Hydrophilic membrane

Abstract

The present application relates to a carrier-free, permanently hydrophilic filtration membrane and a method for forming the same. The membrane comprises a polymeric matrix material and a cross-linked polyoxazoline hydrophilic additive blended in the matrix material.

Description

[0001] This application claims priority to U.S. Provisional Patent Application Serial No. 62 / 938,424, filed November 21, 2019, which is hereby incorporated by reference in its entirety. Technical Field

[0002] This application relates to a permanently hydrophilic filter membrane comprising a polymer matrix material and a cross-linked polyoxazoline hydrophilic additive blended throughout the matrix material. Background Technology

[0003] In many applications of filtration technology, membrane filters with high mechanical strength, thermal stability, relatively inert chemical properties, and insolubility in most organic solvents are desirable. Typically, membrane surface properties may differ from the overall properties of the membrane. Desired surface properties include good wettability, low protein adsorption tendency, controlled ion exchange capacity, and controlled surface chemical reactivity.

[0004] A common approach to achieving the duality of surface properties is to coat a pre-formed film with an oligomer or polymer having the desired surface properties. Typical coating materials include surfactants and water-soluble polymers such as polyvinylpyrrolidone (PVP). However, this method has drawbacks. It is not desirable to simply soak the film in a solution of, for example, a hydrophilic polymer (to hydrophilize the hydrophobic polymer film), because this hydrophilic polymer is easily washed off the film.

[0005] In order to improve the surface properties of membrane filters, various methods have been developed in recent decades to permanently modify the membrane surface.

[0006] U.S. Patent No. 4,698,388 to Ohmura et al. discloses the use of polymeric materials coated with block copolymers. These are synthesized from two vinyl monomers in the presence of a polymeric peroxide. A polymer of one vinyl monomer is uniformly dispersed in the polymeric material, while the other vinyl monomer forms a hydrophilic homopolymer. The durability of the hydrophilic modification, characterized by antistatic properties or surface resistivity, was tested only under mild conditions, namely, rinsing with tap water at room temperature for two hours. No further details are provided regarding the longevity of the hydrophilic modification on the polymeric material.

[0007] U.S. Patent Application Publication No. 2003 / 148017, granted to Tuominen et al., discloses the modification of hydrophobic dialysis membranes based on poly(ether)sulfone by adsorbing copolymers having hydrophobic polypropylene oxide (PPO) segments and hydrophilic polyethylene oxide (PEO) segments. While flushing the copolymer from the membrane into the dialysate is irrelevant in hemodialysis, it is undesirable in the life sciences industry.

[0008] Although there are earlier patents concerning polyethersulfone (PES) / poly(2-ethyl-2-oxazoline) (PEOX) membranes (e.g., U.S. Patent No. 4,900,449 to Kraus et al.) and PES / PVP / PEOX membranes (e.g., U.S. Patent No. 5,178,765 to Hu et al.), these patents do not mention the use of electron beams (e-beams) to further crosslink PEOX to prepare permanently hydrophilic membranes. Furthermore, no discussion is given of how to reduce extractable / leached material.

[0009] U.S. Patent No. 9,045,602, granted to Thom et al., discloses a method for inducing hydrophilicity on a membrane. This U.S. patent focuses on the modification of membrane surfaces. The method involves soaking a microporous membrane in a solution comprising a solvent and a polymer dissolved or dispersed therein to produce an soaked membrane. The soaked membrane is then irradiated with an electron beam to produce a microporous membrane on which the polymer of the soaking solution is immobilized by crosslinking.

[0010] U.S. Patent No. 4,798,847 to Roesink et al. discloses a method for manufacturing a hydrophilic membrane. The method includes blending a hydrophilic polymer with a hydrophobic polymer and crosslinking the hydrophilic polymer. This method requires converting the blended membrane to a non-swelling state prior to the crosslinking reaction.

[0011] This application relates to overcoming these and other deficiencies in the art. Summary of the Invention

[0012] This application relates to a carrier-free, permanent hydrophilic filter membrane comprising: a polymer matrix material; and a cross-linked polyoxazoline hydrophilic additive, wherein the cross-linked polyoxazoline hydrophilic additive is blended and distributed throughout the matrix material.

[0013] A second aspect of this application relates to a filter cartridge comprising a housing and a membrane of this application located within the housing.

[0014] Another aspect of this application relates to a method for forming a permanent hydrophilic filter membrane. The method involves providing one or more casting solutions comprising a polymer of polyoxazoline and a solvent. The one or more solutions are then applied simultaneously or sequentially to a carrier to form a liquid membrane. Phase separation of the one or more casting solutions is achieved in the liquid membrane to form a membrane. The membrane is immersed in water or an aqueous solution. The wet membrane is treated with an electron beam to crosslink the polyoxazoline, and the permanent hydrophilic filter membrane is separated from the carrier.

[0015] The membrane produced by this new method provides significant improvements in membrane hydrophilicity and its stability.

[0016] Hydrophilicity of a hydrophilic membrane is permanently imparted by crosslinking the polyoxazoline throughout the membrane using e-bundle treatment. E-bundle modification results in permanent hydrophilicity and low extractability / leaching content. Attached Figure Description

[0017] Figure 1 This is a partial cross-sectional perspective view of an exemplary filter cartridge of this application.

[0018] Figure 2 This is a cross-sectional perspective view of an exemplary filter cartridge of this application located within the housing during use.

[0019] Figure 3 This is a side view of an apparatus that can be used to carry out the process for preparing the permanent hydrophilic membrane of this application. Detailed Implementation

[0020] This application relates to a carrier-free, permanent hydrophilic filter membrane comprising: a polymer matrix material; and a cross-linked polyoxazoline hydrophilic additive, wherein the cross-linked polyoxazoline hydrophilic additive is blended and distributed throughout the matrix material.

[0021] Membranes can be classified as hydrophilic or hydrophobic. When a hydrophilic membrane comes into contact with water, it will spontaneously wet, meaning that the water will displace air from the pores of the membrane structure without any external force. On the other hand, positive pressure is required for water to enter the pores of a hydrophobic membrane structure to displace air.

[0022] Wetting time is used to characterize the wettability of a membrane in water. It can be determined by adding a drop of 10% NaCl solution to the membrane surface and measuring the time (in seconds) it takes for the membrane to fully permeate. This can be visually observed by the membrane becoming transparent when it is fully permeated.

[0023] The permanent hydrophilic filter membrane of this application may be a microporous membrane or an ultrafiltration membrane.

[0024] Ultrafiltration membranes and microfiltration membranes are used in pressure-driven filtration processes. Practitioners in the field of membrane separation processes can easily distinguish between microfiltration and ultrafiltration membranes, typically based on their applications and structural aspects. Microfiltration and ultrafiltration membranes are manufactured, marketed, and used as separate and distinct products. Despite some overlap in naming, they are different entities and are generally regarded as such in the business world.

[0025] Ultrafiltration membranes are primarily used for concentrating or percolating soluble macromolecules such as proteins, DNA, starch, and natural or synthetic polymers. In most applications, ultrafiltration is performed in tangential flow filtration (TFF) mode, where the feed solution passes through the membrane surface, and molecules smaller than the membrane pore size pass through (filtrate), while the remainder (retentate) is retained on the first side of the membrane. As the fluid also passes through, it needs to be recirculated or added to the retentate stream to maintain effective TFF operation. One advantage of using the TFF method is that, as the fluid continuously sweeps across the membrane surface, it tends to reduce fouling and polarization of the solute at and near the membrane surface, thereby extending membrane life.

