Surface modification of hydrophobic films

Abstract

1. A porous polymer membrane comprising a porous membrane having an average pore size between about 0.001-10.0 microns formed with a first polymer, the substrate having a surface modified with a crosslinked second polymer formed from a polymerizable fluorine-containing monomer containing continuous chains of 5 or less carbon atoms along with fluorine atoms, the monomer being polymerized and crosslinked on the membrane, the membrane containing less than 25 ppb of C6PFCA (perfluorocarboxylic acid), less than 25 ppb of C8PFCA, and less than 25 ppb of combined C9-14PFCA.

Description

Technical Field

[0001] This application claims the benefit of priority to U.S. Provisional Application No. 63 / 285,322, filed Dec. 2, 2021, which is hereby incorporated by reference in its entirety.

[0002] This application relates to membranes for use in the life sciences industry. In particular, embodiments of the technology disclosed herein relate to hydrophobic membranes useful for filtration applications.

[0003] A This disclosure relates to membranes, such as porous membranes further comprising a hydrophobic surface. More specifically, this disclosure relates to microporous or ultrafiltration membranes modified to create a hydrophobic surface including the membrane pore surface, and processes for forming such membranes.

Background Art

[0004] Polytetrafluoroethylene (PTFE) is a commonly used material for membranes in devices used to vent gases. The inherent chemical and biological inertness, thermal stability, and hydrophobicity of PTFE have led to its development as a material of choice in industrial gas vent applications. PTFE membranes are also widely used in the health and related industries. The need to manufacture sterile vent membranes for use in medical / biological devices has also naturally led to the selection of PTFE as a material of choice in membrane applications. Traditionally, sterile materials have been produced by chemical sterilization, particularly by steam treatment, gamma irradiation, or treatment with ethylene oxide. The compatibility of PTFE with sterilizing chemicals and treatments is a known material property characteristic of PTFE, especially at high temperatures. A problem associated with the use of PTFE as a vent membrane material under steam treatment is pore blockage due to condensation of oil, water, or both from the machinery used to generate the steam. The resulting loss of air permeability in the clogged membrane effectively reduces the usefulness of the membrane as a gas vent. This condensation problem led to the search for and development of more hydrophobic and oleophobic membrane materials as alternatives to PTFE. A more serious problem concerns the chemical sterilization of membrane materials for use under sterile conditions. Chemical sterilization using ethylene oxide, in particular, very often results in further problems such as toxicity and waste disposal, which raises serious health, environmental, and economic concerns. These concerns have led to the widespread use of ionizing radiation for sterilizing materials used in medical and biological devices. The main drawback of PTFE is its inherent instability to ionization irradiation. Ionization irradiation of PTFE membranes results in the undesirable property of reduced mechanical strength. This loss of mechanical strength imposes significant limitations on the use of PTFE membranes under moderate pressure.

[0005] Attempts to overcome these drawbacks of irradiation have included the use of coatings placed on films. Coating materials allows for the preservation of desired bulk material properties while altering only the surface and interface properties of the film substrate. Hydrophobic and oleophobic coatings are used in the electronics industry as protective barriers for electronic components. However, coating films has not been a practical approach to modifying the surface properties of films, as the undulating morphology associated with films rarely results in a continuous coating. Furthermore, since coatings are not permanently fixed (bonded) to the underlying substrate, coated materials are very often susceptible to abrasion, such as delamination. Also, organic coatings can produce extracts that may harm biological products. Each of these defects exhibits a limited range of thermal and chemical compatibility. In addition, coatings adversely affect the permeability properties of porous substrates, such as flux.

[0006] Grafting techniques have also been proposed to modify the surface properties of polymer substrates. Typical examples of grafting techniques are shown, for example, in U.S. Patents No. 3,253,057, No. 4,151,225, No. 4,278,777, and No. 4,311,573. Grafting techniques for modifying the surface properties of porous membranes present manufacturing challenges, such as the difficulty of modifying the entire surface of a membrane, including the surface within the pores, while avoiding pore blockage and maintaining the membrane's porosity.

