Highly Oriented Stretched Polytetrafluoroethylene with Excellent Rigidity

Abstract

Provided are self-supporting uniaxially expanded polytetrafluoroethylene (ePTFE) membranes having high inherent strength, high matrix modulus, and high crystallinity. In some embodiments, the ePTFE membrane is stretched in the machine direction. The uniaxially oriented ePTFE membrane has a matrix tensile strength in the machine direction of at least about 1000 MPa, a matrix modulus at ambient temperature (i.e., about 20°C) of at least about 100 GPa, and a crystallinity of at least about 94%. In some embodiments, the ePTFE membrane has a strength of at least about 5 gf / d and a denier of at most about 750 g / 9000 m. Additionally, the uniaxially oriented ePTFE membrane <p2>The orientation is at least about 0.98. Also, the fibrils in the ePTFE membrane have a nearly perfect parallel alignment. The ePTFE membrane can be used to form composites, laminates, fibers, tapes, sheets, tubes, or other three-dimensional objects.< / p2>

Description

Technical Field

[0001] The present invention relates to a microporous fluoropolymer membrane, and more specifically, to a self-supporting, highly stretched polytetrafluoroethylene (ePTFE) membrane having high intrinsic strength, high matrix modulus, high crystallinity, and aligned fibrils.

Background Art

[0002] Polytetrafluoroethylene is an attractive material based on one or more properties such as inertness to many chemicals, biocompatibility, thermal stability, low surface energy, low coefficient of friction, and the ability to be processed into various shape factors such as membranes, fibers, tubes, and the like. By using stretched polytetrafluoroethylene (ePTFE) alone or in composites and / or laminates, articles for use in various applications can be manufactured. Many of these applications can benefit from using materials that are lighter, thinner, stronger, and / or have improved optical properties. As such, there is a continuing need to provide ePTFE articles having improved properties.

Summary of the Invention

Means for Solving the Problems

[0003] According to one aspect ("Aspect 1"), a stretched polytetrafluoroethylene (ePTFE) membrane includes a matrix tensile strength of at least about 1000 MPa in the machine direction, a matrix modulus of at least about 100 GPa at a temperature of 20°C, and a crystallinity of at least about 94%.

[0004] According to another aspect ("Aspect 2") added to Aspect 1, the areal density of the ePTFE membrane is less than about 30 mg / m 2 2.

[0005] According to another aspect added to Aspect 1 (referred to as "Aspect 3"), the <p2>The alignment is 0.98 or more.

[0006] According to another aspect ( "Aspect 4") added to any one of the previous aspects, the bulk denier of the ePTFE membrane is 750 g / 9000 m.

[0007] According to another aspect ( "Aspect 5") added to any one of the previous aspects, the tenacity of the ePTFE membrane is more than about 5 gf / d.

[0008] According to another aspect ( "Aspect 6") added to any one of the previous aspects, the ePTFE membrane is self-supporting.

[0009] According to another aspect ( "Aspect 7") added to any one of the previous aspects, the ePTFE membrane is uniaxially oriented.

[0010] According to another aspect ( "Aspect 8") added to any one of the previous aspects, at least a portion of the ePTFE membrane is coated with a polymer, at least a portion of the polymer is absorbed, or a combination thereof is applied.

[0011] According to another aspect ( "Aspect 9") added to any one of the previous aspects, the ePTFE membrane is in the form of a fiber, sheet, tube, three-dimensional self-supporting structure, die-shaped fiber, die-shaped sheet, die-shaped tube, or die-shaped three-dimensional self-supporting structure.

[0012] According to another aspect ( "Aspect 10") added to any one of the previous aspects, the ePTFE membrane further includes a spacer layer.

[0013] According to another aspect ( "Aspect 11") added to Aspect 10, the spacer layer is selected from a porous polymer, a non-porous polymer, a fluoropolymer, a porous polyolefin, and a non-porous polyolefin.

[0014] According to another aspect ( "Aspect 12"), the composite includes a stretched polytetrafluoroethylene membrane of any one of the previous aspects.

[0015] According to another aspect ( "Aspect 13"), the laminate includes a stretched polytetrafluoroethylene membrane of any one of the previous aspects.

[0016] According to another aspect ( "Aspect 14"), the article includes a stretched polytetrafluoroethylene membrane of Aspects 1 to 11, the composite of Aspect 12, or the laminate of Aspect 13.

[0017] According to another aspect ( "Aspect 15"), a method of forming a uniaxially oriented ePTFE membrane, the method comprising: (1) cutting at least a first piece from a first stretched polytetrafluoroethylene (ePTFE) membrane, (2) obtaining a second stretched polytetrafluoroethylene membrane by biaxially stretching the at least first piece, (3) cutting at least a second piece from the second stretched membrane, (4) forming a stacked sample by positioning the at least one first piece and the at least one second piece in a stacked orientation, (5) repeating steps (1) to (4) until a desired biaxially oriented ePTFE membrane is obtained, and (6) uniaxially stretching the biaxially oriented ePTFE membrane including.

[0018] According to another aspect ( "Aspect 16") added to Aspect 15, the method further includes adding a spacer layer.

[0019] According to another aspect ( "Aspect 17") added to Aspect 16, the spacer layer is selected from a porous polymer, a non-porous polymer, a fluoropolymer, a porous polyolefin, and a non-porous polyolefin.

[0020] According to another aspect added to Aspect 15 (referred to as "Aspect 18"), the ePTFE membrane is uniaxially stretched in the machine direction.

Brief Description of the Drawings

[0021] The accompanying drawings are included for a further understanding of the present disclosure, incorporated herein, and constitute a part of this specification, illustrate embodiments, and, together with the description, serve to explain the principles of the present disclosure.

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[0061] Glossary

Number

[0062] [Number]

[0063] [Number]

[0064] The area-weighted fibril width is given by the following equation: [Number] is calculated using

[0065] [Number] is calculated as surface area: A (m 2 ) volume: V (m 3 ), and the density ρ x (g / m 3 ) of crystalline PTFE.

[0066] The specific surface area (based on w m ) (m 2 / g) is given by the following equation: [Number] is calculated using

[0067] [Number] is calculated as

[0068] Areal density (mass per area) (g / m 2 ): areal density (initial): MPA o and areal density (final): MPA f

[0069] Number of layers (n)

[0070] The area ratio (AR) is given by the following equation: [Number] calculated by [Mode for Carrying Out the Invention]

[0071] As will be readily apparent to those skilled in the art, various aspects of the present disclosure can be realized by any number of methods and apparatuses configured to perform the intended function. For the sake of redundancy, the appended drawings referred to in this specification are not necessarily to scale and may be exaggerated to illustrate various aspects of the present disclosure, and in that regard, the drawings should not be construed as limiting.

[0072] In addition, as used herein, the terms "adjacent" and "adjacent to" mean that when one element is "adjacent" to another element, the element may be directly adjacent to the other element or intervening elements may be present. As used herein, the singular forms "a", "an", and "the" include the plural unless the context clearly dictates otherwise. As used herein, the term "on" means that when one element is on another element, it may be directly on the other element or intervening elements may be present. Needless to say, the terms "fine powder" and "powder" can be used interchangeably herein. Also, the terms "ePTFE membrane" and "membrane" can be used interchangeably herein. Further, in the present application, the term "ePTFE membrane" shall include a single layer or multiple layers of ePTFE membrane. Needless to say, the machine direction and the longitudinal direction are the same and can be used interchangeably herein. In addition, the terms "microporous ePTFE membrane" and "ePTFE membrane" can be used interchangeably herein.

[0073] In one aspect, the present invention relates to a thin self-supporting biaxially oriented polytetrafluoroethylene (ePTFE) membrane having high crystallinity, high intrinsic strength, low areal density (i.e., lightweight), and high light transmittance. Specifically, the ePTFE membrane may have a crystallinity of at least about 94% and a matrix tensile strength in both the longitudinal and transverse directions of at least about 600 MPa. The ePTFE membrane has an areal density of about 100 mg / m 2 Less than, and the overall visual transmittance may be at least 98%. In addition, the ePTFE membrane is transparent or invisible to the naked eye. Further, the ePTFE membrane is stackable, and using this, the transmittance, pore size, and / or bulk mechanical properties can be controlled. Using the ePTFE membrane, composites, laminates, fibers, sheets, tubes, or other three-dimensional objects can be formed. This may or may not be made into smaller parts by subsequently performing dicing or other cutting or separation. In addition, the biaxially oriented ePTFE membrane can be used for filtration applications. In another aspect, the biaxially oriented ePTFE membrane can be uniaxially stretched. This aligns the fibrils in one direction (hereinafter, uniaxially oriented ePTFE membrane). Such an ePTFE membrane may have a tenacity (gf / d) of more than about 5 grams per denier and a bulk denier (g / 9000m) of less than about 750 grams per 9000 meters.

[0074] In the case of polytetrafluoroethylene (PTFE) polymers, particle size, shape, and their distribution are important to obtain the desired porous structure. These particle properties affect the packing density as well as the binding density, thereby affecting the porous structure that can be produced from the particles. The PTFE resin is provided in a granular form, for example, a fine powder form. The PTFE fine powder is formed from primary particles.

[0075] When forming the ePTFE membrane, the PTFE fine powder is first mixed with a lubricant, such as light oil. One specific example of a suitable lubricant is an isoparaffinic hydrocarbon, such as ISOPAR® K (ExxonMobil Chemical, Spring, TX). Other suitable lubricants include aliphatic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, and the like, and are selected based on flammability, evaporation rate, and economic considerations. Needless to say, the term "lubricant" as used herein represents a processing aid that includes (or consists of) a non-compressible fluid that is not a solvent for the polymer under the process conditions. The fluid-polymer surface interaction occurs such that a homogeneous mixture can be formed. Note that the selection of the lubricant is not particularly limited, and the selection of the lubricant is mainly important for safety and convenience. The lubricant can be added to the PTFE powder in an amount of about 242 mL / kg to about 340 mL / kg.

[0076] In at least one embodiment, by mixing the PTFE fine powder and the lubricant, the lubricant is distributed uniformly or substantially uniformly with the PTFE powder. Needless to say, various times and mixing methods can be used to distribute the PTFE powder in the lubricant. Once the lubricant and the PTFE powder are sufficiently distributed, the lubricated powder is compressed into a cylindrical shape (i.e., a pellet). Then, by pushing the pellet through an extruder die with a ram (e.g., typically called paste extrusion or paste processing when a lubricant is present), a cohesive flexible PTFE tape can be produced. As used herein, "cohesive" refers to a tape that is strong enough for further processing. The ram extrusion is performed below the melting temperature of the PTFE polymer (e.g., below 327 °C). The formed tape has an indefinite length and a thickness of less than about 1.0 mm, less than about 0.8 mm, less than about 0.5 mm, or less than about 0.4 mm. The cohesive flexible tape will hereinafter be simply referred to as "tape".

[0077] In subsequent processes, the lubricant is removed from the tape. In the case where ISOPAR® K is the lubricant, the tape may be heated to about 200 °C. In other embodiments, the lubricant can be removed by washing the tape in hexane or other suitable solvents. If the lubricant has sufficient volatility, the lubricant may be removed without a washing step, or may be removed by heat and / or vacuum. However, needless to say, any convenient drying method may be used.

[0078] Next, the tape is stretched simultaneously in the longitudinal and transverse directions (i.e., biaxially). As used herein, the terms "biaxially expanded" and "biaxially oriented" refer to a polymer, membrane, preform, or article that has been stretched in at least two orthogonal directions such that the fibrils are substantially in-plane oriented. In one embodiment, the tape is subsequently stretched only in the machine direction (i.e., uniaxially). As used herein, the terms "uniaxial", "uniaxially oriented", or "uniaxially stretched" refer to a polymer, membrane, preform, or article that has been stretched in only one direction (e.g., the machine direction (MD) or the transverse direction (TD)). The stretching may be carried out with or without heat at a strain rate of up to about 10,000% / sec, up to about 5,000% / sec, up to about 2,500% / sec, up to about 1,000% / sec, up to about 750% / sec, up to about 500% / sec, up to about 250% / sec, up to about 150% / sec, up to about 100% / sec, up to about 75% / sec, up to about 50% / sec, up to about 40% / sec, up to about 35% / sec, up to about 30% / sec, up to about 20% / sec, up to about 10% / sec, or up to about 5% / sec. Additionally, the tape may be stretched (with or without heat) at about 1% / sec to about 10,000% / sec, about 1% / sec to about 5,000% / sec, about 1% / sec to 2,500% / sec, about 1% / sec to about 1,000% / sec, about 1% / sec to about 750% / sec, about 1% / sec to about 500% / sec, about 1% / sec to about 250% / sec, about 1% / sec to about 150% / sec, about 1% / sec to about 100% / sec, about 1% / sec to about 75% / sec, about 1% / sec to about 50% / sec, about 1% / sec to about 40% / sec, about 1% / sec to about 35% / sec, about 1% / sec to about 30% / sec, about 1% / sec to about 20% / sec, about 1% / sec to about 10% / sec, or about 1% / sec to about 5% / sec. Needless to say, an increase in intrinsic strength occurs simultaneously with stretching. The increase in the intrinsic strength of the PTFE polymer depends on the strength of the tape before stretching, the quality of the PTFE resin (e.g., particle size, molecular weight, particle size and / or molecular weight distribution, crystallinity, polymer composition, and the like), the temperature at which stretching is carried out, the stretching rate, and / or the total amount of stretching.

