Electrolytic film

Abstract

Hydrophilic porous polymer films are disclosed that are particularly well suited for use in electrolysis cells that produce hydrogen. The porous polymer films contain one or more high-density polyethylene polymers in combination with one or more hydrophilic additives. The porous films can be formed through gel extrusion or through sintering. Ultra-thin films can be produced that have the desired permeability, hydrophilicity, and mechanical properties necessary for use in the cells.

Description

[Technical Field]

[0001] Related Applications

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 422,048, filed November 3, 2022, and U.S. Provisional Patent Application No. 63 / 506,630, filed June 7, 2023, both of which are incorporated herein by reference. [Background technology]

[0002]

[0002] Recent developments in fuel cell technology and the increasing demand for alternatives to fossil fuels have increased the need for hydrogen production. In addition to being used in fuel cells, hydrogen is also used to produce a variety of different products, including ammonia, other fertilizers, and methanol.

[0003]

[0003] When used as a fuel for fuel cells, hydrogen reacts with oxygen to release water, so that fuel cells can be constructed to emit zero greenhouse gases.

[0004] In one embodiment, hydrogen may be produced by electrolysis of water according to a thermochemical cycle. Using water to produce hydrogen has various advantages and conveniences. For example, hydrogen can be produced from water in a relatively pure state without emitting carbon dioxide.

[0004]

[0005] In one embodiment, hydrogen can be produced by electrolysis from an aqueous solution. For example, an alkaline solution can be used to produce hydrogen during electrolysis. Electrolysis of the alkaline solution can occur in a cell separated by a semipermeable diaphragm or membrane. The diaphragm is positioned to separate the anode from the cathode and to prevent recombination of hydrogen formed at the cathode with oxygen formed at the anode. However, the diaphragm has been a limiting factor in the ability to effectively produce hydrogen gas. For example, the membrane must be able to withstand the operating pressures within the cell and be suitable for use in high current density operation. The diaphragm can also be exposed to significant pH swings within the cell and therefore should be chemically resistant to acids and bases. In addition, the diaphragm should be highly ionically conductive for the transport of hydroxide ions from the cathode to the anode while remaining impermeable to hydrogen and oxygen gases.

[0005]

[0006] Examples of previously used diaphragms are disclosed, for example, in U.S. Patent Application No. 2022 / 0259751 and International Publication Nos. 2022 / 002999 and 2022 / 002904, all of which are incorporated herein by reference. In the past, for example, diaphragms have been manufactured from porous polymer fabrics, for example, made from polyphenylene sulfide fibers. The porous polymer fabrics are then impregnated with a dope solution and used in a two-layer configuration. Summary of the Invention [Problem to be solved by the invention]

[0006]

[0007] Although electrolysis cells have been successful in producing hydrogen, further improvements remain needed. In particular, a need exists for improved semipermeable diaphragms that can be positioned between the anode and cathode in electrolysis cells. For example, in one aspect, a need exists for diaphragms that are lighter and / or thinner than the impregnated fabrics used in the past and that are well suited for use in electrolysis cells. In another aspect, a need also exists for diaphragms for electrolysis cells that include a single layer support. In yet another aspect, a need exists for diaphragms for electrolysis cells that have enhanced hydrophilic structure and / or properties. [Means for solving the problem]

[0007]

[0008] In general, the present disclosure is directed to an improved diaphragm for use as a separator between an anode and a cathode. For example, the diaphragm is particularly well suited for use in electrolysis cells. According to the present disclosure, the diaphragm can be formed from a porous film made from at least one high-density polyethylene polymer. The porous film can be manufactured through a gel extrusion process or through sintering and can incorporate at least one hydrophilic additive. Diaphragms made according to the present disclosure offer numerous advantages, including being relatively lightweight, being able to function as a single-layer diaphragm, having excellent semipermeability properties combined with good mechanical strength, and being chemically resistant.

[0008]

[0009] For example, in one embodiment, the present disclosure is directed to a separator for separating an anode from a cathode. The separator comprises a porous polymer film including a high-density polyethylene polymer having a number average molecular weight of greater than about 500,000 g / mol. For example, the average molecular weight of the polyethylene polymer can be greater than about 600,000 g / mol, e.g., greater than about 700,000 g / mol, e.g., greater than about 1,000,000 g / mol, e.g., greater than about 2,000,000 g / mol, e.g., greater than about 3,000,000 g / mol, e.g., greater than about 4,000,000 g / mol, e.g., greater than about 5,000,000 g / mol, and generally less than about 12,000,000 g / mol, e.g., less than about 10,000,000 g / mol.

[0009]

[0010] The high-density polyethylene polymer may be combined with at least one hydrophilic additive and / or subjected to a plasma treatment to increase the hydrophilic properties of the resulting film. The hydrophilic additive is present in the porous polymer film in an amount of at least about 5 wt%, such as at least about 10 wt%, such as at least about 20 wt%, such as at least about 30 wt%, such as at least about 40 wt%, such as at least about 50 wt%, and generally in an amount less than about 90 wt%, such as less than about 70 wt%.

[0010]

[0011] Alternatively or in addition to incorporating a hydrophilic additive into the film, at least a first surface of the porous polymer film can be plasma oxidized to form polar groups attached to the high-density polyethylene polymer, which enhance the polarity of the surface of the porous polymer film. The plasma oxidized polar groups are present on the first surface of the film in an amount sufficient to enhance the hydrophilic properties.

[0011]

[0012] Porous films made in accordance with the present disclosure may have a thickness of less than about 600 microns, such as less than about 500 microns, for example less than about 400 microns, such as less than about 300 microns, for example less than about 200 microns, for example less than about 150 microns, such as less than about 100 microns, for example less than about 80 microns, and generally may have a thickness of more than about 5 microns, such as more than about 10 microns, for example more than about 20 microns, for example more than about 30 microns.

[0012]

[0013] Contrary to many membranes produced in the past, the separator of the present disclosure may be in the form of a non-fibrous film. In one embodiment, the porous polymer film may comprise an extruded film stretched in at least one direction. For example, the film may be uniaxially stretched or biaxially stretched. Alternatively, the porous polymer film may comprise a sintered film.

[0013]

[0014] As described above, the porous polymer film contains at least one hydrophilic additive. Examples of hydrophilic additives include inorganic particles, hydrophilically modified polymers, such as hydrophilically modified polyethylene polymers, or mixtures thereof. Inorganic particles that can be incorporated into the film include silica, alumina, zirconium oxide, zirconium hydroxide, magnesium oxide, magnesium hydroxide, titanium oxide, titanium hydroxide, barium sulfate, or mixtures thereof. In one embodiment, the hydrophilic additive comprises fumed silica. The inorganic particles generally have a particle size (D50) of less than about 1 micron, for example, less than about 0.8 microns, for example, less than about 0.6 microns, for example, less than about 0.5 microns, and can have a particle size (D50) of more than about 0.001 microns.

[0014]

[0015] The porous polymer film containing the hydrophilic additive can be used alone as a single-layer separator, which can optionally include a coating. For example, the hydrophilic coating can be applied to one or both sides of the film. For example, the coating can include a coating of silica, aluminum oxide, or zirconium oxide. In one embodiment, the porous polymer film does not include polypropylene.

[0015]

[0016] Porous polymer films made in accordance with the present disclosure can have an average pore size greater than about 0.005 microns and generally less than about 1 micron. The porous polymer film has a pore size of about 0.1 ohm.cm at 80° C. in a 30 wt % aqueous KOH solution. 2 It may have an ionic resistivity of less than 1000 .mu.m.

[0016]

[0017] Other features and aspects of the present disclosure are discussed in more detail below.

[0018] A full and enabling disclosure of the present disclosure is more particularly set forth in the remainder of the specification, which includes reference to the accompanying drawings. [Brief explanation of the drawings]

[0017] [Figure 1] 1 illustrates one embodiment of an electrolysis cell incorporating a separator that may be made in accordance with the present disclosure. [Figure 2] 1 is an embodiment of an oxygen plasma method that may be used to treat porous polymeric films according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0018]

[0019] Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention.

[0019] definition

[0020] The melt flow rate of a polymer or polymer composition is measured in accordance with ISO Test 1133 at 190° C. under a load of 21.6 kg.

[0020]

[0021] The density of the polymer is measured in g / cm according to ISO Test 1183. 3 It is measured in units of .

[0022] The average particle size (d50) is measured using laser diffraction / light scattering, for example a suitable HORIBA light scattering instrument.

[0021]

[0023] The average molecular weight of a polymer is determined using the Margolies' formula.

[0024] Tensile modulus, tensile stress at yield, tensile strain at yield, tensile stress at 50% break, tensile stress at break and nominal tensile strain at break are all measured in accordance with ISO Test 527-2 / 1B.