[0026] Microporous membranes are primarily used for removing particles, such as solids, bacteria, and gels, from liquid or gas streams in a point-of-use filtration mode. Point-of-use filtration refers to filtration in which the entire fluid stream passes through the filter without recirculation or retention of the stream. Any material that does not pass through the filter will remain on the upper surface of the filter.

[0027] Regarding this application, compared to microporous membranes, ultrafiltration membranes are defined based on the "Terminology for Membranes and Membrane Processes" published by the International Union of Pure and Applied Chemistry (IUPAC) in *Pure Appl. Chemistry*, 68:1479 (1996), which is hereby incorporated in its entirety. Microfiltration is a pressure-driven membrane-based separation process in which particles larger than 0.1 μm and dissolved macromolecules are rejected. Ultrafiltration is a pressure-driven membrane-based separation process in which particles smaller than 0.1 μm and larger than about 2 nm and dissolved macromolecules are rejected.

[0028] The permanent hydrophilic filter membrane of this application can be symmetrical or asymmetrical.

[0029] As used in this article, "symmetric" refers to a membrane or region that has a generally uniform pore size distribution throughout the membrane or region.

[0030] As used herein, “asymmetry” refers to a membrane or region in which the diameter of the pores varies continuously or discontinuously along the thickness direction of the membrane or region.

[0031] In this application, a membrane “layer” is defined as an independent membrane sheet. One or more membranes can be used in a filter to remove particles.

[0032] In this application, a "region" is located within a membrane layer that has physical properties different from those of the surrounding or adjacent regions. A membrane layer may include one, two, three, or even more regions. One or more membrane layers with multiple regions can be used in a filter to remove particles of different sizes.

[0033] Similarly, the term "monolithic" refers to a structure that, although formed from multiple regions and typically different polymer materials, is combined together to behave as a single structure and does not delaminate or separate during normal use.

[0034] The "throughput" of a filter is defined as the amount of fluid that the filter can handle before reaching the filtration endpoint. This endpoint can be based on the maximum processing time for filtering a batch, or, in the case of constant pressure operation, on the minimum filter flux relative to the initial clean water flux. In this application, the filter throughput is defined as the maximum volume of fluid that can be filtered by the filter. Since filter throughput is determined by the membrane used, membrane throughput is typically measured to predict filter throughput. In the case of constant pressure operation, the volume of fluid filtered per membrane area is the membrane throughput. The maximum volume filtered at 90% of the initial membrane flux is called V90, where the unit is typically expressed in liters per square meter (L / m²). 2 ). Filter or membrane throughput is usually interchangeable with filter or membrane capacity.

[0035] Historically, asymmetric membranes were developed to achieve high flux, improving throughput compared to symmetric membranes. See U.S. Patent No. 4,261,834 to deWinter, which is hereby incorporated by reference in its entirety. The most common asymmetric membranes have a gradient structure, where the pore size gradually and continuously increases from one surface to another. See U.S. Patent No. 4,629,563 to Wrasidlo, which is hereby incorporated by reference in its entirety. Another type of asymmetric membrane structure has a trapping region within the asymmetric membrane, where the pore size decreases and then increases again. See U.S. Patent No. 4,933,081 to Sasaki et al., which is hereby incorporated by reference in its entirety. The benefits of “hourglass” asymmetric membranes include high flow rates and a reduced risk of trapping degradation due to surface scratches.

[0036] The permanent hydrophilic filter membrane of this application may have one or more distinct regions. For example, the membrane may have three distinct regions.

[0037] Generally, membranes with multi-region structures are scientifically more attractive because each region can be fine-tuned to achieve improved overall performance. A multi-region microfiltration membrane comprising at least one symmetrical retention region and at least one pre-filtration region was first patented using sequential casting. See U.S. Patent No. 5,620,790 to Holzki et al., which is hereby incorporated by reference in its entirety. As described in U.S. Patent No. 7,208,200 to Kools (also hereby incorporated by reference in its entirety), sequential casting can create a clear boundary or region with a dense, skin-like structure between the symmetrical retention region and the pre-filtration region. This can lead to a sharp decrease in membrane throughput due to particle buildup at the interface. Furthermore, as described in U.S. Patent No. 5,620,790 to Holzki, the morphology of the symmetrical intermediate region limits its own contribution to the resulting membrane throughput. U.S. Patent No. 7,208,200 to Kools (which is hereby incorporated by reference in its entirety) discloses a co-casting process that smooths the layer-to-layer transition and thus produces improved performance.

[0038] The membrane structure in each different region can be precisely customized by applying different mixtures according to the membrane performance requirements. Furthermore, each region can have its own characteristic morphology; there is no obvious interface between any two adjacent casting regions. The membrane morphology can be changed based on different casting mixtures and process conditions.

[0039] In another embodiment of this application, the total thickness of the membrane is 65-300 μm.

[0040] The membrane of this application may have one or more components independently selected from the group consisting of the following polymer matrix materials: PVDF, polyamides, polyimides, polyethersulfones, polysulfones, polyarylsulfones, cellulose, regenerated cellulose, cellulose esters, polyetherimides, acrylic polymers, methacrylic polymers, and copolymers of acrylic polymers and methacrylic polymers. Preferably, the membrane of this application comprises polyethersulfone and poly(2-ethyl-2-oxazoline).

[0041] As used herein, the term "polymer" means a polymer composition comprising one or more monomers. Representative suitable polymers for forming porous membranes include: polyolefins, such as polyethylene, polypropylene, polymethylpentene, and the like; polystyrene or substituted polystyrene; fluorinated polymers, including poly(tetrafluoroethylene), polyvinylidene fluoride, and the like; polysulfones, such as polysulfone, polyethersulfone, and the like; polyesters, including polyethylene terephthalate, polybutylene terephthalate, and the like; polyamides, including poly(hexamethylene adipamide), poly(p-phenylene terephthalamide), and the like; polyacrylates and polycarbonates; and vinyl polymers, such as polyvinyl chloride and polyacrylonitrile. Copolymers, such as copolymers of butadiene and styrene, fluorinated ethylene-propylene copolymers, ethylene-chlorotrifluoroethylene copolymers, and the like, may also be used.

[0042] In another embodiment of the permanent hydrophilic filter membrane of this application, the polyoxazoline is selected from the group consisting of poly(2-ethyl-2-oxazoline), poly(2-methyl-2-oxazoline), and poly(2-propyl-2-oxazoline). In a more specific embodiment of the membrane of this application, the polyoxazoline is poly(2-ethyl-2-oxazoline).

[0043] The hydrophilic membrane of this application can be prepared using a casting solution containing one or more other hydrophilic polymers. Examples of hydrophilic polymers include polyacrylic acid, polyvinyl alcohol, polyvinyl acetate, polyvinylpyrrolidone, polyethylene glycol, polyvinylpyridine, polyethyleneimine, polyoxazoline, etc.

[0044] In one embodiment, an electron beam (e-beam) is used to crosslink the polymer, for example by the method described in U.S. Patent No. 4,944,879, which is hereby incorporated by reference in its entirety. Typically, the mesh or individual sample passes through an electron curtain generated by an electron beam processor. The processor delivers the desired dose at an accelerating voltage in the range of 100 kV to 200 kV. Typical dose ranges are from 20 kGy to about 150 kGy.

[0045] In another embodiment of the membrane of this application, the polyoxazoline can be crosslinked by an electron beam at a dose of about 20 kGy to 150 kGy.

[0046] Organic extractables are typically measured as total organic carbon (TOC). In one embodiment across all aspects of this application, the membrane-extractable total organic carbon is less than 20 μg C / cm³. 2 or less than 10 μgC / cm 2 .