[0079] The tape is biaxially stretched and, in some embodiments, additionally uniaxially stretched to form an ePTFE membrane. The tape can be stretched at the same or different strain rates and at the same or different temperatures to obtain a microporous ePTFE membrane. As used herein, the term "microporous" shall define an article having pores that are not visible to the naked eye, such as a membrane. The material properties of the ePTFE membrane produced in this way have been found to exceed the comparative properties of conventional membranes by efficiently and completely converting ePTFE primary particles (i.e., PTFE fine powder) into fibrils. It is advantageous for the ePTFE membranes discussed herein to maintain the properties of conventional ePTFE membranes, such as chemical inertness, thermal stability, low surface energy, low coefficient of friction, biocompatibility, and a wide range of service temperatures. The ePTFE membrane can optionally be heat treated at temperatures up to about 390°C. By uniaxially stretching the ePTFE membrane, an ePTFE membrane having uniaxially oriented fibrils, high crystallinity, and high matrix tensile strength in the direction in which it is stretched (i.e., the machine direction (MD) or the transverse direction (TD)) is formed. Hereinafter, although the ePTFE membrane will be described with respect to stretching in the machine direction, it is of course considered that transverse stretching is also included within the scope of the present invention.

[0080] The biaxially oriented ePTFE membrane is extremely thin, having a total membrane thickness of less than about 2 mm, less than about 1.5 mm, less than about 1.0 mm, less than about 0.5 mm, less than about 0.3 mm, less than about 0.1 mm, less than 0.05 mm, less than 0.005 mm, less than 0.001 mm, less than about 500 nm, less than about 400 nm, less than about 300 nm, less than about 200 nm, less than about 100 nm, less than about 50 nm, less than about 25 nm, less than about 10 nm, less than about 5 nm, or less than about 1 nm. As used herein, the term "about" means within ±10% of the recited number or amount. The biaxially oriented ePTFE membrane may be formed to have a total membrane thickness of from about 1 nm to about 100 nm, from about 1 nm to about 90 nm, from about 1 nm to about 80 nm, from about 1 nm to about 70 nm, from about 1 nm to about 60 nm, from about 1 nm to about 50 nm, from about 1 nm to about 40 nm, from about 1 nm to about 30 nm, from about 1 nm to about 20 nm, or from about 1 nm to about 10 nm.

[0081] In at least one embodiment, the thickness per layer of the biaxially oriented ePTFE membrane is less than about 100 nm, less than about 90 nm, less than about 80 nm, less than about 70 nm, less than about 60 nm, less than about 50 nm, or less than 40 nm, less than about 30 nm, less than about 20 nm, less than about 10 nm, less than about 5 nm, less than about 4 nm, less than about 3 nm, less than about 2 nm, less than about 1 nm. In some embodiments, the thickness per layer of the ePTFE membrane is from about 1 nm to about 100 nm, from about 1 nm to about 90 nm, from about 1 nm to about 80 nm, from about 1 nm to about 70 nm, from about 1 nm to about 60 nm, from about 1 nm to about 50 nm, from about 1 nm to about 40 nm, from about 1 nm to about 30, from about 1 nm to about 20 nm, from about 1 nm to about 10 nm, from about 1 nm to about 5 nm, from about 1 nm to about 4 nm, from about 1 nm to about 3 nm, or from about 1 nm to about 2 nm. Different from conventional ePTFE membranes, the biaxially oriented ePTFE membrane is so thin that it is invisible to the naked eye.

[0082] The "invisibility" of the biaxially oriented ePTFE membrane also results at least in part from the fibrillar microstructure of the ePTFE membrane. Broadly speaking, the fibrils are substantially cylindrical in shape. As used herein, the term "substantially cylindrical" is used herein to mean that the aspect ratio in the cross-section of the fibrils in the biaxially oriented ePTFE membrane is from about 1:1 to about 10:1. In addition, the fibrils in the biaxially oriented ePTFE membrane are thin and have a median fibril width of about 80 nm or less. In some embodiments, the median fibril width is less than about 70 nm, less than about 60 nm, less than about 50 nm, less than about 40 nm, less than about 30 nm, less than about 20 nm, or less than about 10 nm. In some embodiments, the median fibril width is from about 10 nm to about 80 nm, from about 10 nm to about 70 nm, from about 10 nm to about 60 nm, from about 10 nm to about 50 nm, from about 10 nm to about 40 nm, from about 10 nm to about 30 nm, or from about 10 nm to about 20 nm. In some embodiments, the median fibril width is from about 20 nm to about 70 nm, from about 30 nm to about 60 nm, from about 40 nm to about 50 nm. In other embodiments, the median fibril width is from about 30 nm to about 80 nm, from about 40 nm to about 80 nm, from about 50 nm to about 80 nm, from about 60 nm to about 80 nm, or from about 70 nm to about 80 nm. The intersection or overlap of two or more fibrils is referred to herein as a "crossover point". In some embodiments, the thickness of the biaxially oriented ePTFE membrane may be the thickness at the crossover point of two fibrils.

[0083] In addition, the areal density per layer is about 100 mg / m 2 (0.1 g / m 2 ) less than, about 90 mg / m 2 (0.09 g / m 2 ) less than, about 80 mg / m 2 (0.08 g / m 2 ) less than, about 70 mg / m 2 (0.07 g / m 2 ) less than, about 60 mg / m 2 (0.06 g / m 2 ) less than, about 50 mg / m 2 (0.05 g / m 2 ) less than about 40 mg / m 2 (0.04 g / m 2 ) less than about 30 mg / m 2 (0.03 g / m 2 ) less than about 20 mg / m 2 (0.02 g / m 2 ) less than about 15 mg / m 2 (0.015 g / m 2 ) less than about 10 mg / m 2 (0.01 g / m 2 ) less than about 5 mg / m 2 (0.005 g / m 2 ) less than about 4 mg / m 2 (0.004 g / m 2 ) less than about 3 mg / m 2 (0.003 g / m 2 ) less than about 2 mg / m 2 (0.002 g / m 2 ) up to 1.0 mg / m 2 (0.001 g / m 2 ) less than about 0.50 mg / m 2 (0.0005 g / m 2 ) less than about 0.40 mg / m 2 (0.0004 g / m 2 ) less than about 0.30 mg / m 2 (0.0003 g / m 2 ) less than about 0.20 mg / m 2 (0.0002 g / m 2 ) less than about 0.10 mg / m 2 (0.0001 g / m 2 ) less than about 0.05 mg / m 2 (0.00005 g / m 2 ) or about 0.003 mg / m 2 (0.000003 g / m 2 ) The biaxially oriented ePTFE membrane that is less than is significantly lightweight. In some embodiments, the areal density per layer is from about 0.003 mg / m 2 (0.000003 g / m 2 ) to about 100 mg / m 2 (0.1 g / m 2 ) about 0.003 mg / m 2 (0.000003 g / m 2 ) to about 90 mg / m 2 (0.09 g / m 2 )、about 0.003 mg / m 2 (0.000003 g / m 2 ) ~ about 80 mg / m 2 (0.08 g / m 2 )、about 0.003 mg / m 2 (0.000003 g / m 2 ) ~ about 70 mg / m 2 (0.07 g / m 2 )、about 0.003 mg / m 2 (0.000003 g / m 2 ) ~ about 60 mg / m 2 (0.06 g / m 2 )、about 0.003 mg / m 2 (0.000003 g / m 2 ) ~ about 50 mg / m 2 (0.05 g / m 2 )、about 0.003 mg / m 2 (0.000003 g / m 2 ) ~ about 40 mg / m 2 (0.04 g / m 2 )、about 0.003 mg / m 2 (0.000003 g / m 2 ) ~ about 30 mg / m 2 (0.03 g / m 2 )、about 0.003 mg / m 2 (0.000003 g / m 2 ) ~ about 20 mg / m 2 (0.02 g / m 2 )、about 0.003 mg / m 2 (0.000003 g / m 2 ) ~ about 10 mg / m 2 (0.01 g / m 2 )、about 0.003 mg / m 2 (0.000003 g / m 2 ) ~ about 1.0 mg / m 2 (0.001 g / m 2 )、about 0.003 mg / m 2 (0.000003 g / m 2 ) ~ about 0.5 mg / m 2 (0.0005 g / m 2 )、about 0.003 mg / m 2 (0.000003 g / m 2 ) to approximately 0.4 mg / m 2 (0.0004 g / m 2 ) and approximately 0.003 mg / m 2 (0.000003 g / m 2 ) to approximately 0.3 mg / m 2 (0.0003 g / m 2 ) and approximately 0.003 mg / m 2 (0.000003 g / m 2 ) to approximately 0.2 mg / m 2 (0.0002 g / m 2 ) and approximately 0.003 mg / m 2 (0.000003 g / m 2 ) to approximately 0.1 mg / m 2 (0.0001 g / m 2 ) or approximately 0.003 mg / m 2 (0.000003 g / m 2 ) to approximately 0.05 mg / m 2 (0.00005 g / m 2 ) is. In some embodiments, the areal density per layer is from about 5 mg / m 2 (0.005 g / m 2 ) to about 100 mg / m 2 (0.1 g / m 2 ) and about 20 mg / m 2 (0.02 g / m 2 ) to about 90 mg / m 2 (0.09 g / m 2 ) or about 30 mg / m 2 (0.03 g / m 2 ) to about 80 mg / m 2 (0.08 g / m 2 ) is.

[0084] Furthermore, the area ratio of the biaxially oriented ePTFE membrane is from about 2,000:1 to about 300,000,000:1. In some embodiments, the area ratio of the biaxially oriented ePTFE membrane is from about 20,000:1 to about 300,000,000:1, from about 40,000:1 to about 300,000,000:1, from about 60,000:1 to about 300,000,000:1, from about 80,000:1 to about 300,000,000:1, from about 100,000:1 to about 300,000,000:1, from about 250,000:1 to about 300,000,000:1, from about 500,000:1 to about 300,000,000:1, from about 1,000,000:1 to about 300,000,000:1, or from about 2,500,000:1 to about 300,000,000:1.

[0085] In addition, the total areal density of the biaxially oriented ePTFE membrane is less than about 100 g / m 2 less than about 10 g / m 2 less than about 5 g / m 2 less than about 1 g / m 2 less than about 0.5 g / m 2 less than about 0.1 g / m 2 less than about 50 mg / m 2 (0.05 g / m 2 ) less than about 10 mg / m 2 (0.01 g / m 2 ) less than about 5.0 mg / m 2 (0.005 g / m 2 ) less than about 4.0 mg / m 2 (0.004 g / m 2 ) less than about 3.0 mg / m 2 (0.003 g / m 2 ) less than about 2.0 mg / m 2 (0.002 g / m 2 ) less than about 1.0 mg / m 2 (0.001 g / m 2 ) less than about 0.50 mg / m 2 (0.0005 g / m 2 ) less than about 0.40 mg / m 2 (0.0004 g / m 2 ) less than about 0.30 mg / m 2 (0.0003 g / m 2 ) less than about 0.20 mg / m 2 (less than 0.0002 g / m 2 ), about 0.10 mg / m 2 (less than 0.0001 g / m 2 ), about 0.07 mg / m 2 (less than 0.00007 g / m 2 ), about 0.05 mg / m 2 (less than 0.00005 g / m 2 ), about 0.03 mg / m 2 (less than 0.00003 g / m 2 ), about 0.007 mg / m 2 (less than 0.000007 g / m 2 ), or about 0.003 mg / m 2 (less than 0.000003 g / m 2 ) may be. In some embodiments, the total areal density of the biaxially oriented ePTFE membrane is about 0.003 mg / m 2 (less than 0.000003 g / m 2 ) to about 100 g / m 2 , about 0.003 mg / m 2 (less than 0.000003 g / m 2 ) to about 10 g / m 2 , about 0.003 mg / m 2 (less than 0.000003 g / m 2 ) to about 1.0 g / m 2 , about 0.003 mg / m 2 (less than 0.000003 g / m 2 ) to about 0.5 g / m 2 , about 0.003 mg / m 2 (less than 0.000003 g / m 2 ) to about 0.1 g / m 2 , about 0.003 mg / m 2 (less than 0.000003 g / m 2 ) to about 50 mg / m 2 (0.05 g / m 2 ), about 0.003 mg / m 2 (less than 0.000003 g / m 2 ) to about 10 mg / m 2 (0.01 g / m 2 ), about 0.003 mg / m 2 (less than 0.000003 g / m 2 ) to about 5 mg / m 2 (0.005 g / m 2 )、about 0.003 mg / m 2 (0.000003 g / m 2 )~about 4.0 mg / m 2 (0.004 g / m 2 )、about 0.003 mg / m 2 (0.000003 g / m 2 )~about 3.0 mg / m 2 (0.003 g / m 2 )、about 0.003 mg / m 2 (0.000003 g / m 2 )~about 2.0 mg / m 2 (0.002 g / m 2 )、about 0.003 mg / m 2 (0.000003 g / m 2 )~about 1.0 mg / m 2 (0.001 g / m 2 )、about 0.003 mg / m 2 (0.000003 g / m 2 )~about 0.50 mg / m 2 (0.0005 g / m 2 )、about 0.003 mg / m 2 (0.000003 g / m 2 )~about 0.40 mg / m 2 (0.0004 g / m 2 )、about 0.003 mg / m 2 (0.000003 g / m 2 )~about 0.30 mg / m 2 (0.0003 g / m 2 )、about 0.003 mg / m 2 (0.000003 g / m 2 )~about 0.20 mg / m 2 (0.0002 g / m 2 )、about 0.003 mg / m 2 (0.000003 g / m 2 )~about 0.10 mg / m 2 (0.0001 g / m 2 )、about 0.003 mg / m 2 (0.000003 g / m 2 )~about 0.07 mg / m 2 (0.00007 g / m 2 )、about 0.003 mg / m 2 (0.000003 g / m 2 ) to approximately 0.05 mg / m 2 (0.00005 g / m 2 ) or approximately 0.10 mg / m 2 (0.010 g / m 2 ) to approximately 10 g / m 2 is.