[0022]

[0025] Contact angle measurements are performed on a Kruss DSA 100 instrument. Film samples (10 x 40 mm) are attached to microscope slides using double-sided adhesive tape. Electrostatic charges are dissipated by passing the prepared sample through a U-electrode static discharger several times. The sample is placed in the measurement device, and a 3.5 μl droplet of test fluid (water or ethylene glycol) is placed on the film. The contact angle is determined 7 seconds after droplet placement through the software (one measurement per second). These seven data points are averaged to yield the contact angle at the point of measurement. Each sample is measured at six different spots, or positions, on each side, and all results are averaged to produce the reported value.

[0023]

[0026] The porosity (%) is measured according to the following procedure. During this procedure, the following ASTM Standards are used as references: D622 Standard Test Method for Apparent Density of Rigid Cellular Plastics; and D729 Standard Test Methods for Density and Specific Gravity (Relative Density) of Plastics by Displacement 1. Use the following equipment: Calibrated Analytical Balance (0.0001 grams); Lorentzen & Wettre Micrometer, code 251 (0.1um); and Deli 2056 art knife.

[0024] procedure: 1.1. Samples and sample preparation Using a specimen art knife, cut each sample material into a minimum of three 60 mm±0.5 x 60 mm±0.5 specimens.

[0025] 1.2. Instruments and Measurements 1.2.1 Using an L&W micrometer, take five thickness readings (average of the five readings) on each 60 mm x 60 mm sample. Record this value as the thickness of that sample.

[0026] 1.2.2 Weigh the sample directly on the balance. Record this value as the weight of this sample. 1.2.3 Mount three specimens of the same sample together and repeat step 1.2.1 and step 1.2.2 to obtain the [bulk] thickness and [bulk] weight. Calculate the density for the three key numbers as follows: aD film = density (film) = Sample weight THK * square D = density of the sample (mg / mm 3 ) Wt = sample weight (mg) THK = sample thickness (mm) Square = sample area (mm 2 ) bD polymer = density (polymer) 0.95 (g / cm 3 ) D Polymer: No pores, density of raw material c. Porosity = (1-D film / D polymer) * 100%

[0027] Pore ​​size can be measured using the Bubble Point Test, which corresponds to ASTM Test Method F316.

[0027] Detailed Description

[0028] It will be understood by those skilled in the art that this discussion is a description of exemplary embodiments only and is not intended to limit the broader aspects of the present disclosure.

[0028]

[0029] In general, the present disclosure is directed to a hydrophilic porous film that is particularly well suited for use as a diaphragm in an electrolytic cell. The hydrophilic porous film is formed from one or more high-density polyethylene polymers. The one or more high-density polyethylene polymers have a relatively high molecular weight. The resulting porous film has superior strength and selective permeability properties at reduced thickness relative to conventional fibrous products used in the past.

[0029]

[0030] During water electrolysis, electrical energy is transformed into hydrogen. The production of hydrogen from electrolysis continues to grow in importance and is a fundamental step and pillar in concerted efforts to reduce greenhouse gas emissions and decarbonize the energy supply. The hydrophilic porous film of the present disclosure is designed to separate the anode from the cathode in an electrolysis cell. The properties of the hydrophilic porous film are carefully controlled so that the film rapidly wets, allowing the passage of electrolyte, while remaining substantially impermeable to the gases produced during the process, i.e., oxygen and hydrogen. Among particular advantages, hydrophilic porous films made according to the present disclosure have high porosity, high hydrophilicity, low gas permeability, and high oxygen resistance at relatively low thicknesses. A variety of different methods and techniques can be used to enhance the hydrophilic properties of the film. Additionally, one or more thermal stabilizers can be incorporated into the film.

[0030]

[0031] 1, one exemplary embodiment of an electrolysis cell 10 is shown. The electrolysis cell 10 includes a separator 12 made in accordance with the present disclosure. The separator 12 illustratively includes a hydrophilic porous film made from one or more high-density polyethylene polymers in combination with one or more hydrophilic additives.

[0031]

[0032] As shown in FIG. 1 , a separator 12 separates an anode assembly 14 from a cathode assembly 16. The anode assembly 14 includes an anode 18. The anode 18 can be made of any suitable material, such as a porous metal structure. The porous metal structure can include, for example, a mesh. In one embodiment, the anode can include a catalyst layer. The catalyst layer can be different for the anode, where oxygen is formed, and the cathode, where hydrogen is formed. The substrate used to fabricate the anode can be made of nickel, iron, mild steel, stainless steel, vanadium, molybdenum, copper, silver, manganese, platinum, graphite, chromium, or a mixture thereof. The catalyst layer, on the other hand, can include elements from the nickel, cobalt, iron, and platinum groups. The above metals can be present in the catalyst layer as oxygen.

[0032]

[0033] Anode 18 may be placed in direct contact with separator 12 or may be spaced apart from separator 12 to form a gap, which may be, for example, less than about 5 mm, such as less than about 3 mm, e.g., less than about 2 mm.

[0033]

[0034] The anode assembly 14 further includes an anode plate 20 positioned adjacent to an anode current collector 22. The anode 18 is in electrical communication with the anode plate 20 via the anode current collector 22. The anode current collector 22 may, for example, be comprised of a porous metal structure. In one embodiment, for example, the anode current collector 22 may comprise a porous foam or mat of nickel or steel.

[0034]

[0035] The anode assembly 14 defines a compartment designed to receive a flow of aqueous solution. By way of example, the anode assembly 14 may include an inlet 24 and a discharge 26. In one embodiment, an alkaline solution is fed through the electrolysis cell 10. The alkaline solution may be, by way of example, in one embodiment, a potassium hydroxide solution.

[0035]

[0036] 1, the inlet 24 is located at the top of the electrolysis cell 10 and the discharge 26 is located at the bottom of the electrolysis cell 10. However, in other embodiments, any suitable flow configuration may be used. During electrolysis, water is converted to hydrogen and oxygen. Oxygen is produced and stored within the anode assembly 14. As shown, oxygen 28 may be discharged from the electrolysis cell 10 in gaseous form.

[0036]

[0037] The cathode assembly 16 includes a cathode 30 in electrical communication with a cathode plate 32 via a cathode current collector 34. The cathode 30 can include any suitable structure, such as a porous web containing a catalyst. The cathode 30 can be catalytically activated, for example, with platinum, palladium, or the like. The cathode 30 can include a single layer or multiple layers. As shown in FIG. 1 , the cathode 30 is placed in direct communication with the separator 12 and can be made from the same materials as described above for the anode 18.

[0037]

[0038] The cathode 30 is electrically coupled to the cathode plate 32 by a cathode current collector 34 to create a compartment for fluid flow. The cathode current collector 34 may have a structure similar to the anode current collector 22 and may, for example, include a porous metal structure. The cathode assembly 16 may include an inlet 36 and a discharge 38 for flowing an aqueous solution, such as potassium hydroxide solution, through the cathode assembly 16. The aqueous solution supplied through the cathode assembly 16 may be the same as or different from the aqueous solution supplied through the anode assembly 14.

[0038]

[0039] During this process, hydrogen is produced within the cathode assembly 16. Hydrogen 40 is released from the electrolysis cell 10 and can be recovered.

[0040] Although not shown, the electrolysis cell 10 may include various gaskets and mounting members to maintain the cells in an integrated arrangement. The electrolysis cell 10 may produce hydrogen 40 from water without producing any greenhouse gas emissions.

[0039]

[0041] As described above, the separator 12 shown in FIG. 1 is made from a high-density or high-molecular-weight hydrophilic porous polyethylene film. The hydrophilic porous films of the present disclosure can be made using different techniques and methods. For example, in one embodiment, the hydrophilic porous film can be made in an extrusion process, such as a gel extrusion process. Alternatively, the hydrophilic porous film can be formed through a sintering process.

[0040]

[0042] Hydrophilic porous films made in accordance with the present disclosure possess numerous physical properties making them particularly well suited for use in electrolysis cell 10, and also offer various advantages and conveniences over fibrous materials used in the past.

[0041]

[0043] For example, high density and high molecular weight polyethylene polymers offer a unique combination of chemical resistance, chemical neutrality, and mechanical strength. Additionally, using the methods described herein, high density polyethylene polymers can be combined with significant amounts of hydrophilic additives to produce porous films that rapidly wet when contacted with water or aqueous solutions, such as potassium hydroxide solution. For example, hydrophilic porous films made according to the present disclosure are particularly well suited for contact with potassium hydroxide solutions containing potassium hydroxide in amounts of about 10% to about 40% by weight, e.g., about 20% to about 35% by weight, and at temperatures above about 50°C, e.g., above about 60°C, e.g., above about 70°C, e.g., above about 80°C, and generally below about 95°C.

