WO2024087771A1 - 一种纤维素超滤膜及其制备方法 - Google Patents

一种纤维素超滤膜及其制备方法 Download PDF

Info

Publication number
WO2024087771A1
WO2024087771A1 PCT/CN2023/110344 CN2023110344W WO2024087771A1 WO 2024087771 A1 WO2024087771 A1 WO 2024087771A1 CN 2023110344 W CN2023110344 W CN 2023110344W WO 2024087771 A1 WO2024087771 A1 WO 2024087771A1
Authority
WO
WIPO (PCT)
Prior art keywords
layer
cellulose
ultrafiltration membrane
polytetrafluoroethylene
membrane
Prior art date
Application number
PCT/CN2023/110344
Other languages
English (en)
French (fr)
Inventor
贾建东
Original Assignee
杭州科百特过滤器材有限公司
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 杭州科百特过滤器材有限公司 filed Critical 杭州科百特过滤器材有限公司
Publication of WO2024087771A1 publication Critical patent/WO2024087771A1/zh

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/14—Ultrafiltration; Microfiltration
    • B01D61/145—Ultrafiltration
    • 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
    • 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
    • B01D71/08—Polysaccharides
    • B01D71/12—Cellulose derivatives
    • 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
    • B01D71/30—Polyalkenyl halides
    • B01D71/32—Polyalkenyl halides containing fluorine atoms
    • B01D71/36—Polytetrafluoroethene
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • C02F1/444—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by ultrafiltration or microfiltration