[0086] The areal density per layer is less than approximately 500 mg / m 2 (0.5 g / m 2 ), less than approximately 400 mg / m 2 (0.4 g / m 2 ), less than approximately 300 mg / m 2 (0.3 g / m 2 ), less than approximately 200 mg / m 2 (0.2 g / m 2 ), less than approximately 100 mg / m 2 (0.1 g / m 2 ), less than approximately 70 mg / m 2 (0.07 g / m 2 ), less than approximately 50 mg / m 2 (0.05 g / m 2 ), less than approximately 30 mg / m 2 (0.03 g / m 2 ), less than approximately 25 mg / m 2 (0.025 g / m 2 ), less than approximately 20 mg / m 2 (0.02 g / m 2 ), less than approximately 15 mg / m 2 (0.015 g / m 2 ), less than approximately 10 mg / m 2 (0.01 g / m 2 ), less than approximately 5 mg / m 2 (0.005 g / m 2 ), less than approximately 4 mg / m 2 (0.004 g / m 2 ), less than approximately 3 mg / m 2 (0.003 g / m 2 ), less than approximately 2 mg / m 2 (0.002 g / m 2 ), less than approximately 1.0 mg / m 2 (0.001 g / m 2 ), less than approximately 0.50 mg / m 2 (0.0005 g / m 2 ) less than about 0.40 mg / m 2 (0.0004 g / m 2 ) less than about 0.30 mg / m 2 (0.0003 g / m 2 ) less than about 0.20 mg / m 2 (0.0002 g / m 2 ) or about 0.10 mg / m 2 (0.0001 g / m 2 ) The uniaxially oriented ePTFE membrane, which is less than, is also significantly lightweight. In some embodiments, the areal density is about 0.10 mg / m 2 (0.0001 g / m 2 ) to about 500 mg / m 2 (0.5 g / m 2 ) about 0.10 mg / m 2 (0.0001 g / m 2 ) to about 400 mg / m 2 (0.4 g / m 2 ) about 0.10 mg / m 2 (0.0001 g / m 2 ) to about 300 mg / m 2 (0.3 g / m 2 ) about 0.10 mg / m 2 (0.0001 g / m 2 ) to about 200 mg / m 2 (0.2 g / m 2 ) about 0.10 mg / m 2 (0.0001 g / m 2 ) to about 100 mg / m 2 (0.1 g / m 2 ) about 0.10 mg / m 2 (0.0001 g / m 2 ) to about 70 mg / m 2 (0.07 g / m 2 ) about 0.10 mg / m 2 (0.0001 g / m 2 ) to about 50 mg / m 2 (0.05 g / m 2 ) about 0.10 mg / m 2 (0.0001 g / m 2 ) to about 30 mg / m 2 (0.03 g / m 2 ) about 0.10 mg / m 2 (0.0001 g / m 2 ) to approximately 20 mg / m 2 (0.02 g / m 2 ), approximately 0.10 mg / m 2 (0.0001 g / m 2 ) to approximately 15 mg / m 2 (0.015 g / m 2 ), approximately 0.10 mg / m 2 (0.0001 g / m 2 ) to approximately 10 mg / m 2 (0.01 g / m 2 ), approximately 0.10 mg / m 2 (0.0001 g / m 2 ) to approximately 5 mg / m 2 (0.005 g / m 2 ), approximately 0.10 mg / m 2 (0.0001 g / m 2 ) to approximately 0.40 mg / m 2 (0.0004 g / m 2 ), approximately 0.10 mg / m 2 (0.0001 g / m 2 ) to approximately 0.30 mg / m 2 (0.0003 g / m 2 ), or approximately 0.10 mg / m 2 (0.0001 g / m 2 ) to approximately 0.20 mg / m 2 (0.0002 g / m 2 ).

[0087] Despite being thin and lightweight, the biaxially stretched ePTFE membrane has high intrinsic strength properties. The matrix tensile strength (MTS) of the ePTFE membrane is at least 600 MPa in both the longitudinal and transverse directions, at least about 650 MPa in both the longitudinal and transverse directions, at least about 700 MPa, at least about 750 MPa, at least about 800 MPa, at least about 850 MPa, at least about 900 MPa, or at least about 1000 MPa. In at least one embodiment, the matrix tensile strength (MTS) of the biaxially oriented ePTFE membrane is from about 600 MPa to about 1000 MPa, from about 650 MPa to about 1000 MPa, from about 700 MPa to about 1000 MPa, from about 750 MPa to about 1000 MPa, from about 800 MPa to about 1000 MPa, from about 850 MPa to about 1000 MPa, or from about 900 MPa to about 1000 MPa in both the longitudinal and transverse directions.

[0088] In addition, the ePTFE membrane additionally uniaxially stretched has higher intrinsic strength properties. In some embodiments, the matrix tensile strength (MTS) of the ePTFE membrane is greater than about 1000 MPa in the machine direction, greater than about 1100 MPa in the machine direction, greater than about 1200 MPa in the machine direction, greater than about 1200 MPa in the machine direction, greater than about 1300 MPa in the machine direction, or greater than about 1400 MPa in the machine direction. In some embodiments, the matrix tensile strength (MTS) of the uniaxially oriented ePTFE membrane is from about 1000 MPa to about 1400 MPa, from about 1100 MPa to about 1400 MPa, from about 1200 MPa to about 1400 MPa, from about 1200 MPa to about 1300 MPa, or from about 1300 MPa to about 1400 MPa in the machine direction. Needless to say, although the matrix tensile strength is provided herein with respect to the machine direction, it can equally apply to the ePTFE membrane stretched in the transverse direction.

[0089] In addition, the matrix storage modulus of the uniaxially oriented ePTFE membrane is at least 100 GPa at ambient temperature (i.e., about 20 °C). In some embodiments, the matrix storage modulus of the uniaxially oriented ePTFE membrane at ambient temperature (i.e., about 20 °C) is from about 100 GPa to about 111 GPa, from about 101 GPa to about 111 GPa, from about 102 GPa to about 111 GPa, from about 103 GPa to about 111 GPa, from about 104 GPa to about 111 GPa, from about 105 GPa to about 111 GPa, from about 106 GPa to about 111 GPa, from about 107 GPa to about 111 GPa, from about 108 GPa to about 111 GPa, from about 109 GPa to about 111 GPa, or from about 110 GPa to about 111 GPa. Further, the bulk denier of the uniaxially oriented ePTFE is about 750 g / 9000 m. In some embodiments, the bulk denier of the uniaxially oriented ePTFE is from about 0.5 g / 9000 m to about 750 g / 9000 m, from about 0.5 g / 9000 m to about 650 g / 9000 m, from about 0.5 g / 9000 m to about 500 g / 9000 m, from about 100 g / 9000 m to about 450 g / 9000 m, from about 0.5 g / 9000 m to about 400 g / 9000 m, from about 0.5 g / 9000 m to about 350 g / 9000 m, from about 0.5 g / 9000 m to about 250 g / 9000 m, from about 0.5 g / 9000 m to about 200 g / 9000 m, from about 0.5 g / 9000 m to about 150 g / 9000 m, from about 0.5 g / 9000 m to about 100 g / 9000 m, from about 0.5 g / 9000 m to about 50 g / 9000 m, from 0.5 g / 9000 m to about 25 g / 9000 m, from about 0.5 g / 9000 m to about 15 g / 9000 m, from about 0.5 g / 9000 m to about 10 g / 9000 m, from about 0.5 g / 9000 m to about 5 g / 9000 m, from about 0.5 g / 9000 m to about 3 g / 9000 m, or from about 0.5 g / 9000 m to about 1 g / 9000 m.

[0090] In addition, the tenacity of the uniaxially oriented ePTFE membrane is at least about 5 gf / d. In some embodiments, the tenacity of the uniaxially oriented ePTFE membrane is from about 5 gf / d to about 8 gf / d, from about 6 gf / d to about 8 gf / d, or from about 6 gf / d to about 7 gf / d. Further, the uniaxially oriented ePTFE membrane has a <p2>It has orientation.

[0091] In addition, the air resistance of the biaxially oriented ePTFE membrane is only slight. In some embodiments, the air resistance of the ePTFE membrane is less than about 30,000 Pa·s / m, less than about 25,000 Pa·s / m, less than about 20,000 Pa·s / m, less than about 15,000 Pa·s / m, less than about 10,000 Pa·s / m, less than about 7,500 Pa·s / m, less than about 5000 Pa·s / m, less than about 2000 Pa·s / m, less than about 1500 Pa·s / m, less than about 1000 Pa·s / m, less than about 750 Pa·s / m, less than about 500 Pa·s / m, less than about 250 Pa·s / m, or about 150 Pa·s / m. In some embodiments, the air resistance is from about 100 Pa·s / m to about 2000 Pa·s / m, from about 100 Pa·s / m to about 1500 Pa·s / m, from about 100 Pa·s / m to about 1000 Pa·s / m, from about 100 Pa·s / m to about 750 Pa·s / m, from about 100 Pa·s / m to about 500 Pa·s / m, from about 100 Pa·s / m to about 250 Pa·s / m, or from about 250 Pa·s / m to about 500 Pa·s / m. The low air resistance combined with the high surface area of the ePTFE membrane enables high-performance filtration devices.

[0092] The biaxially oriented ePTFE membrane also has a total visual transmittance (measured at 380 nm to 780 nm) of about 90% or more, about 95% or more, about 98% or more, about 99% or more, and has high light transmittance. In exemplary embodiments, the total visual transmittance of the biaxially oriented ePTFE membrane may be from about 90% to about 99%, from about 95% to about 99%, or from about 98% to about 99%. In some embodiments, the total visual transmittance of the ePTFE membrane is approximately 100%.

[0093] The fibrils of the (biaxially and uniaxially oriented) ePTFE membrane may optionally be coated with at least one coating composition, such as a polymer or a biological film, whether the ePTFE is porous or non-porous. The coating composition can be deposited on the ePTFE membrane by any conventional coating method, such as solvent coating, spray coating, spin coating, vapor deposition, atomic layer deposition (ALD), or dip coating. Additionally, a coating can also be deposited on the ePTFE membrane by compressing while heating between sheets of components, such as fluorinated ethylene propylene (FEP), polyfluoroacrylate (PFA), and silicone.

[0094] In some embodiments, the coating composition occupies or fills at least a portion of the space through the thickness of the biaxially or uniaxially oriented ePTFE membrane. Examples of polymers and / or biological coatings suitable for coating on or within the ePTFE membrane and / or being absorbed include polyester, polystyrene, polyamide, polyphthalamide, polyamide-imide, polycarbonate, polyethersulfone, polysulfone, polyphenylene sulfide, liquid crystal polymer, polyether ketone, polyether ether ketone, polysiloxane, epoxy, polyurethane, polyimide, polyetherimide, polyacrylate, polyparaxylylene, a terpolymer of tetrafluoroethylene (TFE), VDF (vinylidene fluoride), and HFP (hexafluoropropylene), a copolymer of tetrafluoroethylene (TFE) and perfluoroalkyl vinyl ether (PAVE), a copolymer of tetrafluoroethylene and perfluoro-2,2-dimethyl-1,3-dioxole, perfluoroalkyl vinyl ether, perfluoroalkyl ether, polyvinylidene fluoride (PVDF), ethylene tetrafluoroethylene (ETFE), polychlorotrifluoroethylene (PCTFE), fluorinated ethylene propylene (FEP), perfluoroalkoxy alkane (PFA), polyvinyl alcohol (PVA), CBAS® / heparin coating (commercially available from W.L. Gore & Associates, Inc.), antibacterial agents, antibodies, pharmaceuticals, biological entities, angiogenesis stimulants, and any combination thereof. The amount of coating applied depends on the initial use.

[0095] Biaxially or uniaxially oriented ePTFE membranes are self - supporting, and in some embodiments, the ePTFE membranes are used to reinforce polymer films such as porous polymers, non - porous polymers, fluoropolymers, polyolefins, films, tapes, and other membranes. By "self - supporting" it is meant that the ePTFE membrane does not require a backing layer or a carrier layer. However, since the ePTFE membrane is extremely thin, the edges of the ePTFE membrane are often constrained at the macroscale length. In other words, the integrity of the ePTFE membrane is maintained by constraining the ePTFE membrane around its perimeter (e.g., by "picture framing"). The inherent strength of the membrane is related over various distances and holds the membrane together without providing a backing layer or a support layer behind or under the membrane.