[0047] The polymer casting solution of this application typically comprises at least one polymer and at least one solvent for one or more polymers. The casting solution may contain one or more components that are poor solvents or non-solvents for one or more polymers. Such components are sometimes referred to in the art as "porogens". The mixture is preferably homogeneous. It may optionally contain one or more components that are non-solvents for the polymer. The casting solution may remain stable over time (reaching good solvent quality) or remain metastable over time. This casting solution may also have a lower critical dissolution temperature or an upper critical dissolution temperature. Solvents used include dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, tetramethylurea, acetone, or dimethyl sulfoxide. A wide range of porogens have been used in the art, including formamide, various alcohols and polyhydroxy compounds such as water, various polyethylene glycols, and various salts such as calcium chloride and lithium chloride.

[0048] Examples of other additives include surfactants for further improving wettability and polymers compatible with primary membrane polymers used to modify the mechanical properties of the final membrane.

[0049] Examples of surfactants for manufacturing microporous membranes can be found in U.S. Patent No. 4,290,987 to Soehngen et al., U.S. Patent No. 4,298,666 to Taskier, and U.S. Patent No. 4,501,793 to Sarada, all of which are hereby incorporated by reference in their entirety. As is known in the art, surfactants can be coated onto membranes. One such example of a surfactant is disclosed in U.S. Patent No. 3,853,601 to Taskier, which is also hereby incorporated by reference in its entirety. The disclosed polyolefin microporous membrane (such as a polypropylene microporous membrane) is treated with a silicone glycol copolymer surfactant. The microporous membrane can be impregnated with a combination of a silicone glycol copolymer surfactant and a cationic imidazoline tertiary amine. Surfactants are applied to the polyolefin microporous membrane by contacting the membrane with a dilute solution of about 1 to 10% by weight of one or more surfactants in an organic solvent (such as acetone, methanol, ethanol, or isopropyl) to produce a "replenishment" of the microporous membrane by about 2 to about 20% by weight of the surfactant based on the weight of the uncoated microporous membrane.

[0050] U.S. Patent No. 4,501,793 to Sarada (the entire patent is hereby incorporated by reference) discloses the use of alkylphenoxy poly(vinyloxy)ethanol surfactants. The surfactants used have an HLB (hydrophilic-lipophilic balance) of about 10 to 15. Such surfactants are well known to those skilled in the art and are readily available commercially. Suitable surfactants include, for example, those produced by GAF under the trade name... The 500 and 600 series compounds for sale, such as RC-520, RC-620, RC-630, CO-520, CO-530, CO-610, CO-630, CO-660, CO-720, CA-520, CA-620, and CA-630. Pluronic surfactants can also be added to increase membrane hydrophilicity.

[0051] When comparing the properties of filter membranes, the most commonly used parameters are fluid permeability and bubble point. As used in this article, "permeability" is defined as the overall velocity of fluid flowing through a porous structure through a membrane under a unit pressure difference, typically expressed in liters per (m). 2 Permeability is measured in units of hr·psi. The most common fluids used to measure permeability are air and water.

[0052] As used herein, the "bubble point" is defined as the pressure of gas required to displace the liquid from the largest pores of a porous structure. A sample of the test material is immersed in a liquid that spontaneously fills the pores within the sample. A pressurized gas is then applied to one side of the sample. Initially, the gas does not flow through the sample because the pores are filled with liquid. However, as the gas pressure increases, the gas will displace the largest pores of the liquid at a certain pressure level, and the gas will begin to flow through the sample. The pressure at which the gas begins to flow through the sample is called the bubble point pressure.

[0053] The relationship between the size of the fluid-wetted cylindrical pore and the gas pressure (P, the bubble pressure in the cylindrical pore) required to vent it is as follows:

[0054] D=4γcosθ / P

[0055] Where D is the pore diameter, θ is the contact angle, and γ is the surface tension of the wetting liquid. When the measured bubble pressure can be empirically correlated with the actual membrane pore size, it provides an easily obtainable estimate of the actual non-cylindrical pore size.

[0056] The bubble point of the membrane was measured using a capillary flow porosimeter (model: CFP-1200AEX) manufactured by Porous Materials, Inc. Isopropanol was used as the test solution for the bubble point measurement.

[0057] Fracture strain is defined as the ratio of the film's elongation to its original length when the membrane fractures under stress. The fracture strain of the membrane was tested using a Zwick / Roell Z2.5 machine. Test samples measuring 1 inch × 4.5 inches were pre-cut from the left (L), center (C), and right (R) positions of a 10” wide membrane roll. The left and right samples were taken 1 inch from the membrane edge. The test samples were loaded onto the Zwick machine and then stretched under stress. Stress-strain curves were recorded until the fracture point. The reported value is the average of the test results for the L, C, and R samples. In other embodiments across all aspects of this application, the membrane fracture strain is at least 20%, at least 25%, or at least 30%.

[0058] In other embodiments of this application, the membrane can be pleated without reducing its retention performance. In more specific instances across all aspects of this application, the membrane is pleated.

[0059] As used herein, the term "pleated" or "pleated" is intended to encompass all such cross-sectional shapes. Pleated structures present a larger surface area to the incoming fluid process flow relative to the volume occupied than those presented by using a flat plate. This offers particular advantage when considering the expectation of maximizing device throughput.

[0060] The pleats of the membrane can be configured to be corrugated or spirally positioned, and can have an annular or folded cross-section, such as a W-shaped or M-shaped cross-section. The pleated membrane is typically wound along a vertical axis, and the ends of the pleated membrane are sealed to each other to form a tubular structure or filter tube. In another embodiment, the pleated membrane is sealed as a flat, corrugated filter within a frame sealed to its peripheral edges. In all embodiments, the pleated membrane is designed such that a liquid or gas must pass through the membrane to pass downstream of the membrane.

[0061] The bacterial retention properties of membranes can be tested using the ASTM F838-15 bacterial retention test method. In this test, worst-case processing conditions are used to determine the bacterial retention performance of a sterile filter per centimeter. 2 10% of the filter area is reserved 7 The minimum excitation capability of *Brevundimonas diminuta* (B. diminuta) was tested. Size control was performed for each test to ensure the size of the test organism was appropriate. For devices made with membranes rated at 0.2 μm pore size, it was important that the device be completely retained upon excitation with the *Brevundimonas diminuta* solution. If the membrane is weak enough, cracks will form during membrane folding. Therefore, high diffusivity will be observed in the device, and the device will not be completely retained. Because folding creates cracks, the probability of microorganisms such as *Brevundimonas diminuta* passing through these cracks increases, thus reducing the retention rate—a so-called "degradation" of the membrane retention properties.

[0062] A second aspect of this application relates to a filter cartridge comprising a housing and a membrane of this application located within the housing. The filter cartridge may include the membrane of this application in the form of a filter tube. In one embodiment of this application, the membrane of the filter cartridge is pleated. In another embodiment, the filter is spirally wound in one or more layers, with or without spacers between them. Furthermore, the cartridge may contain more than 0.11 m per inch of housing height. 2 The effective membrane area.

[0063] Figure 1 An example of the filter cartridge of this application is shown in the figure. Figure 1 The filter cartridge 2 comprises a pleated high-throughput membrane 4 of this application surrounding a porous hollow core 6, and is provided with a sealing cap 8 and a second cap 10 having an outlet 12. Optionally, an outer porous protective sleeve is spaced apart from and surrounds the outer surface of the membrane. Preferably, the sleeve is sealed by the sealing cap 8 and the second cap 10 to form an integral cartridge filter. If used, the sleeve holds the membrane in a relatively fixed tubular configuration. The sleeve may be made of a rigid material and have uniformly dispersed pores to allow fluid to flow inward from the peripheral region of the pleated filter tube, through the membrane, into the core 6, and then finally out through the outlet 12 to the second end cap 10.