[0042]

[0044] The hydrophilic porous film of the present disclosure has a pore structure well suited to preventing the recombination of hydrogen gas and oxygen gas during the electrolysis process. Meanwhile, the pore structure of the film is permeable to hydroxide ions from the cathode to the anode. In one embodiment, the hydrophilic porous film has an average pore size greater than about 0.005 microns, for example, greater than about 0.05 microns, for example, greater than about 0.1 microns, for example, greater than about 0.15 microns, for example, greater than about 0.2 microns, for example, greater than about 0.25 microns, for example, greater than about 0.3 microns, for example, greater than about 0.35 microns, for example, greater than about 0.4 microns, for example, greater than about 0.45 microns, for example, greater than about 0.5 microns. The average pore size is generally less than about 2 microns, for example, less than about 1 micron, for example, less than about 0.8 microns, for example, less than about 0.7 microns, for example, less than about 0.6 microns, for example, less than about 0.5 microns.

[0043]

[0045] The porosity of the hydrophilic film is generally greater than about 25%, such as greater than about 30%, for example greater than about 35%, such as greater than about 40%, for example greater than about 45%, such as greater than about 50%, for example greater than about 55%, and generally less than about 80%, such as less than about 70%, for example less than about 65%.

[0044]

[0046] The hydrophilic porous films of the present disclosure are also heat-resistant and pressure-resistant. For example, they are well suited for continuous use at surface temperatures ranging from about 60°C to about 110°C, e.g., from about 75°C to about 90°C, such as those experienced in electrolytic cells. The hydrophilic porous films are also pressure-resistant, providing excellent creep resistance. For example, the porous films can be continuously exposed to surface pressures of about 35 bar to about 50 bar. In addition, the hydrophilic porous films of the present disclosure provide inherent flame retardancy. For example, when tested according to UL94 testing, the films can exhibit a VO rating at thicknesses of only 0.3 mm.

[0045]

[0047] The porous films of the present disclosure also have excellent wettability and are highly hydrophilic. For example, the porous films have a hydrophilicity of about 0.1 ohm.cm in a 30 wt % aqueous potassium hydroxide solution at 80° C.2 By way of example, the film may exhibit an ionic resistivity of less than about 0.08 ohm.cm under the above conditions. 2 Less than, for example, about 0.06 ohm.cm 2 The film may also exhibit a contact angle when measured against water of less than about 110°, such as less than about 105°, for example less than about 102°, for example less than about 100°, such as less than about 98°, for example less than about 96°, for example less than about 94°, such as less than about 92°, for example less than about 90°, such as less than about 88°, for example less than about 86°, for example less than about 84°, for example less than about 82°, for example less than about 80°.

[0046]

[0048] All of the above properties can be obtained at a relatively thin thickness. For example, the porous film of the present disclosure can have a thickness of less than about 500 microns, for example, less than about 400 microns, for example, less than about 300 microns, for example, less than about 200 microns, for example, less than about 150 microns, for example, less than about 100 microns. In one embodiment, the thickness of the porous film can be less than about 90 microns, for example, less than about 85 microns, for example, less than about 80 microns, for example, less than about 75 microns, for example, less than about 70 microns, for example, less than about 65 microns, for example, less than about 60 microns. The thickness of the porous film is generally greater than about 5 microns, for example, greater than about 10 microns, for example, greater than about 20 microns, for example, greater than about 25 microns, for example, greater than about 30 microns, for example, greater than about 35 microns, for example, greater than about 40 microns, for example, greater than about 45 microns, for example, greater than about 50 microns, for example, greater than about 55 microns, for example, greater than about 60 microns.

[0047]

[0049] As described above, the hydrophilic porous film of the present disclosure is formed from at least one high density polyethylene polymer in combination with at least one hydrophilic additive. The at least one high density polyethylene has a viscosity of about 0.93 g / cm 3 or more, for example, about 0.94 g / cm 3 or more, for example, about 0.95 g / cm 3 and generally have a density of about 1 g / cm3 Less than about 0.97 g / cm 3 It may have a density of less than 1000 .mu.m.

[0048]

[0050] High density polyethylene polymers can be made from greater than 90% ethylene-derived units, such as greater than 95% ethylene-derived units, or 100% ethylene-derived units. The polyethylene can be a homopolymer or a copolymer, including a terpolymer with other monomeric units.

[0049]

[0051] High density polyethylene can be high molecular weight polyethylene, very high molecular weight polyethylene, and / or ultra-high molecular weight polyethylene. "High molecular weight polyethylene" refers to polyethylene having a molecular weight of at least about 3×10 5 "Margolies molecular weight" refers to a polyethylene composition having an average molecular weight in g / mol, and as used herein is intended to include very high molecular weight polyethylene and ultra-high molecular weight polyethylene. For purposes of this specification, molecular weights referenced herein are determined according to the Margolies equation ("Margolies molecular weight").

[0050]

[0052] "Very high molecular weight polyethylene" is about 3 x 10 6 Less than 1 × 10 g / mol 6 In some embodiments, the molecular weight of a very high molecular weight polyethylene composition is greater than about 2×10 g / mol. 6 g / mol to approximately 3 × 10 6 between 0.01 and 0.15 g / mol.

[0051]

[0053] "Ultra-high molecular weight polyethylene" is at least about 3 x 10 6 In some embodiments, the molecular weight of the ultra-high molecular weight polyethylene composition is about 3×10 6 g / mol to approximately 30 × 10 6 g / mol, or approximately 3 × 10 6 g / mol to approximately 20 × 10 6g / mol, or approximately 3 × 10 6 g / mol to approximately 10 × 10 6 g / mol, or approximately 3 × 10 6 g / mol to approximately 6 × 10 6 g / mol.

[0052]

[0054] In one embodiment, the high-density polyethylene is a homopolymer of ethylene. In another embodiment, the high-density polyethylene may be a copolymer. For example, the high-density polyethylene may be a copolymer of ethylene and another olefin containing 3 to 16 carbon atoms, e.g., 3 to 10 carbon atoms, e.g., 3 to 8 carbon atoms. These other olefins include, but are not limited to, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 4-methylpent-1-ene, 1-decene, 1-dodecene, 1-hexadecene, and the like. Also useful herein are polyene comonomers such as 1,3-hexadiene, 1,4-hexadiene, cyclopentadiene, dicyclopentadiene, 4-vinylcyclohex-1-ene, 1,5-cyclooctadiene, 5-vinylidene-2-norbornene, and 5-vinyl-2-norbornene. However, if present, the amount of non-ethylene monomer in the copolymer may be less than about 10 mol%, such as less than about 5 mol%, for example less than about 2.5 mol%, for example less than about 1 mol%, where mol% is based on the total moles of monomer in the polymer.

[0053]

[0055] In one embodiment, the high-density polyethylene may have a unimodal molecular weight distribution. Alternatively, the high-density polyethylene may exhibit a bimodal molecular weight distribution. By way of example, a bimodal distribution generally refers to a polymer having a distinct higher molecular weight and a distinct lower molecular weight (e.g., two distinct peaks) on a size-exclusion chromatography or gel permeation chromatography curve. In another embodiment, the high-density polyethylene may exhibit more than two molecular weight distribution peaks, such that the polyethylene exhibits a multimodal (e.g., trimodal, tetramodal, etc.) distribution. Alternatively, the high-density polyethylene may exhibit a broad molecular weight distribution such that the size-exclusion chromatography or gel permeation chromatography curve does not exhibit at least two distinct peaks but instead exhibits one distinct peak that is broader than the peaks of the individual components due to the polyethylene being composed of a blend of a higher molecular weight component and a lower molecular weight component.

[0054]

[0056] Polyethylene can be synthesized using any method known in the art. Polyethylene powder is typically produced by catalytic polymerization of ethylene monomer, optionally with one or more other 1-olefin comonomers, using a heterogeneous catalyst and an organoaluminum or magnesium compound as a cocatalyst, such that the 1-olefin content in the final polymer is 10% or less of the ethylene content. Ethylene is usually polymerized in the gas or slurry phase at relatively low temperatures and pressures. The polymerization reaction can be carried out at temperatures between 50°C and 100°C and pressures in the range of 0.02 to 2 MPa.

[0055]

[0057] The molecular weight of the polyethylene can be adjusted by adding hydrogen. Varying the temperature and / or the type and concentration of co-catalyst may also be used to fine-tune the molecular weight. In addition, the reaction may be carried out in the presence of an antistatic agent to avoid fouling and product contamination.

[0056]

[0058] Suitable catalyst systems include, but are not limited to, Ziegler-Natta catalysts. Typically, Ziegler-Natta catalysts are derived from a combination of a transition metal compound from Groups 4 to 8 of the periodic table and an alkyl or hydride derivative of a metal from Groups 1 to 3 of the periodic table. The transition metal derivatives used usually include metal halides or esters, or combinations thereof. Exemplary Ziegler-Natta catalysts include those based on the reaction product of an organoaluminum or magnesium compound, such as, but not limited to, an alkylaluminum or magnesium, with a titanium, vanadium, or chromium halide or ester. Heterogeneous catalysts can be unsupported or supported on a porous particulate material, such as silica or magnesium chloride. Such supports can be added during catalyst synthesis or obtained as a chemical reaction product of the catalyst synthesis itself.

