description

一种高脱气聚烯烃中空纤维膜及其制备方法与应用 技术领域
本申请涉及脱气膜材料领域，尤其涉及一种高脱气聚烯烃中空纤维膜及其制备方法与应用。
背景技术
因为聚烯烃原料丰富，价格低廉，容易加工成型，综合性能优良，所以聚烯烃是一类产量大，应用广泛的高分子材料。聚烯烃具有相对密度小、耐化学药品性、耐水性好等特点。聚烯烃可用于薄膜、管材、板材、各种成型制品和电线电缆等。
脱气膜是将液体中的气体，如二氧化碳、氧气、氨氮去除的膜分离产品。目前，制备这种膜的主要方法有拉伸致孔法和热致相分离法。其中，拉伸致孔法是通过熔融挤出将结晶性聚合物制成中空纤维膜或薄膜，通过后处理使聚合物沿挤出方向进行双向拉伸，改善膜孔形状大小和孔隙率；热致相分离法是一些聚合物材料在常温下不能溶解，提高温度至其熔融温度以上时可与一些小分子化合物(稀释剂)形成均匀溶液，降温后均相溶液发生固-液或液-液相分离而固化，脱除(稀释剂)后获得微孔材料。
专利CN107998903A公开了应用于膜蒸馏和膜脱气领域的一种聚丙烯中空纤维微孔膜的制备方法，该专利采用以聚丙烯为原料，高级脂肪胺环氧乙烷加成物为稀释剂，采用热致相分离法，获得聚丙烯中空纤维微孔膜。该专利制备的中空纤维微孔膜具有贯通、呈海绵状的微孔结构断面和微孔分布的表面。
上述专利通过热致相法制得具有内外贯通的多孔中空纤维膜，采用热致相 法制备的中空纤维膜需要添加稀释剂，最终制得的中空纤维膜中必然存在稀释剂的残留，而在超纯水的脱气处理过程中，这部分残留物易发生溶出反应，对超纯水的质量具有较大的影响，因此，上述热致相法制得的滤膜并不适合用于超纯水的制备领域。此外，内外贯通的多孔中空纤维膜虽然脱气效果较好，但内外贯通的微孔结构容易使流体流入，流体一旦流入会使膜丧失气液分离的能力，使用寿命较低。
通过本领域技术人员不断的探索，不对称中空纤维膜体现出优异的性能，其中，不对称中空纤维膜具有致密外表面(无法观察到的孔洞结构或可观察到极少数量的孔洞结构)和多孔结构的支撑层，致密外表面可有效避免流体流入中空纤维膜进而降低使用寿命。但目前不对称中空纤维膜的制备工艺并不成熟，如何制备一款具有较高孔隙率、脱氧效率高、机械强度大和使用寿命长的中空纤维膜这一问题一直困扰着研发人员。
发明内容
为了解决上述问题，本发明旨在提供一种高脱气聚烯烃中空纤维膜及其制备方法与应用，通过本申请制备的中空纤维膜具有较高脱氧效率，同时拉伸强度较大，提高了脱气聚烯烃中空纤维膜的性能，延长了使用寿命。
为实现上述目的，本发明提供了如下技术方案：
一种高脱气聚烯烃中空纤维膜，包括主体，所述主体的一侧为朝向内腔的内表面，另一侧为外表面，所述主体内具有非定向曲折通路，所述外表面为致密表面，所述内表面的透气孔面积率为10％-30％；所述中空纤维膜的平均厚度为45-65μm，所述中空纤维膜的平均外径与平均内径之比为1.45-1.55；所述中空纤维膜TOC溶出量不超过3μg/L；所述中空纤维膜的脱氧效率大于80％。
需说明的是，致密表面是扫描电镜在30000倍下拍摄时，其外表面的孔面积率(即孔洞面积：外表面积)不大于5％，即存在无法观察到的孔洞结构或可观察到极少数量的孔洞结构这两种情况。本申请主体的一侧为靠近内腔的内表面，另一侧为外表面，外表面为致密表面，具有较强的疏水性，使水分子难以通过而氧气可以通过，氧气在中空纤维膜内以努森扩散和粘性流并存的方式透过膜孔，当氧气靠近致密表面时，氧气以努森扩散方式透过膜孔，氧气传质阻力主要为氧气分子与膜孔壁的碰撞，氧气分子间碰撞概率大大减小，以湍流的方式在流道内通过，导致氧气透过速率逐渐减小；当氧气靠近内表面时，氧气发生对流，以粘性流方式透过膜孔，主要以层流流动的方式在流道内通过，随着膜孔径的逐渐增大，使氧气透过速率逐渐增大。当中空纤维膜的膜壁厚度增加时，氧气通过膜孔的方式中，粘性流流动的路径与努森扩散的路径之比增大，即增大了氧气分子在膜内以粘性流方式透过膜孔的距离，进而增大氧气透过速率，以使氧气的总流量增加，进一步增大了中空纤维膜的脱氧效率。努森扩散是气体在多孔固体中扩散时，如果孔径小于气体分子的平均自由程，则气体分子对孔壁的碰撞比气体分子间的碰撞要频繁得多。粘性流是膜孔径远大于气体分子平均自由程，气体分子间碰撞概率远大于气体分子与膜孔壁的碰撞概率。自由程是指一个分子与其它分子相继两次碰撞之间，经过的直线路程。对个别分子而言，自由程时长时短，但大量分子的自由程具有确定的统计规律。大量分子自由程的平均值称为平均自由程。
内表面的透气孔面积率为10％-30％，若透气孔面积率过大，则降低中空纤维膜的拉伸强度，进而降低其使用寿命；若透气孔面积率较小，则减少了氧气流通的通道，进而降低脱氧效率；同时当膜壁较厚时，合适的内表面的透气孔面 积率以提供足够多的气体流通面积，避免氧气在靠近内表面区域堆积，增大传质阻力，降低脱氧效率。本申请中空纤维膜的厚度为45-65μm，合适的中空纤维膜的平均外径与平均内径之比，使膜具有合适的氧气流通面积以及合适的内腔容积，以使氧气在内腔具有合适的流通速率；同时避免因中空纤维膜过厚，内径较小，导致内表面的表面积减小，进而减少了氧气流通的通道，增大了氧气扩散的阻力，降低脱氧效率；还可避免因中空纤维膜较薄，降低拉伸强度，进而降低其使用寿命。本申请具有合适的透气孔面积率、膜壁壁厚和中空纤维膜的平均外径与平均内径之比，使其增加氧气流通的通道，同时确保具有较强的拉伸强度。
又由于本申请的外表面为致密表面，孔隙率较低，疏水性较强，避免超纯水通过外表面孔洞进入膜内，即超纯水与外表面的接触面积很小，进而降低了中空纤维膜中有机物的溶出量，本申请中TOC溶出量不超过3μg/L，优选溶出量不超过0.5μg/L；此外，避免外表面孔洞被溶出的TOC堵塞，使氧气具有更好的氧气通过量，以使脱氧效果好。
综上，本申请中空纤维膜具有合适的厚度，外表面为致密表面，以使TOC的溶出量较低，且氧气分子在膜内以粘性流方式透过膜孔的距离较为合适，进而提高了氧气透过速率，同时内表面的透气孔面积率为10％-30％，中空纤维膜的平均外径与平均内径之比为1.45-1.55，使氧气具有足够的流通通道以及具有合适的内腔流通速率，以使中空纤维膜的脱氧效率高于80％；同时保证中空纤维膜具有足够大的拉伸强度。
进一步的，所述内表面具有若干椭圆形的透气孔，所述透气孔的长径取向为所述中空纤维膜的长度方向，所述透气孔的短径取向为所述中空纤维膜周向 方向，所述透气孔的平均长径为150-300nm，所述透气孔的平均短径为10-60nm，所述中空纤维膜的中空度为35％-55％。
在压力的作用下，本申请透气孔承受的应力集中于长径，若透气孔的平均长径过长，易导致孔洞坍塌；若透气孔的平均长径较短，则降低了透气孔的孔洞面积，增大了传质阻力，使氧气透过量降低，进而降低脱氧效率。本申请短径取向为中空纤维膜周向方向，椭圆的短径与长径之比为形状比，当形状比越接近1时，椭圆的长径与短径均需要承受一定的应力，若透气孔的平均短径过长，则中空纤维膜承受应力越大，越易发生破裂，本申请透气孔的平均长径为150-300nm，平均短径为10-60nm，使透气孔的结构更加稳定，不易坍塌或破裂，同时增加了膜孔内氧气分子的流通，进而增加了氧气透过速率，使其具有较好的脱氧效率。
本申请中空纤维膜的中空度为35％-55％，需要说明的是，中空度为实际有效内腔面积占外截面面积的百分数，通过公式1计算得出：
其中W为中空度，单位为％，S1为外截面的面积,单位为mm2；S2为有效空腔的面积,单位为mm2。