[0007] U.S. Patent No. 4,954,256 proposes making the surface of a microporous polymer film more hydrophobic by grafting a fluoropolymer onto the film surface to chemically bond the fluoropolymer to the film surface. Fluoropolymers are formed from monomers containing ethylenically unsaturated groups and fluoroalkyl groups. Grafting is performed by exposing a film in a monomer solution to ionizing radiation. A typical ionizing radiation source is a cobalt-60 gamma-ray source. Fluoropolymers formed from fluorine-containing ethylenically unsaturated monomers are permanently bonded to the microporous film substrate.

[0008] Other prior art attempts disclose a process for preparing hydrophobic / oleophobic films that do not involve surface modification. Rather, it is an in situ process in which both the underlying substrate and the hydrophobic surface of the film are formed simultaneously by a photopolymerization process, thanks to phase separation. The resulting films are mechanically weak and need to be supported / laminated for use as permeable films under relatively moderate pressure. Furthermore, this process produces films with a relatively narrow range of properties, as the film morphology and surface properties are formed simultaneously. Another prior art attempt discloses a process for preparing hydrophobic and oleophobic porous substrates, which involves impregnating the porous substrate with a solution of fluorinated monomers in a carrier solvent, removing the solvent by evaporation, and then polymerization of the remaining monomers. This process is a solid-phase polymerization reaction.

[0009] Another approach involves a porous membrane substrate having a crosslinked polymerizable monomer composition coated on a substrate, as disclosed, for example, in U.S. Patents 4,618,533 and 5,286,382. The monomer composition comprises a polymerizable monomer and a crosslinking agent for the monomer. Conventional energy sources for initiating free radical polymerization, such as ultraviolet (UV) light or heat, can be used to form a crosslinked polymer coating in situ on the porous membrane. This produces a membrane with a surface modified by the crosslinked polymer. U.S. Patent 4,618,533 does not mention forming a crosslinked modified surface from an ethylenically unsaturated monomer having a fluoroalkyl group. However, ethylenically unsaturated monomers having a fluoroalkyl group are disclosed in U.S. Patent 5,286,382.

[0010] U.S. Patent No. 5,037,457 discloses a means for increasing the mechanical strength of a gamma-irradiated PTFE film by laminating the PTFE film onto a porous polyester web. This approach solves the problem of mechanical stability of gamma-irradiated PTFE. The chemical compatibility of the laminated film is limited by the properties of the porous web support. Furthermore, laminates, in particular those formed by the use of adhesives that are often gamma-sensitive, are prone to delamination.

[0011] Superhydrophobic membranes can be manufactured by surface-modifying cast hydrophobic PVDF (DURAPORE®) and hydrophobic PES (EXPRESS®) membranes, which are commercially available from EMD Millipore Corporation (Burlington, Massachusetts, USA). Superhydrophobic PES membranes with several pore sizes, e.g., 0.1, 0.2, 0.45, 0.65, 1, and 5 microns (μm), and one pore size (0.2 μm), have been commercially available for several years. Superhydrophobic modification is carried out by polymerization and crosslinking of fluorocarbon-containing molecules on the membrane surface. Such membranes are frequently used in permeable filtration applications.

[0012] At least one monomer used to make the film surface superhydrophobic is called perfluoroctyl ethyl acrylate (POEA). This chemical is classified in a list of chemicals commonly known as PFAS (perfluoroalkyl substances) and is prohibited by ECHA (European Chemicals Agency) under the REACH program (Registration, Evaluation, Authorization and Restriction of Chemicals). Attempts have been made to substitute POEA with PDA (1H,1H-perfluoro-n-decyl acrylate). However, PDA is also under regulation. Regulatory bodies continue to focus on PFAS, imposing strict threshold limits on the impurity levels of degradation products and potential degradation products associated with these PFAS, which is generally 25 parts per billion (PPB).