Definitions

  • the invention relates to the technical field of membrane materials, and more particularly to a cellulose ultrafiltration membrane and a preparation method thereof.
  • Membrane technology is a new technology for efficient separation in the contemporary world. Compared with traditional distillation and rectification technologies, it has the advantages of high separation efficiency, low energy consumption, and small footprint.
  • the core of membrane separation technology is the separation membrane.
  • polymer filter membrane is a type of separation membrane made of organic high molecular polymers as raw materials according to a certain process; according to the different types of high molecular polymers, polymer filter membranes can be subdivided into cellulose polymer filter membranes, polyamide polymer filter membranes, sulfone polymer filter membranes, polytetrafluoroethylene polymer filter membranes, etc.; in addition, according to the pore size of the membrane, it can be divided into microfiltration membranes, ultrafiltration membranes, nanofiltration membranes and reverse osmosis membranes.
  • Ultrafiltration membrane is a polymer semipermeable membrane used in the ultrafiltration process to separate polymer colloids or suspended particles of a certain size from the solution. It is widely used in the deep treatment of industrial wastewater and process water, such as the concentration, purification and separation of macromolecular substances in the chemical, food and pharmaceutical industries, sterilization of biological solutions, separation of dyes in printing and dyeing wastewater, recovery of glycerin in petrochemical wastewater, recovery of silver in photographic chemical wastewater, and preparation of ultrapure water. In addition, it can also be used for sludge concentration and dehydration.
  • cellulose polymer ultrafiltration membranes made of different materials, cellulose polymer ultrafiltration membranes have higher hydrophilicity and therefore have lower nonspecific adsorption during protein concentration, purification and separation, thereby preventing the adsorption of protein molecules. On the one hand, this prevents the reduction of protein yield, and on the other hand, it prevents the ultrafiltration membrane from being blocked too quickly.
  • composite cellulose ultrafiltration membranes with a substrate layer have appeared on the market, which give the membrane a higher mechanical strength as a whole and increase its practical practicability.
  • the composite ultrafiltration membrane on the market uses non-woven fabric as the base layer, that is, cellulose polymers are coated on the surface of non-woven fabric to form a composite ultrafiltration membrane.
  • the preparation process is relatively simple, but the surface of non-woven fabric is relatively rough.
  • the fiber protrusions and the raised ends of the fibers on the surface can easily puncture the cellulose ultrafiltration layer in the ultrafiltration membrane, causing damage to the surface of the ultrafiltration membrane and seriously affecting the integrity of the membrane.
  • the microporous membrane has a relatively flat surface, and as a base layer to prepare a composite ultrafiltration membrane with good integrity, for example, Xiamen University's patent CN103877867B discloses a cellulose ultrafiltration membrane composed of a microfiltration membrane and a cellulose cortex layer using a 0.2 ⁇ m polytetrafluoroethylene microfiltration membrane as a support layer.
  • the preparation process is that the cellulose membrane liquid is filtered on the microfiltration membrane and freely stacked to form a nanoporous cellulose cortex, so it will not penetrate into the polytetrafluoroethylene microfiltration membrane.
  • the pore size of the polytetrafluoroethylene microfiltration membrane used is too small (0.2 ⁇ m), so it is easy to cause rapid accumulation of solutes at the interface of the microfiltration membrane. Although it has a relatively good retention rate, it will lead to a low overall membrane flux. In actual use, the filtration time is too long, which reduces the efficiency.
  • the purpose of the present invention is to provide a cellulose ultrafiltration membrane and a preparation method thereof.
  • the ultrafiltration membrane uses a microporous membrane containing a polytetrafluoroethylene layer as a base layer and a cellulose polymer as an ultrafiltration layer, has a molecular weight cutoff of 1-750K, has fewer defects, high integrity, uniform pores on the surface of the ultrafiltration layer, fast flow rate, high flux, and short filtration time.
  • the present invention adopts the following technical solution:
  • a cellulose ultrafiltration membrane comprises a main body, wherein the main body has:
  • the main body comprises an ultrafiltration layer, a support layer and a base layer in sequence along the direction of fluid flow;
  • the ultrafiltration layer and the support layer include a cellulose polymer layer, and the base layer includes polytetrafluoroethylene layer,
  • the average pore size of the PMI of the base layer is greater than 0.8 ⁇ m
  • the polytetrafluoroethylene layer is a hydrophilic polytetrafluoroethylene layer
  • the cellulose polymer layer and the polytetrafluoroethylene layer are infiltrated and bonded to form a bonding layer;
  • the average pore size of the first side surface by SEM is 1-90 nm.
  • the cellulose ultrafiltration membrane is a composite membrane, which is composed of a cellulose polymer layer and a polytetrafluoroethylene layer. Compared with the ultrafiltration membrane with an integrally formed structure, the composite ultrafiltration membrane can optimize the functions of each layer, thereby making the performance of the entire membrane more ideal.
  • the main body of the cellulose ultrafiltration membrane of the present invention is composed of an ultrafiltration layer, a support layer and a base layer in sequence along the direction of fluid flow, wherein the ultrafiltration layer mainly plays a role in intercepting substances, one side of the ultrafiltration layer is a first side surface for supplying the liquid to be filtered, and there are holes on the surface with relatively small pore sizes that play a good interception role.
  • the size of the pore size is a key factor in being able to intercept substances, and different pore sizes can intercept substances of different particle sizes; after research, it was found that when the SEM average pore size of the first side surface is 1-90nm, such a pore size is suitable for intercepting various biological molecules (such as antibodies and other substances) with a molecular weight of 1K-750K, which is conducive to obtaining a higher interception efficiency.
  • both the ultrafiltration layer and the transition layer are prepared by phase inversion of cellulose polymers, and are cellulose polymer layers. Therefore, the ultrafiltration layer has strong hydrophilicity and is not easy to adsorb biological molecules such as antibodies, thereby ensuring that the product has a high yield; and there is only one film-forming polymer (i.e., cellulose polymer) in the ultrafiltration layer and the support layer, and no other film-forming polymers exist. Of course, the presence of a very small amount of solvent is not excluded. and pore-forming agents.
  • a microporous membrane including a polytetrafluoroethylene layer is used as the base layer.
  • polytetrafluoroethylene has good anti-pollution and chemical resistance.
  • organic reagents such as acetone, dioxane, etc.
  • the base layer includes a polytetrafluoroethylene layer, and when the surface of the polytetrafluoroethylene layer is in contact with and bonded to the cellulose polymer layer, this is because the surface of the polytetrafluoroethylene layer is relatively flat, and due to its good solvent resistance, it can prevent the surface from being partially dissolved to form pits.
  • the defects of the cellulose polymer layer in the prepared ultrafiltration membrane are relatively small, and the integrity of the ultrafiltration membrane is relatively good; and the base layer can play a supporting role for the cellulose polymer layer, ensuring that the membrane as a whole has good mechanical strength and high compressive strength, and is suitable for long-term stable filtration under high pressure; at the same time, the use of a microporous membrane in the base layer ensures that the membrane as a whole has a high flux and a faster flow rate, and the filtration speed is fast.
  • the solutes will rapidly gather and accumulate at the interface of the polytetrafluoroethylene layer, which can easily cause a significant decrease in flow rate.
  • it is limited to use a base layer PMI with an average pore size of >0.8 ⁇ m, and the polytetrafluoroethylene layer is a hydrophilic polytetrafluoroethylene layer.
  • the cellulose polymer can penetrate into the polytetrafluoroethylene layer to form a bonding layer, thereby eliminating the solute accumulation phenomenon, so that the prepared ultrafiltration membrane has a good flux.
  • the bonding layer can also give the cellulose polymer layer and the polytetrafluoroethylene layer better composite properties, that is, improve the peeling strength of the two, and prevent peeling during use or between the cellulose polymer layer and the polytetrafluoroethylene layer.
  • the average pore size of the base layer PMI in the present invention is too small, or the polytetrafluoroethylene layer is too hydrophobic, it is easy for the cellulose polymer to be unable to penetrate into the polytetrafluoroethylene layer to form a bonding layer, thereby being unable to eliminate the solute accumulation phenomenon, resulting in a decrease in flux; at the same time, the inventors surprisingly found that when a large-pore and hydrophilic polytetrafluoroethylene layer is used as the base layer, the holes on the surface of the ultrafiltration layer can be made more uniform, making the filtration performance of the ultrafiltration membrane more stable and uniform; this may be because in the actual production process, due to large-scale production, the solid content or viscosity of the cellulose polymer casting liquid cannot be kept uniform and stable everywhere, resulting in the final prepared ultrafiltration layer
  • the surface pore size is also relatively uneven; when a small-pore hydrophobic polytetrafluoroethylene layer is used as the base, during the preparation of the phase separation
  • the coagulation bath immerses slowly. When it contacts the cellulose polymer casting liquid that has penetrated into the polytetrafluoroethylene layer, the cellulose polymer casting liquid in the polytetrafluoroethylene layer is basically phase-separated.
  • the macroporous hydrophilic polytetrafluoroethylene layer used in the present invention can make it easier for the coagulation bath to enter from the polytetrafluoroethylene layer side, so as to contact with the cellulose polymer casting liquid that has penetrated into the polytetrafluoroethylene layer faster for phase separation.
  • the cellulose polymer in the casting liquid outside the polytetrafluoroethylene layer interface will be snatched at this time. Moreover, due to the instability of the solid content or viscosity of the cellulose polymer casting liquid, the snatching makes the solid content and viscosity in the casting liquid outside the polytetrafluoroethylene layer interface more uniform and stable, thereby making the surface holes more uniform. At the same time, robbing the solute in the casting liquid outside the interface of the polytetrafluoroethylene layer can also alleviate the solute accumulation phenomenon. In addition, due to the reduction of solute outside the interface of the polytetrafluoroethylene layer, the supporting layer becomes relatively thinner, thereby improving the flux.
  • the SEM average pore size measurement method of the first side surface can be achieved by using a scanning electron microscope to characterize the membrane structure, and then using computer software (such as Matlab, NIS-Elements, etc.) or manually to measure and perform corresponding calculations; during the preparation of the membrane, in the direction perpendicular to the membrane thickness (if the membrane is a flat membrane, this direction is the plane direction; if the membrane is a hollow fiber membrane, this direction is the plane direction). is perpendicular to the radial direction), and its various characteristics such as pore size distribution are roughly uniform and basically consistent; so the average pore size of a part of the corresponding plane can be used to reflect the overall average pore size on the plane.
  • computer software such as Matlab, NIS-Elements, etc.
  • the membrane surface When actually measuring, the membrane surface can be characterized by an electron microscope to obtain a corresponding SEM image. Since the pores on the membrane surface are roughly uniform, a certain area can be selected, such as 1 ⁇ m 2 (1 ⁇ m multiplied by 1 ⁇ m) or 25 ⁇ m 2 (5 ⁇ m multiplied by 5 ⁇ m). The specific area size depends on the actual situation. Then, the pore size of all the pores on the area is measured by corresponding computer software or manually, and then calculated to obtain the average pore size of the surface; the pore area ratio of the inner surface is the ratio of the sum of the areas of all the pores on the surface to the area of the surface; of course, those skilled in the art can also obtain the above parameters by other measurement methods, and the above measurement methods are for reference only.
  • the PMI pore size is obtained by testing with a PMI pore size tester.
  • the PMI pore size of the base layer can be obtained by directly measuring the base layer, or by dissolving the cellulose ultrafiltration membrane with a solvent (for example, using NMMO, ionic liquid, alkali/urea system) or enzymatically hydrolyzing cellulose to obtain the base layer, and then testing it with a PMI pore size tester.
  • the coefficient of dispersion of the average pore size of the first side surface measured by SEM is less than 0.5.
  • the average pore size of the first side surface SEM is relatively uniform, and the coefficient of dispersion is less than 0.5, which ensures that the ultrafiltration layers in different areas can have relatively uniform molecular weight cutoff during use, preventing deviations between the same membrane or batches of membranes, resulting in uneven filtration performance.
  • the base layer includes a substrate layer arranged on the polytetrafluoroethylene layer away from the cellulose polymer layer, the surface of the substrate layer away from the polytetrafluoroethylene layer forms a second side surface, the substrate layer includes a non-woven fabric, the thickness of the non-woven fabric accounts for 30-85% of the thickness of the entire film, and the thickness of the non-woven fabric is 60-300 ⁇ m.
  • the surface strength of the cellulose ultrafiltration membrane is relatively Low, during the subsequent membrane hydrolysis and cleaning during preparation, or during the preparation of filtration products (such as ultrafiltration membrane packages or filter elements), the surface of the cellulose ultrafiltration membrane will inevitably come into contact with some grids with a certain strength.
  • high pressure is often used for filtration (the greater the pressure during membrane filtration, the faster the filtration speed, and the higher the economic benefit per unit time), which makes it easy for the surface of the ultrafiltration membrane to be squeezed by the grid, resulting in rupture of the surface of the ultrafiltration membrane and affecting its integrity.
  • the present invention uses a non-woven fabric as the substrate layer, which can make the ultrafiltration membrane have higher strength.
  • the non-woven fabric substrate layer has a certain compressibility. When high-pressure filtration is performed, the non-woven fabric substrate layer is compressed, thereby playing a good buffering role and preventing the surface of the ultrafiltration membrane from being subjected to greater force, resulting in damage to its integrity, thereby resulting in poor filtration effect.
  • the thickness of the non-woven fabric accounts for 30-85% of the thickness of the whole membrane, and the thickness of the non-woven fabric is 60-300 ⁇ m. This is because the thickness of the non-woven fabric should not be too small as a percentage of the thickness of the whole membrane, otherwise a good buffering effect cannot be achieved.
  • the thickness of the non-woven fabric should not be too large as a percentage of the thickness of the whole membrane, otherwise it will easily cause the ultrafiltration membrane to be too easily compressed and deformed, and it will be difficult to recover to the original thickness after deformation, resulting in changes in the overall working conditions of the membrane during subsequent use, resulting in different filtration efficiencies between different batches.
  • the air permeability of the nonwoven fabric is greater than 50 cc/cm 2 /sec, the fiber thickness is 5-30 ⁇ m, and the gram weight is 15-40 g/m 2 .
  • the non-woven fabric as the substrate layer will also affect the flux of the membrane to a certain extent. Therefore, when the air permeability of the non-woven fabric is greater than 50cc/ cm2 /sec, the substrate layer can have a faster flow rate to prevent it from affecting the flux of the entire membrane. At the same time, the fiber thickness of the non-woven fabric is 5-30 ⁇ m and the gram weight is 15-40g/ m2 , so that the non-woven fabric has moderate compressibility to ensure the integrity of the cellulose ultrafiltration membrane.
  • the thickness of the non-woven fabric, the fiber thickness and the thickness of the entire membrane can be calculated by characterizing the morphology of the membrane structure using a scanning electron microscope, and then measuring it using computer software (such as Matlab, NIS-Elements, etc.) or manually; of course, those skilled in the art can also obtain the above parameters by other measurement methods (such as the overall thickness of the membrane can be obtained by freeze-drying the filter membrane and then measuring it with a measuring tool). The above measurement methods are for reference only.
  • the thickness ratio of the cellulose polymer layer to the polytetrafluoroethylene layer is 0.1-3, the thickness of the cellulose polymer layer is 1.5-60 ⁇ m, and the thickness of the polytetrafluoroethylene layer is 15-90 ⁇ m.
  • the cellulose ultrafiltration membrane can be given a certain mechanical strength.
  • the cellulose polymer layer and the polytetrafluoroethylene layer have relatively thin thicknesses, wherein the thickness ratio of the cellulose polymer layer to the polytetrafluoroethylene layer is 0.1-3, the thickness of the cellulose polymer layer is 1-55 ⁇ m, and the thickness of the polytetrafluoroethylene layer is 15-90 ⁇ m.
  • the thinner thickness of the cellulose polymer layer and the polytetrafluoroethylene layer can make the cellulose ultrafiltration membrane have a higher flux.
  • the thickness of the bonding layer accounts for 10-100% of the thickness of the polytetrafluoroethylene layer, and the thickness of the bonding layer is 10-100 ⁇ m.
  • the thickness of the binding layer is 10-100 ⁇ m, and the thickness of the binding layer accounts for more than 10% of the thickness of the polytetrafluoroethylene layer.
  • the thickness of the binding layer is relatively low. Therefore, even if the cellulose polymer penetrates into the polytetrafluoroethylene layer in the thickness direction, the cellulose ultrafiltration membrane can have a relatively high flux.
  • the base layer is a polytetrafluoroethylene layer
  • the thickness ratio of the cellulose polymer layer to the polytetrafluoroethylene layer is 0.02-1
  • the thickness of the cellulose polymer layer is 1.5-60 ⁇ m
  • the thickness of the polytetrafluoroethylene is 100-300 ⁇ m.
  • the average pore size of the PMI of the polytetrafluoroethylene layer is 1-20 ⁇ m, and the porosity is 60-90%; the surface roughness of the polytetrafluoroethylene layer is 0.7-2 ⁇ m.
  • the average pore size of the polytetrafluoroethylene layer PMI is 1-20 ⁇ m, and the porosity is 60-90%, which can ensure that the cellulose polymer can penetrate into the polytetrafluoroethylene layer well, thereby improving the peel strength of the cellulose ultrafiltration membrane. If the pore size is too small or the porosity is too low, the cellulose polymer will penetrate too little. It is easy to stratify during use, resulting in a decrease in filtration performance. If the average pore size and porosity are too large, the casting liquid will easily penetrate into the polytetrafluoroethylene layer completely during preparation, resulting in the inability to separate the phases to form an ultrafiltration layer.
  • the surface roughness of the polytetrafluoroethylene layer is 0.7-2 ⁇ m, at this roughness, the surface of the polytetrafluoroethylene layer is relatively flat, and the prepared ultrafiltration membrane layer has good integrity. At the same time, it has a certain roughness, which can make the cellulose polymer layer adhere better to the surface of the polytetrafluoroethylene layer and increase the peeling strength. If the roughness is too high, it is easy to cause too many defects in the prepared ultrafiltration layer, resulting in damaged integrity.
  • the water contact angle of the surface of the polytetrafluoroethylene layer is less than 80°, and the water contact angle of the second side surface is within 50° greater than the water contact angle of the first side surface.
  • the dry film was immersed in water and wetted within 5 s.
  • the membrane-making liquid can penetrate quickly during preparation, so that the prepared cellulose ultrafiltration membrane has good peel strength; at the same time, in the prepared cellulose ultrafiltration membrane, the water contact angle of the second side surface is greater than the water contact angle of the first side surface by less than 50°.
  • the coagulation bath needs to penetrate from the second side surface to ensure that the cellulose ultrafiltration membrane in the binding layer can also be phase-separated in time. If the second side surface is too hydrophobic, it is easy to cause the phase separation in the binding layer to be too late, so that the thickness of the cellulose polymer layer finally prepared is too large, and the lack of cellulose polymer in the binding layer not only affects the flux, but also affects the composite performance of the cellulose ultrafiltration membrane.
  • water is used as the test liquid and a contact angle tester is used for testing.
  • a contact angle tester is used for testing.
  • the roughness of the first side surface is 0.1-2.5 ⁇ m
  • the pore area ratio of the first side surface is 1-10%
  • the water contact angle of the first side surface is 10-55°.
  • the cellulose ultrafiltration membrane of the present invention is usually used for the concentration, purification and separation of biomacromolecules, i.e., protein substances.
  • the first side surface needs to have a certain hydrophilicity.
  • the water contact angle of the first side surface of the cellulose ultrafiltration membrane is 10-55°.
  • the cellulose ultrafiltration membrane can ensure that it has a lower protein adsorption in the protein product production application and ensure a higher protein yield.
  • the pore area rate of the first side surface is 1-10%, which can ensure that the pores of the first side surface are relatively few, and the dense pore structure can cooperate with the smaller pore size to ensure the interception efficiency of the ultrafiltration layer of the cellulose ultrafiltration membrane; and the roughness of the first side surface measured by the roughness tester is 0.1-2.5 ⁇ m, which makes the first side surface have a certain roughness, not too smooth, prevent the phenomenon of concentration polarization, avoid the pores being blocked after a short filtering time, and cause a significant decrease in flux, but the first side surface cannot be too rough. Too high roughness will increase the shear force on the surface of the cellulose ultrafiltration membrane during filtration, resulting in a decrease in the effective protein yield.
  • the ultrafiltration layer has ultrafiltration fibers forming a porous structure, and the SEM average diameter of the ultrafiltration fibers is 20-60 nm;
  • the support layer has support fibers forming a porous structure, and the SEM average diameter of the support fibers is 20-85 nm;
  • the ratio of the SEM average diameters of the support fibers and the ultrafiltration fibers is 1.2-2.4.
  • the presence of ultrafiltration fibers in the ultrafiltration layer ensures the stability of the pores inside the ultrafiltration layer and prevents the collapse or shrinkage of the pores.
  • the supporting fibers in the supporting layer can provide good support for the ultrafiltration layer. If the ultrafiltration fibers and supporting fibers are too thick, the filtration velocity of the ultrafiltration layer will be reduced, resulting in a decrease in the overall flux. If the ultrafiltration fibers and supporting fibers are too thin, they will not be able to provide good support and stabilization of the pores.
  • the ratio of the SEM average diameters of the supporting fibers and the ultrafiltration fibers is in the range of 1.2-2.4, the cellulose ultrafiltration membrane has higher mechanical strength and filtration stability.