[0096] Biaxially and uniaxially oriented ePTFE membranes can be formed as a single ePTFE membrane layer. In other embodiments, biaxially and uniaxially oriented ePTFE membranes may have dozens, hundreds, or thousands of ePTFE membrane layers within the ePTFE membrane. In some embodiments, there may be 2 to 4 layers. In other embodiments, there may be 2 to 16 layers within the ePTFE membrane. In further embodiments, there may be 2 to 500 layers, 2 to 1,000 layers, 2 to 5,000 layers, 2 to 10,000 layers, 2 to 25,000 layers, 2 to 50,000 layers, 2 to 100,000 layers, 2 to 500,000 layers, 2 to 1,000,000 layers (or more layers) within the ePTFE membrane. Without wishing to be bound by theory, the only limiting factor for the number of ePTFE layers present within the ePTFE membrane is the time spent stacking and stretching the layers. Typically, the ePTFE membrane stack "grows" 4-fold each time the ePTFE membrane is biaxially stretched. Needless to say, although it is typical that no adhesives or other binders are used to bond the individual ePTFE membranes within the stacked ePTFE membranes, the inclusion of adhesives or other binding materials is not excluded from use herein and is considered to be within the scope of the present invention.

[0097] In another embodiment, the ePTFE membrane (both biaxially and uniaxially oriented) may include ePTFE membranes having the same mechanical properties, ePTFE membranes having different mechanical properties, and / or spacer layers (e.g., different polymer layers such as porous polymers, non-porous polymers, fluoropolymers, porous polyolefins, or non-porous polyolefins). In other words, the ePTFE membrane may be engineered to include different polymer and / or non-polymer layers within the ePTFE membrane. Additionally, one ePTFE membrane layer may differ from another ePTFE layer by the amount of stretch and / or strain rate and / or overall work applied to the layer. By varying the type, stretch, and mechanical properties of any additional layers within the ePTFE membrane, the ePTFE membrane can be formed to match specific bulk properties while maintaining transport, filtration, or separation requirements.

[0098] By forming an ePTFE membrane (biaxially and uniaxially oriented) and / or any additional spacer layers within the ePTFE membrane, the permeability, pore size, and bulk mechanical properties can be controlled. As used herein, the term "permeability" means the ability of a material to pass a fluid (i.e., liquid or gas) through the pores of a membrane or filter material when the material is exposed to a differential pressure across it. In one case, the ePTFE membrane allows for various pore sizes, such as pore sizes of less than about 6 microns in diameter. As used herein, "pore size" means the size of the pores within the ePTFE membrane. The pore size may be from 2 nm to about 6 microns. Additionally, the specific surface area (SSA) of ePTFE, measured by the area weighted fibril width (AWFW), is about 35 m 2 / g to about 120 m 2 / g, about 45 m 2 / g to about 120 m 2 / g, about 55 m 2 / g to about 120 m 2 / g, about 65 m 2 / g to about 120 m 2 / g, about 75 m 2 / g to about 120 m 2 / g, about 80 m 2 / g to about 120 m 2 / g, about 90 m 2 / g to about 120 m 2 / g, about 100 m 2 / g to about 120 m 2 / g, or about 110 m 2 / g to about 120 m 2 / g may be sufficient.

[0099] In some embodiments, the biaxially oriented ePTFE membrane can be used for air filtration applications. In such applications, the quality factor of the ePTFE membrane is at least 65 (kPa -1 ) when the challenge particles are 0.1 micron in diameter and the face velocity is 5.33 cm. Needless to say, the strength of the ePTFE membrane with respect to its weight (intrinsic strength) is higher than that of conventional ePTFE membranes. A higher quality factor value is associated with better filtration performance. In certain embodiments, the quality factor of the biaxially oriented ePTFE membrane is about 65 (kPa -1 ) to about 180 (kPa -1 ), about 70 (kPa -1 ) to about 180 (kPa -1 ), about 80 (kPa -1 ) to about 180 (kPa -1 ), about 90 (kPa -1 ) to about 180 (kPa -1 ), about 100 (kPa -1 ) to about 180 (kPa -1 ), about 110 (kPa -1 ) to about 180 (kPa -1 ), about 120 (kPa -1 ) to about 180 (kPa -1 ), about 130 (kPa -1 ) to about 180 (kPa -1 ), about 140 (kPa -1 ) to about 180 (kPa -1 ), about 150 (kPa -1 ) to about 180 (kPa -1 ), about 160 (kPa -1 ) to about 180 (kPa -1 ), or about 170 (kPa -1 ) to about 180 (kPa -1 ) may be.

[0100] The biaxially oriented ePTFE membrane can be used in applications where it is desirable to filter nanoparticles (e.g., from about 1 nm to about 200 nm) from a liquid medium even when the liquid medium is moving at a high flow rate. Thus, the ePTFE membrane can be used as a filtration material and, by the properties of polytetrafluoroethylene, has chemical attack resistance, biocompatibility, and exhibits high matrix tensile strength (MTS). The filterable matrix can be selected from solutions, suspensions, colloids, biological fluids, components of biological fluids, aqueous materials, or non-aqueous materials. To filter the filterable matrix, the matrix is passed through the ePTFE membrane and the resulting filtrate is collected. In one embodiment, the biaxially oriented ePTFE membrane comprises a nanoparticle retention percentage (%) above the line defined by Equation (1).

Number

[0101] Test method Non-contact thickness measurement The non-contact thickness of the membrane was measured using a KEYENCE LS-7600 laser system (commercially available from KEYENCE America).

[0102] Calculation of membrane density Samples were cut to form square sections 15.2 cm x 15.2 cm. Each sample was weighed using a Mettler Toledo AT20 scale. The density of the sample was calculated using Equation (2) using the thickness calculated by the KEYENCE laser.

Number

[0103] Matrix Tensile Strength (MTS) (Method 1) To determine the MTS of the biaxial ePTFE membrane, sample ePTFE membranes were cut longitudinally and transversely using ASTM D412 - Dogbone Die - Type F (D412F). To determine the MTS of the uniaxial membrane, the sample ePTFE membrane was loaded longitudinally. An INSTRON® 5567 (located in Norwood, Massachusetts, Illinois Tool Works Inc.) tensile testing machine equipped with grips having a flat surface and a "22 lb" (approximately 100 N) load cell was used to measure the tensile break load. The gauge length for the grips was set at 8.26 cm, and the strain rate was 0.847 cm / s. The sample was placed in the grips, and a baseline was obtained by retracting the sample 1.27 cm, followed by performing a tensile test at the above - mentioned speed. Peak force measurement was used for MTS calculation. Equation (3):

Number

[0104] Matrix Tensile Strength (MTS) (Method 2) To determine the MTS of the uniaxial ePTFE membrane, the sample ePTFE membrane was loaded longitudinally using a string grip and a thread grip. The tensile breaking load was measured using an INSTRON® 5567 (Illinois Tool Works Inc., Norwood, Massachusetts) tensile testing machine equipped with the string grip, the thread grip, and a "22 lb" (approximately 100 N) load cell. The gauge length for the grip was set to 15.24 cm, and the strain rate was 0.254 cm / s. After placing the sample in the grip, a baseline was obtained by retracting the sample 1.27 cm, followed by a tensile test at the above-mentioned rate. Peak force measurement was used for MTS calculation.

[0105] Scanning transmission electron microscope (STEM) Low-voltage (STEM) (scanning transmission electron microscopy) is a technique used to visualize thin samples by accelerating a focused beam of electrons through the sample and collecting the transmitted electrons with an appropriate detector. Low-voltage means using a beam acceleration voltage of less than 100 kV (< 30 kV as exemplified in this specification). Image contrast is based on the difference in electron absorption by the membrane due to composition or thickness.

[0106] A scanning electron microscope (Hitachi, SU8000, Tokyo, Japan, Hitachi, Ltd.) equipped with a transmission adapter (STEM) was used and operated at an acceleration voltage of 30 kV or less. The sample was neither pretreated nor post-treated (stained). Samples for the analysis of thin porous films were prepared on a copper grid (PELCO® grid with a central marking, 400 mesh, copper, product # 1GC400, Ted Pella Inc., Redding, California) with a carbon support layer (carbon type - B, 300 mesh, copper, product # 01813, Ted Pella, Inc.).

[0107] X-ray diffractogram of the biaxial sample Using the X27C beamline of the National Synchrotron Light Source at Brookhaven National Laboratory (Upton, New York), two-dimensional (2-d) X-ray diffraction patterns were obtained. The beamline provided a well-collimated monochromatic X-ray beam with a wavelength of 0.1371 nm, a nominal beam photon flux of 10 12 / s, and a diameter of 0.39 mm. The detector was a Rayonix MAR-CCD 2-d imaging system (Rayonix LLC, Evanston, Illinois). The system was set at a sample-detector distance of 67.97 mm and calibrated using an Al2O3 powder standard. The sample was placed between the beam and the detector, and transmission geometry scattered / diffused X-ray images were collected over 480 - 540 seconds. In addition, immediately after imaging each sample, a background image with no sample present was recorded over the same time period. By subtracting the background image from the sample image, the effect of air scattering was removed and the desired diffraction pattern was created.

[0108] X-ray Scattering Method for Uniaxial Samples Wide-angle X-ray scattering tests were performed on a Xenocs brand Xeuss 2.0 SAXS / WAXS Laboratory Beamline system (Xenocs SAS, Sassenage, France). The instrument operates a GeniX3D Cu k at 50 kV and 0.6 mA a A source (wavelength 0.154 nm) and a Dectris brand Pilatus 300K detector (Dectris Ltd., Baden-Daettwil, Switzerland) were used. The beam was collimated with two in-line slits, each opened up to an area of 0.5 mm x 0.5 mm. The sample-detector distance was 71.0 mm (calibrated by a lanthanum hexaboride standard). The “virtual detector” feature of the Xeuss 2.0 system was used to eliminate the blind spot in the detector and also expand its angular range. This was achieved by translating the detector horizontally and then averaging multiple scans. Here, four scans were performed with various horizontal detector offsets, and each scan was accompanied by an exposure time of 15 minutes. By averaging these four scans, a scattering profile was provided. The orientation was quantified from the I vs. φ azimuthal angle using Equation (4).

Number

[0109] As determined by Equation (5), <p2>As it approaches 1, almost complete orientation in the machine direction is achieved. [Number]

[0110] Degree of crystallinity The degree of crystallinity was obtained by peak fitting of the intensity vs. q scan using JMP (registered trademark) 14.1.0 statistical analysis software (SAS institute). The integration range was limited to q = 8.74 - 15.4 (nm -1 ), and a linear background was defined to match the measured intensity at approximately q = 8.74 - 10 (nm -1 ) and q = 14.1 - 15.4 (nm -1 ). After subtracting the linear background, both peaks were fitted using the Pearson VII function.

[0111] As defined in Bowen's U.S. Patent Application Publication No. 2004 / 0173978, the degree of crystallinity was calculated from the area under the fitted 100% crystalline peak (A 100 ) and the area under the fitted amorphous peak (A amorphous ) according to the following equation (6). [Number]

[0112] Bubble point The bubble point was measured using a capillary flow porometer (Model CFP 1500 AE from Porous Materials, Inc., Ithaca, N.Y.) in accordance with the general teachings of ASTM F316 - 03. The sample membrane was placed into the sample chamber and wetted with SilWick silicone fluid (commercially available from Porous Materials, Inc.) having a surface tension of 19.1 dynes / cm. The lower clamp of the sample chamber consisted of a 40 - micron porous metal disk insert (Mott Metallurgical, Fannington, Conn) of the following dimensions (2.54 cm diameter, 3.175 mm thickness). The upper clamp of the sample chamber consisted of an opening with a diameter of 12.7 mm. Capwin software version 6.74.70 was used with the following parameters and set points. Parameter Set Point Maxflow 200000 (cc / m) Bubflow 10 - 127 (cc / m) F / PT 50 Minbppres 0.1 (psi) Zerotime 1 (sec) V2incr 10 (cts) Preginc 1 (cts) Pulse Dela 2 (sec) Maxpress 500 (psi) Pulse Width 0.2 (sec) Mineqtime 30 (sec) Presslew 10 (cts) Flowslew 50 (cts) Eqiter (0.1 sec) 3 Aveiter (0.1 sec) 20 Maxpdif 0.1 (psi) Maxfdif 50 (cc / m) Startp 1 (psi) The values reported for the bubble point were the average of two measurements.

[0113] ATEQ air flow Measure the volumetric flow rate of the air layer passing through the membrane sample. The membrane samples were clamped between two plates in a form that seals an area of 2.99 cm 2 across the flow path. Using an ATEQ (registered trademark) (ATEQ Corp., Livonia, MI) Premier D small flow tester, the air flow rate (L / hr) through each membrane sample was measured by challenging the membrane with an air differential pressure of 1.2 kPa (12 mbar).

[0114] Air flow resistance The air flow resistance was tested using a Textest FX 3300 air permeability tester device manufactured by Textest AG (Zurich, Switzerland). The frigid permeability measurement was the air flow rate expressed in cubic feet per minute per square foot of sample area at the time of the pressure drop across a 12.7 mm water column sample. The air permeability was measured by clamping the sample in a fixture with a circular flange. The fixture provided a circular opening with a diameter of 7 cm (area 38.5 cm 2 ). The upstream side of the sample fixture was connected to a flow meter in parallel with a dry compressed air source.