[0013] Perfluorocarboxylic acids (PFCAs), whether linear or branched, are being considered for use. However, C9-C14 PFCA chemicals are subject to regulation and should not be manufactured and marketed as substances on their own, nor should they be used or marketed in concentrations of (a) other substances as components, (b) mixtures, or (c) articles of which are (a) components of other substances, (b) mixtures, or (c) articles of which are (b) components of C9-C14 PFCAs and their salts combined, or in concentrations of 260 ppB of C9-C14 PFCA-related substances combined. Perfluorocarboxylic acids (linear and / or branched), their salts and PFCA-related substances, namely (a) perfluorocarboxylic acids having the following formula: CnF2n+1-C(=O)OH (n=8, 9, 10, 11, 12, or 13) (including their salts and any combination thereof), (b) any PFCA-related substance (including any combination thereof) in which a perfluoro group having the formula CnF2n+1 (wherein n=8, 9, 10, 11, 12, or 13) is directly bonded to another carbon atom, and (c) any PFCA-related substance (including any combination thereof) having a perfluoro group of the formula CnF2n+1 (wherein n=9, 10, 11, 12, 13, or 14) that is not directly bonded to another carbon atom as one of its structural elements. The following substances are excluded from this designation: (a) CnF2n+1-X (wherein X=F, Cl or Br (wherein n=9, 10, 11, 12, 13 or 14) (including any combination thereof), (b) CnF2n+1-C(=O)OX' (wherein n>13 and X'=any group) (including salts).

[0014] Undecafluorohexanoic acid (PFHxA), its salts and related substances are also highly regulated. PFHxA may not be manufactured, used or put on the market as a substance on its own. The following may also not be used or put on the market: (a) another substance as a component, (b) a mixture, or (c) an article in a concentration of 25 PPB or more relative to the total of PFHxA and its salts, or 1000 PPB relative to the total of PFHxA related substances; (a) any PFHxA related substance (including its salts and polymers) in which a linear or branched perfluoropentyl group having the formula C5F11- is directly bonded to another carbon atom; (b) any PFHxA related substance (including its salts and polymers) having a linear or branched perfluorohexyl group having the formula C6F13-. The following substances are excluded from this chemical formula: (a) C6F13-X (where X=F), (b) C6F13-C(=O)OH, C6F13-C(=O)O-X', or C6F13-CF2-X' (where X' is any group, including salts).

[0015] In light of the above, monomer substitutes for POEA for unregulated surface treatments of porous membranes represent an advance in the art. Porous membranes that are as hydrophobic and / or more hydrophobic as currently available membranes and have unregulated surface treatments represent an advance in the art. In addition, membranes with surface treatments that retain their mechanical strength after exposure to sterile ionizing radiation and do not decompose into PFOA during environmental and other degradation represent an advance in the art. C5 monomers for use with crosslinking agents to produce environmentally friendly surface treatments for membranes represent an advance in the art. [Prior art documents] [Patent Documents]

[0016] [Patent Document 1] U.S. Patent No. 3,253,057 [Patent Document 2] U.S. Patent No. 4,151,225 [Patent Document 3] U.S. Patent No. 4,278,777 [Patent Document 4] U.S. Patent No. 4,311,573 [Patent Document 5] U.S. Patent No. 4,954,256 [Patent Document 6] U.S. Patent No. 4,618,533 [Patent Document 7] U.S. Patent No. 5,286,382 [Patent Document 8] U.S. Patent No. 5,037,457 [Overview of the Initiative]

[0017] Embodiments of the present disclosure include a porous polymer membrane comprising a porous membrane having an average pore size of about 0.001 to 10 microns formed of a first polymer, wherein the substrate has a surface modified with a crosslinked second polymer formed from a polymerizable fluorine-containing monomer containing a continuous chain of 5 or fewer carbon atoms ("C5") together with fluorine atoms, wherein the monomer is polymerized and crosslinked on the membrane, and the membrane comprises less than 25 ppb of C6 PFCA (perfluorocarboxylic acid), less than 25 ppb of C8 PFCA, and less than 25 ppb of combined C9 to 14 PFCA, substantially shown and / or described in relation thereto in at least one of the figures, and a membrane fully described by the claims is disclosed. Novel and inventive features of the present disclosure, as well as details of its exemplary embodiments, will be better understood from the following description and drawings. A novel approach for both monomers and crosslinkers avoided the use of any PFAS molecules with a carbon chain length of C6 or longer in order to meet regulatory requirements. About 15 monomers were procured and screened in the laboratory using both PVDF and PES-based membranes. Three performance characteristics were measured: 1) surface energy (a measure of hydrophobicity), 2) airflow, and 3) water penetration pressure. Some of the new monomers had a surface energy of 25 mJ / m³. 2 We were able to reduce it to less than 19 mJ / m³, but one remained at 19 mJ / m³. 2A target surface energy of less than 1 was achieved. The monomer DDA19 is a dodecane acrylate containing 19 fluorine atoms. Surface chemical targets and methods according to some embodiments of this disclosure include a range of fluorinated functional acrylates / allyls (referred to as monomers) and difunctional acrylates (referred to as crosslinkers), which have been studied using surface modification chemistry as described herein.