[0064] U.S. Patent No. 5,736,044 to Proulx et al. provides further details regarding the construction and function of the replaceable filter cartridge. The pleated filter element can be used alone or in conjunction with a pre-filter. The pre-filter can be located within a housing adjacent to the fluid inlet, or it can be applied to a cartridge adjacent to the outer surface of the membrane.

[0065] Filter cartridges typically comprise a porous filter element housed within a structural housing. In such filters, unfiltered fluid enters the housing through an inlet port and passes through the filter element, which removes contaminants or other impurities from the fluid. The filtered fluid exits through an outlet port. Filter cartridges include "quick-change" cartridges, which typically have an inlet and outlet combined in a single port at one end of the housing, and inline cartridges, in which the inlet and outlet ports are located at opposite ends of the housing. Because the fluid flow is often pressurized, these ports are typically sealed, such as with O-rings or similar seals. Therefore, it is desirable to provide small ports, as larger openings are more difficult to seal (the larger the seal, the greater the force it withstands for a given pressure).

[0066] The housing can be constructed as a single piece or as two or more components structurally attached together to form an assembly. Using a single-piece housing reduces costs compared to multi-piece assemblies. Polymer single-piece housings can be manufactured using any suitable process, including gas- or water-assisted blow molding or injection molding. Blow molding is generally faster and cheaper than injection molding. Compared to injection molding, blow molding also stretches and aligns polymer chains, resulting in stronger and tougher material properties. Either method can produce hollow containers with internal dimensions larger than the desired throat or port size at the connection point, much like plastic bottles. Alternatively, the housing can be metallic and manufactured by casting or spin forming. Furthermore, while single-piece construction offers cost advantages, the housing can alternatively be produced as a two-piece (or more) assembly formed by injection molding or casting.

[0067] Preferably, the pleated filter tube is composed of at least one layer of the high-throughput membrane of this application. Preferably, the membrane is oriented such that fluid introduced into the housing through the fluid inlet begins to pass through the asymmetric membrane via the open side of the asymmetric membrane. Figure 2 One such design is illustrated. Cylinder 2 is located within housing 14. As indicated by arrow 26, the fluid to be filtered, whether liquid or gas, enters through the first port or inlet port 16 to enter the interior of housing 14. As indicated by arrows 20 and 22, the fluid flows through the outer surface 18 of cylinder 2 towards the core and exits through the second port 12 or outlet of housing 14 as indicated by arrow 24. If desired, the fluid flow can be reversed, with the second port 12 acting as the inlet and the first port 16 as the outlet. Fluid can flow from the second port 12 through the core and membrane, across the outer surface 18 of cylinder 2 to the interior of housing 14, and out through the first port 16.

[0068] Another aspect of this application relates to a method for forming a permanent hydrophilic filter membrane. The method involves providing one or more casting solutions comprising a polymer of polyoxazoline and a solvent. The one or more solutions are then applied simultaneously or sequentially to a carrier to form a liquid membrane. Phase separation of the one or more casting solutions is achieved in the liquid membrane to form a membrane. The membrane is immersed in water or an aqueous solution. The wet membrane is treated with an electron beam to crosslink the polyoxazoline, and the permanent hydrophilic filter membrane is separated from the carrier.

[0069] In one embodiment of the method for forming the membrane of this application, the aqueous solution is selected from water and a mixture of one or more multifunctional monomers, including methylenebisacrylamide, Sartomer 9035, and tetra(ethylene glycol) diacrylate, etc.

[0070] In one embodiment of the method for forming a permanent hydrophilic filter membrane, the polyoxazoline is selected from the group consisting of poly(2-ethyl-2-oxazoline), poly(2-methyl-2-oxazoline), and poly(2-propyl-2-oxazoline). In a more specific example, the polyoxazoline is poly(2-ethyl-2-oxazoline). The ratio of polyoxazoline to PES in the formulation can range from 5 wt% to 50 wt%, and in one example, the ratio of polyoxazoline to PES is in the range of 8 wt% to 12 wt%. The polyoxazoline of the membrane can be crosslinked by an electron beam at a dose of about 20 kGy to 150 kGy.

[0071] The casting solution may further comprise one or more independently selected from the group consisting of: formamide, alcohols, polyhydroxy compounds, water, polyethylene glycol, calcium chloride, and lithium chloride. In one embodiment of this application, the casting solution comprises polyethersulfone, N-methyl-2-pyrrolidone, triethylene glycol, and poly(2-ethyl-2-oxazoline).

[0072] The casting solution may have an upper critical dissolution temperature, which allows phase separation to be achieved by cooling the casting solution below its upper critical dissolution temperature. Alternatively, the casting solution may have a lower critical dissolution temperature, which allows phase separation to be achieved by heating the casting solution above its lower critical dissolution temperature. Furthermore, the phase separation can also be achieved through vapor-induced phase separation.

[0073] The casting of permanent hydrophilic membranes can be performed sequentially. Alternatively, casting can be performed simultaneously, such as through co-casting.

[0074] When forming a multi-region membrane, different mixtures of different regions can be formed by changing the concentration of the polymer, solvent or non-solvent, as well as the viscosity of the solution, additives or treatments, or any combination of these, to produce the desired multi-region structure.

[0075] Choosing a solvent to provide a stable, homogeneous solution for casting involves the fundamental principles of polymer solubility. Polymer solvents can be classified as good solvents, non-solvents, and poor solvents. A good solvent is one where the interaction (force) between polymer molecules and solvent molecules is greater than the attraction between one polymer molecule and another. A non-solvent is the opposite. A poor solvent is one where the interaction between the polymer and solvent is equal to the attraction between one polymer molecule and another.

[0076] Typically, multi-region structures can be formed from the same polymer and solvent by varying the concentration, viscosity, additives, and treatment (before, during, or after formation) of the components in the mixture. Alternatively, different polymers can be used for different regions. When using different polymers, compatible polymers must be selected. Furthermore, if possible, the solvent and phase-separating material should be identical or at least compatible so as not to adversely affect other regions.

[0077] Several methods exist for preparing porous polymer structures. The most common method is based on phase separation of the polymer solution. In this type of method, the composition or temperature of the polymer solution changes, making it thermodynamically unstable and causing it to separate into two phases. One phase, containing most of the solvent components, is then removed, while the other phase, containing most of the polymer, becomes the porous structure. Phase separation methods are generally classified into three categories: 1) Vapor-induced phase separation (VIPS), also known as "dry casting" or "air casting"; 2) Liquid-induced phase separation (LIPS), mainly called "immersion casting" or "wet casting"; and 3) Thermally induced phase separation (TIPS), commonly referred to as "melt casting".