若中空度越高，则有效膜面积越小，导致孔隙率降低，膜越薄，纤维越易压缩不易加工，同时降低膜的拉伸强度，且当膜在受到压力时，中空易变形，进而降低膜的性能；若中空度较小，即有效空腔面积较小，则降低了内表面的表面积，减少了氧气流通的通道，增大了氧气扩散的阻力，进而降低脱氧效率。本申请中空纤维膜具有合适的中空度，使膜具有较强的拉伸强度和更好的脱氧效率，同时中空纤维膜抗压，不易变形。
优选的，所述中空纤维膜的最大厚度与最小厚度之差不超过5um，且该差值不超过所述中空纤维膜平均厚度的10％；所述中空纤维膜的孔隙率为30％-50％，所述中空纤维膜是所述内表面的透气孔面积率的1.5-3.5倍。
本申请中空纤维膜的最大厚度与最小厚度之差不超过5μm，可见中空纤维膜的壁厚较为均匀，若该差值过大，则中空纤维膜的壁厚不均匀，使中空纤维膜内气体通过方式混乱，导致氧气在膜内通传质阻力增加，不利于氧气的通过，导致中空纤维膜各处气体通过量不均匀，进而降低脱氧效率，同时易导致其各处拉伸强度不均，进而降低中空纤维膜的拉伸强度。本申请中空纤维膜的孔隙率为30％-50％,使更多的氧气以粘性流方式在孔内通过，增大氧气的通过量，同时保证膜的拉伸强度。若中空纤维膜的孔隙率过大，易使膜的拉伸强度降低；若中空纤维膜的孔隙率较小，则降低膜的氧气通过量，进而降低脱氧效率。中空纤维膜是内表面的透气孔面积率的1.5-3.5倍，若倍数过大，则中空纤维膜的孔隙率较低，氧气通过量较低，进而降低脱氧效率；若倍数较小，则中空纤维膜的孔隙率较大，降低膜的拉伸强度。
再进一步的，所述透气孔的平均长径是平均短径的2-8倍；所述透气孔的最大长径与最小长径之差为150-350nm，所述透气孔的最大短径与最小短径之差为10-100nm。
在透气膜中透气孔的大小及均匀程度，直接影响中空纤维膜的性能，若透气孔的平均长径与平均短径之比过大，则透气孔轴向(膜的长度方向)承受的应力增大，易导致透气孔坍塌，进而降低膜的脱氧效率和拉伸强度；若透气孔的平均长径与平均短径之比较小，则降低了透气孔的平均孔面积，进而降低了氧气的通过量，进一步降低了脱氧效率。若最大长径与最小长径之差较大，则 透气孔在中空纤维膜的轴向分布不均匀，若最大短径与最小短径之差较大，则透气孔在中空纤维膜的周向分布不均匀，无论透气孔在中空纤维膜轴向分布不均还是周向分布不均，均易导致中空纤维膜拉伸强度不均，易发生断裂，进而影响中空纤维膜的性能，同时透气孔的大小分布不均匀，使得氧气在膜内的通过量不均匀，易增大氧气在流动道中的传质阻力，造成氧气透过速率降低，进而降低脱氧效率。本申请透气孔的平均长径是平均短径的2-8倍；透气孔的最大长径与最小长径之差为150-350nm，透气孔的最大短径与最小短径之差为10-100nm，使本申请制备膜具有较为均匀的透气孔，以使膜具有更高的脱氧效率及拉伸强度。
再进一步的，所述中空纤维膜周向方向上，若干个所述透气孔规则排布形成用于透气的透气区；所述透气区长度的方向与所述中空纤维膜的周向一致；所述透气区宽度的方向与所述中空纤维膜的长度方向一致；所述透气区的平均长度为400-1100nm，所述透气区的平均长度大于所述透气区平均宽度。
若干个透气孔规则排布形成一个透气区，中空纤维膜具有若干个透气区，透气区的平均长度大于透气区的平均宽度，透气区近似椭圆形，且平均长度为400-1100nm，当中空纤维膜承受压力时，使透气区具有稳定性，不易坍塌，进而使中空纤维膜的结构更稳定，不易变形。若透气区的平均长度过长，则易导致中空纤维膜周向支撑强度不足而发生变形或坍塌，进而影响膜的性能；透气区的平均长度较小，则易导致非孔洞面积增大，进而降低孔隙率。透气区的平均长度大于透气区平均宽度，以便保持中空纤维膜整体的拉伸强度，避免中空纤维膜长度方向的拉伸强度降低。
再进一步的，所述中空纤维膜的长度方向上，相邻两所述透气区之间的距 离为第一距离，所述第一距离的平均长度为100-350nm；所述中空纤维膜周向相邻两所述透气区之间的距离为第二距离，所述第二距离的平均长度为100-300nm；所述第一距离的平均长度为第二距离的平均长度的2-3倍；在所述透气区长度方向上相邻所述透气孔之间的平均间距为20-70nm；所述透气区的透气孔面积率为25％-70％，所述透气区的透气孔面积率比所述内表面的透气孔面积率高20％-50％。
本申请中透气区具有较高的透气孔面积率，中空纤维膜的长度方向相邻两透气区之间的距离为第一距离，中空纤维膜周向相邻两透气区之间的距离为第二距离。其中，第一距离与第二距离合适的尺寸对透气区具有支撑作用，避免当中空纤维膜承受压力时，因透气区具有较高的透气孔面积率(降低中空纤维膜的拉伸强度)而使其塌陷或断裂；又因为透气孔承受的应力集中于长径，即透气区承受的应力集中于透气区宽度方向，中空纤维膜承受的应力集中于长度方向，所以第一距离的平均长度的尺寸应相对较大，以提供足够的支撑。本申请第一距离平均长度的尺寸为第二距离平均长度的尺寸的2-3倍，若倍数较大，则降低中空纤维膜的孔隙率，若倍数较小，则当中空纤维膜承受压力时，中空纤维膜第一距离的支撑力不足，易导致透气区宽度方向坍塌或断裂。
由于透气区是内表面上气体透过的主要区域，在透气区长度方向上相邻透气孔之间为第三间距，第三间距的平均长度为20-70nm，第三间距的平均长度在一定程度上反映的是内表面上孔洞的多少，当第三间距的平均长度过大时，在内表面一定区域内孔洞的数量较少，较少的孔洞必然会影响脱气效率，同时使得气体透过的阻力大大增加，脱气过程中的压损大大增加；而第三间距的平均长度较小时，在内表面一定区域内会出现较多的孔洞(即在该区域内，孔洞面 积率是过高的，而实体面积率是过低的)，那么这必然是一个大大的缺陷，在外力作用时，很容易造成孔洞的坍塌，从而使得脱气膜无法继续进行脱气作用，使用寿命较短。本申请透气区的孔洞面积率较高，这样才能使得膜丝具有较高的脱气速率；但透气区内的孔洞面积率不能过高，否则存在孔洞塌缩的风险，使用寿命过短；本发明中透气区内的孔洞面积率为30-70％，且所述透气区的孔洞面积率比内表面整体孔洞面积率高20-50％。这样的孔洞面积率进一步保证了中空纤维膜具有较高的脱气速率，同时还具有较强的尺寸稳定性。
再进一步的，所述外表面还具有若干银纹状的裂缝，所述裂缝的宽度不大于20nm；所述外表面的表面能为15-40mN/m。
本申请外表面还具有若干银纹状的裂缝，使外表面的气体通过量增加，进而增大了脱氧效率。若裂缝宽度较大，当中空纤维膜承受压力较大时，易导致液体透过裂缝进入膜内，进而降低膜的使用寿命，因此本申请裂缝宽度不大于20nm，即可增大外表面氧气的透过量，又确保液体不进入膜内。
需要说明的是，表面能是创造物质表面时对分子间化学键破坏的度量。若外表面的表面能过大，则导致外表面的表面张力较大，降低了外表面对液体的阻隔性，当中空纤维膜外表面承载较大压力时，易导致液体透过外表面进入膜内，使透气膜丧失气液分离的作用。若表面能较小，则导致外表面的表面张力过小，降低气体的透过量，进而降低脱氧效率。本申请外表面的表面能为15-40mN/m，使其具有合适的阻隔性能，保证气体较高的通过量，同时有效阻隔液体透过外表面进入膜内。
再进一步的，所述中空纤维膜的主体沿膜厚度方向具有皮层区和多孔区，所述皮层区与多孔区之间连续纤维过渡；所述皮层区的一侧为外表面，所述多 孔区的一侧为内表面；所述皮层区的厚度为0.5-4μm，所述皮层区的厚度占中空纤维膜厚度的1％-8％，所述皮层区的孔隙率不高于10％。