[0057]

[0059] In one embodiment, a suitable catalyst system can be obtained by reacting a titanium(IV) compound with a trialkylaluminum compound in an inert organic solvent at a temperature ranging from -40°C to 100°C, preferably from -20°C to 50°C. The concentrations of the starting materials are 0.1 to 9 mol / L, preferably 0.2 to 5 mol / L, for the titanium(IV) compound and 0.01 to 1 mol / L, preferably 0.02 to 0.2 mol / L, for the trialkylaluminum compound. The titanium component is added to the aluminum compound over a period of 0.1 to 60 minutes, preferably 1 to 30 minutes, and the molar ratio of titanium to aluminum in the final mixture is in the range of 1:0.01 to 1:4.

[0058]

[0060] In another embodiment, a suitable catalyst system is obtained by reacting a titanium(IV) compound with a trialkylaluminum compound in an inert organic solvent at a temperature ranging from -40°C to 200°C, preferably from -20°C to 150°C, in one or two steps. In the first step, the titanium(IV) compound is reacted with the trialkylaluminum compound at a titanium to alumina molar ratio ranging from 1:0.1 to 1:0.8, at a temperature ranging from -40°C to 100°C, preferably from -20°C to 50°C. The concentrations of the starting materials are 0.1 to 9.1 mol / L, preferably 5 to 9.1 mol / L, for the titanium(IV) compound and 0.05 to 1 mol / L, preferably 0.1 to 0.9 mol / L, for the trialkylaluminum compound. The titanium component is added to the aluminum compound over a period of 0.1 to 800 minutes, preferably 30 to 600 minutes. In the second step, if applicable, the reaction product obtained in the first step is treated with a trialkylaluminum compound in a titanium to aluminum molar ratio in the range of 1:0.01 to 1:5 at a temperature in the range of -10°C to 150°C, preferably 10°C to 130°C.

[0059]

[0061] In yet another embodiment, a suitable catalyst system is obtained by a procedure in which, in a first reaction step, magnesium alcoholate is reacted with titanium chloride in an inert hydrocarbon at a temperature between 50° C. and 100° C. In a second reaction step, the reaction mixture formed is subjected to a heat treatment at a temperature between 110° C. and 200° C. for about 10 to 100 hours, with the release of alkyl chlorides until no more alkyl chlorides are released, and then the solid is liberated from the soluble reaction products by washing several times with a hydrocarbon.

[0060]

[0062] In a further embodiment, silica supported catalysts may also be used, such as the commercially available catalyst system Sylopol 5917.

[0063] Using such catalyst systems, polymerization is usually carried out in suspension, continuously or batchwise, in one or more steps, at low pressure and temperature. Polymerization temperatures are typically in the range of 30°C to 130°C, preferably 50°C to 90°C, and the ethylene partial pressure is typically less than 10 MPa, preferably 0.05 MPa to 5 MPa. Trialkylaluminums, such as, but not limited to, isoprenylaluminum and triisobutylaluminum, are used as cocatalysts, with the Al:Ti (cocatalyst to catalyst) ratio being in the range of 0.01 to 100:1, more preferably 0.03 to 50:1. The solvent is an inert organic solvent typically used for Ziegler-type polymerization. Examples include butane, pentane, hexane, cyclohexene, octane, nonane, decane, their isomers, and mixtures thereof. The molecular weight of the polymer is controlled by supplying hydrogen. The ratio of hydrogen partial pressure to ethylene partial pressure is in the range of 0 to 50, preferably 0 to 10. The polymer is isolated and dried under nitrogen in a fluidized bed dryer. The solvent can be removed through steam distillation if a high-boiling solvent is used. Salts of long-chain fatty acids may be added as stabilizers. Typical examples are calcium stearate, magnesium stearate, and zinc stearate.

[0061]

[0064] Optionally, other catalysts, such as Phillips catalysts, metallocenes, and post-metallocenes, can be used. Typically, a cocatalyst, such as an alumoxane or an alkylaluminum or alkylmagnesium compound, is also used. Other suitable catalyst systems include Group 4 metal complexes of phenolate ether ligands.

[0062]

[0065] In one embodiment, the polyethylene particles are made from a polyethylene polymer having a relatively low bulk density as measured in accordance with DIN 53466. By way of example, in one embodiment, the bulk density is generally about 0.4 g / cm 3 less than, for example, about 0.35 g / cm 3 less than, for example, about 0.33 g / cm 3less than, for example, about 0.3 g / cm 3 Less than about 0.28 g / cm 3 less than, for example, about 0.26 g / cm 3 The bulk density is generally less than about 0.1 g / cm 3 greater than, for example, about 0.15 g / cm 3 In one embodiment, the polymer has a density of about 0.2 g / cm 3 ~Approx. 0.27g / cm 3 It has a bulk density of

[0063]

[0066] In one embodiment, the polyethylene particles may be a free-flowing powder. The particles may have a volume median particle size (d50) of less than 600 microns, e.g., less than about 500 microns, e.g., less than about 400 microns, e.g., less than about 300 microns. For example, the median particle size (d50) of the polyethylene particles may be less than about 150 microns, e.g., less than about 125 microns. The median particle size (d50) is generally greater than about 20 microns. The particle size of the powder may be measured using laser diffraction according to ISO 13320.

[0064]

[0067] In one embodiment, 90% of the polyethylene particles may have a particle size less than about 800 microns, such as less than about 700 microns, for example less than 600 microns, such as less than about 500 microns, for example less than about 400 microns, such as less than about 300 microns, for example less than about 250 microns, and generally may have a particle size greater than about 50 microns, such as greater than about 100 microns, for example greater than about 200 microns.

[0065]

[0068] The molecular weight of the polyethylene polymer can vary depending on the specific application. The polyethylene polymer can have, for example, an average molecular weight determined by the Margolies equation. The molecular weight can be determined by first measuring the viscosity number according to DIN EN ISO Test 1628. The dry powder stream is measured using a 25 mm nozzle. The molecular weight is then calculated from the viscosity number using the Margolies equation. The average molecular weight is generally greater than about 500,000 g / mol, for example greater than about 600,000 g / mol, for example greater than about 650,000 g / mol, for example greater than about 1,000,000 g / mol, for example greater than about 2,000,000 g / mol, for example greater than about 2,500,000 g / mol, for example greater than about 3,000,000 g / mol, for example greater than about 4,000,000 g / mol. The average molecular weight is generally less than about 12,000,000 g / mol, e.g., less than about 10,000,000 g / mol. In one embodiment, the number average molecular weight of the high-density polyethylene polymer can be less than about 4,000,000 g / mol, e.g., less than about 3,000,000 g / mol.

[0066]

[0069] The polyethylene may have a viscosity number of at least 500 mL / g, such as at least 700 mL / g, for example at least 1,000 mL / g, up to a viscosity number of less than about 6,000 mL / g, such as less than about 5,000 mL / g, for example less than about 4,000 mL / g, for example less than about 3,000 mL / g, for example less than about 2,000 mL / g, determined in accordance with ISO 1628 part 3 using a concentration in decahydronaphthalene of 0.0002 g / mL.

[0067]

[0070] The high-density polyethylene may have a crystallinity of at least about 40% to 85%, e.g., 45% to 80%. In one embodiment, the crystallinity may be greater than about 50%, e.g., greater than about 55%, e.g., greater than about 60%, e.g., greater than about 65%, e.g., greater than about 70%, and generally less than about 80%.

[0068]

[0071] In producing hydrophilic porous films according to the present disclosure, a variety of different techniques and methods can be used to enhance the hydrophilic properties of the film. In one embodiment, one or more high-density polyethylene polymers described above can be combined with one or more hydrophilic additives. Alternatively or in addition to incorporating a hydrophilic additive into the film, the film or polymer can be plasma oxidized to enhance the hydrophilic properties.

[0069]

[0072] In one embodiment, high-density polyethylene particles are mixed or blended with at least one hydrophilic additive and then formed into a film.The one or more hydrophilic additives are generally incorporated into the film in an amount greater than about 5% by weight, for example, greater than about 10% by weight, for example, greater than about 20% by weight, for example, greater than about 30% by weight, for example, greater than about 35% by weight, for example, greater than about 40% by weight, for example, greater than about 45% by weight, for example, greater than about 50% by weight, for example, greater than about 55% by weight, for example, greater than about 60% by weight, for example, greater than about 65% by weight.The one or more hydrophilic additives are generally present in the film in an amount less than about 90% by weight, for example, less than about 85% by weight, for example, less than about 80% by weight, for example, less than about 75% by weight, for example, less than about 70% by weight, for example, less than about 65% by weight.