[0078] VIPS and LIPS methods rely on mass transfer between the components of a cast polymer solution or mixture and the precipitate medium, which exists in a vapor or liquid state, respectively. TIPS is controlled by temperature variations in the polymer solution. The VIPS method inherently suffers from low mass transfer rates, resulting in long residence times required in the casting machine, leading to a trade-off between long machines with high capital investment and low process rates. The LIPS method operates at relatively high rates because of the higher mass transfer between the polymer solution and the liquid precipitate. While this is an advantage in LIPS methods used to manufacture ultrafiltration and reverse osmosis membranes that require high mass transfer rates to produce small pore sizes, it is complex in methods used to fabricate microporous structures, which typically require moderate mass transfer rates to allow sufficient growth of the dilute phase to form larger pore sizes in the 0.05–10 micrometer range. Several methods have been devised in the prior art to overcome this complexity in order to fabricate microporous structures using the LIPS method. The use of high concentrations of organic solvents or pure organic solvents, as described in U.S. Patent No. 4,203,847 to Grandine and U.S. Patent No. 4,340,479 to Pall (both U.S. Patents are hereby incorporated in their entirety), is a common method in immersion baths. This principle is well analyzed in Wijmans et al., *Journal of Membrane Science*, 14, 263 (1983), which is hereby incorporated in its entirety. The disadvantages of this technique are the use of large quantities of flammable organic liquids requiring explosion-proof manufacturing facilities and the high cost of solvent handling.

[0079] As taught in U.S. Patent No. 5,444,097 to Tkacik (which is hereby incorporated herein by reference in its entirety), the membrane is made of a polymer mixture exhibiting a lower critical dissolution temperature (“LCST”) as measured by cloud point. Heating the mixture above the LCST results in phase separation. This phase separation step is incorporated into the method for membrane pore size control of this application. A vapor-induced phase separation step is also incorporated herein. Dew point and vapor temperature will affect the membrane pore formation process and thus allow for corresponding control of the pore size.

[0080] The method of this application utilizing the LCST process begins with the preparation of a homogeneous mixture of at least one polymer in a solvent system comprising at least one component, which is a solvent for the polymer, wherein the homogeneous solution exhibits a lower critical dissolution temperature. The homogeneous mixture may optionally contain one or more components, which are non-solvents for the polymer. The mixed solution can be prepared by conventional methods, i.e., mixing the polymer with the components of the solvent system. Next, the polymer mixture is shaped into a desired form. The shaped mixture is then heated until phase separation occurs, indicated by turbidity of the solution. The components of the solvent system are then removed by methods such as evaporation or extraction. The conditions of the removal process may further affect the later stages of phase separation and influence the properties of the polymer's porous structure. A preferred method for removing the components of the solvent system involves immersing the shaped, phase-separated polymer mixture in one or more liquid baths comprising at least one non-solvent for the polymer, which is miscible with at least one component of the solvent system. The porous polymer structure may then optionally be subjected to further extraction or drying.

[0081] As taught in U.S. Patent No. 7,842,214 to Romdhane et al. (which is hereby incorporated herein by reference in its entirety), vapor-induced phase separation (i.e., air casting) typically involves a condenser (e.g., water vapor) for inducing a phase inversion. The condenser can be introduced as a vapor into the polymeric material of the membrane. High concentrations of vapor may condense and reduce the thermodynamic stability of the polymeric material dissolved in the solvent. Similar to liquid-induced phase separation, vapor-induced phase inversion creates polymer-rich and polymer-poor regions, resulting in the formation of microstructures. Examples of condensers for vapor-induced phase separation include water, alcohols, amides, and combinations thereof.

[0082] Contact between polymer and accelerator vapors at the surface, and the diffusion of some of the accelerator into the polymer solution, can cause the polymer material to become thermodynamically unstable. The polymer material can precipitate from the solvent in the solution, thus forming microstructures. During phase inversion, regions of the polymer solution layer are enriched with the polymer material that forms the structures, while some regions lack the polymer material that forms pores. After microstructure formation, the membrane can be further subjected to solvent removal and subsequent drying.

[0083] After the polymer mixture is prepared, it is applied to a moving carrier. For carrier-free membranes that do not have a mesh attached to the final membrane, the carrier is typically a plastic film, such as polyethylene terephthalate or polyethylene-coated paper, or a similar smooth, continuous mesh that can be easily removed from the formed membrane.

[0084] In one embodiment of this application, the membrane is produced via a co-casting process. "Co-casting" means that the regions are cast substantially simultaneously with each other, with virtually no time interval between casting regions. Co-casting is an important aspect of this application because it allows for the formation of controlled pore size regions at the junctions of the regions. In other casting techniques known in the prior art, a clear boundary line is formed between sequentially cast regions. The abrupt change in pore size from a more open to a denser structure can lead to undesirable rapid accumulation of particles at the interface and / or the formation of skin regions at the boundary points, thus resulting in a sharp drop in flux. A distinct interface can be replaced by a more subtle variation in pore size between two adjacent regions, possibly due to partial mixing of adjacent co-cast coatings or due to high shear forces at the interface between two adjacent co-cast coatings. Such interface regions are beneficial for the overall retention behavior of the membrane structure. Simultaneously, it allows for the formation of a microporous structure without discernible boundaries within the structure.

[0085] The application of polymer mixtures can be performed by any standard method. The aim is to coat a first mixture onto a carrier, a second mixture onto the first, and a third onto the second. A preferred method is co-casting, which is described in detail in U.S. Patent No. 8,123,992 to Kools, which is hereby incorporated by reference in its entirety. Co-casting can be performed using a three-roller liner apparatus, a pressurized three-groove coating bead, or any other pre-measured or post-metered coating apparatus known in the industry. Co-casting generally allows for the formation of controlled aperture zones at the junctions of the regions; however, even with co-casting techniques, a clear or well-defined boundary can be formed between regions if desired by proper selection of materials and application methods.

[0086] Figure 3A multi-zone forming apparatus 28 for casting multi-zone membranes is shown. As illustrated, apparatus 28 is designed to produce a three-zone liquid film and has three chambers 30, 32, and 34, each containing solution A, solution B, and solution C, with each zone containing one solution for casting. Additional chambers can be added to form additional co-cast zones if desired. The apparatus includes a front wall 36 and a rear wall 42, with partition walls 38 and 40 between the front and rear walls. The partition walls define the volumes of the three chambers. Two side walls complete the apparatus. In operation, the apparatus is fixed to a typical membrane casting machine, and a carrier mesh 50 moves or passes beneath the fixed apparatus, and the three solutions are distributed through gaps or outlets 44, 46, and 48. The thickness of the zone is controlled by the distance (gap) set between the moving mesh and the outlet, as shown by the gap settings 44, 46, and 48. The final liquid zone thickness is a function of the gap distance, solution viscosity, and mesh velocity. The rear wall of the device is typically maintained at a short distance above the carrier to prevent the carrier from wrinkling or being damaged. In practice, the rear wall clearance, carrier velocity, and solution viscosity are adjusted to prevent solution leakage through the rear wall clearance. If required by solution characteristics, or for further control over the final membrane properties, the device may be equipped with individual heating or cooling components for each chamber, or with heating or cooling components for the entire device.

[0087] The die consists of a closed reservoir and an outlet channel with a small cross-section. An extruder or positive displacement pump, or in some cases, a pressurized vessel, feeds the coating into the reservoir at a uniform rate, and all fluid entering the die is extruded from the reservoir under pressure through the channel and transferred to a moving carrier mesh. The channel is positioned perpendicular to the moving carrier mesh. Multi-zone coating requires a die with an independent reservoir and associated feeding methods, as well as an outlet channel for each zone.

[0088] The membrane of this application can be produced using a pre-metered coating process. A pre-metered coating is a coating in which an exact amount of coating solution to be deposited is directed to the coating head. The height of the zone is set by deposition rather than by some post-application component, such as a scraper that sets the structural thickness after the zone metering (often referred to as a "post-metering process"). Pre-metering is applicable to mold coating, as well as sliding coating and curtain coating, and other methods of forming structures.