本申请皮层区的厚度为0.5-4μm，若皮层区较薄则降低膜的拉伸强度，若皮层区较厚，降低氧气的透过量，同时延长氧气在膜内的努森扩散路程，增大氧气的传质阻力，降低氧气的透过速率，进而降低脱氧效率。本申请皮层区的厚度占中空纤维膜厚度的1％-8％，使中空纤维膜具有较高的脱氧效率和拉伸强度；若小于1％-8％，则降低中空纤维膜氧气透过量，进而降低脱氧效率；若大于1％-8％,则降低中空纤维膜的拉伸强度。
再进一步的，所述多孔区的平均孔径由靠近内表面一侧的区域向靠近外表面一侧的区域呈梯度变化；所述多孔区的平均孔径变化梯度为1.5-3nm/μm，所述多孔区的孔隙率为40％-70％，所述多孔区的纤维直径为60-300nm。
本申请中多孔区呈梯度变化，且平均孔径变化梯度为1.5-3nm/μm，可见平均孔径变化梯度较为平缓，使氧气在膜内一直以较高的扩散速率进行扩散。若平均孔径变化梯度较大，则氧气在膜内的扩散方式，从努森扩散突变为粘性流，在突变过程中氧气消耗较大运动能，进而降低气体透过速率。本申请多孔区的纤维直径为60-300nm，以使多孔区具有合适的拉伸强度及孔隙率，本申请多孔区的孔隙率为40％-70％，以使氧气在中空纤维膜内具有较多流道，确保氧气的通过量。
提供的一种上述任意一项所述的高脱气聚烯烃中空纤维膜的制备方法，包括以下步骤：
S1、纺丝，将聚烯烃熔融挤出，在成腔流体的作用下形成具有中空内腔的半成型品；其中，所述聚烯烃的熔融指数为1-7g/min@(Tm+20℃，5kg)，模头 挤出厚度为1.8-2.2mm，所述成腔流体的流速为0.01-0.05ml/min,所述聚烯烃为PE、PP和PMP中的任一种；
S2、预结晶，以空冷的方式对步骤S1中得到的半成型品进行冷却预结晶，得到预结晶半成品；
S3、风冷结晶，以吹风冷却的方式对步骤S2中得到的预结晶半成品进行二次冷却结晶，收卷，得到冷却半成品；
S4、退火定型，将步骤S3中得到的冷却半成品进行热定型处理，冷却后得到热定型半成品；
S5、两次冷拉致孔，将步骤S4中得到的热定型半成品进行第一次冷拉处理，所述第一次冷拉的速率为10-25％/min，所述第一次冷拉的拉伸倍数为15％-25％，得到一次冷拉半成品；对其进行第二次冷拉处理，所述第二次冷拉的速率为15-30％/min，所述第二次冷拉的拉伸倍数为5％-20％，得到二次冷拉半成品；
S6、热拉扩孔，将步骤S5中得到的冷拉半成品进行热拉扩孔，得到热拉半成品；
S7、热定型，将步骤S6中得到的热拉半成品进行二次热定型处理，冷却后得到中空纤维膜。
本申请中将聚烯烃进行熔融处理后挤出，同时通入成腔流体，使其形成未定型的半成品，其中成腔流体的通入可有效避免半成品内凹变形；随后对半成品以空冷的方式对其进行初步定型，形成预结晶半成品。对预结晶半成品以吹风冷却的方式进行冷却结晶，其具有合适的冷却温度、冷却长度及风速，使其结晶并具有合适的结晶度，同时达到合适的收卷温度后进行收卷，得到冷却的半成品。对冷却的半成品进行退火处理，以便消除内部缺陷。对冷却的半成品 进行两次冷拉处理，虽然两次冷拉的速率与拉伸倍率较为接近，但第二次冷拉是在第一冷拉的基础上进行的，即两次冷拉的方式实际上是冷拉速率不断变快和拉伸倍数不断增大的过程。若采用一次冷拉易使拉伸应力过大，不同片晶(存在易拉开片晶和难拉开片晶)的拉伸程度不同，导致制备的膜的孔径不均匀或结构塌陷，本申请采用两次冷拉，第一次冷拉中的拉伸速率和拉伸倍率产生的拉伸应力较小，使容易拉伸的片晶首先被拉开，第二次冷拉的拉伸速率和拉伸倍率均在第一冷拉的基础上进行，以便产生较大的拉伸应力将难拉开的片晶被拉开，进一步使分子链有足够时间松弛，以便解决微纤系带易被拉断和片晶拉开尺寸不均匀等问题，以使制备的膜孔径较为均匀，具有较高的孔隙率，同时两次拉伸的应力分布较为均匀，使制备膜的膜壁更加均匀。本申请采用两次冷拉，先通过小应力进行第一次拉伸，再提高拉伸应力进行第二次拉伸，使制备的膜具有合适的厚度，以使聚烯烃具有合适的取向度，进而增大膜的结晶度，同时膜壁厚度较均匀。
其中，熔融指数值越大，表示该材料的加工流动性越佳，使熔体流动速度更加均匀，致使膜壁厚度更加，反之则越差。当熔融指数较小时，分子链排列的阻碍增大，分子链扩散，晶相结构所需的活化能提高，造成分子链规整排列能力下降，从而使结晶度降低。熔融指数过大时，材料的可塑性变差，不易成型。本申请合适的熔融指数，使制备的中空纤维膜具有合适的厚度，使聚烯烃具有较高的结晶度，增大中空纤维膜的孔隙率，以致增加氧气分子在膜内以粘性流方式透过膜孔的距离；同时具有良好的加工流动性，使膜壁厚度更加均匀，提高原料加工效率，降低能耗和生产成本。本申请的成腔流体优选为氮气，具有合适的流速，若氮气流速过大，则半成品的内表面受力过大，易使其内表面 规整度降低，降低膜壁均匀度；若氮气流速较小，以致无法达到半成品形成内腔所需的支撑力，易使其表面塌陷。氮气合适的流速，使制备膜的膜壁厚度更加均匀。模头挤出的半成品厚度为1.8-2.2mm，若半成品厚度过厚，两次冷拉制备的膜厚度较厚且不均匀；若半成品厚度较薄，经过两次拉伸制备的膜较薄，降低拉伸强度。
本申请的两次冷拉均采用快速冷拉的方式进行拉伸成孔，得到冷拉半成品。在冷却拉伸成孔后，所形成的孔洞会回弹收缩，使平均孔径降低，厚度增加，因此对冷拉半成品进行热拉扩孔处理，使其具有合适的平均孔径，导致其具有合适的气体通过量。最后进行热定型处理，在合适的温度和时间下，对其形成的孔及膜厚度进行定型处理。冷拉的主要作用是将片晶拉开，并形成初始的微纤系带结构，而热拉的主要作用是将冷拉阶段产生的微孔扩大，片晶分离度增加并使微纤系带结构更加稳定。
进一步的，所述步骤S1中，所述模头挤出温度为(Tm+10)-(Tm+70)℃，所述聚烯烃的熔点为Tm；模头长径比为2-5；所述聚烯烃分子量为6万-10万，所述聚烯烃分子量分布指数为1-5。
本申请中模头挤出的温度为聚烯烃熔点以上10-40℃，优选为聚烯烃熔点以上15-38℃，聚合物熔体的流动粘度受温度影响较为显著，一般粘度随着温度的升高而降低。当模头挤出的温度过低时，使聚烯烃的粘度增加，增大挤出模头的阻力，使聚烯烃挤出量不稳定，进而导致膜厚度不稳定，同时熔体所受应力降低导致纤维的取向度降低，进而降低膜的结晶度，导致膜的拉伸强度和透气氧效率降低；当模头挤出的温度过高时，不但易导致聚烯烃发生热降解，力学性能明显下降，进而降低膜的机械性能；还易导致聚合物分子的链段活动能力 增加，熔体的流动性增大，使其粘度降低，使制备的膜的厚度降低，进而影响气体的通过量。本申请合适的模头挤出温度和熔融指数使制备的膜厚度更加均匀，且保证良好孔隙率，又确保具有较强的机械性能，同时在合适的摸头挤出温度范围内，当摸头挤出温度较高时，易使极少部分聚烯烃分解，使制备的膜的外表面具有银纹状裂缝。
模头长径比为螺杆有效长度和螺杆直径之比。当长径比较小时，挤出机的自由体积减小，出口膨胀效应越大，使大分子在孔道内受剪切力作用越小，所形成的规整结构越少，结晶度降低，制备膜的孔洞数量降低，使膜的孔隙率降低；同时无法有效的解决纺丝过程中产生的孔口胀大现象，进而影响膜的厚度以及制备膜的机械性能。孔口胀大现象，也称为巴拉斯效应，指当高聚物流体从小孔、毛细管或狭缝中挤出时，挤出物的直径或厚度会明显的大于孔口的尺寸。当长径比过大时，螺杆施加的压力过大，影响制备膜的性能。本申请合适的模头长径比使膜具有合适的结晶度且膜壁厚度均匀。