[0070]

[0073] In one aspect, the hydrophilic additive can include inorganic particles. The inorganic particles can include, for example, oxide particles, hydroxide particles, sulfate particles, etc. For example, the inorganic particles can include metal oxide particles, metal hydroxide particles, or a mixture thereof.

[0071]

[0074] Examples of hydrophilic additives that can be incorporated into the films of the present disclosure include particles made from silica, alumina, zirconium oxide, zirconium hydroxide, magnesium oxide, magnesium hydroxide, titanium oxide, titanium hydroxide, barium sulfate, or mixtures thereof. Still other examples of hydrophilic additives include particles of bismuth oxide, cerium oxide, bismuth hydroxide, cerium hydroxide and / or nitrides and / or carbides of elements from Group IV of the periodic table.

[0072]

[0075] In one particular embodiment, the hydrophilic additive comprises fumed or precipitated silica particles.

[0076] Inorganic particles generally have a small particle size. For example, the particles may have an average particle size (D50) of less than about 20 microns, for example, less than about 15 microns, for example, less than about 10 microns, for example, less than about 5 microns, for example, less than about 2 microns, for example, less than about 1 micron, for example, less than about 0.8 microns, for example, less than about 0.7 microns, for example, less than about 0.6 microns, for example, less than about 0.5 microns, for example, less than about 0.4 microns, for example, less than about 0.3 microns, for example, less than about 0.2 microns, for example, less than about 0.1 microns. The particle size is generally greater than about 0.01 microns, for example, greater than about 0.05 microns, for example, greater than about 0.1 microns. In one embodiment, the particle size is generally greater than about 2 microns, for example, greater than about 5 microns, for example, greater than about 8 microns.

[0073]

[0077] The one or more inorganic hydrophilic particles can be present in the porous polymer film in an amount of at least about 5 wt%, for example, at least about 10 wt%, for example, at least about 20 wt%, for example, at least about 30 wt%, for example, at least about 40 wt%, for example, at least about 50 wt%, for example, at least about 60 wt%, for example, at least about 70 wt%, and generally in an amount less than about 90 wt%, for example, less than about 75 wt%. In some embodiments, high-density polyethylene particles serve as a binder for the inorganic particles.

[0074]

[0078] Instead of or in addition to inorganic particles, the hydrophilic additive can also include a hydrophilic polymer, such as a hydrophilically modified thermoplastic polymer. The hydrophilically modified polymer can, for example, include a polymer in which hydrophilic groups are grafted onto the polymer chain. The hydrophilically modified polymer can include a hydrophilically modified high-density polyethylene polymer. The high-density polyethylene polymer can have any of the properties described above for the polyethylene polymer used to form the matrix of the film.

[0075]

[0079] In one embodiment, the hydrophilic additive can include a polyolefin polymer, particularly a polyethylene polymer, functionalized with an organic acid, such as an organic acid anhydride. For example, a polyolefin polymer, such as a polyethylene polymer, can be modified to include hydrophilic carboxyl groups. The carboxyl groups can be added to the polymer by oxidation, polymerization, or grafting. For example, in one embodiment, a carboxyl-containing unsaturated monomer can be grafted onto a polyolefin polymer, such as a polyethylene polymer. The carboxyl-containing unsaturated monomer can be, for example, maleic anhydride.

[0076]

[0080] For example, in one embodiment, the hydrophilic additive can be a polyethylene polymer functionalized with maleic anhydride. The polyethylene polymer can be the same as or a different polyethylene polymer from the high-density polyethylene polymer combined with the hydrophilic additive. For example, the polyethylene polymer functionalized with maleic anhydride can be a low-density polyethylene polymer, such as a linear low-density polyethylene polymer. Alternatively, the polyethylene polymer functionalized with maleic anhydride can be a high-density polyethylene polymer. The high-density polyethylene polymer can have a molecular weight greater than about 300,000 g / mol, e.g., greater than about 500,000 g / mol, e.g., greater than about 700,000 g / mol, and generally less than about 12,000,000 g / mol.

[0077]

[0081] The maleic anhydride-functionalized polyethylene generally contains maleic anhydride in an amount greater than about 1.5 wt%, e.g., greater than about 1.8 wt%, e.g., greater than about 2 wt%, e.g., greater than about 2.5 wt%, e.g., greater than about 3 wt%, e.g., greater than about 3.5 wt%, e.g., greater than about 4 wt%, e.g., greater than about 4.5 wt%, e.g., greater than about 10 wt%, e.g., greater than about 20 wt%. The maleic anhydride-functionalized polyethylene generally contains maleic anhydride in an amount less than about 60 wt%, e.g., less than about 50 wt%, e.g., less than about 40 wt%, e.g., less than about 20 wt%, e.g., less than about 10 wt%, e.g., less than about 8 wt%, e.g., less than about 5 wt%. The maleic anhydride-functionalized polyethylene can be in the form of a powder or particles that are combined or compounded with high-density polyethylene particles.

[0078]

[0082] In other embodiments, the hydrophilic additive may be a fatty alcohol glycol ether, such as an ethylene-vinyl alcohol copolymer. The hydrophilic additive may also be an ethylene acrylic acid copolymer. The ethylene acrylic acid copolymer may generally have an acrylic acid content of more than 5 wt%, for example, more than about 8 wt%, for example, more than about 10 wt%, and may generally have an acrylic acid content of less than about 30 wt%, for example, less than about 20 wt%, for example, less than about 15 wt%, for example, less than about 12 wt%.

[0079]

[0083] The hydrophilic additive may be any suitable olefin-containing acrylate polymer and / or graft copolymer. An olefin polymer, such as polyethylene, may serve as the graft base and may be grafted to at least one vinyl polymer or one ether polymer.

[0080]

[0084] Examples of such hydrophilic additives include ethylene-acrylic acid copolymers, ethylene-maleic anhydride copolymers, ethylene-alkyl (meth)acrylate-maleic anhydride terpolymers, ethylene-alkyl (meth)acrylate-glycidyl (meth)acrylate terpolymers, ethylene-acrylic ester-methacrylic acid terpolymers, ethylene-acrylic ester-maleic anhydride terpolymers, and ethylene-methacrylic acid-alkali metal methacrylic acid (ionomer) terpolymers. In one embodiment, the hydrophilic additive may be a random terpolymer of ethylene, methyl acrylate, and glycidyl methacrylate. The terpolymer may have a glycidyl methacrylate content of about 5% to about 20%, e.g., about 6% to about 10%. The terpolymer may have a methyl acrylate content of about 20% to about 30%, e.g., about 24%.

[0081]

[0085] In one embodiment, the hydrophilic additive can be a polyethylene polymer grafted with acrylic acid. The amount of acrylic acid grafted to the polyethylene polymer can generally be greater than about 0.5% by weight, for example, greater than about 1% by weight, for example, greater than about 2% by weight, for example, greater than about 3% by weight, for example, greater than about 4% by weight. The amount of acrylic acid grafted to the polyethylene polymer is generally less than about 25% by weight, for example, less than about 15% by weight, for example, less than about 12% by weight, for example, less than about 10% by weight, for example, less than about 8% by weight.

[0082]

[0086] In one embodiment, once the acrylic acid is grafted to the polyethylene polymer, the acrylic acid can be saponified. Saponification can occur on the polymer resin or polymer particles, or can occur after the article is formed. In one aspect, the acrylic acid groups can be saponified by contacting the acrylic acid groups with a saponifying agent. Any suitable saponifying agent can be used, such as a base. The saponifying agent can be, for example, a basic solution, such as a sodium hydroxide solution.

[0083]

[0087] The hydrophilic additive may be linear or branched, a homopolymer, or a copolymer (e.g., random, graft, block, etc.) epoxy-functionalized, e.g., containing terminal epoxy groups, skeletal oxirane units, and / or pendant epoxy groups. For example, the hydrophilic additive may be a copolymer including at least one monomer component containing epoxy functionality. The monomer units of the hydrophilic additive may vary. For example, the hydrophilic additive may include an epoxy-functional methacrylic monomer unit. As used herein, the term "(meth)acrylic" generally refers to both acrylic and methacrylic monomers, as well as salts and esters thereof, such as acrylate and methacrylate monomers. Epoxy-functional (meth)acrylic monomers that can be incorporated into the hydrophilic additive include, but are not limited to, those containing 1,2-epoxy groups, such as glycidyl acrylate and glycidyl methacrylate. Other suitable epoxy-functional monomers include allyl glycidyl ether, glycidyl ethacrylate, and glycidyl itaconate.