  • the thickness of the ultrafiltration layer is 0.1-5um
  • the thickness of the support layer is 0.5-50um
  • the The ratio of the support layer thickness to the ultrafiltration layer thickness is 2-13.
  • the ultrafiltration layer In order to ensure that the ultrafiltration layer plays a good interception role in filtration, the ultrafiltration layer needs to have a certain thickness. However, if the thickness of the ultrafiltration layer is too thick, it will not only fail to further improve the interception efficiency, but also lead to a decrease in the overall flux of the membrane.
  • the support layer plays a supporting and protective role on the ultrafiltration layer, which can not only increase the pore stability of the ultrafiltration layer, but also improve the integrity of the ultrafiltration layer. Therefore, the support layer needs to have a certain thickness. However, if the thickness of the support layer is too thick, it will easily lead to a decrease in the overall flow rate of the membrane. When the ratio of the support layer thickness to the ultrafiltration layer thickness is controlled within the range of 2-13, the cellulose ultrafiltration membrane has higher mechanical strength and better integrity.
  • the SEM average pore size of the support layer gradually increases along the fluid flow direction, with a change gradient of 20-450nm/1 ⁇ m.
  • the SEM average pore size of the support layer gradually increases along the direction of fluid flow, that is, the pore size close to the ultrafiltration layer is small, which can increase the support for the ultrafiltration layer, while the pore size close to the polytetrafluoroethylene layer is larger, which can give the membrane an overall high flux.
  • the gradient of change is too large, it will easily reduce the overall strength of the cellulose ultrafiltration membrane and shorten the filtration service life of the cellulose ultrafiltration membrane.
  • the thickness, pore size and fiber diameter of each layer of the cellulose ultrafiltration membrane can be calculated by using a scanning electron microscope to characterize the morphology of the membrane structure, and then using computer software (such as Matlab, NIS-Elements, etc.) or manual measurement; of course, those skilled in the art can also obtain the above parameters by other measurement methods (such as the thickness of each layer can be obtained by freeze-drying the filter membrane and then measuring it with a measuring tool). The above measurement methods are for reference only.
  • the thickness of the ultrafiltration membrane is 130-420 um;
  • the cut-off standard molecular weight of the ultrafiltration membrane is 1K-750K;
  • the tensile strength of the ultrafiltration membrane is not less than 10MPa;
  • the water flux of 100K cellulose ultrafiltration membrane is 1-1.8 mL/min/cm 2 .
  • the filter membrane of the present invention is a composite membrane, the pore size in most areas is relatively large. In order to ensure the mechanical properties, the overall thickness of the membrane is relatively thick.
  • the ultrafiltration membrane of the present invention has a retention efficiency of more than 90% for substances with a molecular weight of 1kD-750kD, and the retention efficiency is high, which shows that the membrane is particularly suitable for biological purification and meets the needs of practical applications; the protein yield of this membrane is not less than 90%, which shows that the effective substance protein in the fluid is not easily adsorbed on the membrane.
  • the membrane pores will not be blocked, ensuring that the filter membrane still has a high service life, and on the other hand, it ensures that the content of various proteins of the effective substance in the fluid changes very little, the protein is basically not lost, and the economic benefit is guaranteed.
  • An important indicator for evaluating the mechanical strength of a filter membrane is the tensile strength of the filter membrane. Under certain conditions, the greater the tensile strength of the filter membrane, the better the mechanical strength of the filter membrane.
  • the wet tensile strength of the filter membrane of the present invention is not less than 10 MPa (measured under wet membrane conditions), has a large tensile strength, good mechanical properties, high industrial practical value, and can fully meet market demand. At the same time, by conducting a flow rate test on the filter membrane, it is shown that the flow rate of the filter membrane is large, the filtration time is short, and the time cost is low.
  • the surface of the polytetrafluoroethylene layer forming the bonding layer is a polytetrafluoroethylene layer bonding surface, and the bonding surface includes nodes and fiber filaments, and the nodes are connected to each other through the fiber filaments.
  • the polytetrafluoroethylene layer can have different structures according to different preparation processes.
  • the inventors have found that not all polytetrafluoroethylene layers have good effects as base layers, but polytetrafluoroethylene layers with nodes and nodes connected to each other by fiber filaments have better effects as base layers.
  • the surface of polytetrafluoroethylene membranes with nodes and fiber filament structures is smoother. This is because the fiber filaments between the nodes are obtained by stretching, so they do not have raised ends.
  • the surface open porosity of the polytetrafluoroethylene membrane with nodes and fiber filament structures is high (fiber filaments are more porous).
  • the fibers are thinner and directly open-pore), which makes it easier for the cellulose polymer layer to penetrate and form a permeable layer compared to other structural forms.
  • it can increase the composite ability and improve the peeling strength.
  • the nodes have higher strength, while the fiber filaments are relatively easy to deform. The combination of the two can increase the overall strength and elasticity of the membrane.
  • the area of the node occupied by the bonding surface of the polytetrafluoroethylene layer is S1;
  • the area of the fiber filaments occupying the bonding surface of the polytetrafluoroethylene layer is S2;
  • the S1:S2 is 0.13-7; the S1 is 4-40%; and the S2 is 5-35%.
  • the strength of the substrate layer is likely to be low. If the area S1 of the nodes in the polytetrafluoroethylene layer bonding surface accounts for too large a proportion, and the area S2 of the fiber filaments in the polytetrafluoroethylene layer bonding surface accounts for too small a proportion, the cellulose polymer layer is likely to have difficulty in penetrating, resulting in a solute accumulation effect and reduced flux.
  • the peeling strength decreases due to too little bonding with the fiber filaments.
  • a too small proportion of the fiber filaments can also lead to a decrease in the elasticity of the entire membrane, resulting in the ultrafiltration membrane being too brittle.
  • the node proportion, width and density, fiber proportion, width and density on the polytetrafluoroethylene bonding surface can be characterized by using a scanning electron microscope to characterize the membrane structure, and then measured using computer software (such as Matlab, NIS-Elements, etc.) or manually, and corresponding calculations can be performed; in the preparation process of the membrane, in the direction perpendicular to the membrane thickness (if the membrane is a flat membrane, the direction is the plane direction; if the membrane is a hollow fiber membrane, the direction is perpendicular to the radius direction), its various characteristics such as node width and density, fiber width and density distribution are roughly uniform and basically consistent; therefore, the node width and density, fiber width and density of a part of the corresponding plane can be used to reflect the overall node width and density, fiber width and density on the plane; when actually measuring, the outer surface of the membrane can be characterized by an electron microscope to obtain the corresponding SEM image, and since the node proportion, width and density, fiber width and density on the outer surface of the membrane are
  • the average width of the node is 1-6 ⁇ m, and the difference between the maximum width and the minimum width of the node is less than 7 ⁇ m; the average width of the fiber filament is 0.1-1.2 ⁇ m, and the difference between the maximum width and the minimum width of the fiber filament is less than 1.5 ⁇ m.
  • the average width of the nodes affects the mechanical strength of the polytetrafluoroethylene layer. If it is too small, the strength of the polytetrafluoroethylene as the base layer will be low, resulting in a decrease in the strength of the entire membrane. If the width of the nodes is too large, it will easily lead to the inability of the casting liquid to penetrate well at the nodes during preparation, which will not only affect the peel strength of the ultrafiltration membrane, but also lead to an increase in defects in the ultrafiltration layer and reduce its integrity.
  • the number of connected cellulose fibers in a length of 50 ⁇ m along the node direction is 15-70.
  • the fiber density has a great influence on membrane permeability and bonding. If the density is too small, not only will the overall strength be reduced, but there will not be enough fibers in the bonding layer to bond with the support layer, resulting in a decrease in peel strength. If the density is too large, the overall surface porosity will decrease, and the casting liquid will not be able to penetrate well during preparation, resulting in a decrease in the peel strength of the ultrafiltration membrane.
  • the material of the cellulose polymer layer includes one or more of regenerated cellulose and cellulose ester.
  • the present invention also provides a method for preparing a cellulose ultrafiltration membrane:
  • the water contact angle on the surface of the polytetrafluoroethylene porous membrane is less than 80°, and the pore size of the polytetrafluoroethylene porous membrane is greater than 0.8 ⁇ m;
  • the cellulose polymer is at least one of cellulose nitrate, cellulose acetate and regenerated cellulose;
  • the cellulose acetate is selected from one or more of cellulose diacetate, cellulose triacetate, cellulose nitrate, cellulose acetate butyrate and cellulose acetate propionate.
  • the polar solvent includes at least one of acetone, dioxane, dimethylacetamide, N-methylpyrrolidone, acetic acid, propionic acid, butyric acid and valeric acid;
  • the pore former includes at least one of polyvinyl pyrrolidone, polyethylene glycol and polyvinyl alcohol.
  • the casting liquid has a viscosity of 6000-40000 cpa.s.
  • phase separation coagulation duration is 5-60s
  • the coagulation bath is water
  • the phase separation temperature is 20-40°C.
  • the concentration of the sodium hydroxide aqueous solution is between 0.01 mol/L and 1 mol/L; the hydrolysis time is between 30° C. and 80° C., and the time is 40 min to 200 min.
  • the preparation of the cellulose ultrafiltration membrane includes cross-linking
  • the cross-linking is to cross-link the cellulose ultrafiltration membrane with a water-soluble cross-linking agent in an alkaline environment, the cross-linking time is 20-400 minutes, and the temperature is 30°C-60°C; the cross-linking agent is at least one of halogenated epoxides, diepoxides, dihalogenated alkanes and dihalogenated alcohols.
  • the casting liquid is firstly prepared, wherein the cellulose polymer has relatively good hydrophilicity and low non-specific adsorption, and is therefore very suitable for the purification, concentration and separation of proteins, and can be used as the solute part of the casting liquid.
  • the polar solvent is used to form a solvent system, which fully dissolves the cellulose polymer to form a uniform and stable casting liquid.
  • the pore-forming agent can not only effectively control the viscosity of the system and inhibit the formation of macropores in the membrane during the phase separation process, but also effectively improve the stability of the membrane flow rate. In addition, it can also greatly improve the hydrophilicity of the formed membrane, so that the membrane has a higher hydrophilicity and reduces protein adsorption.
  • the casting liquid is cast onto a substrate to form a liquid film.
  • the solute part in the casting liquid needs to penetrate into the microporous layer on the substrate during casting.
  • the casting liquid can penetrate into the polytetrafluoroethylene porous membrane to form a bonding layer, thereby eliminating the solute accumulation phenomenon, so that the prepared ultrafiltration membrane has good flux.
  • the binding layer can also give the cellulose polymer layer and the polytetrafluoroethylene layer in the finally prepared cellulose ultrafiltration membrane better composite performance, that is, improve the peel strength of the two, prevent the cellulose polymer layer and the polytetrafluoroethylene layer from peeling off during use; preferably, the PMI average pore size of the polytetrafluoroethylene porous membrane is 1-20 ⁇ m, the porosity is 60-90%; the surface roughness is 0.7-2 ⁇ m, and the surface includes nodes and fiber filaments, and the nodes are interconnected by fiber filaments. Under this condition, the casting liquid can penetrate better, and a cellulose ultrafiltration membrane with better composite performance and filtration performance can be obtained.
  • the viscosity of the casting liquid is also one of the factors that determine good penetration.
  • the viscosity of the casting liquid is 6000-40000 cpa.s, thereby ensuring that the cellulose ultrafiltration membrane has a suitable thickness and an ideal membrane pore structure and pore size, thereby achieving good composite performance and filtration performance; this is because if the viscosity of the casting liquid is too high, the casting liquid cannot penetrate into the substrate layer well, and even the solvent penetrates into the substrate layer, while the solute is not permeable, resulting in The accumulation of solutes on the surface of the substrate layer causes a decrease in the final composite performance and filtration performance. If the viscosity is too low, the casting liquid will completely penetrate, and ultimately it will be impossible to form an ultrafiltration layer that can be used for interception, which also cannot meet actual needs.
  • the subsequent phase separation solidification is to immerse the substrate coated with the liquid film in water for phase separation solidification.
  • the phase separation solidification lasts for 5-60s.
  • the casting liquid is properly phase separated to ensure that the film with an ideal membrane pore size is obtained.
  • the present invention uses a hydrophilic and macroporous polytetrafluoroethylene porous membrane as the substrate.
  • the coagulation bath is more likely to enter from the bottom surface of the substrate layer, so that the cellulose polymer that penetrates into the substrate layer can also be phase-separated and solidified relatively earlier, thereby snatching the solute outside the upper surface of the substrate layer.
  • it can alleviate the solute accumulation phenomenon.
  • the support layer becomes relatively thinner, thereby increasing the flux.
  • hydrolysis is carried out in a sodium hydroxide aqueous solution, and then washing is performed to form a solid membrane.
  • cross-linking can be performed later in accordance with actual needs.
  • the hydroxyl groups in the solid membrane react with functional groups such as epoxy and halogen, thereby making the membrane structure more mechanically strong and less prone to swelling.
  • the membrane's alkali resistance is improved, and its service life is longer.
  • it is more conducive to the efficient interception of small molecular weight biomolecules (such as 3K and 5K biomolecules).
  • a microporous membrane including a polytetrafluoroethylene layer is used as a base layer.
  • the surface of the polytetrafluoroethylene layer is relatively flat and has strong solvent resistance.
  • the defects of the cellulose polymer layer in the prepared ultrafiltration membrane are relatively small, so the integrity of the ultrafiltration membrane is relatively good; and the base layer can play a supporting role for the cellulose polymer layer, ensuring that the membrane as a whole has good mechanical strength and high compressive strength, and is suitable for long-term stable filtration under high pressure; at the same time, the cellulose polymer can penetrate into the polytetrafluoroethylene layer to form a binding layer, thereby eliminating the solute accumulation phenomenon, so that the prepared ultrafiltration membrane has good flux and composite performance, and prevents peeling during use; finally, during the subsequent phase separation, the coagulation bath is more likely to enter from the second side surface, so that the cellulose in the binding layer The polymer can also undergo phase separation and solidification relatively earlier, thereby being able to s
  • FIG1 is a SEM image of the first side surface of the ultrafiltration membrane prepared in Example 1 of the present invention.
  • FIG2 is a SEM image of a cross section of an ultrafiltration membrane prepared in Example 1 of the present invention.
  • FIG3 is a SEM image of the bonding surface of the polytetrafluoroethylene layer in the base layer of Example 1 of the present invention.
  • FIG4 is a SEM image of the first side surface of the ultrafiltration membrane prepared in Example 10 of the present invention.
  • FIG5 is a SEM image of a cross section of an ultrafiltration membrane prepared in Example 10 of the present invention.
  • FIG6 is a SEM image of the first side surface of the ultrafiltration membrane prepared in Example 12 of the present invention.
  • FIG7 is a SEM image of a cross section of an ultrafiltration membrane prepared in Example 12 of the present invention.
  • FIG8 is a diagram of the substrate layer used in the preparation of Example 17 of the present invention, at a magnification of 2000 ⁇ ;
  • FIG. 9 is a schematic diagram of a membrane package diffusion flow test device of the present invention.
  • Embodiment 1 A method for preparing a cellulose ultrafiltration membrane comprises the following steps:
  • the cross-linking agent is epichlorohydrin
  • the concentration of the cross-linking agent in the aqueous solution is 10%
  • the cross-linking time is 150 minutes
  • the temperature is 45°C.
  • Embodiment 2 A method for preparing a cellulose ultrafiltration membrane, comprising the following steps:
  • the hydrophilic substrate is a polytetrafluoroethylene porous membrane
  • the cross-linking agent is epichlorohydrin
  • the concentration of the cross-linking agent in the aqueous solution is 10%
  • the cross-linking time is 100 minutes
  • the temperature is 50°C.
  • Embodiment 3 A method for preparing a cellulose ultrafiltration membrane, comprising the following steps:
  • the hydrophilic substrate is a polytetrafluoroethylene porous membrane
  • the cross-linking agent is epichlorohydrin
  • the concentration of the cross-linking agent in the aqueous solution is 10%
  • the cross-linking time is 70 minutes
  • the temperature is 55°C.
  • Embodiment 4 A method for preparing a cellulose ultrafiltration membrane, comprising the following steps:
  • the hydrophilic substrate is a polytetrafluoroethylene porous membrane
  • Embodiment 5 A method for preparing a cellulose ultrafiltration membrane, comprising the following steps:
  • the hydrophilic substrate is a polytetrafluoroethylene porous membrane
  • the cross-linking agent is epichlorohydrin
  • the concentration of the cross-linking agent in the aqueous solution is 10%
  • the cross-linking time is 350 minutes
  • the temperature is 58°C.
  • Embodiment 6 A method for preparing a cellulose ultrafiltration membrane, comprising the following steps:
  • the hydrophilic substrate is a polytetrafluoroethylene porous membrane
  • Embodiment 7 A method for preparing a cellulose ultrafiltration membrane, comprising the following steps:
  • the hydrophilic substrate is a polytetrafluoroethylene porous membrane
  • Embodiment 8 A method for preparing a cellulose ultrafiltration membrane, comprising the following steps:
  • the hydrophilic substrate is a polytetrafluoroethylene porous membrane
  • Embodiment 9 A method for preparing a cellulose ultrafiltration membrane, comprising the following steps:
  • the hydrophilic substrate is a polytetrafluoroethylene porous membrane
  • Embodiment 10 A method for preparing a cellulose ultrafiltration membrane, comprising the following steps:
  • the hydrophilic substrate is a polytetrafluoroethylene porous membrane
  • Embodiment 11 A method for preparing a cellulose ultrafiltration membrane, comprising the following steps:
  • the hydrophilic substrate is a polytetrafluoroethylene porous membrane
  • Example 12 A method for preparing a cellulose ultrafiltration membrane, comprising the following steps:
  • the hydrophilic substrate is a polytetrafluoroethylene porous membrane
  • Example 13 A method for preparing a cellulose ultrafiltration membrane, comprising the following steps:
  • the hydrophilic substrate is a polytetrafluoroethylene porous membrane
  • Example 14 A method for preparing a cellulose ultrafiltration membrane, comprising the following steps:
  • the hydrophilic substrate is a polytetrafluoroethylene porous membrane
  • Example 15 A method for preparing a cellulose ultrafiltration membrane, comprising the following steps:
  • the hydrophilic substrate is a polytetrafluoroethylene porous membrane
  • Example 16 A method for preparing a cellulose ultrafiltration membrane, comprising the following steps:
  • the hydrophilic substrate is a polytetrafluoroethylene porous membrane
  • Example 17 The difference from Example 1 is that a hydrophilic PTFE having another structure as shown in FIG8 is used. As a base layer.
  • Comparative Example 1 Same as Example 1, the base layer used is shown in Table 2-1 and Table 2-2 below.
  • Comparative Example 2 Same as Example 1, the base layer used is shown in Table 2-1 and Table 2-2 below.
  • the cellulose ultrafiltration membrane prepared in the embodiment has a good membrane structure, and the defects of the cellulose polymer layer in the prepared ultrafiltration membrane are relatively small, so the integrity of the ultrafiltration membrane is relatively good; at the same time, the cellulose polymer can penetrate into the polytetrafluoroethylene layer to form a bonding layer, thereby eliminating the solute accumulation phenomenon, so that the prepared ultrafiltration membrane has good flux and composite performance, and prevents peeling during use; finally, it can also facilitate the regulation of the thickness of the support layer, making the support layer relatively thinner, thereby increasing the flux.
  • the cellulose composite ultrafiltration membranes prepared in Examples 1-10 of the present invention purify various biomolecules by tangential flow filtration; their molecular weight cutoffs are 3K-750K, and their retention efficiencies are greater than 90%, ensuring that biomolecules of various molecular weights can be efficiently retained.
  • the flow rate test of each embodiment of the present invention shows that the membrane has a relatively high flux, that is, a faster flow rate, and can quickly filter the fluid containing biomolecules, with high economic benefits.
  • Comparative Examples 1 and 2 do not use the composite substrate layer, so the flux is lower when the molecular weight cutoff is the same.
  • Protein yield test (can be tested according to the protein yield test method used in China CN201010154974.7-Ultraporous membrane and its preparation method, or other methods can be used for testing).
  • the protein yield of the ultrafiltration membrane of the embodiment is greater than 90%, which can obtain a higher protein yield and high economic benefit.
  • the cellulose ultrafiltration membranes of Examples 1-5 were used to prepare a 3K membrane package of 0.11 m2 .
  • the specific method is as follows: a membrane package with a filtration area of 0.11 m2 was prepared, and the test device was assembled as shown in Figure 9.
  • the feed tank 01 was connected to the liquid inlet hole on one side of the filter membrane package through a liquid inlet pipe, and the liquid inlet pipe was connected to a pump 02, a drain valve 03 and an air valve 04.
  • the waste tank 05 was connected to the liquid inlet hole on the other side of the filter membrane package through a reflux pipe, and the reflux valve 06 was installed on the reflux pipe.
  • the beaker 07 was connected to the filtrate hole of the filter membrane package through a permeation pipe, and the permeation valve 08 was installed on the permeation pipe to open and close the beaker 07 and the filtrate hole; a 50 ml measuring cylinder 09 was filled with water and inverted in a 500 ml beaker 07 filled with water.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Water Supply & Treatment (AREA)
  • Manufacturing & Machinery (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Hydrology & Water Resources (AREA)
  • Environmental & Geological Engineering (AREA)
  • Organic Chemistry (AREA)
  • Separation Using Semi-Permeable Membranes (AREA)