不同分子量及分子量分布对结晶度及晶核大小有一定的影响，由分子量的多分散性可知高、低分子量组分之间存在明显的相互作用，当分子量分布较宽时，则高、低分子量组分间相互作用增大，由于高低分子组分量的结晶速率不同，低分子量组分结晶速度快，先结晶，导致先结晶的高分子链“冻结”了为结晶的高分子链而使结晶度降低，同时低分子量组分的快速结晶限制了晶核的长大，导致晶核尺寸降低，使形成的孔较小，进而降低气体的通过量。若分子量分布变窄，高、低分子量组分之间相互作用下降，以相近的速度结晶，有利于晶核的生成，且使晶核分布趋于均匀，进而使制备的中空纤维膜孔洞分布较为均匀，进而具有合适的孔隙率及较大的机械性能，导致具有合适的气体通过 量及较大的拉伸强度。
因此本申请中聚烯烃具有合适的分子量，分子量为6万-10万，且分子量分布较窄，分子量分布为1-5，使本申请在制备中空纤维膜的过程中晶核分布趋于均匀，进而使制备膜的孔洞分布较为均匀，进而具有合适的孔隙率及较大的机械性能，具有合适的气体通过量及较大的拉伸强度。
再进一步的，所述步骤S1中，所述聚烯烃为PP时，所述PP的等规度大于99％，结晶度为45％-75％，熔融指数为2-5g/min@(190℃，5kg)；或，所述聚烯烃为PE时，所述PE为mLLDPE,该mLLDPE的密度为0.91-0.93g/cm3,分子量分布指数为2-2.5，支化度为0.1-0.4；或，所述聚烯烃为PMP时，所述PMP的维卡软化点为160-170℃。
本申请的聚烯烃优选为PP，且PP的等规度大于99％。其中，等规度是指聚合物中全同立构和间同立构的聚合物占所有聚合物分子总的百分比，等规度越大PP的对称性越好、无支链或支链很少或侧基体积小的、大分子间作用力大的高分子容易相互靠紧，使其越容易结晶，进而在制备中空纤维过程中具有较好的结晶度，本申请PP的具有合适的结晶度和熔融指数，使PP具有良好的加工流动性，以提高原料加工效率，降低能耗和生产成本，同时使制备的膜厚度更加均匀，进而使膜形成的孔洞更加均匀，以使氧气通过膜孔的透过速率较为均匀，具有较好的气体通过量。
本申请中聚烯烃为PE时，优选为分子链结构较为规整的mLLDPE，当mLLDPE的支化度较高时，mLLDPE分子链中的短支链越多分子运动和进行有序排列的空间位阻越大，结晶度越低。本申请mLLDPE具有合适的支化度，使其具有较大的结晶度。当mLLDPE分子量分布较窄时，使得分子间作用力较大，有利于其分子 链机密堆砌，使得各个链段的运动速度更加接近，提高其结晶度。本申请mLLDPE具有合适的分子量分布指数，使其具有较大的结晶度。本申请的mLLDPE的密度为0.91-0.93g/cm3，其中，密度由共聚用单体在聚烯烃链中的浓度决定。共聚用单体浓度控制短支链数目(其长度取决于共聚用单体类型)从而控制树脂密度。由于mLLDPE中缺少长支链使聚合物不缠结，避免形成孔的孔径过大。综上，本申请mLLDPE制备的中空纤维膜具有较高结晶度，孔径分布均匀且平均孔径较小，进而中空纤维膜具有较高孔隙率，增加氧气在膜内流通的通道，以提高氧气在膜内的透过速度，使脱氧效率得以提升，同时保证了机械强度。其中，支化度(Degree of branching)是指在高分子链中分支点的密度或者是相邻支链之间的链段长度或者是链段的相对分子量。
当本申请聚烯烃采用PMP时，PMP的维卡软化点为160-170℃，使中空纤维膜受热时的尺寸稳定性好，热变形小，即耐热抗形变能力好，刚性大，模量高。
再进一步的，所述步骤S2中，所述空冷的温度比所述模头挤出温度低110-220℃，所述空冷的距离为30-1000mm。
模头挤出温度高于聚烯烃熔点温度，以便不影响表面的规整度，避免温度过低发生结晶影响其后续步骤中的结晶度，使聚烯烃处于熔融状态挤出形成半成型品，半成型品通过空冷的方式进行冷却，对半成型品进行定型。当空冷的温度过低时，使半成型品在定型的过程中直接形成结晶，进而导致结晶不均匀，使膜内孔径不均匀，进而降低氧气在膜内的透过速率。当空冷温度过高时，半成品定型不充分，在进行风冷结晶处理过程中，表面易造成凹陷，使膜的膜壁厚度不均匀，进而影响膜的性能。半成品空冷距离过长，熔融状态的物料易受 外界因素的影响产生抖动，膜的厚度也随之变化，造成膜壁厚度均匀性差；半成品空冷距离较短，使得定型不充分，使制备的膜的膜壁均匀相差。
本申请采用合适的空冷温度和空冷的距离，使得在空冷过程中不形成结晶，定型完全，同时避免所制备膜的膜壁厚度不均匀。
再进一步的，所述步骤S3中，所述预结晶半成品风冷的冷却长度为4-8m；风冷温度为40-70℃；所述风冷结晶过程中气流速度为30-60m/min。
需要说明的是，当风冷的温度过高时，无法使其外表面迅速冷却，进而无法形成致密表面，易使液体透过中空纤维膜，使其丧失液体脱气的效果。当风冷温度过低时，沿膜厚度方向迅速冷却的面积增加，进而增大了皮层的厚度，导致中空纤维膜的气体通过量降低。本申请具有合适的风冷温度，使其制备的中空纤维膜不但具有较大的气体通过量，而且具有较高的机械强度。
本申请合适的冷却温度使其外表面迅速冷却，使外表面形成致密表面，且具有皮层区，但内表面仍然处于高温状态，吹风冷却至合适的长度，在合理的长度范围内使内表面温度降至可收卷的温度，节省工艺成本。
风冷结晶过程中气流与预结晶半成品的相对速度为30-60m/min，若相对速度过快，外表面易塌陷，使膜的膜壁均匀性差；若相对速度过慢，使其冷却速度过慢，外表面无法形成致密表面，进而影响膜的性能。本申请合适的相对速度，使膜的外表面形成致密表面，且具有合适的气体通过量和机械性能。
再进一步的，所述步骤S5中，所述第一次冷拉的温度比所述聚烯烃的玻璃化温度高25-72℃，所述第二次冷拉的温度比所述聚烯烃的玻璃化温度高35-80℃。
本申请每一次冷拉温度均比聚烯烃玻璃化温度高，当冷拉的温度较高时， 相邻晶核之间易发生团聚，导致中空纤维膜的孔洞大小不均，孔分布不均；当冷拉的温度较低时，相邻晶核之间的纤维温度低时缺乏弹性，容易发生断裂，进而影响膜的性能，降低机械强度，影响膜的脱气效果。第一次冷拉主要是将容易拉伸的片晶首先被拉开，因此第一次冷拉温度不易过高，以避免片晶拉伸不均匀；第二次冷拉温度相较于第一次冷拉温度较高，以便将难拉开的片晶被拉开，同时避免第二次冷拉温度过高，导致中空纤维膜的孔洞大小不均，孔分布不均。本申请具有合适的第一次冷拉温度和第二次冷拉温度，使制备的中空纤维膜具有合适的平均孔径，且孔洞分布均匀，同时具有较强的拉伸强度，进而使中空纤维膜具有良好的气体通过量。
再进一步的，所述步骤S6中的热拉温度比所述步骤S5中第一次冷拉的温度至少高60-103℃；所述热拉速度为所述第一次冷拉速度的10％-30％；所述热拉为第一次冷拉的拉伸倍数的2-7倍。
当热拉的温度较高时，由于热诱导结晶和拉伸应力诱导结晶的发生，促使纤维快速结晶，导致大分子链段未能沿拉伸方向充分拉伸，同时在高温下聚合物分子链已发生断裂，从而无法达到扩孔的效果，降低中空纤维膜的拉伸强度。当热拉温度较低时，无法达到聚合物大分子链段自由分运动的温度，使半成品具有较低的弹性，导致拉伸不充分，或拉伸过程中纤维断裂，从而无法达到扩孔的效果。其中热拉采用多段、缓慢拉伸扩孔的方式进行，优选为5次热拉；且优选热拉的速度为第一次冷拉速度的10％，在合适的速度下进行快速冷拉，即可避免速度过快发生拉伸断裂，又可以使晶核快速断裂以至形成孔洞的大小更加均匀，本申请具有合适的热拉伸温度，且热拉温度比第一次冷拉温度高至少60-103℃，可达到拉伸扩孔的理想效果，同时具有较大拉伸强度，具有较大的 气体通过量，过滤效果好。