[0084]

[0088] Examples of other monomers include, for example, ester monomers, olefin monomers, and amide monomers. In one embodiment, the hydrophilic additive can include at least one linear or branched α-olefin monomer, such as one having 2 to 20 carbon atoms or 2 to 8 carbon atoms. Specific examples include ethylene; propylene; 1-butene; 3-methyl-1-butene; 3,3-dimethyl-1-butene; 1-pentene; 1-pentene having one or more methyl, ethyl, or propyl substituents; 1-hexene having one or more methyl, ethyl, or propyl substituents; 1-heptene having one or more methyl, ethyl, or propyl substituents; 1-octene having one or more methyl, ethyl, or propyl substituents; 1-nonene having one or more methyl, ethyl, or propyl substituents; ethyl-, methyl-, or dimethyl-substituted 1-decene; 1-dodecene; and styrene.

[0085]

[0089] In one embodiment, the hydrophilic additive may be a terpolymer containing epoxy functionality. By way of example, the hydrophilic additive may include a methacrylic component containing epoxy functionality, an α-olefin component, and a methacrylic component without epoxy functionality. For example, the hydrophilic additive may be poly(ethylene-co-methacrylate-co-glycidyl methacrylate), which has the structure:

[0086] [ka]

[0087] (wherein a, b, and c are 1 or more) It has.

[0090] In another embodiment, the hydrophilic additive can be a random copolymer of ethylene, ethyl acrylate, and maleic anhydride, having the structure:

[0088] [ka]

[0089] (wherein x, y, and z are 1 or greater) It has.

[0091] The relative proportions of the various monomer components of the copolymer hydrophilic additive are not particularly limited. For example, in one embodiment, the epoxy-functional methacrylic monomer component can form about 1 wt.% to about 25 wt.%, or about 2 wt.% to about 20 wt.% of the copolymer hydrophilic additive. The α-olefin monomer can form about 55 wt.% to about 95 wt.%, or about 60 wt.% to about 90 wt.% of the copolymer hydrophilic additive. When utilized, other monomer components (e.g., non-epoxy-functional methacrylic monomers) can comprise about 5 wt.% to about 35 wt.%, or about 8 wt.% to about 30 wt.% of the copolymer hydrophilic additive.

[0090]

[0092] The molecular weight of the hydrophilic additives can vary widely. For example, the hydrophilic additives can have a number average molecular weight of from about 7,500 to about 250,000 grams per mole, in some embodiments from about 15,000 to about 150,000 grams per mole, and in some embodiments from about 20,000 to 100,000 grams per mole, with a polydispersity index typically ranging from 2.5 to 7.

[0091]

[0093] In yet another embodiment, the hydrophilic additive may be a surfactant that can be melt-processed with the high-density polyethylene resin. For example, the surfactant may be a nonionic surfactant that is in a solid form at 23°C. In one aspect, for example, the hydrophilic additive may be an alkyl polyethylene glycol ether. The alkyl polyethylene glycol ether may be made from a linear, saturated C10-C28, e.g., C16-C18, fatty alcohol. For example, the surfactant may be the reaction product of a fatty alcohol with ethylene oxide. The surfactant may contain an ethoxylation degree of greater than about 8 mol, e.g., greater than about 10 mol, e.g., greater than about 20 mol, e.g., greater than about 30 mol, e.g., greater than about 40 mol, and generally less than about 100 mol, e.g., less than about 80 mol, e.g., less than about 60 mol.

[0092]

[0094] The hydrophilically modified polymer, for example a hydrophilically modified polyethylene polymer, may be present in the film in an amount greater than about 2 wt%, such as greater than about 5 wt%, for example greater than about 10 wt%, for example greater than about 15 wt%, such as greater than about 20 wt%, for example greater than about 30 wt%, for example greater than about 40 wt%, such as greater than about 50 wt%, and generally less than about 98 wt%, such as less than about 80 wt%, for example less than about 60 wt%, for example less than about 40 wt%, for example less than about 20 wt%, for example less than about 12 wt%.

[0093]

[0095] In one embodiment, porous polymer films can be plasma oxidized to enhance their hydrophilic properties. The plasma oxidation method can be used alone or in combination with one or more hydrophilic additives. Oxygen plasma treatment not only significantly improves the compatibility of porous polymer films with electrolytes, enhancing ionic conductivity, but also does so without adversely affecting the mechanical properties of the films.

[0094]

[0096] For example, in one embodiment, the plasma method of the present disclosure is carried out using microwave discharge. Additionally, the method can be carried out at very low pressures and extremely short contact times to preserve the physical properties of the porous polymer film.

[0095]

[0097] One embodiment of a plasma process that may be used in accordance with the present disclosure is shown in Figure 2. Referring to Figure 2, the plasma process includes a microwave supply 50 in communication with a vacuum chamber 52 via a resonant cavity 53. The resonant cavity 53 may include or be associated with an impedance matching system. A substrate holder 54 is housed within the vacuum chamber 52. The vacuum chamber 52 is also associated with a pressure monitoring system 58.

[0096]

[0098] To apply a vacuum to the chamber 52, the chamber 52 may be placed in communication with a pump 56. The vacuum chamber 52 is also in communication with an exhaust system 60.

[0099] As shown in Figure 2, vacuum chamber 52 may also be placed in fluid communication with one or more gas supplies. In the embodiment shown in Figure 2, three different gas supplies are shown at 62, 64, and 66. Each gas supply 62, 64, and 66 is placed in association with a corresponding mass flow controller 68, 70, and 72. Gas supplies 62, 64, and 66 are for supplying oxygen, alone or in combination with other gases, to vacuum chamber 52.

[0097]

[0100] As described above, in one embodiment, a microwave plasma reactor is used to deliver oxygen plasma to the porous polymer film. While other plasma reactors may be used in accordance with the present disclosure, in one embodiment, a low-pressure plasma system with microwave discharge is preferred. Alternatively, an inductively coupled plasma system containing an RF generator may be used. However, the two reactors differ in many respects, including the manufacturing conditions and applied methods. For example, when using a microwave reactor, the porous polymer film sample is placed outside the active plasma zone, whereas in an inductively coupled plasma reactor, the sample may be subjected to a significant amount of ion bombardment. Therefore, the flux of charged particles reaching the sample may differ between the two methods.

[0098]

[0101] During oxygen plasma treatment, the porous polymer film sample is placed into a vacuum chamber 52, which is evacuated using a pump 56. Plasma is then generated by a microwave supply 50 in association with one or more gases containing oxygen, which are supplied to the vacuum chamber 52. The source of oxygen can vary depending on the particular application. In one embodiment, pure oxygen gas is supplied to the vacuum chamber 52. However, in alternative embodiments, oxygen can be combined with other gases, such as inert gases. For example, oxygen can be combined with nitrogen. In one embodiment, air is supplied to the plasma chamber 52. Other sources of oxygen include hydrogen peroxide, water (vapor), nitrous oxide, ozone, etc. In one embodiment, the gas supplied to the plasma chamber 52 contains more than about 20% oxygen by volume, such as more than about 30% oxygen by volume, such as more than about 50% oxygen by volume.

[0099]

[0102] During oxygen plasma treatment, ionized gas is formed, which contains a variety of different positive and negative ions, and optionally free radicals, photons, and neutral species. The ionized gas initiates a reaction on the surface of the porous polymer film, which ultimately modifies the surface chemistry. For example, polyethylene polymer can be oxidized in the presence of oxygen. The plasma-oxidized surface can contain a variety of different polar groups, which, for example, enhance the polarity of the surface of the porous polymer film.

[0100]

[0103] Conditions within the plasma chamber 52 during the plasma process may vary. In one embodiment, the oxygen plasma process is carried out at low pressure. For example, the pressure within the chamber may be maintained at less than 1 atmosphere. For example, the pressure within the chamber may be less than about 10,000 Pa, e.g., less than about 5,000 Pa, e.g., less than about 1,000 Pa, e.g., less than about 500 Pa, e.g., less than about 300 Pa, e.g., less than about 200 Pa. In one embodiment, the process is carried out at very low pressure, e.g., less than about 150 Pa, e.g., less than about 130 Pa, e.g., less than about 100 Pa, e.g., less than about 80 Pa, e.g., less than about 50 Pa, e.g., less than about 30 Pa. The temperature during the process may generally be less than about 60° C., e.g., less than about 50° C., e.g., less than about 40° C., e.g., less than about 30° C., e.g., less than about 28° C., e.g., less than about 25° C., and generally greater than about 15° C., e.g., greater than about 20° C.