Abstract

本发明公开了一种纤维素超滤膜及其制备方法，涉及膜材料技术领域，包括主体，沿流体流经方向上依次为超滤层、支撑层和基底层；超滤层和支撑层包括纤维素类聚合物层，基底层包括聚四氟乙烯层，基底层PMI平均孔径＞1μm；聚四氟乙烯层为亲水聚四氟乙烯层；纤维素类聚合物层和聚四氟乙烯层渗透结合形成结合层；第一侧表面SEM平均孔径为1-90nm；本发明中聚四氟乙烯层表面相对平整，耐溶剂性强，制备得到的超滤膜中纤维素类聚合物层缺陷相对较小，因此超滤膜的完整性相对较好，同时纤维素类聚合物能够渗透进入聚四氟乙烯层中，形成结合层，从而消除溶质堆积现象，使得制备得到的超滤膜具有良好的通量及复合性能。

Description

一种纤维素超滤膜及其制备方法 技术领域
本发明涉及膜材料技术领域，更具体的说是涉及一种纤维素超滤膜及其制备方法。
背景技术
膜技术是当代高效分离的新技术，与传统的蒸馏、精馏等技术相比，它具有分离效率高，能耗低，占地面积小等优点，膜分离技术的核心就是分离膜。其中聚合物滤膜是一类以有机高分子聚合物为原材料，根据一定工艺制成的分离膜；其中根据高分子聚合物种类的不同，聚合物滤膜可以细分为纤维素类聚合物滤膜，聚酰胺类聚合物滤膜，砜类聚合物滤膜，聚四氟乙烯类聚合物滤膜等；此外，也可以根据膜的孔径大小可以分为微滤膜、超滤膜、纳滤膜及反渗透膜。
超滤膜是一种用于超滤过程能将一定大小的高分子胶体或悬浮颗粒从溶液中分离出来的高分子半透膜。广泛用于工业废水和工艺水的深度处理，如化工、食品和医药工业中大分子物质的浓缩、纯化和分离，生物溶液的除菌，印染废水中染料的分离，石油化工废水中回收甘油，照相化学废水中回收银以及超纯水的制备，此外，还可用于污泥浓缩脱水等。
在不同材料的聚合物超滤膜中，纤维素类聚合物超滤膜由于具有较高的亲水性，因此在进行蛋白质的浓缩、纯化和分离中非特异性吸附性较低，从而能够防止蛋白质分子的吸附，一方面防止了蛋白质收率的降低，另一方面能够防止超滤膜过快的堵塞。
然而，纤维素类聚合物超滤膜由于强度较低，因此市面上出现了具有基材层复合纤维素超滤膜，赋予了膜整体较高的机械强度，增加实际实用性。通常， 市面上的复合超滤膜采用无纺布作为基底层，即将纤维素类聚合物涂敷于无纺布表面形成复合超滤膜，制备工艺相对简单，然而无纺布表面相对粗糙，纤维素涂覆于无纺布基材层上时，表面上纤维凸起部以及纤维翘起的端部非常容易将超滤膜中的纤维素超滤层戳破，导致超滤膜表面受损，严重影响膜完整性。
而微孔膜具有相对平整的表面，作为基底层制备复合超滤膜具有良好的完整性，例如，厦门大学公开专利CN103877867B公开了采用0.2μm聚四氟乙烯微滤膜为支撑层，获得由微滤膜和纤维素皮层的纤维素超滤膜。但其制备的过程为纤维素制膜液过滤在微滤膜上经自由堆积形成纳米孔纤维素皮层，因此其并不会渗透进入到聚四氟乙烯微滤膜中，同时，采用的聚四氟乙烯微滤膜孔径过小(0.2μm)，从而容易在微滤膜界面处出现溶质迅速聚集堆积的现象，虽然具有相对较好的截留率，但会导致膜整体通量较低，在实际使用时过滤时间过长，降低了效率。
发明内容
本发明所要达到的目的是提供一种纤维素超滤膜及其制备方法，该超滤膜以包含聚四氟乙烯层的微孔膜作为基底层，以纤维素类聚合物作为超滤层，具有1-750K的截留分子量，同时缺陷较少，完整性高，超滤层表面孔均匀，流速快，通量高，过滤时间短。
为了达到上述目的，本发明采用如下技术方案：
一种纤维素超滤膜，包括主体，所述主体具有：
供给待过滤液体的第一侧表面、以及
透过所述主体排出透过液的第二侧表面；
所述主体沿流体流经方向上依次为超滤层、支撑层和基底层；
所述超滤层和支撑层包括纤维素类聚合物层，所述基底层包括聚四氟乙烯 层，
所述基底层PMI平均孔径＞0.8μm；
所述聚四氟乙烯层为亲水聚四氟乙烯层；
所述纤维素类聚合物层和聚四氟乙烯层渗透结合形成结合层；
所述第一侧表面SEM平均孔径为1-90nm。
本发明中，纤维素超滤膜为复合膜，由纤维素类聚合物层及聚四氟乙烯层组成，相较于一体成型结构的超滤膜，复合超滤膜能够使得各层功能达到最佳化，从而使得整膜性能能够更加理想。
本发明纤维素超滤膜主体沿流体流经方向上依次为超滤层、支撑层和基底层，其中，超滤层主要起着对物质的截留作用，超滤层的一侧为供给待过滤液体的第一侧表面，该表面上存在着孔径相对较小，起到良好截留作用的孔洞，众所周知，孔径的大小是能够截留物质的关键因素，不同的孔径能够截留不同粒径的物质；经过研究发现，当第一侧表面的SEM平均孔径为1-90nm，这样的孔径大小，适合截流分子量为1K-750K的各种生物分子物质(如抗体等物质)，利于获得较高的截留效率，同时，以切向流的形式对各种生物蛋白制品进行浓缩、纯化，可以对膜表面截留颗粒进行冲刷扫除，防止膜表面的堵塞；支撑层的存在是对超滤层起到一个保护作用，防止结合层上的毛刺等纤维结构对超滤层的膜孔结构造成影响甚至破坏，继而影响膜整体的截留效率，进一步保证超滤层能高效截留相应物质。
本发明中超滤层和过渡层均是由纤维素类聚合物经过相转化制备得到，为纤维素类聚合物层，因此超滤层具有很强的亲水性，不容易吸附抗体等生物分子，确保产物具有较高的收率；且在超滤层和支撑层仅存在一种成膜聚合物(即纤维素类聚合物)，不存在其他成膜聚合物，当然也不排除存在极少量的溶剂 和成孔剂等物质。
本发明中，采用包含聚四氟乙烯层的微孔膜作为基底层，首先，聚四氟乙烯具有良好的抗污染性和耐化学试剂性，在制备时，由于本发明采用的是溶解后铸膜液流延分相的制备方法，在铸膜液制备时会采用一些对基材层溶解性也同样较强的有机试剂(例如丙酮、二氧六环等)，因此，当基底层耐化学试剂性不加时，容易导致铸膜液中的溶剂对基底层也同样有一定的溶解效果，使得原本相对平整的基底层表面具有较多的坑洼，表面变得不平整，导致最后制备得到的纤维素超滤膜表面缺陷较多，完整性相对较差。而基底层包含聚四氟乙烯层，且由聚四氟乙烯层表面和纤维素类聚合物层接触结合时，这是由于聚四氟乙烯层表面相对平整，且由于较好的耐溶剂性能够防止表面被部分溶解形成坑洼，因此制备得到的超滤膜中纤维素类聚合物层缺陷相对较小，超滤膜的完整性相对较好；并且，基底层能够对纤维素类聚合物层起到一个支撑作用，保证了膜整体具有不错的机械强度，耐压强度较高，适合在较高压力作用下进行长时间稳定的过滤；同时，基底层采用微孔膜保证了膜整体具有较高的通量和较快的流速，过滤速度快。
但同时也发现，将纤维素类聚合物铸膜液涂覆于聚四氟乙烯层表面相转化时，在聚四氟乙烯层界面处会发生溶质迅速聚集堆积的现象，从而容易造成流量的大幅度下降的现象，而本发明中，限定了采用基底层PMI平均孔径＞0.8μm，同时聚四氟乙烯层为亲水聚四氟乙烯层，在这基础上，制备过程中，纤维素类聚合物能够渗透进入聚四氟乙烯层中，形成结合层，从而消除溶质堆积现象，使得制备得到的超滤膜具有良好的通量，同时，结合层也能够赋予纤维素类聚合物层和聚四氟乙烯层之间更好的复合性能，即提高两者的剥离强度，防止在使用过程中，或者纤维素类聚合物层和聚四氟乙烯层之间出现剥离的现象。
若本发明中基底层PMI平均孔径过小，或者聚四氟乙烯层过于疏水，则容易出现纤维素类聚合物无法渗透进入聚四氟乙烯层形成结合层的情况，从而无法消除溶质堆积现象，造成通量下降；同时，发明人惊奇的发现采用大孔径及亲水的聚四氟乙烯层作为基材层时能够使得超滤层表面的孔洞更加均匀，使得超滤膜的过滤性能更加稳定均一；这可能是由于在实际生产过程中，由于是大批量生产，纤维素类聚合物铸膜液的固含量或粘度不可能处处保持均一稳定，导致最终制备到的超滤层表面孔径也较为不均一；采用小孔径疏水的聚四氟乙烯层作为基底时，在制备分相过程中，小孔径疏水的聚四氟乙烯层凝固浴渗透较慢，在分相时，分相先从纤维素类聚合物铸膜液上表面开始(浸入凝固浴中时，此处最先接触)，并逐渐向内分相，而形成超滤层后，由于超滤层表面孔径小，凝固浴浸入较慢，与渗透入聚四氟乙烯层的纤维素类聚合物铸膜液接触时，聚四氟乙烯层的纤维素类聚合物铸膜液基本分相完成，而本发明采用大孔亲水聚四氟乙烯层能够使得凝固浴更容易从聚四氟乙烯层侧进入，从而更快与渗透入聚四氟乙烯层的纤维素类聚合物铸膜液接触进行分相，因此此时会抢夺在聚四氟乙烯层界面外铸膜液中的纤维素类聚合物，并且由于纤维素类聚合物铸膜液的固含量或粘度的不稳定，抢夺的发生让处在聚四氟乙烯层界面外的铸膜液中固含量及粘度变得更为均一稳定，从而使得表面孔洞变得更为均一。同时抢夺聚四氟乙烯层界面外的铸膜液中溶质，也能够缓解溶质堆积现象，并且由于聚四氟乙烯层界面外的溶质减少，使得支撑层相对变薄，从而提高了通量。
第一侧表面的SEM平均孔径测量方式可以通过使用扫描电子显微镜对膜结构进行形貌表征后，再利用计算机软件(如Matlab、NIS-Elements等)或手工进行测量，并进行相应计算；在膜的制备过程中，在垂直于膜厚度方向上(如果膜是平板膜形态，则该方向是平面方向；如果膜是中空纤维膜形态，则该方向 是垂直于半径方向)，其各项特征如孔径分布是大致均匀的，基本保持一致；所以可以通过在相应平面上部分区域的平均孔径大小，来反映该平面上整体的平均孔径大小。在实际进行测量时，可以先用电子显微镜对膜表面进行表征，获得相应的SEM图，而由于膜表面孔洞大致是均匀的，因此可以选取一定的面积，例如1μm2(1μm乘以1μm)或者25μm2(5μm乘以5μm)，具体面积大小视实际情况而定，再用相应计算机软件或者手工测出该面积上所有孔洞的孔径，然后进行计算，获得该表面的平均孔径；内表面的孔洞面积率即为该表面上所有孔洞面积之和与该表面的面积之比；当然本领域技术人员也可以通过其他测量手段获得上述参数，上述测量手段仅供参考。
本发明中PMI孔径通过PMI孔径测试仪进行测试得到，基底层PMI孔径可以直接测量基底层得到，也可以通过将纤维素超滤膜进行溶剂溶解(例如采用NMMO、离子液体、碱/尿素体系)或者酶解纤维素的方式得到基底层，再通过PMI孔径测试仪进行测试得到。
进一步的，所述第一侧表面SEM平均孔径的离散系数小于0.5。
本发明中，第一侧表面SEM平均孔径相对均一，离散系数小于0.5，这使得在使用过程中，不同区域内的超滤层都能具备相对均一的截留分子量，防止同一张膜或者批次膜之间产生偏差，导致过滤性能的不均一。
进一步的，所述基底层包括设于聚四氟乙烯层远离纤维素类聚合物层的基材层，所述基材层远离聚四氟乙烯层的表面形成第二侧表面，所述基材层包括无纺布，所述无纺布厚度占所述整膜厚度的30-85％，所述无纺布的厚度为60-300μm。
本发明中，虽然基底层和纤维素类聚合物层之间相互渗透能够增加整体的通量和剥离强度，增加了使用寿命，但是，由于纤维素超滤膜表面强度相对较 低，在制备时后续的膜水解、清洗中，或者过滤产品制备时(例如超滤膜包或滤芯)时，纤维素超滤膜表面免不了与一些具有一定强度的网格接触，而由于在制备和过滤使用时，在条件允许的情况，往往采用高压进行过滤(滤膜过滤时的压力越大，过滤速度越快，单位时间经济效益越高)，从而容易使得超滤膜表面被网格等挤压，导致超滤膜表面的破裂，影响其完整性，而本发明中采用了无纺布作为基材层，能够使得超滤膜具有更高的强度，并且，无纺布基材层具有一定的可压缩能力，在进行高压过滤时，无纺布基材层被压缩，从而能够起到良好的缓冲作用，防止超滤膜表面受到更大的力导致其完整性受损，从而导致过滤效果不佳。其中，无纺布厚度占所述整膜厚度的30-85％，无纺布的厚度为60-300μm，这是由于无纺布的厚度占整膜的厚度不宜过小，过小则无法达到良好的缓冲作用，同时，无纺布的厚度占整膜的厚度也不宜过大，过大容易导致超滤膜过于容易压缩形变，同时形变后较难恢复至原有厚度，导致后续使用时的膜整体工况发生改变，使得不同批次之间过滤效率不同。
进一步的，所述无纺布的透气性大于50cc/cm2/sec，纤维粗细为5-30μm，克重为15-40g/m2。
本发明中，无纺布作为基材层也会在一定程度上影响膜的通量，因此，无纺布的透气性大于50cc/cm2/sec时，能够使得基材层具有较快的流速，防止其对整膜通量的影响，同时，无纺布的纤维粗细为5-30μm，克重为15-40g/m2，使得无纺布具有适度的可压缩性，保证纤维素超滤膜的完整性。
无纺布的厚度、纤维粗细以及整膜的厚度可以通过使用扫描电子显微镜对膜结构进行形貌表征后，再利用计算机软件(如Matlab、NIS-Elements等)或手工进行测量后计算测得；当然本领域技术人员也可以通过其他测量手段获得上述参数(如膜整体厚度可以通过将滤膜冷冻干燥，在用测量工具测量获得)， 上述测量手段仅供参考。
进一步的，所述纤维素类聚合物层与聚四氟乙烯层的厚度之比为0.1-3，所述纤维素类聚合物层的厚度为1.5-60μm，所述聚四氟乙烯层的厚度为15-90μm。
本发明中，由于无纺布基材层的存在，可以赋予纤维素超滤膜一定的机械强度，于此同时，纤维素类聚合物层和聚四氟乙烯层具有相对较薄的厚度，其中，纤维素类聚合物层与聚四氟乙烯层的厚度之比为0.1-3，所述纤维素类聚合物层的厚度为1-55μm，所述聚四氟乙烯层的厚度为15-90μm，较薄的纤维素类聚合物层和聚四氟乙烯层厚度能够使得纤维素超滤膜具有更高的通量。
进一步的，所述结合层的厚度占聚四氟乙烯层厚度的10-100％，所述结合层的厚度为10-100μm。
本发明中，结合层的厚度为10-100μm，且结合层的厚度占聚四氟乙烯层厚度大于10％，一方面，能够保证纤维素超滤膜具有良好的机械强度和剥离强度，另一方面，虽然结合层内由于纤维素类聚合物渗入聚四氟乙烯层内会影响其通量，但由于聚四氟乙烯层厚度较低，因此，即使聚四氟乙烯层厚度方向均渗透入纤维素类聚合物也能够使得纤维素超滤膜具有相对较高的通量。
进一步的，基底层为聚四氟乙烯层，所述纤维素类聚合物层与聚四氟乙烯层的厚度之比为0.02-1，所述纤维素类聚合物层的厚度为1.5-60μm，所述聚四氟乙烯的厚度为100-300μm。