[0089] After the area is coated onto a moving carrier, the nascent membrane is immediately exposed to the environment of a controlled gas chamber. Thermally induced phase separation can be initiated by a controlled roller temperature, while moisture-induced phase separation may begin due to moisture absorbed from the gas chamber. The nascent membrane is then immersed in a liquid that is a non-solvent for the polymer and miscible with both the solvent and the pore-forming agent. This results in non-solvent-induced phase separation and ultimately the formation of a porous membrane. Water is an example of a non-solvent liquid that can be used for nascent membranes.

[0090] The resulting composite membrane is then typically separated from the carrier and washed to remove residual solvents and other materials. The membrane is then dried. It can be washed with water or dried using a vacuum drum dryer.

[0091] In the coagulation of multi-zone liquid films, coagulation begins at the surface of the liquid film that first contacts the coagulation bath and then proceeds through subsequent zones of the multi-zone liquid film. As the coagulant diffuses through these zones, each zone dilutes and alters the coagulant. Such changes in the properties of the coagulant affect the formation of each zone and the final multi-zone membrane. The thickness, composition, and location of each zone relative to the others will influence the membrane structure and properties. Each zone forms differently from zones made from single-zone solutions or single-zone laminates.

[0092] In another embodiment, the regions are sequentially cast onto previous castings. In sequential casting, a solution comprising a polymer is typically cast into the film, one over the other, followed by quenching in a non-solvent for the polymer. A first solution is applied in the region (bottom region) onto a carrier (such as a non-porous carrier), and a second solution is applied in the region (upper region) onto the first solution, and so on. Subsequently, the film can be separated from the carrier after quenching; however, if desired, the carrier (porous or non-porous) can be incorporated into the final structure.

[0093] The membrane can be cast manually (e.g., by hand pouring, casting, or coating onto a casting surface and applying quenching fluid to the surface) or automatically (e.g., by pouring or otherwise casting onto a moving bed). There should be a time interval between castings of the solution. Preferably, the time interval is about 2 seconds or longer. For example, the time interval can range from about 2 seconds to about 35 seconds or from about 2 seconds to about 10 seconds.

[0094] Various devices known in the art can be used for casting. Suitable devices include, for example, mechanical coaters comprising a doctor blade, scraper, or spray / pressurization system. An example of a coating apparatus is an extrusion die or trough coater comprising a casting chamber into which the casting formulation (including a solution of polymer) can be introduced and extruded under pressure through a narrow trough.

[0095] The carrier, on which the casting solution is placed, is then immersed in a quenching bath to achieve phase separation of the polymer solution. In the quenching bath, precipitation or coagulation begins at the surface of the liquid film that first contacts the bath and then proceeds through subsequent regions. After formation, the film is typically washed (e.g., in deionized water) to remove residual solvent and then dried.

[0096] The permanently hydrophilic membrane of this application can be used for terminal filtration such as sterile filtration and virus filtration, as well as tangential flow filtration, such as ultrafiltration in the life sciences industry. It can also be used in other industrial applications requiring separation media.

[0097] Without crosslinking PEOX into a hydrophilic membrane using the method described in this application, the resulting membrane will have a high TOC. Furthermore, the resulting membrane will not possess permanent hydrophilicity. The e-bundle crosslinking method permanently establishes hydrophilicity and reduces TOC without compromising mechanical properties.

[0098] Unless the context otherwise requires, preferences and options for a given aspect, feature, embodiment, or parameter of the technology described herein should be considered as having been disclosed together with any and all preferences and options for all other aspects, features, embodiments, and parameters of the technology.

[0099] The following examples are presented to illustrate various aspects of this application, but are not intended to limit the scope of the claimed application.

[0100] Example

[0101] Materials and methods

[0102] After the membrane was modified by e-beam, its properties, including TOC, flow time, wetting time, and fracture strain, were tested.

[0103] e-beam modification

[0104] The membrane was modified by electron beam irradiation (EBLab, Comet Technologies) using an accelerating voltage of 200 kV and a dose exposure ranging from approximately 20 kGy to 150 kGy. The membrane was fed into the e-beam irradiation chamber at a speed of 3–15 m / min. The e-beam irradiation chamber was inertized with nitrogen. After e-beam irradiation, the membrane was washed sequentially with methanol and water and dried before further characterization.

[0105] Extractable / leaching results

[0106] Extractable / leached substances in water were characterized by the amount of TOC (total organic carbon). A 47 mm pan for each membrane sample was die-cut and autoclaved at 126°C for 1 hour, then immersed in 40 g of water at ambient temperature for 24 hours. The TOC of the extracted solutions was tested using a Sievers Model 900 TOC analyzer. TOC standards were prepared using potassium hydrogen phthalate, a 1000 ppm carbon stock solution, and diluted with water to 10 ppm carbon.

[0107] Wetting time

[0108] The membrane was baked in air at 135°C for 2 hours and then cooled to ambient temperature before testing the wetting time. The wetting time was determined by wetting the membrane with a 10% NaCl solution according to the following procedure: A drop of 10% NaCl solution (30 μL–60 μL) was placed on the membrane surface, and the wicking time into the membrane was recorded in seconds. Measurements were continued until the membrane beneath the NaCl solution drop was completely wetted.

[0109] Flowing time

[0110] After e-beam treatment, the membrane was dried at 70°C for 1 hour, and then the flow time was tested (the time it takes for 500 ml of water to pass through a 47 mm membrane at a pressure of -25 Hg; flow time is inversely proportional to permeability).

[0111] Bubble Point Test

[0112] A 25 mm membrane disc was die-cut, and isopropyl alcohol (IPA) or Galwick alcohol was used as a wetting agent for the membrane bubble point test. The test was performed using a capillary flow porosimeter manufactured by Porous Materials (CFP-1200 / AEX). The bubble point is inversely proportional to the pore size and is used to indicate the pore size of the membrane.

[0113] Fracture strain test

[0114] Membrane sample strips measuring 1 inch × 4.5 inches were cut from the left, center, and right sides of the membrane roll, and the breaking strain was measured using a Zwick / Roell Z2.5 machine. Test samples were pre-cut from the left (L), center (C), and right (R) positions of a 10” wide membrane roll. Both left and right samples were taken 1 inch from the membrane edge. The reported value is the average of the test results for the L, C, and R samples. Testing was conducted at 23°C and 18–25% relative humidity. 0.98 N was used for load sensor performance checks, and a preload of 0.05 N was applied during testing. Flat clamps with a clamp pressure of 30 psi and a distance of 1.5 inches between the clamps were used. The test speed was 2 inches per minute. Data were collected when the membrane was stretched to its breaking point.

[0115] Example 1 - Permanent hydrophilic membrane using water as an immersion agent during e-beam modification

[0116] A permanent hydrophilic membrane with a bubble point of 20 psi (IPA, PMI) was prepared by three-tank casting using a blend of polyethersulfone and PEOX (Aquazol 500, Polymer Chemistry Innovations, Inc.), and then crosslinked by e-beam irradiation after immersion in water.

[0117] Three mixtures, comprising a top mixture, a middle mixture, and a bottom mixture, were prepared according to the formulations in Table 1. The formulations included polyethersulfone (Sumitomo PES 5200P), N-methyl-2-pyrrolidone (NMP), triethylene glycol (TEG), and PEOX. All three mixtures were tested, and viscosity and cloud point data are further presented in Table 1. The nascent membrane was cast onto a mylar support on top of a casting roller using a three-slot mold. The flow rates were 2.8 L / h for the top mixture, 33.7 L / h for the middle mixture, and 5.6 L / h for the bottom mixture. The nascent membrane was partially formed on the casting roller by controlling air exposure conditions and roller temperature. The nascent membrane was cured in a forming bath and then extracted in hot water. Process conditions are shown in Table 2. The membrane was finally dried before performance testing. The properties of the cast film (RSG2701L) (including flow time, bubble point and fracture strain) were tested, and the results are shown in Table 3.