[0115] Measurement of light transmittance Spectrophotometry was performed using a spectrophotometer (Jasco V-670; located in Pfungstadt, Germany, JASCO Deutschland GmbH) equipped with a double-beam integrating sphere attachment (150 mm diameter, ILN-725). The spectrophotometer consists of a deuterium & tungsten-halogen lamp, a single Czerny-Turner type monochromator (1200 lines / mm diffraction grating), and a photomultiplier tube (PMT) detector. The light from the monochromator is split into a sample beam and a reference beam before entering the integrating sphere. The integrating sphere is formed to perform unidirectional irradiation and diffuse detection. The sample beam irradiates a 20 mm x 20 mm sample placed on the integrating incident port at normal incidence, while the reference beam passes through an open port on the integrating sphere. The sample beam and the reference beam alternately enter the PMT detector and, after synchronous rectification, are converted into digital signals.

[0116] The bandwidth of the monochromator was set to 10 nm, and the grating wavelength was scanned from 250 nm to 800 nm at an operating speed of 2000 nm / min. The source was changed from a deuterium lamp to a tungsten-halogen lamp at 340 nm. Signals were recorded at 2 nm intervals. "Dark correction" spectra (blocking the sample beam) and "baseline correction" spectra (the sample beam passing through the open port) were collected. That is, these spectra were used to report the transmittance spectra expressed as a percentage of the incident light.

[0117] The total visual transmittance was calculated by weighting the transmittance spectrum by the CIE standard light source and the CIE colorimetric standard observer (see ASTM D1003-13: Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics). The D65 light source and the 1931 2-deg standard observer were used in the calculations presented herein. The transmittance percentages within the UVA and UVB ranges were calculated by calculating the average percentage transmittance values in the wavelength ranges of 315 - 400 nm and 280 - 315 nm, respectively.

[0118] Determination of the average fibril width Selected samples were imaged by STEM and manually characterized by 50 measurements of the projected width of the fibrils (e.g., Figure 11). Uniform sampling was facilitated by using a random number generator to highlight 50 regions, and then the operator traced the outline of the nearest fibril, preferably a fibril fragment that had not already been characterized. Generally, the marked fibrils were square and had an aspect ratio greater than 1. The nominal projected width of the fibrils was calculated from the ratio of the area of the object divided by the length. This is more representative and informative than a single width measurement, as it necessarily forces the projected width measurement to be perpendicular to the major axis of the square shape. To confirm this method, a line was drawn through the centroid of the manually identified region that was orthogonal to the major axis at the calculated width calculated according to equation (7).

Number

[0119] Dynamic mechanical analyzer (DMA) matrix storage modulus and loss modulus Measurements of the matrix storage modulus and loss modulus were performed using a TA Instruments Q800 system (New Castle, Delaware, TA Instruments) equipped with a clamped sample fixture. The DMA was calibrated according to the standard TA Instruments procedure. The dimensions of the sample were obtained using a 10x microscope equipped with a reticle graduated in 0.1 mm increments for width and a KEYENCE LS7010 high-precision non-contact micrometer (Keyence Corp., Itasca, Illinois) for thickness. The sample mass was measured using a Mettler-Toledo A120 microbalance (Mettler-Toledo, LLC, Columbus, Ohio). The sample was then placed in the instrument and a preload of 5 mN was applied. The sample length was obtained at 25 °C from the calibrated DMA clamp position. A sine wave strain of true strain amplitude 0.001 and frequency 1 Hz was applied with an additional constant load. This constant load was just sufficient to keep the sample in tension throughout the application of the sine wave strain. The sample was equilibrated at -50 °C for 10 minutes and then the temperature was ramped to 150 °C at 2 °C / min. The magnitude and phase angle of the combined sine wave force acting on the sample were measured once per second throughout the heating ramp and used to calculate the storage modulus and loss modulus. The storage modulus and loss modulus were multiplied by the ratio ρ true / ρ sample to obtain the desired matrix modulus. ρ true was assumed to be 2.3 g / cm 3 of crystalline poly(tetrafluoroethylene), while ρ sample was calculated from the measured dimensions and mass of the sample.

[0120] Air filtration performance measurement The particle filtration efficiency membrane filtration efficiency test was carried out using dioctyl phthalate (DOP) aerosol on the TSI CERTITEST (registered trademark) model 8160 automatic filter tester in accordance with the procedures specified in the TSI CERTITEST (registered trademark) model 8160 automatic filter tester operation and service manual (TSI Incorporated, St. Paul, Minnesota). The sample test area was 77.8 cm, and the face velocity was 5.32 cm / sec.

[0121] The quality factor Q was calculated using Equation (8). f was determined. [Number]

[0122] The penetration rate P is the fraction of particles that penetrate or pass through the sample, and Δp is the pressure drop (kPa) at an air velocity of 5.33 cm / s. A higher quality factor is associated with better filtration performance (see William C. Hinds, Aerosol Technology: Properties, Behavior, and Measurement of Airborne Particles, Second Ed., John Wiley & Sons; Hoboken, NJ (1994)). The quality factors are compared using the same face velocity and test aerosol particle size. The quality factor is defined in units of mutual pressure (kPa -1 ). [Number]

[0123] Determination of liquid permeability and retention rate by bead test The bead test measures the transmittance and bead retention of the membrane sample. The membrane sample was constrained within a 25 mm filter holder. The membrane was first wetted with an isopropyl alcohol (IPA)-DI aqueous solution (70:30 v / v IPA: water). Using air pressure, this solution was forced through the membrane. 7 grams of the solution was made to flow through the sample, followed by 10 grams of an aqueous solution consisting of 1% by volume of the nonionic surfactant TRITON® X-100 (CAS 9002-93-1; located in St. Louis, Missouri, Sigma Aldrich) in DI water. The membrane was then challenged with a solution of 0.025 μm diameter polystyrene latex beads (Fluoro-Max R25 red fluorescent polymer microspheres; located in Waltham, Massachusetts, Thermo Fisher Scientific) dispersed in an aqueous solution consisting of 1% by volume of TRITON® X-100 in DI water. In this case, the membrane was challenged with an amount of beads sufficient to cover the membrane surface area with a single monolayer of beads. The concentrations of the beads and the filtrate in the challenge solution were determined using an Agilent Technologies Cary Eclipse fluorescence spectrophotometer (located in Santa Clara, California, Agilent Technologies).

[0124] The transmittance of the membrane was calculated using Equation (9).

Equation

[0125] In Equation (9), k is the transmittance of the membrane, g is the mass of the aliquot of the filtrate, A is the physical area of the membrane sample within the filter holder, t is the time required to collect the aliquot of the filtrate, and P is the pressure difference across the membrane. In Equation (9), g / t is the mass flow rate through the membrane, and g / At is the mass velocity through the membrane.

[0126] The percentage of beads in the solution retained by the membrane was calculated using Equation (10).

Number

[0127] In Equation (10), C challenge is the concentration of beads in the challenge solution, and C filtrate is the concentration of beads in the filtrate.

Example

[0128] Unless otherwise specified herein, all scientific and technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The present invention is further defined in the following examples. Needless to say, these examples show preferred embodiments of the present invention, but are for illustrative purposes only. From the above discussion and these examples, those skilled in the art can identify the essential features of the present invention and make various changes and modifications to the present invention to adapt it to various applications and conditions without departing from the spirit and scope of the present invention.

[0129] Example 1 The following example discloses the production of a single-layer PTFE membrane having a very low areal density (e.g., an areal density of less than 10 mg / m 2 ).

[0130] Polytetrafluoroethylene (PTFE) fine powder (Wilmington, Delaware, E.I. DuPont de Nemours) was blended with ISOPAR® K isoparaffinic hydrocarbon lubricant (Spring, Texas, ExxonMobil Chemical) at a target ratio of 110 mL per pound (approximately 0.454 kg) of fine powder (0.156 g of lubricant / total g) (lubricant grams / total mixture mass). The lubricated powder was compressed into a cylindrical shape and tape was provided by ram extrusion at 49 °C. The tape was 16.2 cm wide and 0.762 mm thick. ISOPAR® K was removed by heating to approximately 200 °C, thereby forming a dried tape (“initial tape”). 98 square mm was cut from the initial tape. The areal density of the initial tape (before pantograph stretching) was determined to be 1130 grams per square meter (g / m 2 ). All initial tape areal densities used herein are meant to be 1150 ± 100 g / m 2 . A summary of the process parameters used in Example 1 is shown in Table 1.

[0131] First pass Using a pantograph machine, a 98 square mm dried tape was heated in a furnace set at 300 °C (set point) for 120 seconds and then simultaneously stretched in the longitudinal (machine direction (MD)) and transverse (TD) directions (biaxially) at a target ratio of approximately 4:1 in each direction while maintaining a temperature of approximately 300 °C. The average engineering strain rate target was set at 36% / second. The pantograph was opened at a constant speed target over approximately 8 seconds. The ePTFE membrane was cooled to room temperature (approximately 22 °C) while being constrained by the pantograph.

[0132] Second pass The cooled ePTFE membrane pieces from the first pass were recovered for further stretching, i.e., the "second pass". Using the same pantograph machine, the selected membranes were heated in a furnace set at 300 °C for 120 seconds, and then stretched simultaneously in the longitudinal direction (machine direction (MD)) and the transverse direction (TD) at a target ratio of approximately 10:1 in each direction while maintaining a temperature of approximately 300 °C. The average engineering strain rate target was set at 9% / second. The pantograph opened at a constant speed target for approximately 100 seconds. The second pass ePTFE membranes were cooled to room temperature (approximately 22 °C) while being restrained by the pantograph.

[0133] Third pass The cooled ePTFE membrane pieces from the second pass were selected for further stretching, i.e., the "third pass". Using the same pantograph machine, the selected membranes were reheated in a furnace set at 300 °C for 120 seconds, and then stretched simultaneously in the longitudinal direction (machine direction (MD)) and the transverse direction (TD) at a target ratio of approximately 10:1 in each direction while maintaining a temperature of approximately 300 °C. The constant acceleration set point was 1% / second. The pantograph opened at a constant acceleration set point for approximately 230 seconds. The second pass ePTFE membranes were cooled to room temperature (approximately 22 °C) while being restrained by the pantograph.

[0134] The ePTFE membranes were cooled to room temperature (approximately 22 °C) while being restrained by the pantograph. A summary of the process parameters of Example 1 is shown in Table 1.

[0135] The cooled and stretched ePTFE membranes from the third pass were recovered from the pantograph and placed on a frame (152.4 mx 152.4 mm) with an adhesive applied to the back surface. Using the frame as a cutting guide, the ePTFE membranes were weighed, and the average areal density value was calculated to be 4.3 mg / m 2 The lightest sample was 2.4 mg / m 2 It was (Table 2). The area ratio is defined as the ratio of the areal density before and after a series of stretching operations. The ePTFE membrane obtained from the third pass showed an area ratio of 122,690:1 to 459,273:1 depending on the process conditions (Table 2). Figures 1 to 3 show the same sample (2.40 mg / m 2 , Sample E1G) at three different magnifications. Residual primary particles were not observed. Figure 4 is from the second piece where the same strain path was used, but the furnace was set at 322 °C (Sample E1H). The STEM image of Sample E1I is provided as Figure 5. Table 1 summarizes the process parameters.

Table 1

Table 2

[0136] Example 2 The following example discloses the production of a PTFE membrane having a very low areal density (e.g., an areal density of less than 10 mg / m 2 per layer). The layer formation of this ePTFE membrane is up to 256 layers, and the area ratio is up to about 34,000,000:1.

[0137] PTFE fine powder (E.I. DuPont de Nemours) was blended with ISOPAR® K isoparaffinic hydrocarbon lubricant at a target ratio of 110 mL per pound of fine powder (approximately 0.454 kg) (0.156 g of lubricant / total g) (grams of lubricant / mass of total mixture). The lubricated powder was compressed into a cylindrical shape and tape was provided by ram extrusion at 49 °C. The tape was 16.2 cm wide and 0.762 mm thick. The ISOPAR® K was removed by heating the tape to approximately 200 °C. 98 square mm was cut from the dried tape. A summary of the process parameters used in Example 2 is shown in Table 3.

[0138] The first pass Using a pantograph machine, four square tapes were heated in a furnace set at 300°C for 240 seconds, and then simultaneously stretched in the longitudinal and transverse directions at a target ratio of approximately 7:1 in each direction while maintaining a temperature of approximately 300°C. The average engineering strain rate target was set at 36% / second. The pantograph opened at a constant speed target over approximately 16.7 seconds. The ePTFE membrane was cooled to room temperature (approximately 22°C) while being constrained by the pantograph. Four pieces (each consisting of four layers) were recovered from the cooled ePTFE membrane pieces and set aside for further stretching, i.e., the second pass. By repeating the first pass process once more, another 16 layers were created. By combining both 16-layer samples, a 32-layer sample was formed.

[0139] Second pass Using the same pantograph machine, both 16-layer stacks (32 layers in total) were heated in a furnace set at 300°C for a target of 240 seconds, and then simultaneously stretched in the longitudinal and transverse directions at a target ratio of approximately 7:1 in each direction while maintaining a temperature of approximately 300°C. The average engineering strain rate target was set at 5% / second. The pantograph opened at a constant speed target over approximately 120 seconds. The ePTFE membrane was cooled to room temperature (approximately 22°C) while being constrained by the pantograph.