进一步的，所述聚四氟乙烯层PMI平均孔径为1-20μm，孔隙率为60-90％；所述聚四氟乙烯层表面粗糙度为0.7-2μm。
本发明中，聚四氟乙烯层PMI平均孔径为1-20μm，孔隙率为60-90％，能够保证纤维素类聚合物能够较好的渗透进入聚四氟乙烯层中，从而提高纤维素超滤膜的剥离强度，若孔径过小或孔隙率过低，纤维素类聚合物渗透过少，在 使用过程中容易分层，导致过滤性能下降，而平均孔径和孔隙率过大，则在制备时铸膜液容易完全渗透进入聚四氟乙烯层中，导致无法分相形成超滤层；同时，由于聚四氟乙烯层表面粗糙度为0.7-2μm，在该粗糙度下，聚四氟乙烯层表面相对平整，制备得到的超滤膜层具有良好的完整性，同时，具有一定的粗糙度，能够使得纤维素类聚合物层与聚四氟乙烯层表面更好的粘附，增加剥离强度，而若粗糙度过高，则容易导致制备得到的超滤层缺陷过多，导致完整性受损。
进一步的，所述聚四氟乙烯层表面水接触角＜80°，所述第二侧表面的水接触角比第一侧表面的水接触角大50°以内。
进一步的，将干膜浸润至水中，在5s内润湿。
本发明中，为了使得纤维素类聚合物能够良好的渗透进入聚四氟乙烯层中，因此需要保证聚四氟乙烯层表面具有良好的亲水性，当聚四氟乙烯层表面水接触角＜80°，或者将干膜浸润至水中，在5s内润湿时，在制备时制膜液能够快速的渗透，从而使得制备得到的纤维素超滤膜具有良好的剥离强度；同时，制备得到的纤维素超滤膜中，第二侧表面的水接触角比第一侧表面的水接触角大50°以内，这是由于在制备时，凝固浴需要从第二侧表面渗入，确保结合层内的纤维素超滤膜也能够及时分相，而若第二侧表面过于疏水时，容易导致结合层内分相过迟，使得最终制备得到的纤维素类聚合物层厚度过大，且结合层内纤维素类聚合物的不足，不但影响了通量，同时也会影响纤维素超滤膜的复合性能。
本发明中，是指以水作为测试液，用接触角测试仪进行测试，当10-100微升水滴均匀到材料表面一瞬间时(0.4s内)形成规则的接触角。
进一步的，所述第一侧表面的粗糙度为0.1-2.5μm，所述第一侧表面孔面积率为1-10％，第一侧表面的水接触角为10-55°。
本发明纤维素超滤膜通常用于生物大分子，即蛋白质类物质的浓缩、纯化及分离，在此过程中，为了确保蛋白收率，降低第一侧表面的非特异性吸附性，第一侧表面需要具备一定的亲水性，本发明中，纤维素超滤膜第一侧表面的水接触角为10-55°，在此基础上，纤维素超滤膜能够保证在蛋白产物生产应用中能够具有较低的蛋白吸附性，确保较高的蛋白收率。同时，第一侧表面孔面积率为1-10％，可以保证第一侧表面的孔隙相对较少，而致密的孔结构能够配合较小的孔径保证纤维素超滤膜超滤层的截留效率；并且，用粗糙度测试仪测量第一侧表面的粗糙度为0.1-2.5μm，这使得第一侧表面具有一定的粗糙度，不至于过于光滑，防止浓差极化的现象产生，避免在过滤较短的时间后孔就被堵塞，造成通量的大幅下降，但第一侧表面也不能过于粗糙，过高的粗糙度会增加过滤时蛋白在纤维素超滤膜表面受到的剪切力，导致有效蛋白收率的下降。
进一步的，所述超滤层内具有形成多孔结构的超滤纤维，所述超滤纤维的SEM平均直径为20-60nm；
所述支撑层内具有形成多孔结构的支撑纤维，所述支撑纤维的SEM平均直径为20-85nm；
所述支撑纤维和超滤纤维的SEM平均直径之比为1.2-2.4。
超滤层中超滤纤维的存在，确保了超滤层内部孔洞的稳定性，防止孔洞的坍塌或收缩，同时，支撑层内的支撑纤维能够对超滤层起到良好的支撑作用；其中，超滤纤维、支撑纤维过粗，会降低超滤层过滤流速，造成整体通量的下降，而超滤纤维、支撑纤维过细，则无法起到良好的支撑稳定孔洞的作用，当支撑纤维和超滤纤维的SEM平均直径之比为1.2-2.4范围内时，纤维素超滤膜具有较高的机械强度和过滤稳定性。
进一步的，所述超滤层厚度为0.1-5um，所述支撑层的厚度为0.5-50um，所 述支撑层厚度与超滤层厚度之比为2-13。
为保证超滤层在过滤中起到良好的截留作用，超滤层需要具有一定的厚度，但是，若超滤层厚度过后，不但无法进一步提高截留效率，还会导致膜整体通量的下降；而支撑层对超滤层起到支撑保护的作用，不但能够增加超滤层的孔洞稳定性，同时也能提高超滤层的完整性，因此，支撑层需要具有一定的厚度，但支撑层厚度过厚也容易导致膜整体流速的下降，将支撑层厚度与超滤层厚度之比控制为2-13范围内，纤维素超滤膜具有较高的机械强度和较好的完整性。
进一步的，所述支撑层SEM平均孔径沿流体流动方向逐渐变大，变化梯度为20-450nm/1μm。
支撑层的SEM平均孔径沿流体流动方向逐渐变大，即靠近超滤层侧孔径小，能够增加对超滤层的支撑性，而靠近聚四氟乙烯层侧孔径较大，能够赋予膜整体高通量，但变化梯度过大则容易使得纤维素超滤膜整体强度下降，降低纤维素超滤膜过滤使用寿命。
纤维素超滤膜各层的厚度、孔径、纤维直径可以通过使用扫描电子显微镜对膜结构进行形貌表征后，再利用计算机软件(如Matlab、NIS-Elements等)或手工进行测量后计算测得；当然本领域技术人员也可以通过其他测量手段获得上述参数(如各层厚度可以通过将滤膜冷冻干燥，在用测量工具测量获得)，上述测量手段仅供参考。
进一步的，所述超滤膜的厚度为130-420um；
所述超滤膜的截留标准分子量为1K-750K；
所述超滤膜拉伸强度不低于10MPa；
在压力为0.68bar，温度为25℃的条件下，100K纤维素超滤膜水通量为1-1.8mL/min/cm2。
当膜的厚度过小时，其膜的机械强度就会较低；当膜的厚度过大时，其过滤时间就会过长，时间成本过大；本发明的滤膜由于是复合膜，其大部分区域孔径相对较大，为了保证机械性能，膜整体的厚度相对较厚，经过研究，其厚度适合为130-420μm，保证了滤膜不仅具有较高的机械强度，而且过滤时间较短，时间成本较低；本发明中超滤膜对于分子量为1kD-750kD的物质的截留效率大于90％，截留效率高，说明了膜特别适合应用于生物纯化，满足实际应用的需求；与此膜的蛋白质收率不低于90％，说明了流体中的有效物质蛋白质不容易吸附在膜上，一方面不会将膜孔堵住，保证滤膜依然具有较高的使用寿命，另一方面保证流体中的有效物质各种蛋白质的含量变化很小，蛋白质基本不会损失，经济效益有保证。评价滤膜机械强度大小的重要指标就是滤膜的拉伸强度；在一定条件下，滤膜的拉伸强度越大，也就说明了该滤膜的机械强度越好；本发明滤膜的湿拉伸强度不低于10MPa(在膜湿润条件下测得)，具有较大的拉伸强度，其机械性能较好，工业实用价值较高，完全能够满足市场需求；同时通过对滤膜进行流速测试，说明了滤膜的流速较大，过滤时间短，时间成本较低。
进一步的，所述聚四氟乙烯层形成结合层的表面为聚四氟乙烯层结合面，所述结合面包括结点和纤维丝，所述结点之间通过纤维丝相互连接。
聚四氟乙烯层可根据制备工艺的不同，而具有不同的结构，然而发明人发现，并不是任何结构的聚四氟乙烯层作为基底层是都具有良好的效果，而具有结点，且结点之间通过纤维丝相互连接的聚四氟乙烯层作为基底层时具有更好的效果。首先，相比其他结构形式(例如烧结法制备)的聚四氟乙烯膜，具有节点和纤维丝结构的聚四氟乙烯膜表面更为平整，这是由于结点之间的纤维丝通过拉伸得到，因此不会具有翘起的端部，作为基底层能够实现复合超滤膜良好的完整性；其次，具有结点和纤维丝结构的聚四氟乙烯膜表面开孔率高(纤 维丝较细，直接均为开孔)，相对于其他结构形式更容易使得纤维素类聚合物层渗透形成渗透层，同时能够增加复合能力，提高剥离强度；最后，结点处具有较高的强度，而纤维丝处相对容易变形，两者结合能够增加膜整体的强度与弹性。
进一步的，所述结点占聚四氟乙烯层结合面的面积为S1；
所述纤维丝占聚四氟乙烯层结合面的面积为S2；
所述S1:S2为0.13-7；所述S1为4-40％；所述S2为5-35％。
本发明中，若结点占聚四氟乙烯层结合面的面积S1占比过小，纤维丝占聚四氟乙烯层结合面的面积S2过大，则容易出现基材层强度较低的情况，而若结点占聚四氟乙烯层结合面的面积S1占比过大，纤维丝占聚四氟乙烯层结合面的面积S2过小，则容易出现纤维素类聚合物层渗透困难，出现溶质堆积效应，降低通量，同时渗透后由于与纤维丝结合过少，导致剥离强度下降的现象产生，并且，纤维丝占比过小也能够导致整膜弹性下降，出现超滤膜过脆的现象。
聚四氟乙烯结合面上的结点占比、宽度和密度、纤维丝占比、宽度和密度可以通过使用扫描电子显微镜对膜结构进行形貌表征后，再利用计算机软件(如Matlab、NIS-Elements等)或手工进行测量，并进行相应计算；在膜的制备过程中，在垂直于膜厚度方向上(如果膜是平板膜形态，则该方向是平面方向；如果膜是中空纤维膜形态，则该方向是垂直于半径方向)，其各项特征如结点宽度和密度，纤维宽度和密度分布是大致均匀的，基本保持一致；所以可以通过在相应平面上部分区域的结点宽度和密度，纤维宽度和密度来反映该平面上整体的结点宽度和密度，纤维宽度和密度；在实际进行测量时，可以先用电子显微镜对膜外表面进行表征，获得相应的SEM图，而由于膜外表面上结点占比、宽度和密度，纤维宽度和密度大致是均匀的，因此可以选取一定的面积，例如 1000μm2(40μm乘以25μm)或者10000μm2(100μm乘以100μm)，具体面积大小视实际情况而定，再用相应计算机软件或者手工测出该面积上结点宽度和密度，纤维宽度和密度，从而获得该表面的结点占比、宽度和密度、纤维丝占比、宽度和密度；当然本领域技术人员也可以通过其他测量手段获得上述参数，上述测量手段仅供参考。
进一步的，所述结点的平均宽度为1-6μm，所述结点最大宽度和最小宽度之差＜7μm；所述纤维丝的平均宽度为0.1-1.2μm，所述纤维丝的最大宽度和最小宽度之差＜1.5μm。
结点的平均宽度影响聚四氟乙烯层的机械强度，若过小，作为基底层的聚四氟乙烯强度较低，导致整膜的强度下降，而结点的宽度过大，容易导致制备时铸膜液在结点处无法良好渗透，不但影响超滤膜的剥离强度，同时还会导致超滤层缺陷增加，降低其完整性。
进一步的，沿所述结点方向的50μm长度上，连接的纤维素的数量为15-70根。
纤维丝密度，对于膜渗透结合具有较大的影响，若密度过小，不但整体强度减小，同时会使得结合层中无法有足够数量的纤维丝与支撑层结合，导致剥离强度的下降，而若密度过大，导致整体表面孔隙下降，会使得制备时铸膜液无法良好渗透，导致超滤膜剥离强度下降。
进一步的，所述纤维素类聚合物层材质包括再生纤维素、纤维素酯中的一种或多种。
本发明还提供了一种纤维素超滤膜的制备方法：
S1：制备铸膜液，所述铸膜液包括下列重量份物质组成：
纤维素类聚合物10-30份；极性溶剂40-60份；成孔剂20-40份；
S2：将铸膜液流延到亲水基底上形成液膜；所述亲水基底为聚四氟乙烯多孔膜；
所述聚四氟乙烯多孔膜表面水接触角小于80°，所述聚四氟乙烯多孔膜孔径大于0.8μm；
S3：分相凝固，将液膜浸入凝固浴中分相固化，制得成膜；
S4：将成膜置于氢氧化钠水溶液中进行水解，水解后清洗形成纤维素超滤膜。
进一步的，所述纤维素类聚合物为硝酸纤维素、醋酸纤维素和再生纤维素中的至少一种；
所述醋酸纤维素选自二醋酸纤维素、三醋酸纤维素、硝酸纤维素、醋酸丁酸纤维素和醋酸丙酸纤维素中的一种或多种。
进一步的，所述极性溶剂包括丙酮、二氧六环、二甲基乙酰胺、N-甲基吡咯烷酮、乙酸、丙酸、丁酸和戊酸中的至少一种；
所述成孔剂包括聚乙烯吡咯烷酮、聚乙二醇和聚乙烯醇中的至少一种。
进一步的，所述铸膜液粘度为6000-40000cpa.s。
进一步的，所述分相凝固持续时间为5-60s，所述凝固浴为水，分相温度为20-40℃。
进一步的，所述氢氧化钠水溶液浓度为0.01mol/L-1mol/L之间；水解时间为30℃-80℃之间，时间为40min-200min。
进一步的，所述纤维素超滤膜的制备包括交联；
所述交联为将纤维素超滤膜在碱性环境下和水溶性交联剂进行交联，交联时间为20-400min，温度为30℃-60℃；所述交联剂为卤代环氧化物，双环氧化合物，双卤代烷烃和双卤代醇中的至少一种。
本发明在制备过程中，首先进行铸膜液的配置，其中，纤维素类聚合物具有相对较好的亲水性，非特异性吸附较低，因此非常适宜蛋白的纯化、浓缩与分离，可作为铸膜液溶质部分，极性溶剂用于形成溶剂体系，溶解充分溶解纤维素类聚合物，形成均一稳定的铸膜液，成孔剂不但能够有效控制体系的粘度，抑制膜在分相过程中形成大孔，还能有效提高膜流速的稳定性，此外还能够大大改善成膜的亲水性，使得膜具有较高的亲水性，降低蛋白吸附。
随后，将铸膜液流延到基材上形成液膜，本发明中，为了使得纤维素超滤膜具有较高的通量，因此在流延时铸膜液中的溶质部分需要渗透进入基材上的微孔层中，而发明人发现，采用不同材质的基膜，其与纤维素类聚合物的相容性具有较大差异，而采用亲水聚四氟乙烯多孔膜作为基材层，当聚四氟乙烯多孔膜表面水接触角小于80°，聚四氟乙烯多孔膜孔径大于0.8μm时，铸膜液能够渗透进入聚四氟乙烯多孔膜中，形成结合层，从而消除溶质堆积现象，使得制备得到的超滤膜具有良好的通量，同时，结合层也能够赋予最终制备得到的纤维素超滤膜中纤维素类聚合物层和聚四氟乙烯层之间更好的复合性能，即提高两者的剥离强度，防止在使用过程中，或者纤维素类聚合物层和聚四氟乙烯层之间出现剥离的现象；作为优选，聚四氟乙烯多孔膜的PMI平均孔径为1-20μm，孔隙率为60-90％；表面粗糙度为0.7-2μm，同时表面包括结点和纤维丝，结点之间通过纤维丝相互连接，在此条件下，能够使得铸膜液更好的渗透，得到复合性能与过滤性能更好的纤维素超滤膜。同时，在流延步骤中，铸膜液粘度也是决定能够良好渗透的因素之一，本发明中，铸膜液粘度为6000-40000cpa.s，从而保证了纤维素超滤膜具有合适的厚度以及理想的膜孔结构和孔径大小，从而达到良好的复合性能及过滤性能；这是由于若铸膜液粘度过高，则铸膜液无法良好渗透入基材层中，甚至会出现溶剂渗透进入，而溶质为透过的现象，导 致溶质在基材层表面的堆积，造成最终复合性能及过滤性能的下降，而粘度过低，则会导致铸膜液完全渗透，最终无法形式能够用于截留的超滤层，同样无法满足实际需求。