[0101]

[0104] According to the present disclosure, the contact time between the porous polymer film and the oxygen plasma may be relatively short in one embodiment. For example, in one embodiment, each side of the porous polymer film may be exposed to the plasma for less than about 30 seconds, e.g., less than about 25 seconds, e.g., less than about 20 seconds, e.g., less than about 15 seconds, e.g., less than about 12 seconds, e.g., less than about 10 seconds, e.g., less than about 8 seconds, e.g., less than about 6 seconds. The contact time is generally greater than about 1 second, e.g., greater than about 2 seconds, e.g., greater than about 3 seconds. It has been discovered that extremely short contact times impart the necessary ionic conductivity without adversely affecting the physical properties of the film, especially when using microwave-generated plasma at low pressures.

[0102]

[0105] To form a porous film according to the present disclosure from high density polyethylene polymer and one or more hydrophilic additives, the polymer composition is either gel extruded or sintered.

[0103] Gel extrusion

[0106] When forming a gel-extruded porous film, one or more high-density polyethylene polymers and one or more hydrophilic additives are combined with a plasticizer to form a gel, and the resulting gel is fed through an extrusion device. During the film-forming process, the plasticizer can be substantially or completely removed from the resulting polymer article. For example, the resulting article can contain less than about 10% by weight of plasticizer, such as less than about 5% by weight, such as less than about 2% by weight, such as less than about 1% by weight, such as less than about 0.5% by weight, such as less than about 0.1% by weight. The resulting article can contain 0% or more than about 0.5% by weight, such as more than about 1% by weight, such as more than about 2% by weight.

[0104]

[0107] The plasticizer may include, for example, a hydrocarbon oil, an alcohol, an ether, an ester, such as a diester, or a mixture thereof. Suitable plasticizers include, for example, mineral oil, paraffinic oil, decalin, and the like. Other plasticizers include xylene, dioctyl phthalate, dibutyl phthalate, stearyl alcohol, oleyl alcohol, decyl alcohol, nonyl alcohol, diphenyl ether, n-decane, n-dodecane, octane, nonane, kerosene, toluene, naphthalene, tetralin, and the like. In one embodiment, the plasticizer may include a halogenated hydrocarbon, such as monochlorobenzene. Cycloalkanes and cycloalkenes may also be used, such as camphene, methane, dipentene, methylcyclopentadiene, tricyclodecane, 1,2,4,5-tetramethyl-1,4-cyclohexadiene, and the like. The plasticizer may also include mixtures and combinations of any of the above.

[0105]

[0108] The plasticizer is generally present in the composition used to form the polymeric article in an amount greater than about 50% by weight, such as greater than about 55% by weight, for example, greater than about 60% by weight, for example, greater than about 65% by weight, for example, greater than about 70% by weight, for example, greater than about 75% by weight, for example, greater than about 80% by weight, for example, greater than about 85% by weight, for example, greater than about 90% by weight, for example, greater than about 95% by weight, for example, greater than about 98% by weight. In fact, the plasticizer can be present in an amount up to about 99.5% by weight.

[0106]

[0109] The high-density polyethylene particles, plasticizer, and one or more hydrophilic additives are blended together to form a homogeneous gel-like material, which is then extruded through a die of a desired shape. In one embodiment, the composition can be heated in an extruder. For example, the plasticizer can be combined with the particle mixture and fed into the extruder. The plasticizer and particle mixture form a homogeneous gel-like material, which is then run through the extruder to form a polymer article with little to no impurities.

[0107]

[0110] During this process, at least a portion of the plasticizer is removed from the final product. This plasticizer removal process can occur due to evaporation when a relatively volatile plasticizer is used. Alternatively, an extraction liquid can be used to remove the plasticizer. The extraction liquid can include, for example, a hydrocarbon solvent. Examples of extraction liquids include dichloromethane, trichloroethane, trichloroethylene, or mixtures thereof. Other extraction liquids include acetone, chloroform, alkanes, hexene, heptene, alcohol, or mixtures thereof. In one embodiment, the extraction liquid is selected to also control the amount of molecular weight maintaining package removed from the composition.

[0108]

[0111] In one embodiment, the resulting film is not stretched and is calendered by feeding it through the nip of calendar rolls.

[0109]

[0112] If desired, the resulting polymeric article may be stretched at an elevated temperature below the melting point of the polyethylene polymer to enhance strength and elasticity. Suitable temperatures for stretching are within the range of about ambient temperature to about 155°C. The stretch ratio can generally be greater than about 4, such as greater than about 6, such as greater than about 8, such as greater than about 10, such as greater than about 15, such as greater than about 20, such as greater than about 25, such as greater than about 30. In certain embodiments, the stretch ratio can be greater than about 50, such as greater than about 100, such as greater than about 110, such as greater than about 120, such as greater than about 130, such as greater than about 140, such as greater than about 150. The stretch ratio is generally less than about 1,000, such as less than about 800, such as less than about 600, such as less than about 400. In one embodiment, a lower stretch ratio is used, such as from about 4 to about 10. The polymeric article may be stretched uniaxially or biaxially.

[0110] Sintered Film

[0113] In an alternative embodiment, the hydrophilic porous film of the present disclosure can be formed through a sintering process. During sintering, polyethylene particles are compacted and formed into a solid mass without using heat and / or pressure to melt the polymer. Sintering high-density polyethylene particles according to the present disclosure produces a porous structure with fluid capillaries well suited for ion permeability while remaining impermeable to gases. During sintering, a polymer with a relatively high molecular weight is used. The polymer can have an average molecular weight of, for example, greater than about 500,000 g / mol, such as greater than about 1,000,000 g / mol, such as greater than about 1,500,000 g / mol, or greater than about 2,000,000 g / mol.

[0111]

[0114] In one embodiment, the high density polyethylene polymer selected for sintering has a very low melt flow rate, or a melt flow rate that is too low to be measured.

[0112]

[0115] In one embodiment, one or more high-density polyethylene polymers in the form of particles are combined with one or more hydrophilic additives and any other desired additives and mixed together. For example, these components can be dry mixed using, for example, a tumbler mixer, an electric blender, or combined through shaking.

[0113]

[0116] Porous articles, such as films, can be formed by a free-sintering method, which involves introducing the polyethylene polymer powder described above, either partially or entirely, into a closed space, such as a mold, and subjecting the powder to be molded to sufficient heat to cause the polyethylene particles to soften, expand, and contact each other. Suitable processes include compression molding and casting. The mold can be made of steel, aluminum, or other metals. The polyethylene polymer powder used in the molding process is generally ex-reactor grade, meaning that the powder is not sieved or crushed before being introduced into the mold. The additives discussed above can, of course, be mixed with the powder.

[0114]

[0117] The mold is heated in a convection oven, hydraulic press, or infrared heater to a sintering temperature of between about 140°C and about 300°C, e.g., between about 160°C and about 300°C, e.g., between about 170°C and about 240°C, to sinter the polymer particles. The heating time and temperature vary and depend on the mass of the mold and the geometry of the molded article. However, the heating time is typically within the range of about 10 to about 100 minutes. During sintering, the surfaces of the individual polymer particles fuse at their contact points to form a porous structure. The mold is then cooled, and the porous article is removed. Generally, molding pressure is not required. However, if porosity adjustment is required, a proportionally lower pressure can be applied to the powder.

[0115]

[0118] In one aspect, porous polymeric films can be produced through a sintering process. Alternatively, cylindrical porous articles can be formed and delivered through a skiving process to produce films with desired properties and thickness.

[0116]

[0119] In addition to one or more high-density polyethylene polymers and one or more hydrophilic additives, the polymer composition used to produce the porous film of the present disclosure can contain a variety of other additives and components. For example, the extruded or sintered film produced according to the present disclosure can also contain heat stabilizers, light stabilizers, UV absorbers, acid scavengers, flame retardants, lubricants, colorants, etc.

[0117]

[0120] In one embodiment, a heat stabilizer may be present in the composition, including, but not limited to, a phosphite, an amine antioxidant, a phenolic antioxidant, or any combination thereof.

[0118]

[0121] In one embodiment, an antioxidant may be present in the composition, including, but not limited to, a secondary aromatic amine, a benzofuranone, a sterically hindered phenol, or any combination thereof.

[0119]

[0122] In one embodiment, a light stabilizer may be present in the composition, including, but not limited to, 2-(2'-hydroxyphenyl)-benzotriazole, 2-hydroxy-4-alkoxybenzophenone, nickel-containing light stabilizer, 3,5-di-tert-butyl-4-hydroxybenzoate, sterically hindered amines (HALS), or any combination thereof.

[0120]

[0123] In one embodiment, a UV absorber may be present in the composition in place of or in addition to the light stabilizer, including, but not limited to, a benzotriazole, a benzoate, or a combination thereof or any combination thereof.

[0121]

[0124] In one embodiment, a halogenated flame retardant may be present in the composition, including, but not limited to, tetrabromobisphenol A (TBBA), tetrabromophthalic anhydride, didecachloropentacyclooctadecadiene (dechlorane), hexabromocyclodedecane, chlorinated paraffins, or any combination thereof.