[0018] In some embodiments, the PVDF or PES membrane has pore sizes of any suitable size for various filtration applications, as is known to those skilled in the art. In some embodiments, the membrane has pore sizes of 0.001 to 10.0 microns. In some embodiments, the membrane has pore sizes of 0.01 to 5.0 microns. In some embodiments, the membrane has pore sizes of 0.05 to 1 micron. In some embodiments, the membrane has pore sizes of 0.1 to 0.22 microns. In some embodiments, the membrane has pore sizes of about 0.2 to 0.45 microns. Also, in some embodiments, the substrate includes woven or nonwoven materials. For example, suitable substrates include polyethylene, polypropylene, nylon and other suitable polyolefins and / or polyamides.

[0019] These and other advancements embodied herein will become apparent from the following description, claims, and drawings. The various benefits, aspects, novel and inventive features of the present disclosure, as well as the exemplary embodiments of the vent filtration device including the coated membrane and its coated membrane, will be more fully understood from the following description and drawings. Embodiments of the present disclosure include a porous polymer membrane that can be incorporated into a filter unit to facilitate the ventilation of air or gas. Thus, a more specific description of the embodiments of the present disclosure, briefly summarized above, in a manner in which the features disclosed herein can be understood in detail, can be obtained by reference to the accompanying drawings. However, it should be noted that the accompanying drawings show only typical embodiments of the present disclosure, and thus the described embodiments should not be considered to limit its scope, as other equally effective surface treatments, methods, and / or materials may be acceptable. It should also be understood that elements and features of one embodiment can be found in other embodiments without further elaboration, and that the same reference numbers, where possible, have been used to indicate equivalent elements common to the drawings. As used herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which these embodiments pertain.

[0020] A surface is considered hydrophobic when its static water contact angle θ is >90°, and generally hydrophilic when θ is <90°. Superphobic (superhydrophobic) is defined herein as having a static water contact angle θ of about >150°.

[0021] Membrane surface modification or treatment is defined as a chemical process for obtaining surface properties, such as hydrophobicity, while retaining bulk membrane properties such as mechanical and chemical resistance, morphology, pore size, etc.

Brief Description of the Drawings

[0022] [Figure 1] A flowchart of a method for producing a coated film according to several embodiments of this disclosure is shown. [Modes for carrying out the invention]

[0023] Embodiments of the present disclosure include polyethersulfone (PES) and / or polyvinylidene fluoride (PVDF) films having surface modifications with various short-chain fluorocarbon acrylic or allyl-based molecules. PES and PVDF films having the above surface treatments exhibited a significant increase in the superhydrophobicity of the film surface. The film embodiments discussed herein are often used for various air filtration applications. The surface treatment step was achieved by polymerization of acrylate molecules followed by crosslinking with diacrylate molecules under an electron beam or ultraviolet (UV) energy source. The enhanced superhydrophobic performance shown herein is measured as surface energy. It should be understood that in some embodiments, the PES or PVDF films include pore sizes of any size suitable for various filtration applications, as is known to those skilled in the art. In some embodiments, the films include pore sizes of 0.001 to 10.0 microns. In some embodiments, the films include pore sizes of 0.01 to 5.0 microns. In some embodiments, the films include pore sizes of 0.05 to 1 micron. In some embodiments, the membrane has a pore size of 0.1 to 0.22 microns. In some embodiments, the membrane has a pore size of about 0.2 to 0.45 microns. In some embodiments, the substrate includes woven or nonwoven fabrics. For example, suitable substrates include polyethylene, polypropylene nylon, and other suitable polyolefins and / or polyamides. Both these membranes and substrates may be treated with the surface treatments discussed herein to produce porous polymer membranes for filtration applications.

[0024] A novel approach for both monomers and crosslinkers avoided the use of any PFAS molecules with a carbon chain length greater than C6 to meet regulatory requirements. Approximately 15 monomers were procured and screened in the laboratory using both PVDF and PES-based films. Three performance characteristics were measured: 1) surface energy (a measure of hydrophobicity), 2) airflow, and 3) water intrusion pressure. Some of the new monomers had a surface energy of 25 mJ / m². 2 We were able to reduce it to less than 19 mJ / m³, but one remained at 19 mJ / m³. 2 The target energy of less than 10 was achieved. The monomer DDA19 shown is a dodecane acrylate containing 19 fluorine atoms.