[0140] Third pass Four samples (each 32 layers) were recovered from the cooled ePTFE membrane pieces and layer-formed (128 layers in total) for further stretching, i.e., the "third pass". Using the same pantograph machine, the membrane was reheated in a furnace set at 300°C for a target of 240 seconds, and then simultaneously stretched in the longitudinal and transverse directions at a target ratio of approximately 8:1 in each direction while maintaining a temperature of approximately 300°C. The simultaneous stretching was performed at a constant acceleration set point of 1% / second for the target ratio of 8:1 in each direction. The pantograph opened over approximately 208 seconds in the third pass. The ePTFE membrane was cooled to room temperature (approximately 22°C) while being constrained by the pantograph.

[0141] Fourth pass Four samples (128 layers) were recovered from the cooled ePTFE membrane sheet and layer formed (128 layers in total) for further stretching, i.e., the "fourth pass". Using the same pantograph machine, the membrane was reheated in a furnace set at 300 °C for a target of 120 seconds and then stretched simultaneously in the longitudinal and transverse directions at a target ratio of approximately 3:1 in each direction while maintaining a temperature of approximately 300 °C. The simultaneous stretching was carried out at a constant acceleration set point of 1% / second with respect to the target ratio of 3:1 in each direction. The pantograph was open for approximately 110 seconds during the fourth pass. The stretched ePTFE membrane was cooled to room temperature (approximately 22 °C) while being restrained by the pantograph.

[0142] The ePTFE membrane was recovered from the machine and placed on a frame (152.4 mm x 152.4 mm) with an adhesive applied to the back surface. Using the frame as a cutting guide, the ePTFE membrane was weighed and the areal density was calculated to be 0.00047 g / m 2 / layer, and the ePTFE membrane was 0.0605 g / m 2 (Sample E2A, Table 4). The area ratio and areal density of the other ePTFE membranes (both the ePTFE membrane and the stack of ePTFE membranes) were set and are described in Table 4.

[0143] In addition, three additional ePTFE membranes consisting of 128 layers using the first three paths above were generated for Example 2 (E2B - D). Each ePTFE membrane was individually loaded for the fourth and fifth stretches. Using the same pantograph machine, the membranes were heated in a furnace set to 300 °C for a target of 120 seconds, then stretched simultaneously in the longitudinal and transverse directions at a target ratio of approximately 4:1 (E2B), 5:1 (E2C), or 6:1 (E2D) in each direction while maintaining a temperature of approximately 300 °C. The simultaneous stretching in Examples E2B - D was performed at a constant acceleration set point of 1% / second. The pantograph opened in the fourth pass for approximately 139 (E2B), 161 (E2C), or 179 (E2D) seconds. At the end of each stretch (E2B - E2D), the stretched ePTFE membranes were cooled to room temperature (approximately 22 °C) while being restrained by the pantograph. The ePTFE membranes were recovered from the machine and placed on a frame (152.4 mm x 152.4 mm) with an adhesive applied to the back surface. The frame was used as a cutting guide to weigh the ePTFE membranes. Table 4 includes the ratio set value for the fourth pass, the area ratio, the areal density of the stack of ePTFE membranes, the areal density of each layer, and the translation time in the final pass.

[0144] In addition, three additional ePTFE membranes were generated for Example 2 (E2E - G) mainly for observing images of STEM (Figs. 6 - 8).

[0145] Example E2E was processed using the same procedure as Example E2D with the following two exceptions. The residence time before stretching was shortened from 240 seconds (E2D) before the third pass to 120 seconds (E2E), and for the area ratio set point in the final pass, the fourth pass target ratio was increased from a set point of 6:1 (E2D) in both directions to a set point of 8:1 (E2E) in both directions. The pantograph opened in the fourth pass for approximately 208 seconds (E2E). The stretched ePTFE membranes were cooled to room temperature (approximately 22 °C) while being restrained by the pantograph. The ePTFE membranes were recovered from the machine and placed on a frame (152.4 mm x 152.4 mm) with an adhesive applied to the back surface.

[0146] Example E2F was processed using the same steps as Example E2E, with the following two exceptions. The number of layers loaded for the fourth draw was increased from 128 (E2E) to 256 (E2F), and the fourth pass target ratio was increased from a setpoint of 8:1 (E2E) in each direction to a setpoint of 9:1 (E2F) in both directions. The drawn ePTFE membrane was cooled to room temperature (approximately 22 °C) while being constrained with a pantograph. The ePTFE membrane was recovered from the machine and placed on a frame (152.4 mm x 152.4 mm) with an adhesive applied to the back surface.

[0147] Example E2G was processed using the same steps as Example E2E, with the following two exceptions. The number of layers loaded for the second draw was decreased from 32 (E2E) to 16 (E2G), and the fourth pass was not used. The drawn ePTFE membrane was cooled to room temperature (approximately 22 °C) while being constrained with a pantograph. The ePTFE membrane was recovered from the machine and placed on a frame (152.4 mm x 152.4 mm) with an adhesive applied to the back surface. The frame was used as a cutting guide to weigh the ePTFE membrane, and it was calculated that the areal density was 0.009 g / m 2 / layer, and the ePTFE membrane was 1.175 g / m 2 (Sample E2G, Table 4). The area ratios and areal densities (both for the ePTFE membrane and the stack of ePTFE membranes) for these and other ePTFE membranes were calculated and are listed in Table 4.

Table 3

Table 4

[0148] Example 3 The following examples disclose the manufacture of PTFE membranes with a very low areal density per layer where the ePTFE layer is up to 1024 and the area ratio is up to approximately 300,000,000:1.

[0149] PTFE fine powder (E.I. DuPont de Nemours) was blended with ISOPAR® K isoparaffinic hydrocarbon lubricant at a target ratio of 110 mL per pound of fine powder (approx. 0.454 kg) (0.156 g of lubricant / total g) (lubricant grams / total mixture mass). The lubricated powder was compressed into a cylindrical shape and tape was provided by ram extrusion at 49 °C. The tape was 16.2 cm wide and 0.762 mm thick. ISOPAR® K was removed by heating the tape to approximately 200 °C. 98 square mm was cut from the dried tape. A summary of the process parameters used in Example 3 is shown in Table 5.

[0150] First pass Using a pantograph machine, four square tapes were heated in a furnace set at approximately 322 °C (set point) for a target of 240 seconds, then simultaneously stretched in the longitudinal and transverse directions at a target ratio of approximately 10:1 in each direction while maintaining a temperature of approximately 322 °C. The average engineering strain rate target was set at 36% / second. The pantograph opened at a constant speed target over approximately 25 seconds. The ePTFE membrane was cooled to room temperature (approx. 22 °C) while being restrained by the pantograph. Another 32 layers were created by repeating the first pass process one more time.

[0151] Second pass Using the same pantograph machine, both 42-layer stacks (64 layers in total) were heated in a furnace set at approximately 322 °C for a target of 240 seconds, then simultaneously stretched in the longitudinal and transverse directions at a target ratio of approximately 10:1 in each direction while maintaining a temperature of approximately 322 °C. The average engineering strain rate target was set at 3.6% / second. The pantograph opened at a constant speed target over approximately 250 seconds. The stretched membrane was cooled to room temperature (approx. 22 °C) while being restrained by the pantograph.

[0152] Third pass Four samples (64 layers each) were recovered from the cooled ePTFE membrane sheets and laminated (256 layers total) for further stretching, i.e., the “third pass”. Using the same pantograph machine, the stacked ePTFE membranes were reheated in the furnace to approximately 322 °C over a target of 240 seconds and then stretched simultaneously in the longitudinal and transverse directions at a target ratio of approximately 8:1 (E3B) or 10:1 (E3A) in each direction while maintaining a temperature of approximately 322 °C. As the pantograph accelerated to a speed target of 3.5 mm / s, simultaneous stretching was performed at a constant acceleration target of 1% / s up to 400% strain (λ sp = 5:1) in both directions, and stretching was completed at a constant speed setpoint of 5% / s (3.5 mm / s in this specific case based on an original length input of 70 mm (“r / s” speed mode)). The pantograph was open for approximately 221 seconds (E3B) or 261 seconds (E3A) during the third pass. The stretched membranes were cooled to room temperature (approximately 22 °C) while being restrained by the pantograph.

[0153] Fourth pass Samples (256 layers) were recovered from the cooled ePTFE membrane sheets and stacked (1024 layers total) for further stretching, i.e., the “fourth pass”. Using the same pantograph machine, the membranes were reheated in the furnace to approximately 322 °C over a target of 120 seconds and then stretched simultaneously in the longitudinal and transverse directions at a target ratio of approximately 7:1 in each direction while maintaining a temperature of approximately 322 °C. As the pantograph accelerated to a speed setpoint of 3.5 mm / s, simultaneous stretching was performed at a constant acceleration setpoint of 1% / s up to 400% strain (λ sp = 5:1) in both directions, and stretching was completed at a constant speed setpoint of 5% / s (3.5 mm / s in this specific case based on an original length input of 70 mm (“r / s” speed mode)). The pantograph was open for approximately 201 seconds during the fourth pass. The stretched membranes were cooled to room temperature (approximately 22 °C) while being restrained by the pantograph.

[0154] The ePTFE membrane was recovered from the machine and placed on a frame (152.4 mm x 152.4 mm) with an adhesive applied to the back surface. Using the frame as a cutting guide, the ePTFE membrane was weighed, and the areal density was calculated to be 0.005 - 0.016 g / m 2 / layer, and the mass per area (MPA, areal density) of the ePTFE membrane was 0.005 - 0.016 mg / m 2 (Table 6). Two different positions were measured for sample E3A (i.e., E3A~1 and E3A~2), while three different positions were measured for sample E3B (i.e., E3B~1, E3B~2, and E3B~3). STEM images of samples E3A (Figure 9) and E3B (Figure 10) were formed.

[0155] A maximum of 298,611,016:1 was possible (Table 6). The lowest areal density of the completed ePTFE membrane stack was approximately 3.9 mg / m 2 (Table 6). The lowest areal density of the completed ePTFE membrane stack was approximately 3.9 mg / m

Table 5

Table 6

[0156] Example 4 The following example discloses the production of an ePTFE membrane having an areal density on the order of 0.6 - 2.0 grams / m 2 to facilitate the measurement of the membrane thickness (per layer).

[0157] PTFE fine powder (E.I. DuPont de Nemours) was blended with ISOPAR® K isoparaffinic hydrocarbon lubricant at a target ratio of 110 mL per pound (approximately 0.454 kg) of fine powder (0.156 g of lubricant / total g) (grams of lubricant / total mass of the mixture). The lubricated powder was compressed into a cylindrical shape and tape was provided by ram extrusion at 49 °C. The tape was 16.2 cm wide and 0.762 mm thick. ISOPAR® K was removed by heating to approximately 200 °C. 98 square mm was cut from the dried tape. A summary of the process parameters used in Example 4 is shown in Table 7.

[0158] First pass Using a pantograph machine, four square tapes were heated in a furnace set at approximately 300 °C for a target of 120 (set point) (Sample E4B) or 240 (set point) seconds (E4A, E4C and E4D), then simultaneously in the longitudinal and transverse directions, each at a target ratio of approximately 7:1 in each direction, while maintaining a temperature of approximately 300 °C. The average engineering strain rate target was set at 36% / second. The pantograph opened at a constant speed target over approximately 16.6 seconds. The ePTFE membrane was cooled to room temperature (approximately 22 °C) while being restrained by the pantograph.

[0159] Second pass Using the same pantograph machine, stacks (16, 32 or 48 layers in total, details in Table 7) were heated in a furnace set at approximately 300 °C for a target of 120 (E4B) or 240 seconds (E4A, E4C and E4D), then simultaneously in the longitudinal and transverse directions, each at a target ratio of approximately 7:1 in each direction, while maintaining a temperature of approximately 300 °C. The average engineering strain rate target was set at 5% / second. The pantograph opened at a constant speed target over approximately 120 seconds. The stretched membrane was cooled to room temperature (approximately 22 °C) while being restrained by the pantograph.

[0160] Third pass Four samples were recovered from the cooled ePTFE membrane pieces, and a total of 128 layers (E4A - C) or 192 layers (E4D) were stacked for further stretching, i.e., the third pass. Using the same pantograph machine, a stack of 128 or 192 layers was added. The ePTFE membrane was reheated in a furnace set to approximately 300 °C for a target of 120 (E4A - C) seconds or 180 (E4D) seconds, and then stretched simultaneously in the longitudinal and transverse directions at a target ratio of approximately 8:1 in each direction while maintaining a temperature of approximately 300 °C. As the pantograph accelerated to a speed setpoint of 3.5 mm / s, the simultaneous stretching was performed at a constant acceleration setpoint of 1% / s up to 400% strain (λ sp = 5:1) in both directions, and the stretching (E4A, E4C - D) was completed at a constant speed setpoint of 5% / s (3.5 mm / s in this specific case based on an original length input of 70 mm). The pantograph was open for approximately 221 seconds during the stretching of E4A and E4C - D. The simultaneous stretching of Example (E4B) was performed at a constant acceleration target of 1% / s up to a target ratio of 8:1 in each direction. The entire third pass translation took approximately 210 seconds in Example E4B. The stretched membrane was cooled to room temperature (approximately 22 °C) while being restrained by the pantograph. The ePTFE membrane was recovered from the machine and placed on a frame (152.4 mm x 152.4 mm) with an adhesive applied to the back surface.