[0118] Table 1: Mixtures of RSG2701L membranes with cloud point and viscosity data

[0119] Mixtures Top Mixture Middle mixture Bottom Mixture PES (wt%) 10.9 16.5 14.0 PEOX (wt%) 1.3 2.0 1.7 NMP (wt%) 30.1 29.2 29.6 TEG (wt%) 57.7 52.3 54.7 Cloud point (°C) 48.7 49.6 48.3 Viscosity (cP) 1495 10918 4739

[0120] Note: Viscosity was measured at 35°C using a Brookfield viscometer (LVDV-II+P) with an S62 spindle at 10 rpm.

[0121] Table 2: Casting conditions for RSG2701L membrane

[0122]

[0123] The RSG2701L membrane was pre-wetted by immersing it in water, and then e-beam modified with different doses. The e-beam modified membranes were rinsed with methanol, then with water, and finally dried before performance testing. Table 3 discloses the properties of the e-beam modified membranes, including TOC, flow time, wetting time, bubble point, and fracture strain. It is evident that e-beam modification significantly reduces TOC from approximately 40 μg C / cm³ when the e-beam dose is equal to or greater than 50 kGy. 2 Reduced to less than 6 μgC / cm 2 Equally important, when the membrane is modified with e-beams, the flow time can be significantly shortened. Furthermore, within the e-beam dosage range studied here, e-beam modification does not affect the bubble point or fracture strain.

[0124] Table 3: Performance of RSG2701L membrane modified by e-beam when water is used as the coating solution

[0125]

[0126] Data unavailable.

[0127] Example 2 - Permanent hydrophilic membranes using N,N'-methylenebisacrylamide solution as an impregnating agent during e-beam modification.

[0128] The permanent hydrophilic membrane with a bubble point of 20 psi (IPA, PMI) was prepared by triple casting with a mixture of PES and PEOX and then crosslinked by e-beam irradiation after pre-wetting with a solution of N,N'-methylenebisacrylamide (MBAm, Millipore Sigma catalog number 146072).

[0129] Instead of water, the RSG2701L membrane (prepared as in Example 1) was pre-wetted in aqueous solutions of different concentrations of MBAm and then modified by exposure to an e-beam dose of 50 kGy. MBAm is a crosslinking agent that exhibits hydrophilicity once crosslinked on the membrane surface. Membrane properties, including TOC, flow time, wetting time, and fracture strain, were tested, and the results are shown in Table 4. Incorporation of MBAm significantly improved wettability while having little effect on TOC and fracture strain. The effect on flow time was also minimal when the MBAm concentration was below 0.4%. Permanent hydrophilicity was demonstrated, as shown in Table 8 of Example 4.

[0130] Table 4: Performance of RSG2701L membrane modified by e-beam when used as a coating solution in MBAm aqueous solution

[0131]

[0132] Example 3 - Permanent hydrophilic membranes using Sartomer 9035 solution as an impregnating agent during e-beam modification

[0133] The permanently hydrophilic membrane with a bubble point of 32 psi (IPA, PMI) was prepared by three-tank casting of a mixture of PES and PEOX and then crosslinked by e-beam irradiation after pre-wetting with a Sartomer 9035 (SR9035, Arkema Group) solution.

[0134] A hydrophilic three-zone membrane (RSI2318P) with a bubble point of 32 psi (IPA, PMI) was prepared according to the method described in Example 1. Tables 5 and 6 list the mixing formulations and casting conditions used for this membrane. After casting, the membrane (RSI2318P) was pre-wetted in solutions of different concentrations of Sartomer 9035 (SR9035) and then modified by exposure to e-beams at a dose of 50 kGy. The SR9035 solution improved the wettability of the membrane while having little effect on the TOC. Membrane performance data are listed in Table 7.

[0135] Table 5: Mixtures of RSI2318P membranes with cloud point and viscosity data

[0136] Mixtures Top Mixture Middle mixture Bottom Mixture PES (wt%) 13 17.5 14.5 PEOX (wt%) 1.3 1.75 1.45 NMP (wt%) 29.21 29.8 32.16 TEG (wt%) 56.49 50.95 51.89 Cloud point (°C) 47.6 54.1 60.5 Viscosity (cP) 3089 13047 3779

[0137] Note: Use a Brookfield viscometer (LVDV-II+P) to measure viscosity at 35°C with an S62 spindle at 10 rpm.

[0138] Table 6: Casting conditions for membrane RSI2318P

[0139]

[0140] Table 7: Performance of e-beam modified RSI2318P membrane when SR9035 aqueous solution is used as coating solution

[0141]

[0142] When the concentration of Sartamomer 9035 is 0.8 wt% or higher, its concentration may negatively affect the membrane flow rate. However, after e-beam exposure and rinsing with methanol and water, the membrane exhibits good hydrophilicity. Permanent hydrophilicity has been demonstrated, as shown in Table 8 of Example 4.

[0143] Example 4 - Permanent hydrophilicity test using methanol extraction

[0144] To confirm whether the e-beam-modified membranes are permanently hydrophilic, the modified membranes were subjected to Soxhlet extraction with methanol for 48 hours. Table 8 includes the wetting times before and after the 48-hour Soxhlet extraction in methanol. Clearly, the membranes without e-beam exposure lost their hydrophilicity after methanol extraction, showing wetting times >30 seconds. This is because PEOX in the membrane is filtered out during methanol extraction. In contrast, the e-beam-modified membranes retained their original hydrophilicity, as indicated by wetting times <4 seconds after methanol Soxhlet extraction. This suggests that the hydrophilicity of the e-beam-modified membranes is stable.

[0145] Table 8: Membrane wetting time before and after 48 hours of Soxhlet extraction in methanol.

[0146]

[0147] Although preferred embodiments have been described and illustrated in detail herein, it will be apparent to those skilled in the art that various modifications, additions, substitutions, etc., may be made without departing from the spirit of this application, and therefore such modifications, additions, substitutions, etc., are considered to be within the scope of this application as defined in the following claims.

Claims

1. A carrier-free, permanently hydrophilic filter membrane, comprising: Polymer matrix materials; and A cross-linked polyoxazoline hydrophilic additive, wherein the cross-linked polyoxazoline hydrophilic additive is blended throughout the matrix material, and the permanently hydrophilic filter membrane has a C / cm² content of less than 20 μg. 2 The total extractable organic carbon content. The permanent hydrophilic filter membrane is formed by a method comprising the following steps: One or more casting solutions are provided, the casting solutions comprising a polymer of polyoxazoline and a solvent; Simultaneously or sequentially, the casting liquid or solution is applied to the carrier to form a liquid film; Phase separation of one or more of the casting solutions is achieved in the liquid film to form a film; Immerse the membrane in water or an aqueous solution; The wet film was treated with an electron beam to crosslink the polyoxazoline; as well as The permanent hydrophilic filter membrane is separated from the carrier.

2. The permanent hydrophilic filter membrane according to claim 1, wherein the membrane is a microporous membrane.

3. The permanent hydrophilic filter membrane according to claim 1, wherein the membrane is an ultrafiltration membrane.

4. The permanent hydrophilic filter membrane according to claim 1, wherein the extractable total organic carbon content is less than 10 μgC / cm³. 2 .

5. The permanent hydrophilic filter membrane according to claim 1, wherein the polyoxazoline is selected from the group consisting of poly(2-ethyl-2-oxazoline), poly(2-methyl-2-oxazoline), and poly(2-propyl-2-oxazoline).