[0025] Surface chemical targets and methods according to some embodiments of this disclosure comprise a series of fluorinated functional acrylates / allyls (referred to as monomers) and difunctional acrylates (referred to as crosslinkers), which have been studied using surface modification chemistry as described herein.

[0026] Table 3 shows the surface energy in millijoules (mJ / m²), which is a measure of the superhydrophobicity of the film surface, for various chemical solutions / mixtures investigated as surface treatments for various films. 2 We will disclose an overview of ).

[0027] Table 4 discloses the surface energies of current superhydrophobic chemistry (POEA chemistry). Various chemical formulations were identified from a series of studies conducted under various formulation conditions. The polymerization and crosslinking steps were initiated using a UV source as the energy source. It is intended herein that the polymerization and / or crosslinking process may be initiated using other sources, chemical sources, and other energy sources.

[0028] [Table 1] TIFF0007830635000002.tif213161

[0029] [Table 2]

[0030] [Table 3]

[0031] [Table 4]

[0032] Table 5 discloses a comparison of the membrane performance (surface energy, airflow, and water intrusion pressure) of various chemicals used, as well as current (POEA) and novel DDA19 chemicals.

[0033] DDA19 is the name of a monomer of dodecane acrylate containing 19 fluorine groups. The chemical structure of 2-propenoic acid, 3,3,4,4,5,5,6,6,7,7,9,9,10,10,11,11,12,12,12-nonadecafluorododecyl ester (DDA19) may include the following:

[0034] [ka]

[0035] [Table 5]

[0036] Table 6 outlines formulations according to some embodiments of the present disclosure.

[0037] [Table 6] TIFF0007830635000009.tif62165

[0038] Table 7 shows the pre- and post-gamma treatment results of films coated with a novel coating containing less than 25 ppb of C6 PFCA (perfluorocarboxylic acid), less than 25 ppb of C8 PFCA, and less than 25 ppb of combined C9-14 PFCA. The values ​​shown in Table 7 (expressed in nanograms / gram) vary from lot to lot, but are not substantial and are, for example, less than 25 ppb.

[0039] [Table 7]

[0040] [Table 8]

[0041] Polymerization and crosslinking of polymerizable monomers onto a porous membrane substrate are carried out using a reagent bath so that the surface of the porous membrane, including the inner surface of the porous membrane, is coated with the crosslinked polymer.

[0042] A reagent bath containing (1) an ethylenically unsaturated polymerizable monomer having at least one fluoroalkyl group, (2) a polymerization initiator if necessary, and (3) a crosslinking agent in a solvent for these three reagents is brought into contact with a porous membrane substrate under conditions that result in polymerization of the monomer and deposition of the resulting crosslinked polymer onto the porous membrane substrate.

[0043] Figure 1 shows a flowchart of Method 100 for preparing a coated film, according to some embodiments of the present disclosure. In step 102 of Method 100, a solution is prepared. For example, a polymer solution involves preparing a chemical solution / mixture of a monomer (e.g., DDA19) and a crosslinking agent (e.g., HDDA) together with an initiator (e.g., DMPA / I651) in a DMTS solvent. I651 is a photoinitiator with CAS#24650-42-8, commercially available as IRGACURE by Ciba Corp. in New York, USA. Many initiators may be used in some embodiments of the present disclosure.

[0044] In step 104, a film is prepared, which may be an asymmetric or symmetric film. The film may also be a PES or PVDF film. One way to prepare the film is to prepare a film sheet for coating with the chemical solution / mixture from step 102. For example, a basement film of the desired size (e.g., 5 inches x 3 inches) is cut into either PVDF or PES.

[0045] In step 106, the chemical solution / mixture is applied to the membrane surface. The application of the chemical solution / mixture can be done either by immersing the membrane sheet in a chemical mixture solution in a tray, for example, a glass tray, or by directly placing the chemical solution / mixture onto the membrane surface (in some embodiments, a moist membrane surface) using, for example, a pipette or other delivery means.