热拉速率过低时(可以理解的是，此处所谓的热拉速率，是在冷拉速率确定的基础上，以冷拉速率的倍率对热拉速率进行表征)，拉伸应力有足够时间作用到各区域，此时，片晶的分子链以及片晶和无定形区边界处的分子链有足够时间发生松弛并被拉出，从而使部分片晶转化为微纤系带，微纤系带结构过多、片晶结构过少，导致微孔结构恶化。热拉速率过高时，拉伸应力分布不均匀、松弛时间较长的分子链来不及转变，最终导致只有部分松弛时间较短的分子链转变为微纤系带结构，并且，片晶和无定形区边界处的分子链容易被过当拉伸，从而堵塞产生的微孔结构，导致微孔闭合，微孔结构恶化。本申请中热拉伸具有合适的拉伸速率，使中空纤维膜在制备过程中，具有较多的片晶结构，使其具有较大的孔隙率，进而增大气体的通过量，同时增大气体透过速率。
拉伸倍数指纤维经拉伸后的长度与拉伸前长度的比值。当拉伸倍数较高时，拉伸应力较高，过高的拉伸应力破坏了纤维原有有序的晶区，降低了纤维的结晶度。当拉伸倍数较低时，无法达到预期的膜厚度和孔径尺寸。本申请热拉的拉伸倍数为第一次冷拉的拉伸倍数的2-7倍，使得制备的中空纤维膜具有合适的膜厚度和孔径尺寸，且不影响中空纤维膜制备过程中的结晶度。
冷拉和热拉两者是相互关联、相互影响的过程，两者的工艺参数之间存在较高的关联度，而并非是两个孤立的步骤，例如温度、拉伸速率和拉伸倍数等，对工艺参数进行调整时，必须对两者整体的工艺参数进行统一的调节。
再进一步的，所述步骤S4中，所述退火定型使温度降至75-150℃，退火定型时间为20-50min。
所述步骤S7中，所述热定型温度比退火温度高5-30℃；热定型时间为 0.5-3min。
需要说明的是，以上限定能够使纤维的内层在退火定型后具有较高的结晶度、良好的结晶规整度和取向度，因而在拉伸成孔时，能够获得良好的孔隙结构，而在热定型时，能够很好的消除纤维内层存在的应力残留，从而使纤维以及纤维上的微孔结构具有高度稳定性。而对于纤维的致密表面而言，特定的退火定型温度能够降低致密表面的结晶度、结晶取向度和规整度，从而降低拉伸成孔过程中致密表面产生微孔结构的可能，而在热定型时，较高的温度不但能够消除致密表面的缺陷，还能促进致密表面的结晶行为进行，提高致密表面的结晶度，从而提高致密表面的机械性能。
退火定型和热定型的各项工艺参数之间也是相互关联的，这是由于，退火定型后纤维的结晶度、晶型、规整度等，对于纤维的微孔结构影响都很大。而不同的片晶厚度、不同的微纤系带尺寸等，所需的热定型的工艺参数都不同。
还提供一种上述任意一项所述的高脱气聚烯烃中空纤维膜的用途，所述聚烯烃为PP，所述中空纤维膜用于超纯水中氧气的脱除，所述中空纤维膜的氧气渗透速率为15-30L/(min·bar·m2)，所述中空纤维膜的拉伸强度不低于150CN，所述中空纤维膜的断裂伸长率为30％-150％。
本申请聚烯烃制备的中空纤维膜主要用于超纯水中氧气的脱除，具有较快的渗透速率，可达到15-30L/(min·bar·m2)；同时具有较强的拉伸强度，不低于150CN；且断裂长率为30％-150％，使所制备的中空纤维膜具有较高的氧气透过速率，从而使其脱氧效率高于80％，同时使其具有较好的拉伸强度。
通过本申请能够带来如下有益效果：本申请提供的中空纤维膜具有较合适的厚度，膜的壁厚更加均匀，同时具有较大的结晶度、较高的孔隙率、以增加 氧气在膜内的流道和增大氧气在膜内的透过速率，进而使中空纤维膜具有较大的脱氧效率，同时保证中空纤维膜具有较大的拉伸强度。
附图说明
此处所说明的附图用来提供对本申请的进一步理解，构成本申请的一部分，本申请的示意性实施例及其说明用于解释本申请，并不构成对本申请的不当限定。在附图中：
图1为实施例4制备获得的中空纤维膜内表面的扫描电镜(SEM)图，其中放大倍率为10000×；
图2为实施例4制备获得的中空纤维膜内表面的扫描电镜(SEM)图，其中放大倍率为20000×；
图3为实施例4制备获得的中空纤维膜外表面的扫描电镜(SEM)图，其中放大倍率为20000×；
图4为本申请脱氧气效率测试的装置示意图。
附图标记：1、透气区；2、第二距离；3、第一距离。
具体实施方式
下面结合附图和实施例，对本发明进一步详细说明。
如未特殊说明，在下述实施例中，制备中空纤维膜所用的原料及设备均可通过商业途径购得。其中，采用日立公司提供的型号为S-5500的扫描电镜对滤膜的结构形貌进行表征。
实施例1提供了一种脱气用中空纤维膜的制备方法，具体步骤如下：
S1、纺丝，将PP熔融挤出，在氮气的作用下形成具有中空内腔的半成型品；其中，氮气的流速为0.03ml/min，PP的熔融指数为4.5g/min@(190℃，5kg)， 模头挤出厚度为1.8mm，模头挤出温度为210℃，模头长径比为3；PP分子量为8.5万，PP分子量分布指数为4.5，PP的等规度大于99％，结晶度为50％。
S2、预结晶，以空冷的方式对步骤S1中得到的半成型品进行冷却预结晶，得到预结晶半成品；空冷的温度为100℃，半成品空冷的距离为500mm。
S3、风冷结晶，以吹风冷却的方式对步骤S2中得到的预结晶半成品进行二次冷却结晶，收卷，得到冷却半成品；预结晶半成品风冷的冷却长度为4.5m；风冷温度为65℃；风冷结晶过程中气流速度为55m/min。
S4、退火定型，将步骤S3中得到的冷却半成品进行热定型处理，冷却后得到热定型半成品；退火定型使温度降至90℃，退火定型时间为48min。
S5、两次冷拉致孔，将步骤S4中得到的热定型半成品进行第一次冷拉处理，第一次冷拉的速率为15％/min，第一次冷拉的拉伸倍数为25％，得到一次冷拉半成品；对其进行第二次冷拉处理，第二次冷拉的速率为20％/min，第二次冷拉的拉伸倍数为10％，得到二次冷拉半成品，其中，第一次冷拉的温度30℃，第二次冷拉的温度为20℃。
S6、热拉扩孔，将步骤S5中得到的冷拉半成品进行热拉扩孔，得到热拉半成品；热拉温度为100℃；热拉速度为第一次冷拉速度的15％；热拉的拉伸倍数为第一次冷拉的拉伸倍数的6.5倍。
S7、热定型，将步骤S6中得到的热拉半成品进行二次热定型处理，冷却后得到中空纤维膜；热定型温度为100℃；热定型时间为2min。
实施例2提供了一种脱气用中空纤维膜的制备方法，具体步骤如下：
S1、纺丝，将PP熔融挤出，在氮气的作用下形成具有中空内腔的半成型品；其中，氮气的流速为0.02ml/min，PP的熔融指数为2.5g/min@(190℃，5kg)， 模头挤出厚度为2mm；模头挤出温度为180℃，模头长径比为4；PP分子量为6.5万，PP分子量分布指数为0.5，PP的等规度大于99％，结晶度为65％。
S2、预结晶，以空冷的方式对步骤S1中得到的半成型品进行冷却预结晶，得到预结晶半成品；空冷的温度为30℃，半成品空冷的距离为850mm。
S3、风冷结晶，以吹风冷却的方式对步骤S2中得到的预结晶半成品进行二次冷却结晶，收卷，得到冷却半成品；预结晶半成品风冷的冷却长度为7.5m；风冷温度为45℃；风冷结晶过程中气流速度为35m/min。
S4、退火定型，将步骤S3中得到的冷却半成品进行热定型处理，冷却后得到热定型半成品；退火定型使温度降135℃，退火定型时间为25min。
S5、两次冷拉致孔，将步骤S4中得到的热定型半成品进行第一次冷拉处理，第一次冷拉的速率为23％/min，第一次冷拉的拉伸倍数为18％，得到一次冷拉半成品；对其进行第二次冷拉处理，第二次冷拉的速率为16％/min，第二次冷拉的拉伸倍数为15％，得到二次冷拉半成品；第一次冷拉的温度为10℃，第二次冷拉的温度50℃。