后续的分相凝固则为将涂覆有液膜的基材浸入水中分相固化，分相凝固持续时间为5-60s，通过选择合适的铸膜液和合适的分相时间，使得铸膜液进行合适的分相，确保获得理想膜孔径大小的成膜，同时本发明采用亲水及大孔聚四氟乙烯多孔膜作为基材，在分相时，凝固浴更容易从基材层底面进入，使得渗透入基材层中的纤维素类聚合物同样能够相对更早的进行分相固化，从而能够抢夺基材层上表面外的溶质，一方面能够缓解溶质堆积现象，另一方面由于聚四氟乙烯层外的溶质减少，使得支撑层相对变薄，从而增加通量。
最后，采用氢氧化钠水溶液中进行水解，水解后清洗形成固态膜，并且，结合实际需求，后续还可进行交联，在在交联改性的过程中，固态膜中的羟基会与环氧、卤素等官能团发生反应，从而使膜结构机械强度更高，不容易发生溶胀，同时还使得膜的耐碱性得到提高，使用寿命更长。同时更有利于高效截留那些小分子量的生物分子(如3K，5K的生物分子)。
本发明中，采用包含聚四氟乙烯层的微孔膜作为基底层，首先，聚四氟乙烯层表面相对平整，耐溶剂性强，制备得到的超滤膜中纤维素类聚合物层缺陷相对较小，因此超滤膜的完整性相对较好；且基底层能够对纤维素类聚合物层起到一个支撑作用，保证了膜整体具有不错的机械强度，耐压强度较高，适合在较高压力作用下进行长时间稳定的过滤；同时纤维素类聚合物能够渗透进入聚四氟乙烯层中，形成结合层，从而消除溶质堆积现象，使得制备得到的超滤膜具有良好的通量及复合性能，防止在使用过程中出现剥离的现象；最后，在后续相分离时，凝固浴更容易从第二侧表面进入，使得在结合层中的纤维素类 聚合物同样能够相对更早的进行分相固化，从而能够抢夺聚四氟乙烯层外的溶质，保证第一侧表面SEM平均孔径的均一，同时也能缓解溶质堆积现象，并便于支撑层厚度的调控，使得支撑层相对变薄，从而增加通量。
附图说明
下面结合附图对本发明作进一步说明：
图1为本发明实施例1制备获得的超滤膜第一侧表面的SEM图；
图2为本发明实施例1制备获得的超滤膜截面的SEM图；
图3为本发明实施例1基底层中聚四氟乙烯层结合面SEM图；
图4为本发明实施例10制备获得的超滤膜第一侧表面的SEM图；
图5为本发明实施例10制备获得的超滤膜截面的SEM图；
图6为本发明实施例12制备获得的超滤膜第一侧表面的SEM图；
图7为本发明实施例12制备获得的超滤膜截面的SEM图；
图8为本发明实施例17制备时所用的基底层，放大倍数2000×；
图9为本发明膜包扩散流测试装置示意图。
具体实施方式
为了能够更清楚地理解本发明的上述目的、特征和优点，下面结合附图和具体实施方式对本发明进行进一步的详细描述。需要说明的是，在不冲突的情况下，本申请的实施例及实施例中的特征可以相互组合。
在下面的描述中阐述了很多具体细节以便于充分理解本发明，但是，本发明还可以采用其他不同于在此描述的其他方式来实施，因此，本发明的保护范围并不受下面公开的具体实施例的限制。
实施例1：一种纤维素类超滤膜的制备方法，包括以下步骤：
S1：制备铸膜液，所述铸膜液包括下列重量份物质组成：
二醋酸纤维素10份；极性溶剂丙酮40份；成孔剂聚乙烯醇22份；铸膜液粘度6000cps；
S2：将铸膜液流延到基底层上形成液膜；所述亲水基底为聚四氟乙烯多孔膜；基底层中聚四氟乙烯层结合面如图3所示；
S3：分相凝固，将液膜浸入凝固浴水中，在25℃分相固化10s，制得成膜；
S4：将成膜置于0.1mol/L氢氧化钠水溶液中，在60℃下水解120min，水解后清洗形成纤维素超滤膜；
S5：将水解后的膜放置在pH＝10的碱性环境下和水溶性交联剂进行交联，交联结束后进行清洗得到超滤膜；其中交联剂为环氧氯丙烷，水溶液中交联剂浓度为10％，交联时间为150min，温度为45℃。
制备得到的超滤膜形貌如图1-图2所示。
实施例2：一种纤维素类超滤膜的制备方法，包括以下步骤：
S1：制备铸膜液，所述铸膜液包括下列重量份物质组成：
二醋酸纤维素12份；极性溶剂二氧六环43份；成孔剂聚乙二醇23份；铸膜液粘度7000cps；
S2：将铸膜液流延到基底层上形成液膜；所述亲水基底为聚四氟乙烯多孔膜；
S3：分相凝固，将液膜浸入凝固浴水中，在25℃分相固化15s，制得成膜；
S4：将成膜置于0.1mol/L氢氧化钠水溶液中，在60℃下水解120min，水解后清洗形成纤维素超滤膜；
S5：将水解后的膜放置在pH＝10的碱性环境下和水溶性交联剂进行交联，交联结束后进行清洗得到超滤膜；其中交联剂为环氧氯丙烷，水溶液中交联剂浓度为10％，交联时间为100min，温度为50℃。
实施例3：一种纤维素类超滤膜的制备方法，包括以下步骤：
S1：制备铸膜液，所述铸膜液包括下列重量份物质组成：
二醋酸纤维素10份；极性溶剂二甲基乙酰胺41份；成孔剂聚乙烯吡咯烷酮25份；铸膜液粘度6000cps；
S2：将铸膜液流延到基底层上形成液膜；所述亲水基底为聚四氟乙烯多孔膜；
S3：分相凝固，将液膜浸入凝固浴水中，在25℃分相固化20s，制得成膜；
S4：将成膜置于0.3mol/L氢氧化钠水溶液中，在40℃下水解60min，水解后清洗形成纤维素超滤膜；
S5：将水解后的膜放置在pH＝10的碱性环境下和水溶性交联剂进行交联，交联结束后进行清洗得到超滤膜；其中交联剂为环氧氯丙烷，水溶液中交联剂浓度为10％，交联时间为70min，温度为55℃。
实施例4：一种纤维素类超滤膜的制备方法，包括以下步骤：
S1：制备铸膜液，所述铸膜液包括下列重量份物质组成：
二醋酸纤维素13份；极性溶剂N-甲基吡咯烷酮45份；成孔剂聚乙烯醇20份；铸膜液粘度8000cps；
S2：将铸膜液流延到基底层上形成液膜；所述亲水基底为聚四氟乙烯多孔膜；
S3：分相凝固，将液膜浸入凝固浴水中，在30℃分相固化10s，制得成膜；
S4：将成膜置于0.3mol/L氢氧化钠水溶液中，在40℃下水解60min，水解后清洗形成纤维素超滤膜；
S5：将水解后的膜放置在pH＝10的碱性环境下和水溶性交联剂进行交联，交联结束后进行清洗得到超滤膜；其中交联剂为环氧氯丙烷，水溶液中交联剂 浓度为10％，交联时间为250min，温度为35℃。
实施例5：一种纤维素类超滤膜的制备方法，包括以下步骤：
S1：制备铸膜液，所述铸膜液包括下列重量份物质组成：
二醋酸纤维素12份；极性溶剂丙酮42份；成孔剂聚乙二醇21份；铸膜液粘度7000cps；
S2：将铸膜液流延到基底层上形成液膜；所述亲水基底为聚四氟乙烯多孔膜；
S3：分相凝固，将液膜浸入凝固浴水中，在30℃分相固化15s，制得成膜；
S4：将成膜置于0.3mol/L氢氧化钠水溶液中，在40℃下水解60min，水解后清洗形成纤维素超滤膜；
S5：将水解后的膜放置在pH＝10的碱性环境下和水溶性交联剂进行交联，交联结束后进行清洗得到超滤膜；其中交联剂为环氧氯丙烷，水溶液中交联剂浓度为10％，交联时间为350min，温度为58℃。
实施例6：一种纤维素类超滤膜的制备方法，包括以下步骤：
S1：制备铸膜液，所述铸膜液包括下列重量份物质组成：
二醋酸纤维素14份；极性溶剂丙酮44份；成孔剂聚乙烯吡咯烷酮22份；铸膜液粘度9000cps；
S2：将铸膜液流延到基底层上形成液膜；所述亲水基底为聚四氟乙烯多孔膜；
S3：分相凝固，将液膜浸入凝固浴水中，在30℃分相固化20s，制得成膜；
S4：将成膜置于0.3mol/L氢氧化钠水溶液中，在40℃下水解80min，水解后清洗形成纤维素超滤膜；
实施例7：一种纤维素类超滤膜的制备方法，包括以下步骤：
S1：制备铸膜液，所述铸膜液包括下列重量份物质组成：
二醋酸纤维素14份；极性溶剂二甲基乙酰胺43份；成孔剂聚乙烯醇24份；铸膜液粘度10000cps；
S2：将铸膜液流延到基底层上形成液膜；所述亲水基底为聚四氟乙烯多孔膜；
S3：分相凝固，将液膜浸入凝固浴水中，在30℃分相固化30s，制得成膜；
S4：将成膜置于0.3mol/L氢氧化钠水溶液中，在40℃下水解90min，水解后清洗形成纤维素超滤膜；
实施例8：一种纤维素类超滤膜的制备方法，包括以下步骤：
S1：制备铸膜液，所述铸膜液包括下列重量份物质组成：
二醋酸纤维素15份；极性溶剂N-甲基吡咯烷酮44份；成孔剂聚乙二醇27份；铸膜液粘度12000cps；
S2：将铸膜液流延到基底层上形成液膜；所述亲水基底为聚四氟乙烯多孔膜；
S3：分相凝固，将液膜浸入凝固浴水中，在30℃分相固化40s，制得成膜；
S4：将成膜置于0.3mol/L氢氧化钠水溶液中，在40℃下水解100min，水解后清洗形成纤维素超滤膜。
实施例9：一种纤维素类超滤膜的制备方法，包括以下步骤：
S1：制备铸膜液，所述铸膜液包括下列重量份物质组成：
二醋酸纤维素17份；极性溶剂丙酮48份；成孔剂聚乙烯吡咯烷酮25份；铸膜液粘度16000cps；
S2：将铸膜液流延到基底层上形成液膜；所述亲水基底为聚四氟乙烯多孔膜；
S3：分相凝固，将液膜浸入凝固浴水中，在35℃分相固化20s，制得成膜；
S4：将成膜置于0.2mol/L氢氧化钠水溶液中，在50℃下水解120min，水解后清洗形成纤维素超滤膜。
实施例10：一种纤维素类超滤膜的制备方法，包括以下步骤：
S1：制备铸膜液，所述铸膜液包括下列重量份物质组成：
二醋酸纤维素19份；极性溶剂二氧六环48份；成孔剂聚乙烯醇30份；铸膜液粘度20000cps；
S2：将铸膜液流延到基底层上形成液膜；所述亲水基底为聚四氟乙烯多孔膜；
S3：分相凝固，将液膜浸入凝固浴水中，在35℃分相固化30s，制得成膜；
S4：将成膜置于0.3mol/L氢氧化钠水溶液中，在50℃下水解150min，水解后清洗形成纤维素超滤膜。
制备得到的超滤膜形貌如图4-图5所示。
实施例11：一种纤维素类超滤膜的制备方法，包括以下步骤：
S1：制备铸膜液，所述铸膜液包括下列重量份物质组成：
二醋酸纤维素19份；极性溶剂二甲基乙酰胺49份；成孔剂聚乙二醇33份；铸膜液粘度24000cps；
S2：将铸膜液流延到基底层上形成液膜；所述亲水基底为聚四氟乙烯多孔膜；
S3：分相凝固，将液膜浸入凝固浴水中，在35℃分相固化35s，制得成膜；
S4：将成膜置于0.3mol/L氢氧化钠水溶液中，在60℃下水解170min，水解后清洗形成纤维素超滤膜。
实施例12：一种纤维素类超滤膜的制备方法，包括以下步骤：
S1：制备铸膜液，所述铸膜液包括下列重量份物质组成：
二醋酸纤维素21份；极性溶剂N-甲基吡咯烷酮51份；成孔剂聚乙烯吡咯烷酮35份；铸膜液粘度27000cps；
S2：将铸膜液流延到基底层上形成液膜；所述亲水基底为聚四氟乙烯多孔膜；
S3：分相凝固，将液膜浸入凝固浴水中，在35℃分相固化40s，制得成膜；
S4：将成膜置于0.5mol/L氢氧化钠水溶液中，在40℃下水解60min，水解后清洗形成纤维素超滤膜。
制备得到的超滤膜形貌如图6-图7所示。
实施例13：一种纤维素类超滤膜的制备方法，包括以下步骤：
S1：制备铸膜液，所述铸膜液包括下列重量份物质组成：
二醋酸纤维素24份；极性溶剂丙酮53份；成孔剂聚乙烯醇35份；铸膜液粘度29000cps；
S2：将铸膜液流延到基底层上形成液膜；所述亲水基底为聚四氟乙烯多孔膜；
S3：分相凝固，将液膜浸入凝固浴水中，在35℃分相固化50s，制得成膜；
S4：将成膜置于0.5mol/L氢氧化钠水溶液中，在70℃下水解60min，水解后清洗形成纤维素超滤膜。
实施例14：一种纤维素类超滤膜的制备方法，包括以下步骤：
S1：制备铸膜液，所述铸膜液包括下列重量份物质组成：
二醋酸纤维素25份；极性溶剂二氧六环52份；成孔剂聚乙二醇36份；铸膜液粘度30000cps；
S2：将铸膜液流延到基底层上形成液膜；所述亲水基底为聚四氟乙烯多孔 膜；
S3：分相凝固，将液膜浸入凝固浴水中，在40℃分相固化20s，制得成膜；
S4：将成膜置于0.5mol/L氢氧化钠水溶液中，在50℃下水解100min，水解后清洗形成纤维素超滤膜。
实施例15：一种纤维素类超滤膜的制备方法，包括以下步骤：
S1：制备铸膜液，所述铸膜液包括下列重量份物质组成：
二醋酸纤维素27份；极性溶剂二甲基乙酰胺57份；成孔剂聚乙烯吡咯烷酮38份；铸膜液粘度34000cps；
S2：将铸膜液流延到基底层上形成液膜；所述亲水基底为聚四氟乙烯多孔膜；
S3：分相凝固，将液膜浸入凝固浴水中，在40℃分相固化40s，制得成膜；
S4：将成膜置于0.5mol/L氢氧化钠水溶液中，在50℃下水解120min，水解后清洗形成纤维素超滤膜。
实施例16：一种纤维素类超滤膜的制备方法，包括以下步骤：
S1：制备铸膜液，所述铸膜液包括下列重量份物质组成：
硝酸纤维素29份；极性溶剂N-甲基吡咯烷酮59份；成孔剂聚乙烯醇40份；铸膜液粘度38000cps；
S2：将铸膜液流延到基底层上形成液膜；所述亲水基底为聚四氟乙烯多孔膜；
S3：分相凝固，将液膜浸入凝固浴水中，在40℃分相固化50s，制得成膜；
S4：将成膜置于0.5mol/L氢氧化钠水溶液中，在60℃下水解100min，水解后清洗形成纤维素超滤膜。
实施例17：与实施例1的区别在于，采用如图8所示其他结构的亲水PTFE 作为基底层。
对比例1：与实施例1相同，所用基底层如下表2-1、表2-2所示。
对比例2：与实施例1相同，所用基底层如下表2-1、表2-2所示。
一：结构表征：将上述实施例及对比例的膜结构进行表面及端面形貌表征，具体数值如下：
表1：膜截面形貌结构：
表2-1：基底层(聚四氟乙烯层)结构