[0046] In step 108, the film sheet having a chemical solution / mixture is exposed to an energy source, such as a UV / electron beam source for polymerization reactions, to generate a polymer coating on the film surface.

[0047] In step 110, a washing step is used to remove unreacted chemical solutions / mixtures using solvents (e.g., methanol and water).

[0048] In step 112, a drying step is used to dry the washed film (for example, at 100°C for 15 minutes). Method 100 is completed after step 112.

[0049] It has been found that by selecting an appropriate solvent system, the hydrophobicity of a surface-treated film can be controlled so that the coated film does not wet with solvents having a surface tension greater than about 21 dynes / cm. Many such solvent systems are available. One such suitable solvent for use with embodiments according to this disclosure is decamethyltetrasiloxane (DMTS). Another monomer is 1H,1H-perfluoro-3,6,9-trioxatridecane-1-ol acrylate (PTTA). The generic name of initiator I651 is 2,2-dimethoxy-2-phenylacetophenone (DMPA).

[0050] When using fluorine-containing polymerizable monomers having an unsaturation degree greater than 1, it is not necessary to add additional monomers in the coating of this disclosure. The three reactants, for example, polymerizable monomer, polymerization initiator, and crosslinking agent, are brought into contact with the porous membrane as a mixture in a solvent compatible with these three reactants and the porous membrane, and as a result, the desired free radical polymerization and crosslinking are achieved without the formation of a considerable amount of slowly extractable byproducts. If easily extractable byproducts are formed, they can be removed by performing a washing step with a suitable solvent after the coating step.

[0051] Generally, polymerizable monomers are present in the reactant solution at a concentration between about 2% and about 20%. In some embodiments, the concentration is between about 2.5% and 7.5% based on the weight of the polymerizable monomer. Crosslinking agents are present in an amount between about 0.5% and about 5% by weight, based on the weight of the polymerizable monomer. Polymerization initiators are present in an amount between about 0.1% and about 1% by weight, based on the weight of the polymerizable monomer. In some embodiments, the initiator is present in an amount between about 0.15% and 0.17%. Crosslinking agents can function as polymerizable monomers because they are available without monomers.

[0052] Polymerization and crosslinking can be carried out by exposing the monomer reaction system to ultraviolet (UV) light, a heat source, and / or ionizing radiation. Because it is rapid, embodiments of the present disclosure include the use of UV light. This process includes immersing a membrane substrate in a solution containing monomers, a crosslinking agent, and an initiator; placing the membrane between two UV-transparent sheets, such as polyethylene; and exposing this sandwich to UV light. This process can be carried out continuously, and the desired crosslinked coating is formed within minutes after UV exposure begins. By controlling the reactant concentrations and UV exposure as described above, a plug is removed, and a composite having the same porous structure as the membrane substrate is produced. Furthermore, the produced composite membrane is wettable only with solvents having a surface tension of less than approximately 21 dynes / cm. That is, the composites and / or coated membranes of the present disclosure have a highly hydrophobic surface. Also, the composites and / or coated membranes of the present disclosure retain their mechanical strength even after exposure to sterile ionizing radiation.

[0053] The composites of this disclosure, after being sterilized by exposure to gamma rays typically between approximately 2 and 5 megarads, can withstand forward or reverse pressures of at least 10 PSI. In addition, the sterilized membrane composites of this disclosure retain a desired degree of hydrophobicity so as not to be wetted by aqueous solutions containing surfactants. The composites are useful as gas vents for selectively passing gases while preventing the passage of organic and aqueous liquids, such as in the apparatus described herein by reference to U.S. Patent No. 3,854,907. Embodiments of this disclosure include membranes suitable for use in filtration devices. The membranes are hydrophobic membranes incorporated into filtration devices that allow for selective gas passage, i.e., are impermeable to aqueous solutions, such as when an aqueous solution is filtered through a hydrophilic filter before intravenous administration. As an integral part of the filtration device, the membranes remain hydrophobic, i.e., impermeable to aqueous solutions, in their functional use as gas vent membranes and in their incorporation into vent filter devices.

[0054] Some embodiments of the present disclosure are intended to include porous polymer films on which a surface treatment agent is disposed, containing less than 25 ppb of C6 PFCA (perfluorocarboxylic acid), less than 25 ppb of C8 PFCA, and less than 25 ppb of a combination of C9-14 PFCA, upon exposure to gamma rays up to 50 kGy.