[0161] Using the frame as a cutting guide, the ePTFE membranes E4A - E4D were weighed and measured. The areal density of the ePTFE membrane E4A was calculated to be 0.0076 g / m 2 / layer, and the ePTFE membrane was 0.974 g / m 2 . The measured average layer thickness of the 128 - layer type ePTFE membrane was 7.76 microns. This corresponded to approximately 60 nm per layer. Table 7 includes the details of this sample and a similar sample that was exposed to approximately 350 °C for a target of 5 minutes (i.e., "heat - treated") to promote dimensional stability. The areal density of the ePTFE membrane E4B was calculated to be 0.0049 g / m 2 / layer, and the membrane was 0.632 g / m 2 It was. The measured average layer thickness of the 128-layer ePTFE membrane was 4.95 microns. This corresponded to approximately 39 nm per layer. Table 7 includes details of the processes of two additional similar samples compressed to reduce thickness using the methods described herein. ePTFE membrane E4C was the compressed area of ePTFE membrane E4A. ePTFE membrane E4C was placed in a laboratory press under 2.07 MPa (300 psi) for approximately 30 minutes at approximately 22 °C. ePTFE membrane E4D was placed in an autoclave under pressure at 1.73 MPa (250 psi) at approximately 200 °C for 40 minutes. The areal density of ePTFE membrane E4C was calculated to be 0.0076 g / m 2 / layer, and the membrane was 0.974 g / m 2 It was. The measured average layer thickness of the 128-layer ePTFE membrane was 1.50 microns. This corresponded to approximately 11.7 nm per layer. The areal density of ePTFE membrane E4D was 0.016 g / m 2 / layer, and the membrane was 2.038 g / m 2 It was. The measured average layer thickness of the 192-layer ePTFE membrane was 3.50 microns. This corresponded to approximately 18.2 nm per layer.

[0162] Table 8 shows that the 128-layer and 192-layer ePTFE membranes were heavy and thick enough to measure wall thickness. The calculated thickness per layer of each uncompressed ePTFE membrane was consistent with approximately twice the width of a typical fibril measured from STEM microscope images to be approximately 20 - 30 nm. Using a density of 2.2 g / cc for PTFE, the solid volume fraction and porosity were calculated. The compressed ePTFE membranes showed a reduction in porosity and thickness per layer.

[0163] Densification method Method 1: Laboratory press The ePTFE membrane E4C was placed inside the Caver Laboratory Press Model M (at Fred S. Carver Inc., Menomonee Falls, Wisconsin). The laboratory press was operated at room temperature (approximately 22 °C) with a 3” diameter (approximately 0.0762 m) anvil at the top to generate approximately 300 psi (~2.07 MPa) over approximately 30 minutes.

[0164] Method 2: Laboratory autoclave The ePTFE membrane was placed inside an autoclave bag fabricated from KAPTON® polyimide film (E.I. DuPont de Nemours Inc., Wilmington, Delaware). The assembly was placed inside an Econoclave® 3 feet x 5 feet laboratory autoclave (ASC Process Systems, Valencia, California) using an applied pressure of 250 psi (approximately 1.72 MPa) and a temperature set point of 200 °C over approximately 70 minutes.

Table 7

Table 8

[0165] Example 5 The following examples disclose the manufacture of stacked ePTFE membranes (stacks of up to 192 layers by layer formation and simultaneous stretching), and the measurement of various membrane parameters including fibril width average value, area-weighted fibril width (AWFW), fibril width median, specific surface area, bubble point, air flow resistance, and areal density.

[0166] A relatively high air flow rate at a specific pressure indicates a high transmittance. In other words, the required pressure for a higher flow rate is low. Air flow resistance is a function of the structure, and most simple models use the solid volume fraction and the representative fibril radius as the main factors. More sophisticated models address slip as a reduction in fibril radius, such that these are a small fraction of the mean free path of air under standard conditions, here 65 nm. Other factors involved in generating a membrane with a high air flow rate are the uniformity of the fibril distribution, fibril shape, and orientation. If each fibril is separated by the same distance, a uniform distribution of fibrils is maximized. A distribution with low uniformity is represented by aggregated fibril aggregates and shows a delay in higher transmittance. Fibril shape can also change air flow resistance.

[0167] One way to determine the average fibril width is to manually measure the width of fibrils within a representative sample. Figure 4 (ePTFE membrane E1H) was used to calculate the width average value and the width median value (Figure 11) by manually measuring the fibril width (measuring 50 fibrils). The fibril measurements were expressed in nanometers (nm). From Figure 11 (ePTFE membrane E1H), it is clear that the projected width is overly simplified as smaller fibrils are observed to aggregate on larger fibrils based on the grayscale intensity change across the fibril width. The bar graph of the fibril measurements from Figure 11 is shown in Figure 12. The data is fitted to a lognormal distribution.

[0168] PTFE fine powder (E.I. DuPont de Nemours) was blended with ISOPAR® K isoparaffinic hydrocarbon lubricant at a target ratio of 110 mL per pound (approximately 0.454 kg) of fine powder (0.156 g of lubricant / total g) (lubricant grams / total mixture mass). The lubricated powder was compressed into a cylindrical shape and tape was provided by ram extrusion at 49°C. The tape was 16.2 cm wide and 0.762 mm thick. ISOPAR® K was removed by heating to approximately 200°C. The dried tape was cut into 98 square mm pieces. A summary of the process parameters used in Example 5 is shown in Table 9.

[0169] First pass Using a pantograph machine, four square tapes were heated in a furnace set at 300°C (set point) for a target of 120 (E5A - G) or 240 seconds (E5H - J), and then simultaneously stretched in the longitudinal and transverse directions at a target ratio (λ sp ) of 4:1, 7:1 or 9:1 (Table 9) while maintaining a temperature of approximately 300°C. The average engineering strain rate target was set at 36% / second. The pantograph opened at a constant speed target over approximately 8.3, 16.6, or 22 seconds based on the target ratio (Table 9). The stretched ePTFE membrane was cooled to room temperature (approximately 22°C) while being restrained by the pantograph.

[0170] Second pass Samples were retrieved from the cooled ePTFE membrane sheets for further stretching, i.e., the “second pass”. Table 9 shows the specific number of layers stacked for the second pass of each sample. Using the same pantograph machine, the ePTFE layer stack was heated in an oven set at 300 °C for a targeted 120 (E5A–G) or 240 (E5H–J) seconds, then stretched simultaneously in the longitudinal and transverse directions at targeted ratios of 6.35:1 (E5J), 7:1 (E5H–I), or 10:1 (E5A–G) in each direction while maintaining a temperature of approximately 300 °C. The average engineering strain rate target was 4% / second to 9% / second (Table 9). The pantograph opened at a constant speed target over approximately 100 (E5A–BG), 150 (E5H), 120 (E5I), and 134 (E5J) seconds (Table 9). The ePTFE membrane was cooled to room temperature (approximately 22 °C) while being constrained by the pantograph.

[0171] Third pass Samples were retrieved from the cooled ePTFE membranes and stacked if further stretching, i.e., a third pass, was required. Using the same pantograph machine, the membranes were reheated in an oven set at 300 °C for a targeted 120 (E5A–G), 180 (E5I), or 240 (E5H and E5J) seconds, then stretched simultaneously in the longitudinal and transverse directions at targeted ratios of approximately 7:1 (E5H and E5J), 8:1 (E5I), or 10:1 (E5A–G) (Table 9) in each direction while maintaining a temperature of approximately 300 °C. Biaxial stretching was performed at a constant acceleration set point of 1% / s (E5A–E5H and E5J). In the case of Example E5I, biaxial stretching was performed at a constant acceleration set point of 1% / s until 400% strain (λ = 5:1 in both directions) as the pantograph accelerated to a speed set point of 3.5 mm / s, and then at a constant speed set point of 5% / s (3.5 mm / s based on the original length input of 70 mm in this specific case) (“r / s” speed mode) with a targeted ratio of λ in both directions sp = 5:1), and then at a constant speed set point of 5% / s (3.5 mm / s based on the original length input of 70 mm in this specific case) (“r / s” speed mode) with a targeted ratio of λ in both directions sp Stretching was completed at a ratio of 8:1. The pantograph opened over approximately 221 (E5I), 230 (E5A - G), and 195 (E5H and E5J) seconds. The selected samples (E5E - G and E5I) were heat conditioned (heat treated) in a furnace at a set point of 350 °C for 300 seconds while restrained on the pantograph. The ePTFE membrane was cooled to room temperature (approximately 22 °C) while being restrained by the pantograph.

[0172] The cooled and stretched ePTFE membrane from the third pass was recovered from the pantograph and placed on a frame (152.4 mm x 152.4 mm) with an adhesive applied to the back surface. The fibril width average value, area - weighted fibril width (AWFW), fibril width median, specific surface area, bubble point, air flow resistance, and areal density are listed in Table 10.

Table 9

Table 10

[0173] Example 6 The following example discloses the manufacture of an ePTFE membrane and the measurement of various membrane parameters including quality factor, air flow resistance, areal density, particle capture efficiency, and penetration rate. The air filtration performance was measured as described in the test method section.

[0174] PTFE fine powder (E.I. DuPont de Nemours) was blended with ISOPAR® K isoparaffinic hydrocarbon lubricant at a target ratio of 110 mL per pound (approximately 0.454 kg) of fine powder (0.156 g of lubricant / total g) (grams of lubricant / total mass of the mixture). The lubricated powder was compressed into a cylindrical shape and then tape was provided by ram extrusion at 49 °C. The tape was 16.2 cm wide and 0.762 mm thick. ISOPAR® K was removed by heating to approximately 200 °C. The dried tape was cut into 98 square mm pieces. A summary of the process parameters used in Example 6 is shown in Table 11.

[0175] First pass Using a pantograph machine, single (E6A - C) layer or up to four (E6D) square tapes were layer - formed and then heated in a furnace set at 300 °C (set point) for 120 (E6A - C) or 240 seconds (E6D). Then, simultaneously in the longitudinal and transverse directions, at the target ratio (λ sp ) of 4:1, 7:1 or 9:1 (Table 11), it was stretched while maintaining a temperature of about 300 °C. The average engineering strain rate target was set at 36% / second. The pantograph opened at a constant speed target over approximately 8.3, 16.6 or 22 seconds based on the target ratio (Table 11). The ePTFE membrane was cooled to room temperature (approximately 22 °C) while being restrained by the pantograph.

[0176] Second pass Samples were retrieved for further stretching, i.e., the second pass, from the cooled membranes. The specific number of ePTFE membranes loaded for the second pass of each sample is shown in Table 11. Using the same pantograph machine, the ePTFE layer stack was heated in a furnace set at 300 °C for the target 120 (E6A - C) or 240 (E6D) seconds, and then simultaneously in the longitudinal and transverse directions, it was stretched at the target ratio of 7:1 or 10:1 in each direction while maintaining a temperature of about 300 °C. The average engineering strain rate targets were 5% / s, 9% / s or 4% / s (Table 11). The pantograph opened at a constant speed target over approximately 120 (E6A - B), 100 (E6C) and 150 (E6D) seconds. The stretched membrane was cooled to room temperature (approximately 22 °C) while being restrained by the pantograph.

[0177] Third pass Samples were recovered from the cooled ePTFE membranes and stacked if further stretching, i.e., a third pass, was required. Using the same pantograph machine, the membranes were reheated in an oven set to 300 °C for a target of 120 (E6A–C) or 240 (E6D) seconds, then stretched simultaneously in the longitudinal and transverse directions at a target ratio of approximately 8:1 (E6A–B), 10:1 (E6C), or 7:1 (E6D) in each direction while maintaining a temperature of approximately 300 °C. The average strain rate target was 1% / s. The pantograph was opened at a constant acceleration target over approximately 208 (E6A–B), 230 (E6C), or 195 (E6D) seconds. Two samples, E6B and E6D, were exposed to heat at approximately 350 °C for 5 minutes. The expanded membranes were cooled to room temperature (approximately 22 °C) while being constrained by the pantograph.

[0178] The ePTFE membranes were recovered from the machine and placed on a frame (152.4 mm x 152.4 mm) with an adhesive applied to the back surface for further testing. As described in the Test Methods section, the air flow resistance and filtration efficiency of the samples were tested. The results of the air filtration are shown in Table 12. A plot of particle diameter versus quality factor (Q f ) for samples E6A, E6B, E6C, E6D, and E6E (Comparative Example 1) is shown in FIG. 24. FIG. 24 shows the improvement in the quality factor of samples E6A–E6D relative to Comparative Example E6E.

[0179] The ePTFE samples were detached from the tape and weighed on a Mettler Toledo AT 20. The fibril widths were measured for samples E6A and E6B and are shown in FIGS. 25 and 26. FIGS. 27 and 28 show samples E6A and E6B at a lower magnification, respectively. The fibril width measurement results are shown in Table 13.

[0180] Comparative Example 1 An ePTFE membrane was manufactured according to the general teachings described in Gore's U.S. Patent No. 3,953,566. The mass per unit area of the ePTFE membrane (Sample E6E) was 5.6 g / m 2 It was 6.68 mmH2O for air flow resistance, and the capture efficiency for 0.1 micron DOP challenge particles tested at a face velocity of 5.33 cm / s was 98.344% (Table 12).

Table 11

Table 12

Table 13

[0181] Example 7 The following example discloses the manufacture of ePTFE membranes subsequently used for light transmittance measurements.