表2-2：基底层(无纺布)结构
表3：膜表面结构：

由上表可知，实施例制得的纤维素类超滤膜具有较好的膜结构，制备得到的超滤膜中纤维素类聚合物层缺陷相对较小，因此超滤膜的完整性相对较好；同时纤维素类聚合物能够渗透进入聚四氟乙烯层中，形成结合层，从而消除溶质堆积现象，使得制备得到的超滤膜具有良好的通量及复合性能，防止在使用过程中出现剥离的现象；最后，同时也能便于支撑层厚度的调控，使得支撑层相对变薄，从而增加通量。
二、性能特征
1、过滤精度测试：具体结果如下表所示：

本发明实施例1-10制得的纤维素类复合超滤膜以切向流过滤的方式纯化各种生物分子；其截流分子量为3K-750K，其截留效率均大于90％，确保能够高效截留各种分子量的生物分子。
2、通量测试：在25℃温度下，50ml试验液去离子水经过直径为47mm的滤膜，记录时间计算通量；其中实施例10至16的压力为0.68bar；实施例1至9，对比例1-2的压力为3.8bar；具体结果如下表所示：

本发明各实施例通过流速测试，该膜具有相对较高的通量，即较快的流速，能够快速过滤含生物分子的流体，经济效益高。而对比例1和对比例2不采用复合要求的基底层，因此在截留分子量相同的情况下，通量较低。
3、机械强度测试：对湿态膜进行拉伸强度进行测试，实施例1-16超滤膜拉伸强度均不低于10MPa，弹性模量均大于200MPa，机械性能相对较高，在使用时具有较高的耐压性，而实施例17拉伸强度和弹性模量较低，不符合实际使用要求。
4、蛋白质收率测试(可以根据中国CN201010154974.7-超多孔膜及其制备方法中所使用的蛋白质收率测试方法进行测试，也可以用其他方法进行测试)，实施例超滤膜的蛋白质收率均大于90％，能够得到较高的蛋白质收率，经济效益高。
5、扩散流测试，将实施例1-5纤维素超滤膜制备得到0.11m2的3K膜包，进行扩散流测试时，具体方法为：制备成过滤面积为0.11㎡的膜包，如图9所示将测试装置进行组装，进料罐01通过进液管道与过滤膜包一侧的进液孔连通，进液管道连接有泵02、排液阀03和空气阀04，废料罐05通过回流管道与过滤膜包另一侧的进液孔连通，回流阀06安装在回流管道上，烧杯07通过透过管道与过滤膜包的滤液孔连通，透过阀08安装在透过管道上以开闭烧杯07与滤液孔的通断；用水填充50ml量筒09并将其倒置在装有水的500mL烧杯07中。测试时，先关闭空气阀04，压力调节器设置为0bar(0psi)；然后，关闭进料阀和排液阀03，打开空气阀04、回流阀06和透过阀08，将膜包进料-回流管道中的水去除，然后将压力调节器缓慢调节至0.35bar(5psi)，使空气流过系统，直到水停止从回流阀 06所在的回流管道排出；关闭回流阀06，使空气压力从滤液孔去除透过管道中的水，缓慢调节压力调节器至1bar(15psi)；当气泡速率稳定时，记录对应的时间以及量筒09中的空气量；当5-10mL的气体被收集时，再次记录下对应的时间和空气体积；计算扩散流(mL/min/@15psi)；结果如下表所示。
上述数据可知，采用本发明限定范围内的结点-纤维素结构的聚四氟乙烯层和具有无纺布基材层作为基底层时能够在使用时赋予膜相对更好的完整性，而实施例3和实施例5的虽然扩散流较大，完整性相对较差，但也在实际可用标准(＜12mL/min@15psi)内。
以上已详细描述了本发明的较佳实施例，但应理解，在阅读了本发明的上述讲授内容之后，本领域技术人员可以对本发明作各种改动或修改。这些等价形式同样落于本申请所附权利要求书所限定的范围。