[0122]

[0125] In one embodiment, non-halogenated flame retardants may be present in the composition, including, but not limited to, resorcinol diphosphate tetraphenyl ester (RDP), ammonium polyphosphate (APP), phosphinic acid derivatives, triaryl phosphates, trichloropropyl phosphate (TCPP), magnesium hydroxide, aluminum trihydroxide, and antimony trioxide.

[0123]

[0126] In one embodiment, a lubricant may be present in the composition, including but not limited to silicone oil, wax, molybdenum disulfide, or any combination thereof.

[0124]

[0127] In one embodiment, colorants may be present in the composition, including but not limited to inorganic and organic based color pigments.

[0128] In one embodiment, an acid scavenger may be present in the polymer composition. Examples of the acid scavenger may include alkali metal salts or alkaline earth metal salts. The salt may include a salt of a fatty acid, such as a stearate. Other acid scavengers include carbonates, oxides, or hydroxides. Specific acid scavengers that may be incorporated into the polymer composition include metal stearates, such as calcium stearate. Still other acid scavengers include zinc oxide, calcium carbonate, magnesium oxide, and mixtures thereof.

[0125]

[0129] These additives may be used alone or in any combination thereof. Generally, each additive may be present in an amount of at least about 0.05 wt.%, for example, at least about 0.1 wt.%, for example, at least about 0.25 wt.%, for example, at least about 0.5 wt.%, for example, at least about 1 wt.%, and generally may be present in an amount of less than about 20 wt.%, for example, less than about 10 wt.%, for example, less than about 5 wt.%, for example, less than about 4 wt.%, for example, less than about 2 wt.%. The sum of all wt.% of the components used in the polymer composition, including any additives, if present, equals 100 wt.%.

[0126]

[0130] After the hydrophilic porous polymer film of the present disclosure is formed, the film can be directly incorporated into the electrolytic cell shown in Figure 1. Optionally, a hydrophilic coating can be applied to one or both sides of the film. The coating can include silica, aluminum oxide, zirconium oxide, or any of the other hydrophilic inorganic materials described above. In one embodiment, both sides of the film are coated with a hydrophilic coating.

[0127]

[0131] For example, in one embodiment, a dope solution can be coated onto each side of the film, for example, using an extrusion coating method. The dope solution can include, for example, a polymer resin in combination with hydrophilic particles and a solvent. The hydrophilic particles can include any of the hydrophilic inorganic particles described above. The organic solvent can be selected so that the polymer resin is dissolved therein. The solvent can be an inorganic solvent that is miscible with water. Examples of solvents include N-methyl-pyrrolidone, N-ethyl-pyrrolidone, N-butyl-pyrrolidone, N,N-dimethylformamide, formamide, dimethyl sulfoxide, N,N-dimethylacetamide, acetonitrile, or a mixture thereof.

[0128]

[0132] The polymer resin can include a fluoropolymer, such as polytetrafluoroethylene. Alternatively, the polymer resin can be an olefin resin, such as polyethylene or polypropylene, polyethylene terephthalate, or polystyrene. In one aspect, the polymer resin is vinylidene fluoride.

[0129]

[0133] The dope solution may also optionally contain a variety of other components, such as organic or inorganic compounds. Organic compounds that may be present include polyethylene glycol, polyethylene oxide, polypropylene glycol, ethylene glycol, tripropylene glycol, glycerol, polyhydric alcohols, dibutyl phthalate, diethyl phthalate, diundecyl phthalate, isononanoic acid, polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl acetate, polyethyleneimine, polyacrylic acid, methylcellulose, dextran, or mixtures thereof.

[0130]

[0134] After the film is coated with the dope solution, the dope solution may be subjected to phase inversion to transform the dope into a porous hydrophilic coating.

[0135] The phase inversion step includes the so-called liquid-induced phase separation (LIPS) step, the vapor-induced phase separation (VIPS) step, or a combination of a VIPS step and a LIPS step. Both LIPS and VIPS are non-solvent-induced phase inversion methods.

[0131]

[0136] In the LIPS process, the dope-coated substrate is contacted with a non-solvent that is miscible with the solvent of the dope solution. Typically, this is accomplished by immersing the dope-coated substrate in a non-solvent bath, also known as a coagulation bath. The non-solvent can be water, a mixture of water and an aprotic solvent selected from the group consisting of N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and dimethylacetamide (DMAC), an aqueous solution of a water-soluble polymer such as PVP or PVA, or a mixture of water and an alcohol such as ethanol, propanol, or isopropanol.

[0132]

[0137] The temperature of the bath may be between 20°C and 90°C, for example between 40°C and 70°C.

[0138] Migration of the solvent from the coated polymer layer to the non-solvent bath and back to the polymer layer results in phase inversion and the formation of a three-dimensional porous polymer network. Impregnation of the applied dope solution into the support results in full adsorption between the resulting hydrophilic layer on the porous film.

[0133]

[0139] These and other modifications and variations to the present invention may be practiced by those skilled in the art without departing from the spirit and scope of the invention, which is more particularly set forth in the appended claims. In addition, it should be understood that aspects of the various embodiments may be interchangeable both in whole or in part. Furthermore, those skilled in the art will appreciate that the foregoing description is by way of example only and is not intended to limit the invention as further set forth in such appended claims.

Claims

1. a separator separating the anode from the cathode, A porous polymer film is provided, the porous polymer film comprises a high density polyethylene polymer having a number average molecular weight greater than about 500,000 g / mol, the film having a thickness of about 5 microns to about 600 microns, the porous polymer film comprising: (a) containing a hydrophilic additive present in said porous polymeric film in an amount of at least about 5% by weight; and / or (b) plasma oxidized to increase the hydrophilic properties of the film; The separator.

2. 10. The separator of claim 1, wherein the porous polymer film has a porosity of about 25% to about 85%.

3. 3. The separator according to claim 1 or 2, wherein the high-density polyethylene polymer has a number average molecular weight of more than about 600,000 g / mol, such as more than about 700,000 g / mol, for example more than about 1,000,000 g / mol, such as more than about 2,000,000 g / mol, for example more than about 3,000,000 g / mol, such as more than about 4,000,000 g / mol, and less than about 12,000,000 g / mol, for example less than about 10,000,000 g / mol.

4. 4. The separator of claim 1, wherein the porous polymer film comprises an extruded film that has been stretched or calendered in at least one direction.

5. The separator of claim 1 , wherein the porous polymer film comprises a sintered film.

6. The separator of any one of claims 1 to 5, wherein the porous polymer film has a thickness of about 5 microns to about 500 microns, for example, about 20 microns to about 150 microns.

7. 7. The separator of claim 1, which is a single layer porous polymer film that may optionally include a coating.

8. 9. The separator of claim 8, wherein the single-layer porous polymer film comprises a coating, the coating comprising a hydrophilic coating, such as a coating comprising silica, aluminum oxide, or zirconium oxide.

9. 10. The separator of claim 9, wherein the single layer porous polymeric film includes a hydrophilic coating on each side of the porous polymeric film.

10. The separator of claim 1 , wherein the separator is polypropylene-free.

11. The separator according to claim 1 , wherein the film contains the hydrophilic additive, the hydrophilic additive includes inorganic particles, and the inorganic particles have a particle size D50 of 20 μm or less.

12. 12. The separator of claim 11, wherein the hydrophilic additive is present in the porous polymer film in an amount of at least about 10 wt%, such as at least about 20 wt%, for example in an amount of at least about 30 wt%, such as at least about 40 wt%, for example in an amount of at least about 50 wt%, for example in an amount of at least about 60 wt%, and in an amount less than about 90 wt%.

13. 13. The separator of claim 1, wherein the porous polymer film has an average pore size greater than about 0.005 microns and less than about 1 micron.

14. 13. The separator of claim 11 or 12, wherein the hydrophilic additive comprises silica, alumina, zirconium oxide, zirconium hydroxide, magnesium oxide, magnesium hydroxide, titanium oxide, titanium hydroxide, barium sulfate, or a mixture thereof.

15. 13. The separator of claim 11 or 12, wherein the hydrophilic additive comprises a hydrophilically modified polyethylene polymer.

16. The separator of claim 11 or 12, wherein the hydrophilic additive comprises fumed silica.

17. The porous polymer film has a resistivity of 0.1 ohm.cm in a 30 wt % aqueous KOH solution at 80°C. ２ 17. The separator of claim 1 having an ionic resistivity of less than 0.

15.

18. 18. The separator of any one of claims 1 to 17, wherein the film is plasma oxidized.

19. 20. The separator of claim 18, wherein the film is plasma oxidized to form polar groups attached to the high density polyethylene polymer that enhance the polarity of the surface of the porous polymer film.

20. A water electrolysis device comprising the separator according to claim 1 disposed between a cathode and an anode.

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