S6、热拉扩孔，将步骤S5中得到的冷拉半成品进行热拉扩孔，得到热拉半成品；热拉温度95℃；热拉速度为第一次冷拉速度的25％；热拉的拉伸倍数为第一次冷拉的拉伸倍数的2.5倍。
S7、热定型，将步骤S6中得到的热拉半成品进行二次热定型处理，冷却后得到中空纤维膜；热定型温度为140℃；热定型时间为0.5min。
实施例3提供了一种脱气用中空纤维膜的制备方法，具体步骤如下：
S1、纺丝，将mLLDPE熔融挤出，在氮气的作用下形成具有中空内腔的半成型品；其中，氮气的流速为0.04ml/min，mLLDPE的熔融指数为4.5g/min@(130℃， 5kg)，模头挤出厚度为2.2mm；模头挤出温度为180℃，模头长径比为2.5；mLLDPE分子量为6.5万，mLLDPE分子量分布指数为2.2；mLLDPE的密度为0.91g/cm3,支化度为0.35。
S2、预结晶，以空冷的方式对步骤S1中得到的半成型品进行冷却预结晶，得到预结晶半成品；空冷的温度30℃，半成品空冷的距离为1500mm。
S3、风冷结晶，以吹风冷却的方式对步骤S2中得到的预结晶半成品进行二次冷却结晶，收卷，得到冷却半成品；预结晶半成品风冷的冷却长度为6m；风冷温度为55℃；风冷结晶过程中气流速度为40m/min。
S4、退火定型，将步骤S3中得到的冷却半成品进行热定型处理，冷却后得到热定型半成品；退火定型使温度降至100℃，退火定型时间为35min。
S5、两次冷拉致孔，将步骤S4中得到的热定型半成品进行第一次冷拉处理，第一次冷拉的速率为18％/min，第一次冷拉的拉伸倍数为20％，得到一次冷拉半成品；对其进行第二次冷拉处理，第二次冷拉的速率为25％/min，第二次冷拉的拉伸倍数为10％，得到二次冷拉半成品。第一次冷拉的温度为-5℃，第二次冷拉的温度8℃。
S6、热拉扩孔，将步骤S5中得到的冷拉半成品进行热拉扩孔，得到热拉半成品；热拉温度为75℃；热拉速度为第一次冷拉速度的10％；热拉为第一次冷拉的拉伸倍数的4.5倍。
S7、热定型，将步骤S6中得到的热拉半成品进行二次热定型处理，冷却后得到中空纤维膜。热定型温度比退火温度高110℃；热定型时间为1min。
实施例4提供了一种脱气用中空纤维膜的制备方法，具体步骤如下：
S1、纺丝，将PP融挤出，在氮气的作用下形成具有中空内腔的半成型品； 其中，氮气的流速为0.035ml/min，PP的熔融指数为3g/min@(190℃，5kg)，模头挤出厚度为1.9mm；模头挤出温度为260℃，模头长径比为4.5；PP分子量为8万，PP分子量分布指数为2，PP的等规度大于99％，结晶度为60％。
S2、预结晶，以空冷的方式对步骤S1中得到的半成型品进行冷却预结晶，得到预结晶半成品；空冷的温度为60℃，半成品空冷的距离为600mm。
S3、风冷结晶，以吹风冷却的方式对步骤S2中得到的预结晶半成品进行二次冷却结晶，收卷，得到冷却半成品；预结晶半成品风冷的冷却长度为5m；风冷温度为50℃；风冷结晶过程中气流速度为50m/min。
S4、退火定型，将步骤S3中得到的冷却半成品进行热定型处理，冷却后得到热定型半成品；退火定型使温度降至110℃，退火定型时间为40min。
S5、两次冷拉致孔，将步骤S4中得到的热定型半成品进行第一次冷拉处理，第一次冷拉的速率为12％/min，第一次冷拉的拉伸倍数为23％，得到一次冷拉半成品；对其进行第二次冷拉处理，第二次冷拉的速率为28％/min，第二次冷拉的拉伸倍数为7％，得到二次冷拉半成品。第一次冷拉的温度为50℃，第二次冷拉的温度为30℃。
S6、热拉扩孔，将步骤S5中得到的冷拉半成品进行热拉扩孔，得到热拉半成品；热拉温度为110℃；热拉速度为第一次冷拉速度的20％；热拉的拉伸倍数为第一次冷拉的拉伸倍数的5倍。
S7、热定型，将步骤S6中得到的热拉半成品进行二次热定型处理，冷却后得到中空纤维膜，热定型温度为130℃；热定型时间为2.5min。
实施例5提供了一种脱气用中空纤维膜的制备方法，具体步骤如下：
S1、纺丝，将PMP熔融挤出，在氮气的作用下形成具有中空内腔的半成型 品；其中，氮气的流速为0.015ml/min，PMP的熔融指数为3.5g/min@(190℃，5kg)，模头挤出厚度为2.1mm，模头挤出温度为270℃，模头长径比为4.5；PMP分子量为9.8万，PMP分子量分布指数为3，结晶度为55％。
S2、预结晶，以空冷的方式对步骤S1中得到的半成型品进行冷却预结晶，得到预结晶半成品；空冷的温度为50℃，半成品空冷的距离为200mm。
S3、风冷结晶，以吹风冷却的方式对步骤S2中得到的预结晶半成品进行二次冷却结晶，收卷，得到冷却半成品；预结晶半成品风冷的冷却长度为5.5m；风冷温度为60℃；风冷结晶过程中气流速度为45m/min。
S4、退火定型，将步骤S3中得到的冷却半成品进行热定型处理，冷却后得到热定型半成品；退火定型使温度降至145℃，退火定型时间为30min。
S5、两次冷拉致孔，将步骤S4中得到的热定型半成品进行第一次冷拉处理，第一次冷拉的速率为20％/min，第一次冷拉的拉伸倍数为15％，得到一次冷拉半成品；对其进行第二次冷拉处理，第二次冷拉的速率为19％/min，第二次冷拉的拉伸倍数为20％，得到二次冷拉半成品，其中，第一次冷拉的温度55℃，第二次冷拉的温度为65℃。
S6、热拉扩孔，将步骤S5中得到的冷拉半成品进行热拉扩孔，得到热拉半成品；热拉温度为125℃；热拉速度为第一次冷拉速度的20％；热拉的拉伸倍数为第一次冷拉的拉伸倍数的3倍。
S7、热定型，将步骤S6中得到的热拉半成品进行二次热定型处理，冷却后得到中空纤维膜；热定型温度为170℃；热定型时间为1min。
实施例6提供了一种脱气用中空纤维膜的制备方法，具体步骤如下：
S1、纺丝，将PP熔融挤出，在氮气的作用下形成具有中空内腔的半成型品； 其中，氮气的流速为0.035ml/min，PP的熔融指数为4g/min@(190℃，5kg)，模头挤出厚度为2.1mm，模头挤出温度为200℃，模头长径比为3.5；PP分子量为8万，PP分子量分布指数为3.5，PP的等规度大于99％，结晶度为70％。
S2、预结晶，以空冷的方式对步骤S1中得到的半成型品进行冷却预结晶，得到预结晶半成品；空冷的温度为80℃，半成品空冷的距离为900mm。
S3、风冷结晶，以吹风冷却的方式对步骤S2中得到的预结晶半成品进行二次冷却结晶，收卷，得到冷却半成品；预结晶半成品风冷的冷却长度为7m；风冷温度为70℃；风冷结晶过程中气流速度为60m/min。
S4、退火定型，将步骤S3中得到的冷却半成品进行热定型处理，冷却后得到热定型半成品；退火定型使温度降至80℃，退火定型时间为45min。
S5、两次冷拉致孔，将步骤S4中得到的热定型半成品进行第一次冷拉处理，第一次冷拉的速率为10％/min，第一次冷拉的拉伸倍数为21％，得到一次冷拉半成品；对其进行第二次冷拉处理，第二次冷拉的速率为23％/min，第二次冷拉的拉伸倍数为16％，得到二次冷拉半成品，其中，第一次冷拉的温度40℃，第二次冷拉的温度为35℃。
S6、热拉扩孔，将步骤S5中得到的冷拉半成品进行热拉扩孔，得到热拉半成品；热拉温度为105℃；热拉速度为第一次冷拉速度的23％；热拉的拉伸倍数为第一次冷拉的拉伸倍数的6倍。
S7、热定型，将步骤S6中得到的热拉半成品进行二次热定型处理，冷却后得到中空纤维膜；热定型温度为95℃；热定型时间为3min。