Claims (27)

  1. 一种纤维素超滤膜，包括主体，所述主体具有：
    供给待过滤液体的第一侧表面、以及
    透过所述主体排出透过液的第二侧表面；
    所述主体沿流体流经方向上依次为超滤层、支撑层和基底层；
    其特征在于：
    所述超滤层和支撑层包括纤维素类聚合物层，所述基底层包括聚四氟乙烯层，所述基底层PMI平均孔径＞0.8μm；
    所述聚四氟乙烯层为亲水聚四氟乙烯层；
    所述纤维素类聚合物层和聚四氟乙烯层渗透结合形成结合层；
    所述第一侧表面SEM平均孔径为1-90nm。
  2. 根据权利要求1所述的纤维素超滤膜，其特征在于，所述第一侧表面SEM平均孔径的离散系数小于0.5。
  3. 根据权利要求1所述的纤维素超滤膜，其特征在于，所述基底层包括设于聚四氟乙烯层远离纤维素类聚合物层的基材层，所述基材层远离聚四氟乙烯层的表面形成第二侧表面，所述基材层包括无纺布，所述无纺布厚度占所述整膜厚度的30-85％，所述无纺布的厚度为60-300μm。
  4. 根据权利要求3所述的纤维素超滤膜，其特征在于，所述无纺布的透气性大于50cc/cm2/sec，纤维粗细为5-30μm，克重为15-40g/m2。
  5. 根据权利要求3所述的纤维素超滤膜，其特征在于，所述纤维素类聚合物层与聚四氟乙烯层的厚度之比为0.1-3，所述纤维素类聚合物层的厚度为1-55μm，所述聚四氟乙烯层的厚度为15-90μm。
  6. 根据权利要求3所述的纤维素超滤膜，其特征在于，所述结合层的厚度占聚四氟乙烯层厚度的10-100％，所述结合层的厚度为10-100μm。
  7. 根据权利要求1所述的纤维素超滤膜，其特征在于，基底层为聚四氟乙烯层，所述纤维素类聚合物层与聚四氟乙烯层的厚度之比为0.02-1，所述纤维素类聚合物层的厚度为1.5-60μm，所述聚四氟乙烯的厚度为100-300μm。
  8. 根据权利要求1所述的纤维素超滤膜，其特征在于，所述聚四氟乙烯层PMI平均孔径为1-20μm，孔隙率为60-90％；所述聚四氟乙烯层表面粗糙度为0.7-2μm。
  9. 根据权利要求1所述的纤维素超滤膜，所述聚四氟乙烯层表面水接触角＜80°，所述第二侧表面的水接触角比第一侧表面的水接触角大50°以内。
  10. 根据权利要求1所述的纤维素超滤膜，其特征在于，将干膜浸润至水中，在5s内润湿。
  11. 根据权利要求1所述的纤维素超滤膜，其特征在于，所述第一侧表面的粗糙度为0.1-2.5μm，所述第一侧表面孔面积率为1-10％，第一侧表面的水接触角为10-55°。
  12. 根据权利要求1所述的纤维素超滤膜，其特征在于，所述超滤层内具有形成多孔结构的超滤纤维，所述超滤纤维的SEM平均直径为20-60nm；
    所述支撑层内具有形成多孔结构的支撑纤维，所述支撑纤维的SEM平均直径为20-85nm；
    所述支撑纤维和超滤纤维的SEM平均直径之比为1.2-2.4。
  13. 根据权利要求1所述的纤维素超滤膜，其特征在于，所述超滤层厚度为0.1-5um，所述支撑层的厚度为0.5-50um，所述支撑层厚度与超滤层厚度之比为2- 13。
  14. 根据权利要求1所述的纤维素超滤膜，其特征在于，所述支撑层平均孔径沿流体流动方向逐渐变大，变化梯度为20-450nm/1μm。
  15. 根据权利要求1所述的纤维素超滤膜，其特征在于，
    所述超滤膜的厚度为130-420um；
    所述超滤膜的截留标准分子量为1K-750K；
    所述超滤膜拉伸强度不低于10MPa；
    在压力为0.68bar，温度为25℃的条件下，100K纤维素超滤膜水通量为1-1.8mL/min/cm2。
  16. 根据权利要求1所述的纤维素超滤膜，其特征在于，所述聚四氟乙烯层由拉伸法制备得到，且形成结合层的表面为聚四氟乙烯层结合面，所述结合面包括结点和纤维丝，所述结点之间通过纤维丝相互连接。
  17. 权利要求16所述的纤维素超滤膜，其特征在于，所述结点占聚四氟乙烯层表面的面积为S1；
    所述纤维丝占聚四氟乙烯层表面的面积为S2；
    所述S1:S2为0.13-7；
    所述结点占结合面表面的面积S1为4-40％；所述纤维丝占结合面表面的面积S2为5-35％。
  18. 根据权利要求16所述的纤维素超滤膜，其特征在于，所述结点的平均宽度为1-6μm，所述结点最大宽度和最小宽度之差＜7μm；所述纤维丝的平均宽度为0.1-1.2μm，所述纤维丝的最大宽度和最小宽度之差＜1.5μm。
  19. 根据权利要求16所述的纤维素超滤膜，其特征在于，沿所述结点方向的 50μm长度上，连接的纤维素的数量为15-70根。
  20. 根据权利要求1所述的纤维素超滤膜，其特征在于，所述纤维素类聚合物层材质包括再生纤维素、纤维素酯中的一种或多种。
  21. 根据权利要求1所述的纤维素超滤膜的制备方法，其特征在于：
    S1：制备铸膜液，所述铸膜液包括下列重量份物质组成：
    纤维素类聚合物10-30份；极性溶剂40-60份；成孔剂20-40份；
    S2：将铸膜液流延到亲水基底上形成液膜；所述亲水基底为聚四氟乙烯多孔膜；
    所述聚四氟乙烯多孔膜表面水接触角小于80°，所述聚四氟乙烯多孔膜PMI孔径大于1μm；
    S3：分相凝固，将液膜浸入凝固浴中分相固化，制得成膜；
    S4：将成膜置于氢氧化钠水溶液中进行水解，水解后清洗形成纤维素超滤膜。
  22. 根据权利要求21所述的制备方法，其特征在于：
    所述纤维素类聚合物为硝酸纤维素、醋酸纤维素和再生纤维素中的至少一种；
    所述醋酸纤维素选自二醋酸纤维素、三醋酸纤维素、硝酸纤维素、醋酸丁酸纤维素和醋酸丙酸纤维素中的一种或多种。
  23. 根据权利要求21所述的纤维素超滤膜的制备方法，其特征在于：
    所述极性溶剂包括丙酮、二氧六环、二甲基乙酰胺、N-甲基吡咯烷酮、乙酸、丙酸、丁酸和戊酸中的至少一种；
    所述成孔剂包括聚乙烯吡咯烷酮、聚乙二醇和聚乙烯醇中的至少一种。
  24. 根据权利要求21所述的纤维素超滤膜的制备方法，其特征在于：所述铸膜 液粘度为6000-40000cpa.s。
  25. 根据权利要求21所述的纤维素超滤膜的制备方法，其特征在于：所述分相凝固持续时间为5-60s，所述凝固浴为水，分相温度为20-40℃。
  26. 根据权利要求21所述的纤维素超滤膜的制备方法，其特征在于：所述氢氧化钠水溶液浓度为0.01mol/L-1mol/L之间；水解时间为30℃-80℃之间，时间为40min-200min。
  27. 根据权利要求21所述的纤维素超滤膜的制备方法，其特征在于：所述纤维素超滤膜的制备包括交联；
    所述交联为将纤维素超滤膜在碱性环境下和水溶性交联剂进行交联，交联时间为20-400min，温度为30℃-60℃；所述交联剂为卤代环氧化物，双环氧化合物，双卤代烷烃和双卤代醇中的至少一种。
PCT/CN2023/110344 2022-10-27 2023-07-31 一种纤维素超滤膜及其制备方法 WO2024087771A1 (zh)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CN202211329602.2 2022-10-27
CN202211329602.2A CN115591405A (zh) 2022-10-27 2022-10-27 一种纤维素超滤膜及其制备方法

Publications (1)

Publication Number Publication Date
WO2024087771A1 true WO2024087771A1 (zh) 2024-05-02

Family

ID=84850178

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/CN2023/110344 WO2024087771A1 (zh) 2022-10-27 2023-07-31 一种纤维素超滤膜及其制备方法

Country Status (2)

Country Link
CN (1) CN115591405A (zh)
WO (1) WO2024087771A1 (zh)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115591405A (zh) * 2022-10-27 2023-01-13 杭州科百特过滤器材有限公司（Cn） 一种纤维素超滤膜及其制备方法
CN116712868B (zh) * 2023-06-30 2023-10-31 杭州科百特过滤器材有限公司 一种高机械强度的纤维素除病毒膜及其制备工艺

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101837249A (zh) * 2010-06-13 2010-09-22 苏州绿膜科技有限公司 复合聚氯乙烯中空纤维超滤膜及其制备方法
CN102068924A (zh) * 2010-12-22 2011-05-25 中国科学院长春应用化学研究所 一种聚四氟乙烯复合膜及其制备方法
CN103551054A (zh) * 2013-11-14 2014-02-05 中科瑞阳膜技术（北京）有限公司 一种超滤膜及其制备方法
CN105396466A (zh) * 2015-11-06 2016-03-16 北京化工大学 一种纤维素纳米纤维-氧化石墨烯杂化的复合超滤膜及其制备方法
US20200360866A1 (en) * 2017-08-25 2020-11-19 Beijing Normal University Composite porous membrane and preparation method therefor and use thereof
CN112755812A (zh) * 2020-12-18 2021-05-07 中化(宁波)润沃膜科技有限公司 一种具有中间层的高通量交联复合纳滤膜及其制备方法
CN115591405A (zh) * 2022-10-27 2023-01-13 杭州科百特过滤器材有限公司（Cn） 一种纤维素超滤膜及其制备方法

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101837249A (zh) * 2010-06-13 2010-09-22 苏州绿膜科技有限公司 复合聚氯乙烯中空纤维超滤膜及其制备方法
CN102068924A (zh) * 2010-12-22 2011-05-25 中国科学院长春应用化学研究所 一种聚四氟乙烯复合膜及其制备方法
CN103551054A (zh) * 2013-11-14 2014-02-05 中科瑞阳膜技术（北京）有限公司 一种超滤膜及其制备方法
CN105396466A (zh) * 2015-11-06 2016-03-16 北京化工大学 一种纤维素纳米纤维-氧化石墨烯杂化的复合超滤膜及其制备方法
US20200360866A1 (en) * 2017-08-25 2020-11-19 Beijing Normal University Composite porous membrane and preparation method therefor and use thereof
CN112755812A (zh) * 2020-12-18 2021-05-07 中化(宁波)润沃膜科技有限公司 一种具有中间层的高通量交联复合纳滤膜及其制备方法
CN115591405A (zh) * 2022-10-27 2023-01-13 杭州科百特过滤器材有限公司（Cn） 一种纤维素超滤膜及其制备方法

Also Published As

Publication number Publication date
CN115591405A (zh) 2023-01-13

Similar Documents

Publication Publication Date Title
WO2024087771A1 (zh) 一种纤维素超滤膜及其制备方法
EP0772489B1 (en) Cellulosic ultrafiltration membrane
JP3328394B2 (ja) 複合微多孔膜
US5958989A (en) Highly asymmetric ultrafiltration membranes
JP5504560B2 (ja) 液体処理用の中空糸膜
CN115608165B (zh) 一种除病毒用不对称的纤维素类滤膜及其制备方法
US4220543A (en) Ethylene-vinyl alcohol membranes having improved properties and a method of producing the same
CN113842792A (zh) 一种除病毒用不对称的pes滤膜及其制备方法
JP2000505719A (ja) 高度多孔性ポリ二フッ化ビニリデン膜
WO2003015902A2 (en) High strength asymmetric cellulosic membrane
CN111888953B (zh) 一种降低反渗透膜表面粗糙度的方法
CN116236925A (zh) 一种非对称再生纤维素除病毒滤膜及其制备工艺
CN116943451B (zh) 一种除病毒复合膜及其制备方法
CN105727771B (zh) 一种类肝素改性的聚乙烯醇水凝胶薄层纳米复合血液透析膜及其制备方法
CN112789102A (zh) 制备高选择性促进输送膜的方法
JP3617194B2 (ja) 選択透過性分離膜及びその製造方法
KR100557264B1 (ko) 중공사막 및 그의 제조 방법
JPH10230148A (ja) 半透膜
CN115569521A (zh) 一种纤维素类复合超滤膜及其制备方法
CN112295423B (zh) 多孔膜及滤芯
JP4029312B2 (ja) 選択透過性中空糸膜
JP3570713B2 (ja) ビール濾過用積層フィルター
JP4689790B2 (ja) アニオンコポリマーブレンドの内部親水性膜
WO2024087772A1 (zh) 一种除病毒复合膜及其制备工艺
CN117282280B (zh) 一种除病毒用复合膜及其制备方法