6. The permanent hydrophilic filter membrane according to claim 5, wherein the polyoxazoline is poly(2-ethyl-2-oxazoline).

7. The permanent hydrophilic filter membrane according to claim 1, wherein the polyoxazoline is cross-linked by an electron beam at a dose of 20 kGy to 150 kGy.

8. The permanent hydrophilic filter membrane according to claim 1, wherein the polymer matrix material is one or more polymers independently selected from the group consisting of: PVDF, polyamides, polyimides, polysulfones, cellulose esters, polyetherimides, acrylic polymers, methacrylic polymers, and copolymers of acrylic polymers and methacrylic polymers.

9. The permanent hydrophilic filter membrane according to claim 1, wherein the polymer matrix material is one or more polymers independently selected from the group consisting of: PVDF, polyamides, polyimides, polyethersulfones, polyarylsulfones, cellulose esters, polyetherimides, acrylic polymers, methacrylic polymers, and copolymers of acrylic polymers and methacrylic polymers.

10. The permanent hydrophilic filter membrane according to claim 1, wherein the membrane comprises polyethersulfone and poly(2-ethyl-2-oxazoline).

11. The permanent hydrophilic filter membrane according to claim 1, wherein the membrane is symmetrical.

12. The permanent hydrophilic filter membrane according to claim 1, wherein the membrane is asymmetric.

13. The permanent hydrophilic filter membrane according to claim 1, wherein the membrane has a breaking strain of at least 20%.

14. The permanent hydrophilic filter membrane according to claim 1, wherein the membrane has a breaking strain of at least 25%.

15. The permanent hydrophilic filter membrane according to claim 1, wherein the membrane has a breaking strain of at least 30%.

16. The permanent hydrophilic filter membrane according to claim 1, wherein the membrane has one or more distinct regions.

17. The permanent hydrophilic filter membrane according to claim 16, wherein the membrane has three distinct regions.

18. The permanent hydrophilic filter membrane according to claim 1, wherein the total thickness of the membrane is from 65 μm to 300 μm.

19. The permanent hydrophilic filter membrane according to claim 1, wherein the membrane is pleated.

20. A filter cartridge comprising: shell; as well as The membrane according to claim 1 is located within the outer casing.

21. The cartridge according to claim 20, wherein the total extractable organic carbon content is less than 10 μg C / cm³. 2 .

22. The cartridge according to claim 20, wherein the polyoxazoline is selected from the group consisting of poly(2-ethyl-2-oxazoline), poly(2-methyl-2-oxazoline), and poly(2-propyl-2-oxazoline).

23. The cartridge according to claim 22, wherein the polyoxazoline is poly(2-ethyl-2-oxazoline).

24. The tube of claim 20, wherein the polyoxazoline is crosslinked by an electron beam at a dose of 20 kGy to 150 kGy.

25. The cylinder of claim 20, wherein the polymer matrix material is one or more polymers independently selected from the group consisting of: PVDF, polyamides, polyimides, polysulfones, cellulose esters, polyetherimides, acrylic polymers, methacrylic polymers, and copolymers of acrylic polymers and methacrylic polymers.

26. The cylinder of claim 20, wherein the polymer matrix material is one or more polymers independently selected from the group consisting of: PVDF, polyamides, polyimides, polyethersulfones, polyarylsulfones, cellulose esters, polyetherimides, acrylic polymers, methacrylic polymers, and copolymers of acrylic polymers and methacrylic polymers.

27. The cartridge of claim 20, wherein the membrane comprises polyethersulfone and poly(2-ethyl-2-oxazoline).

28. The cylinder of claim 20, wherein the breaking strain of the membrane is greater than 20%.

29. The cylinder according to claim 28, wherein the breaking strain of the membrane is greater than 25%.

30. The cylinder according to claim 29, wherein the rupture strain of the membrane is greater than 30%.

31. The filter cartridge of claim 20, wherein the outer casing has a height greater than 0.11m per inch. 2 The effective membrane area.

32. A method for forming a permanent hydrophilic filter membrane according to claim 1, the method comprising: One or more casting solutions are provided, the casting solutions comprising a polymer of polyoxazoline and a solvent; Simultaneously or sequentially, the casting liquid or solution is applied to the carrier to form a liquid film; Phase separation of one or more of the casting solutions is achieved in the liquid film to form a film; Immerse the membrane in water or an aqueous solution; The wet film was treated with an electron beam to crosslink the polyoxazoline; as well as The permanent hydrophilic filter membrane is separated from the carrier.

33. The method of claim 32, wherein the aqueous solution is selected from a mixture of water and one or more polyfunctional monomers.

34. The method of claim 33, wherein the one or more monomers are methylenebisacrylamide, Sartamomer 9035, tetra(ethylene glycol) diacrylate, and mixtures thereof.

35. The method of claim 33, wherein the extractable total organic carbon content is less than 10 μg C / cm³. 2 .

36. The method of claim 32, wherein the polyoxazoline is selected from the group consisting of poly(2-ethyl-2-oxazoline), poly(2-methyl-2-oxazoline), and poly(2-propyl-2-oxazoline).

37. The method of claim 36, wherein the polyoxazoline is poly(2-ethyl-2-oxazoline).

38. The method of claim 32, wherein the polyoxazoline is crosslinked by an electron beam at a dose of 20 kGy to 150 kGy.

39. The method of claim 32, wherein the casting solution comprises polyethersulfone, N-methyl-2-pyrrolidone, triethylene glycol and poly(2-ethyl-2-oxazoline).

40. The method of claim 32, wherein the fracture strain of the membrane is greater than 20%.

41. The method of claim 40, wherein the fracture strain of the membrane is greater than 25%.

42. The method of claim 40, wherein the fracture strain of the membrane is greater than 30%.

43. The method of claim 32, wherein the polymer is one or more polymers independently selected from the group consisting of: PVDF, polyamides, polyimides, polysulfones, cellulose esters, polystyrene, polyetherimides, acrylic polymers, methacrylic polymers, and copolymers of acrylic polymers and methacrylic polymers.

44. The method of claim 32, wherein the polymer is one or more polymers independently selected from the group consisting of: PVDF, polyamides, polyimides, polyethersulfones, polyarylsulfones, cellulose esters, polystyrene, polyetherimides, acrylic polymers, methacrylic polymers, and copolymers of acrylic polymers and methacrylic polymers.

45. The method of claim 32, further comprising: The membrane is then folded.

46. ​​The method of claim 32, wherein the casting solution has an upper critical dissolution temperature, and wherein the phase separation is achieved by cooling the solution to below its upper critical dissolution temperature.

47. The method of claim 32, wherein the casting solution has a lower critical dissolution temperature, and wherein the phase separation is achieved by heating the solution to a temperature above its lower critical dissolution temperature.

48. The method of claim 32, wherein the phase separation is achieved by vapor-induced phase separation.

49. The method of claim 32, wherein the casting solution further comprises one or more independently selected from the group consisting of: formamide, alcohol, water, calcium chloride, and lithium chloride.

50. The method of claim 32, wherein the casting solution further comprises one or more independently selected from the group consisting of: formamide, polyhydroxy compounds, water, calcium chloride, and lithium chloride.

51. The method of claim 32, wherein the casting solution further comprises one or more independently selected from the group consisting of: formamide, water, polyethylene glycol, calcium chloride, and lithium chloride.

52. The method of claim 32, wherein the application of the casting solution is performed sequentially.

53. The method of claim 32, wherein the application of the casting solution is performed simultaneously.

54. The method of claim 52, wherein the application of the casting solution is performed by co-casting.

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