对比例1提供了一种脱气用中空纤维膜的制备方法，具体步骤如下：
S1、纺丝，将PP熔融挤出，在氮气的作用下形成具有中空内腔的半成型品； 其中，氮气的流速为0.2ml/min，PP的熔融指数为0.5g/min@(190℃，5kg)，模头挤出厚度为3mm，模头挤出温度为210℃，模头长径比为3；PP分子量为8.5万，PP分子量分布指数为4.5，PP的等规度大于99％，结晶度为50％。
S2、预结晶，以空冷的方式对步骤S1中得到的半成型品进行冷却预结晶，得到预结晶半成品；空冷的温度比模头挤出温度低100℃，半成品空冷的距离为500mm。
S3、风冷结晶，以吹风冷却的方式对步骤S2中得到的预结晶半成品进行二次冷却结晶，收卷，得到冷却半成品；预结晶半成品风冷的冷却长度为4.5m；风冷温度为65℃；风冷结晶过程中气流速度为55m/min。
S4、退火定型，将步骤S3中得到的冷却半成品进行热定型处理，冷却后得到热定型半成品；退火定型使温度降至90℃，退火定型时间为48min。
S5、两次冷拉致孔，将步骤S4中得到的热定型半成品进行第一次冷拉处理第一次冷拉的速率为15％/min，第一次冷拉的拉伸倍数为25％，得到一次冷拉半成品；对其进行第二次冷拉处理，第二次冷拉的速率为20％/min，第二次冷拉的拉伸倍数为10％，得到二次冷拉半成品，其中，第一次冷拉的温度30℃，第二次冷拉的温度为20℃。
S6、热拉扩孔，将步骤S5中得到的冷拉半成品进行热拉扩孔，得到热拉半成品；热拉温度为100℃；热拉速度为第一次冷拉速度的15％；热拉的拉伸倍数为第一次冷拉的拉伸倍数的6.5倍。
S7、热定型，将步骤S6中得到的热拉半成品进行二次热定型处理，冷却后得到中空纤维膜；热定型温度为100℃；热定型时间为2min。
对比例1与实施例1其他步骤参数相同的条件下，改变了PP熔融指数、模头挤 出厚度和氮气的流速，使中空纤维膜的厚度增加，降低了膜壁均匀性。
对比例2提供了一种脱气用中空纤维膜的制备方法，具体步骤如下：
S1、纺丝，将PP熔融挤出，在氮气的作用下形成具有中空内腔的半成型品；其中，氮气的流速为0.25ml/min，PP的熔融指数为4.5g/min@(190℃，5kg)，模头挤出厚度为1.8mm，模头挤出温度为210℃，模头长径比为3；PP分子量为8.5万，PP分子量分布指数为4.5，PP的等规度大于99％，结晶度为50％。
S2、预结晶，以空冷的方式对步骤S1中得到的半成型品进行冷却预结晶，得到预结晶半成品；空冷的温度比模头挤出温度低100℃，半成品空冷的距离为500mm。
S3、风冷结晶，以吹风冷却的方式对步骤S2中得到的预结晶半成品进行二次冷却结晶，收卷，得到冷却半成品；预结晶半成品风冷的冷却长度为4.5m；风冷温度为65℃；风冷结晶过程中气流速度为55m/min。
S4、退火定型，将步骤S3中得到的冷却半成品进行热定型处理，冷却后得到热定型半成品；退火定型使温度降至90℃，退火定型时间为48min。
S5、两次冷拉致孔，将步骤S4中得到的热定型半成品进行第一次冷拉处理，第一次冷拉的速率为35％/min，第一次冷拉的拉伸倍数为10％，得到一次冷拉半成品；对其进行第二次冷拉处理，第二次冷拉的速率为40％/min，第二次冷拉的拉伸倍数为3％，得到二次冷拉半成品，其中，第一次冷拉的温度40℃，第二次冷拉的温度为30℃。
S6、热拉扩孔，将步骤S5中得到的冷拉半成品进行热拉扩孔，得到热拉半成品；热拉温度为100℃；热拉速度为第一次冷拉速度的15％；热拉的拉伸倍数为第一次冷拉的拉伸倍数的6.5倍。
S7、热定型，将步骤S6中得到的热拉半成品进行二次热定型处理，冷却后得到中空纤维膜；热定型温度为100℃；热定型时间为2min。
对比例2与实施例1其他步骤参数相同的条件下，改变了两次冷拉的拉伸速率和拉伸倍数，使中空纤维膜的孔隙率降低，进而降低了中空纤维膜的气体通过量。
性能实验
一、结构表征
对各实施例以及对比例所获得的中空纤维膜分别进行纵截面、内表面和外表面的形貌表征，主体中各层的厚度和平均孔径的测量，中空纤维膜的纤维平均直径、孔隙率和中空度的测量，以及内表面透气孔和透气区面积率的测试，其中，测量数据见表1-4，实施例4的形貌表征结果见图1-图3。
表1中，壁厚均匀度指，对各实施例或对比例中制得的中空纤维膜的膜壁厚度进行测量，每一根中空纤维膜截取4段，对每段进行一次壁厚测量，每次测量间隔20cm。其中，记录壁厚的最大数值为dmax，记录壁厚最小的数值为dmin，并根据四次测量的壁厚计算出平均壁厚△d，根据下式计算壁厚均匀度：
其中，壁厚均匀度越小，说明中空纤维膜的厚度越均匀，一般壁厚均匀度不大于5％。
表1各示例膜结构的表征(1)

表2各示例膜结构的表征(2)
表3各示例膜结构的表征(3)
表4各示例膜结构的表征(4)

二、性能测试
对各示例所得中空纤维膜进行拉伸性能的测试，采用拉力试验机进行拉伸强度测试。
对各示例所得中空纤维膜进行气体通过量测试，图4为脱氧气效率测试的装置示意图。
以各实施例或对比例中制得的中空纤维膜为原料，组装成膜面积为0.1mm2的组件，并以该组件作为试样，进行气体通量的检测。
在组件入口处通入压力为0.1MPa的气体，气体分别为氧气和二氧化碳，组件出口与流量计相连，记录组件在单位时间内的气体通量。
一般来说，气体通量越大，说明该组件的脱气效率越高，相应的，该中空纤维膜的脱气效率越高。
以各实施例或对比例中制得的中空纤维膜为原料，组装成膜面积为0.65mm2的组件，并将溶氧仪、水路和组件相连，以进行测试。水路用于输送脱气液，组件用于对脱气液进行脱气处理，溶氧仪用于检测脱气处理后脱气液的含氧量。
其中，膜外侧走脱气液，脱气液为去离子水，脱气液的温度为25℃。膜内侧进行真空扫吹。
步骤1、检测脱气液的初始氧含量，在水路中泵入脱气液，此时关闭真空设备，使膜内侧为常压状态，脱气液经过组件(未进行脱气)后经过溶氧仪，保持脱气液进入溶氧仪内的流量为约1.8GLH。实时观察溶氧仪表上溶氧量示数的 变化，待溶氧仪示数稳定后(5min内溶氧仪表的示数变化低于1％时)，读取溶氧仪表上溶氧量示数O始。
步骤2、检测脱气后脱气液的最终氧含量，在步骤1的基础上，打开真空设备对膜内层进行真空扫吹，以对脱气液进行脱气处理，真空扫吹时保持真空度示数为-0.094MPa(50torr)。实时观察溶氧仪表上溶氧量示数的变化，待溶氧仪示数稳定后(5min内溶氧仪表的示数变化低于1％时)，视为已经开始脱气并达到平衡，读取溶氧仪表上溶氧量示数O终。根据下式计算脱氧效率：
对各示例所得中空纤维膜进行氧气渗透速率的测试。
在温度为25℃，压强为0.1bar，膜样品面积为0.1平方米的条件下，使膜样品的一面经受待测气体(氧气，二氧化碳)；将待测气体供入中空纤维膜的内腔；用流量计(日本KOFLOC/4800)测定透过样品膜壁的气体的体积流速；从膜内到膜外测试3次，从膜外到膜内也测试三次，然后取平均值，该平均值即为该膜的气体渗透速率。气体渗透速率单位：L/(min·bar·m2)。
表5各示例的性能测试结果

以上所述仅为本申请的实施例而已，并不用于限制本申请。对于本领域技术人员来说，本申请可以有各种更改和变化。凡在本申请的精神和原理之内所作的任何修改、等同替换、改进等，均应包含在本申请的权利要求范围之内。

Claims (19)

  1. 一种高脱气聚烯烃中空纤维膜，包括主体，所述主体的一侧为朝向内腔的内表面，另一侧为外表面，所述主体内具有非定向曲折通路，其特征在于，所述外表面为致密表面，所述内表面的透气孔面积率为10％-30％；