[0055] Porous polymer films according to some embodiments of the present disclosure include polyvinylidene fluoride, nylon, polyamide, polyimide, polyethersulfone, polysulfone, polyarylsulfone, cellulose, regenerated cellulose, cellulose ester, acrylic polymer, methacrylic polymer, copolymer acrylic methacrylic polymer, and combinations thereof.

[0056] The water penetration test approach is a "pressurized" wetting / adsorption test that allows for the indirect evaluation of the hydrophobicity of the inner surface of porous membranes. This pressurized wetting / adsorption approach can be extended to solutions other than aqueous nutrient mixtures to evaluate membrane performance under various operating conditions (e.g., aeration).

[0057] All ranges of formulations listed herein include ranges between them, and endpoints may be included or excluded. Optionally included ranges originate from integer values ​​(or one original endpoint) between them, on the order of the listed magnitudes or the next smaller magnitude. For example, if the lower limit is 0.2, optional included endpoints could be 0.3, 0.4, ... 1.1, 1.2, etc., as well as 1, 2, 3, etc.; if the upper limit is 8, optional included endpoints could be 7, 6, etc., as well as 7.9, 7.8, etc. One-sided limits, such as 3 or more, similarly include consistent limits (or ranges) starting from integer values ​​on the order of the listed magnitudes or one lower magnitude. For example, 3 or more includes 4 or 3.1 or more.

[0058] Throughout this specification, any reference to “one embodiment,” “a particular embodiment,” “one or more embodiments,” “several embodiments,” or “a particular embodiment” indicates that the features, structures, materials, or properties described in relation to that embodiment are included in at least one embodiment of this disclosure. Therefore, occurrences of phrases such as “in one or more embodiments,” “a particular embodiment,” “in one embodiment,” “several embodiments,” or “in a particular embodiment” throughout this specification do not necessarily refer to the same embodiment.

[0059] While several embodiments have been discussed above, other implementations and applications are also within the scope of the following claims. Although this specification describes specific embodiments with reference, it should be understood that these embodiments are merely illustrative of the principles and applications of the disclosure. Therefore, it should be further understood that numerous modifications can be made to the exemplary embodiments and other configurations and patterns can be devised without departing from the spirit and scope of the embodiments relating to this disclosure. Furthermore, specific features, structures, materials, or properties may be combined in any preferred manner in one or more of the embodiments.

[0060] Patent applications, patent documents, and non-patent references cited herein are incorporated herein by reference in their entirety in the entirety as if each individual publication or reference were specifically and individually described herein in its entirety. Any patent application for which this application claims priority is also incorporated herein by reference in the form set forth above for publications and references.

Claims

1. A porous polymer film, Formed from the first polymer, between 0.1 and 0.22 microns It includes a porous membrane having an average pore size, The porous polymer film has a surface modified with a crosslinked second polymer formed from a polymerizable fluorine-containing monomer containing a continuous chain of five or fewer carbon atoms together with a fluorine atom, wherein the monomer is polymerized and crosslinked on the film, and the film has less than 25 ppb of C6PFCA (perfluorocarboxylic acid), less than 25 ppb of C8PFCA, and less than 25 ppb of combined C9-14PFCA.

2. The porous polymer film according to claim 1, wherein, after exposure to gamma rays up to 50 kGy, the C6PFCA (perfluorocarboxylic acid) content is less than 25 ppb, the C8PFCA content is less than 25 ppb, and the combined C9-14PFCA content is less than 25 ppb.

3. The porous polymer film according to claim 1, wherein the first polymer comprises polyvinylidene fluoride, nylon, polyamide, polyimide, polyethersulfone, polysulfone, polyarylsulfone, cellulose, regenerated cellulose, cellulose ester, acrylic polymer, methacrylic polymer, copolymer acrylic methacrylic polymer, and combinations thereof.

4. The porous polymer film according to claim 1, which is an asymmetric or symmetric film.

5. The porous polymer membrane according to claim 1, wherein the porous polymer membrane comprises a polyvinylidene fluoride membrane or a polyethersulfone membrane.

6. The porous polymer membrane according to claim 1, wherein the porous polymer membrane can be incorporated into a filter unit for the ventilation of air or gas.

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