    所述中空纤维膜的平均厚度为45-65μm，所述中空纤维膜的平均外径与平均内径之比为1.45-1.55；
    所述中空纤维膜TOC溶出量不超过3μg/L；
    所述中空纤维膜的脱氧效率大于80％。
  2. 根据权利要求1所述的高脱气聚烯烃中空纤维膜，其特征在于，所述内表面具有若干椭圆形的透气孔，所述透气孔的长径取向为所述中空纤维膜的长度方向，所述透气孔的短径取向为所述中空纤维膜周向方向，所述透气孔的平均长径为150-300nm，所述透气孔的平均短径为10-60nm，所述中空纤维膜的中空度为35％-55％。
  3. 根据权利要求1所述的高脱气聚烯烃中空纤维膜，其特征在于，所述中空纤维膜的最大厚度与最小厚度之差不超过5um，且该差值不超过所述中空纤维膜平均厚度的10％；
    所述中空纤维膜的孔隙率为30％-50％，所述中空纤维膜孔隙率为所述内表面的透气孔面积率的1.5-3.5倍。
  4. 根据权利要求1所述的高脱气聚烯烃中空纤维膜，其特征在于，所述透气孔的平均长径是平均短径的2-8倍；
    所述透气孔的最大长径与最小长径之差为150-350nm，所述透气孔的最大短径与最小短径之差为10-100nm。
  5. 根据权利要求1所述的高脱气聚烯烃中空纤维膜，其特征在于，所述中 空纤维膜周向方向上，若干个所述透气孔规则排布形成用于透气的透气区；
    所述透气区长度的方向与所述中空纤维膜的周向一致；所述透气区宽度的方向与所述中空纤维膜的长度方向一致；
    所述透气区的平均长度为400-1100nm，所述透气区的平均长度大于所述透气区平均宽度。
  6. 根据权利要求5所述的高脱气聚烯烃中空纤维膜，其特征在于，所述中空纤维膜的长度方向上，相邻两所述透气区之间的距离为第一距离，所述第一距离平均长度为100-350nm；所述中空纤维膜周向上，相邻两所述透气区之间的距离为第二距离，所述第二距离平均长度为100-300nm；所述第一距离平均长度不大于第二距离平均长度的3倍。
  7. 根据权利要求5所述的高脱气聚烯烃中空纤维膜，其特征在于，所述透气区的透气孔面积率为30％-70％，所述透气区的透气孔面积率比所述内表面的透气孔面积率高20％-50％；
    在所述透气区长度方向上相邻所述透气孔之间的平均间距为20-70nm。
  8. 根据权利要求1所述的高脱气聚烯烃中空纤维膜，其特征在于，所述外表面还具有若干银纹状的裂缝，所述裂缝的宽度不大于20nm；所述外表面的表面能为15-40mN/m。
  9. 根据权利要求1所述的高脱气聚烯烃中空纤维膜，其特征在于，所述中空纤维膜的主体沿膜厚度方向具有皮层区和多孔区，所述皮层区与多孔区之间连续纤维过渡；
    所述皮层区的一侧为外表面，所述多孔区的一侧为内表面；
    所述皮层区的厚度为0.5-4μm，所述皮层区的厚度占中空纤维膜厚度的 1％-8％，所述皮层区的孔隙率不高于10％。
  10. 根据权利要求9所述的高脱气聚烯烃中空纤维膜，其特征在于，所述多孔区的平均孔径由靠近内表面一侧的区域向靠近外表面一侧的区域呈梯度变化；
    所述多孔区的平均孔径变化梯度为1.5-3nm/μm，所述多孔区的孔隙率为40％-70％，所述多孔区的纤维直径为60-300nm。
  11. 根据权利要求1-10任意一项所述的高脱气聚烯烃中空纤维膜的制备方法，其特征在于，包括以下步骤：
    S1、纺丝，将聚烯烃熔融挤出，在成腔流体的作用下形成具有中空内腔的半成型品；
    其中，所述聚烯烃的熔融指数为1-7g/min@(Tm+20℃，5kg)，模头挤出厚度为1.8-2.2mm，所述成腔流体的流速为0.01-0.05ml/min；
    所述聚烯烃为PE、PP和PMP中的任一种；
    S2、预结晶，以空冷的方式对步骤S1中得到的半成型品进行冷却预结晶，得到预结晶半成品；
    S3、风冷结晶，以吹风冷却的方式对步骤S2中得到的预结晶半成品进行二次冷却结晶，收卷，得到冷却半成品；
    S4、退火定型，将步骤S3中得到的冷却半成品进行热定型处理，冷却后得到热定型半成品；
    S5、两次冷拉致孔，将步骤S4中得到的热定型半成品进行第一次冷拉处理，所述第一次冷拉的速率为10-25％/min，所述第一次冷拉的拉伸倍数为15％-25％，得到一次冷拉半成品；对其进行第二次冷拉处理，所述第二次冷拉 的速率为15-30％/min，所述第二次冷拉的拉伸倍数为5％-20％，得到二次冷拉半成品；
    S6、热拉扩孔，将步骤S5中得到的冷拉半成品进行热拉扩孔，得到热拉半成品；
    S7、热定型，将步骤S6中得到的热拉半成品进行二次热定型处理，冷却后得到中空纤维膜。
  12. 根据权利要求11所述的高脱气聚烯烃中空纤维膜的制备方法，其特征在于，所述步骤S1中，所述模头挤出温度为(Tm+10)-(Tm+70)℃，所述聚烯烃的熔点为Tm；模头长径比为2-5；所述聚烯烃分子量为6万-10万，所述聚烯烃分子量分布指数为1-5。
  13. 根据权利要求11所述的高脱气聚烯烃中空纤维膜的制备方法，其特征在于，所述步骤S1中，所述聚烯烃为PP时，所述PP的等规度大于99％，结晶度为45％-75％，熔融指数为2-5g/min@(190℃，5kg)；或，所述聚烯烃为PE时，所述PE为mLLDPE,该mLLDPE的密度为0.91-0.93g/cm3,分子量分布指数为2-2.5，支化度为0.1-0.4；或，所述聚烯烃为PMP时，所述PMP的维卡软化点为160-170℃。
  14. 根据权利要求11所述的高脱气聚烯烃中空纤维膜的制备方法，其特征在于，所述步骤S2中，所述空冷的温度比所述模头挤出温度低110-220℃，所述半成品空冷的距离为30-1000mm。
  15. 根据权利要求11所述的高脱气聚烯烃中空纤维膜的制备方法，其特征在于，所述步骤S3中，所述预结晶半成品风冷的冷却长度为4-8m；风冷温度为40-70℃；所述风冷结晶过程中气流速度为30-60m/min。
  16. 根据权利要求11所述的高脱气聚烯烃中空纤维膜的制备方法，其特征在于，所述步骤S5中，所述第一次冷拉的温度比所述聚烯烃的玻璃化温度高25-72℃，所述第二次冷拉的温度比所述聚烯烃的玻璃化温度高35-80℃。
  17. 根据权利要求11所述的高脱气聚烯烃中空纤维膜的制备方法，其特征在于，所述步骤S6中的热拉温度比所述步骤S5中第一次冷拉的温度至少高60-103℃；所述热拉速度为所述第一次冷拉速度的10％-30％；所述热拉的拉伸倍数为第一次冷拉的拉伸倍数的2-7倍。
  18. 根据权利要求11所述的高脱气聚烯烃中空纤维膜的制备方法，其特征在于，所述步骤S4中，所述退火定型使温度降至75-150℃，退火定型时间为20-50min；
    所述步骤S7中，所述热定型温度比退火温度高5-30℃；热定型时间为0.5-3min。
  19. 根据权利要求1-10任意一项所述的高脱气聚烯烃中空纤维膜的用途，其特征在于，所述聚烯烃为PP，所述中空纤维膜用于超纯水中氧气的脱除，所述中空纤维膜的氧气渗透速率为15-30L/(min·bar·m2)，所述中空纤维膜的拉伸强度不低于150CN，所述中空纤维膜的断裂伸长率为30％-150％。
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