[0182] PTFE fine powder (E.I. DuPont de Nemours) was blended with ISOPAR® K isoparaffinic hydrocarbon lubricant at a target ratio of 110 mL per pound (approx. 0.454 kg) of fine powder (0.156 g of lubricant / total g) (g of lubricant / total mass of mixture). The lubricated powder was compressed into a cylindrical shape and tapes were provided by ram extrusion at 49 °C. The tapes were 16.2 cm wide and 0.762 mm thick. ISOPAR® K was removed by heating to approximately 200 °C. The dry tapes were cut into 98 square mm. A summary of the process parameters used in Example 7 is shown in Table 14.

[0183] First pass Using a pantograph machine, one or four square tapes were heated in a furnace set at 300 °C (set point) for 240 (E7A) or 120 (E7B) seconds, then stretched simultaneously in the longitudinal and transverse directions at various target ratios (Table 13). The average engineering strain rate target was determined for samples E7A and E7B (Table 13). The pantograph opened at a constant speed target for approximately 16.6 (E7A) or 8.4 (E7B) seconds. The ePTFE membranes were cooled to room temperature (approx. 22 °C) while being restrained by the pantograph.

[0184] Second pass Samples were recovered from the cooled ePTFE membrane for further stretching, i.e., the second pass. Using the same pantograph machine, single-layer (E7B) or 16-layer (E7A) stacks were heated in the furnace to approximately 300 °C over a target of 120 (E7B) or 240 (E7A) seconds, then stretched simultaneously in the longitudinal and transverse directions at a target ratio of approximately 7:1 (E7A) or 10:1 (E7B) in each direction while maintaining a temperature of approximately 300 °C. The average engineering strain rate target was set at 5% / s (E7A) or 9% / s (E7B). The pantograph opened at a constant speed target over approximately 120 (E7A) or 100 (E7B) seconds. The ePTFE membrane was cooled to room temperature (approximately 22 °C) while being restrained by the pantograph.

[0185] Third pass Samples were recovered from the cooled ePTFE membrane and stacked as needed for further stretching, i.e., the third pass. Using the same pantograph machine, 3-layer (E7B) and 48-layer (E7A) samples were heated in the furnace set at approximately 300 °C over a target of 120 seconds, then stretched simultaneously in the longitudinal and transverse directions at a target ratio of approximately 7:1 (E7B) or 8:1 (E7A) (Table 14) in each direction while maintaining a temperature of approximately 300 °C. The average strain rate target was set at 1% / s. The pantograph opened at a constant acceleration target over approximately 208 (E7A) or 195 (E7B) seconds. The ePTFE membrane was cooled to room temperature (approximately 22 °C) while being restrained by the pantograph.

[0186] The ePTFE membrane was recovered from the machine and placed on a frame (152.4 mm x 152.4 mm) with an adhesive applied to the back side for further testing. As described in the section on test methods, the air flow resistance of the sample was tested. The ePTFE sample was detached from the tape and weighed on a Mettler Toledo AT 20. As described in the section on test methods, the selected samples were also tested for light transmittance. The results of the light transmittance test are shown in Table 15 and Figure 29. Figure 29 is a plot of wavelength vs. % transmittance for both the 3-layer sample (E7B, black line) and the 48-layer sample (E7A, gray line).

Table 14

Table 15

[0187] Example 8 This example emphasizes that the strength with respect to the weight ratio of a relatively balanced ePTFE membrane composed of extremely fine similar fibrils, which exhibits an exceptionally high crystallinity of at least 94%, is improved. Stacking and simultaneous stretching were employed to generate sample masses for bulk mechanical characterization and to reduce the time at the synchrotron for structural characterization. The amorphous content and relative strength balance were determined using X-ray diffraction (XRD).

[0188] PTFE fine powder (DuPont) was blended with ISOPAR® K isoparaffinic hydrocarbon lubricant at a target ratio of 110 mL per pound (approximately 0.454 kg) of fine powder (0.156 g of lubricant / total g) (grams of lubricant / total mass of mixture). The lubricated powder was compressed into a cylindrical shape and tape was provided by ram extrusion at 49 °C. The tape was 16.2 cm wide and 0.762 mm thick. ISOPAR® K was removed by heating to approximately 200 °C. The dry tape was cut into 98 square mm pieces. A summary of the process parameters used in this example is shown in Table 16.

[0189] First pass Using a pantograph machine, up to four square tapes were heated in a furnace set at 300 °C (Samples E8A and E8B) or 322 °C (Samples E8C and E8D) for 240 seconds, and then simultaneously stretched in the longitudinal and transverse directions at a target ratio of 7:1 (E8C - D) or 9:1 (E8A - B) in each direction (Table 16). The average engineering strain rate target was set at 36% / s. The pantograph opened at a constant speed target over approximately 16.6 (E8C - D) and 22.2 (E8A - B) seconds. The ePTFE membrane was cooled to room temperature (approximately 22 °C) while being restrained by the pantograph.

[0190] Second pass Samples were recovered from the cooled ePTFE membrane for further stretching, i.e., the second pass. Table 16 lists the specific number of layers loaded for the second pass under each condition. Using the same pantograph machine, samples with 16 layers (E8B) or 32 layers (E8A and E8C - D) were heated in the furnace to approximately 300 °C (E8A - B) or 322 °C (E8C - D) for 240 seconds, and then simultaneously stretched in the longitudinal and transverse directions at a target ratio of approximately 7:1 in each direction while maintaining the set point temperature. The average engineering strain rate target was set at 4% / s (E8A - B) or 5% / s (E8C - D) (Table 16). The pantograph opened at a constant speed target over approximately 150 (E8A - B) or 120 (E8C - D) seconds. The ePTFE membrane was cooled to room temperature (approximately 22 °C) while being restrained by the pantograph.

[0191] Third pass Samples were recovered from the cooled ePTFE membranes and stacked as needed for further stretching, i.e., the third pass. Using the same pantograph machine, the ePTFE membranes (using 64 layers (E8B) and 128 layers (E8A and E8C - D)) were reheated in a furnace set at 300 °C (E8A - B) or 322 °C (E8C - D) for 120 (E8C - D) or 240 (E8A - B) seconds, and then simultaneously stretched in the longitudinal and transverse directions at a target ratio of approximately 7:1 (E8A - B) or 8:1 (E8C - D) in each direction while maintaining the set point temperature (Table 16). The average strain rate target was 1% / s. The pantograph opened at a constant acceleration over approximately 195 (E8A - B) or 208 (E8C - D) seconds. Samples E8B and E8D were heat conditioned in a furnace at the set point of 350 °C for the target 300 seconds while restrained on the pantograph. The ePTFE membranes were cooled to room temperature (approximately 22 °C) while restrained by the pantograph.

[0192] The ePTFE membranes were recovered from the machine and placed on a frame (152.4 mm x 152.4 mm) with an adhesive applied to the back for further testing. The tensile test results included in Table 17 show that the intrinsic strength with respect to the weight metrics exceeds the values previously reported in the art (see Comparative Examples - Table 18). Samples E8C and E8D were further characterized by X - ray diffraction (XRD) (Figure 30, sample E8C (not heat - treated) and Figure 31, sample E8D (heat - treated)), and the results are consistent with an isotropic orientation within the MD - TD plane. These results are consistent with the results of balanced strength. Figure 32 is a plot of q (nm -1 ) versus intensity over the range 10 - 45 nm for both the heat - treated sample (sample E8D, top trace) and the non - heat - treated sample (sample E8C, bottom trace). Figure 32 is a plot of q (nm -1 ) versus intensity (10 - 20 nm -1 ) over the range 10 - 20 nm for sample E8D (heat - treated, top trace) and sample E8C (non - heat - treated sample, bottom trace) -1 ) -1 ) is the plot. Figures 32 and 33 demonstrate that the ePTFE membrane has a very high degree of crystallinity. Additionally, the narrowness of the peak centered at q = 12.8 nm (Figure 33) suggests that there are few defects in the crystal packing of these ePTFEs. The crystallinity of Example E8C was 99%. The crystallinity of Example E8D was 99.2%. -1 The narrowness of the peak centered at -1 (Figure 33) suggests that there are few defects in the crystal packing of these ePTFEs. The crystallinity of Example E8C was 99%. The crystallinity of Example E8D was 99.2%.

Table 16

Table 17

[0193] Comparative Examples 2 - 4 The matrix tensile strengths of Comparative ePTFE Examples 2 - 4 in the prior art are listed in Table 18.

Table 18

[0194] Example 9 The following example describes the preparation and analysis of a low - mass uniaxially oriented ePTFE membrane having high intrinsic strength in the fibril direction.

[0195] PTFE fine powder (E.I. DuPont de Nemours) was blended with ISOPAR® K isoparaffinic hydrocarbon lubricant at a target ratio of 110 mL per pound (approximately 0.454 kg) of fine powder (0.156 g of lubricant / total g) (grams of lubricant / total mass of mixture). The lubricated powder was compressed into a cylindrical shape and tapes were provided by ram - extruding at 49°C. The tapes were 16.2 cm wide and 0.762 mm thick. ISOPAR® K was removed by heating to approximately 200°C. 98 square mm was cut from the dried tapes. A summary of the process parameters used in Example 9 is shown in Table 19.

[0196] First pass Using a pantograph machine, two different samples, each having four tape layers, were heated in an oven set at approximately 300 °C (set point) for 240 seconds, and then simultaneously stretched in the longitudinal (machine direction) and transverse directions at a target ratio of approximately 10:1 in each direction while maintaining a temperature of approximately 300 °C. The average engineering strain rate target was set at 36% / second. The pantograph opened at a constant speed target over approximately 25 seconds. The ePTFE membrane was cooled to room temperature (approximately 22 °C) while being constrained by the pantograph.

[0197] Second pass Four pieces (each of four layers) were recovered from the cooled ePTFE membrane pieces for further stretching, i.e., for the second pass. Using the same pantograph machine, a sample containing a 16-layer stack was heated in an oven set at approximately 300 °C for a target of 240 seconds, and then simultaneously stretched in the longitudinal and transverse directions at a target ratio of approximately 10:1 in each direction while maintaining a temperature of approximately 300 °C. The average engineering strain rate target was set at 3.6% / second. The pantograph opened at a constant speed target over approximately 250 seconds. The ePTFE membrane was cooled to room temperature (approximately 22 °C) while being constrained by the pantograph.

[0198] Third pass Four samples (each of 16 layers) were recovered from the cooled membrane, and two stacks of 16 layers (32 layers in total) were loaded for further stretching, i.e., for the "third pass". Using the same pantograph machine, the membrane was reheated in the oven to approximately 300 °C for a target of 120 seconds, and then simultaneously stretched in the longitudinal and transverse directions at a target ratio of 3:1 (Example E9A) or 5:1 (Example E9B) in each direction while maintaining a temperature of approximately 300 °C. The average strain rate target was set at 1% / second. The pantograph opened at a constant acceleration over approximately 110 (E9A) or 161 (E9B) seconds. The ePTFE membrane was cooled to room temperature (approximately 22 °C) while being constrained by the pantograph.

[0199] Any fourth pass Using the same pantograph machine, for sample E9B, a 32-layer sample was reheated in the furnace to approximately 300 °C over a target of 120 seconds, and then simultaneously in the longitudinal and transverse directions, while maintaining a temperature of approximately 300 °C, it was stretched at a target ratio of approximately 3:1 in each direction. The simultaneous stretching was performed at a constant acceleration set point of 1% / second. The pantograph opened at a constant acceleration over approximately 110 (E9B) seconds.

[0200] The second-to-last pass Using the same pantograph machine, while releasing the ePTFE membrane from lateral restraint, it was left fixed in the machine direction. The ePTFE membrane was heated in a furnace set to approximately 300 °C over a target of 120 seconds, and then stretched in the longitudinal direction only at a target ratio of 6:1 (machine direction), while allowing the ePTFE membrane to freely neck down (i.e., narrow) in the transverse direction. The pantograph opened at a constant acceleration set point over approximately 170 (E9A - B) seconds. The stretching was performed at a constant acceleration set point of 1% / s.

[0201] The final pass Using the same pantograph machine, a 32-layer sample was heated in a furnace set to approximately 350 °C over a target of 300 seconds, and then stretched only in the machine (longitudinal) direction at a target ratio of approximately 1.5:1 (sample E9A) or 1.67:1 (sample E9B), while maintaining a temperature of approximately 350 °C. The stretching was performed at a constant acceleration set point of 1% / second. The pantograph opened at a constant acceleration over approximately 40 (E9A) or 51 (E9B) seconds.

[0202] The ePTFE membrane was recovered from the machine and placed on a frame (152.4 mm x 152.4 mm) with an adhesive applied to the back surface. Using the frame as a cutting guide, the linear density (bulk denier) was calculated by weighing the ePTFE membrane, and mechanical data was collected using the matrix tensile test in the section of the above test method. Sample E9A was further characterized using dynamic mechanical analysis (DMA), and at ambient temperature (i.e., approximately 20 °C), the matrix Storage showed a modulus of elasticity of 100 GPa (Figure 34 )。Sample E9A was further characterized by XRD (Figure 35 ). The XRD is consistent with a very high degree of crystal orientation. <p2>The orientation function is 0.989, and 1.0 corresponds to a perfect parallel alignment (Figure 36 ). The crystallinity was determined to be 94.6%. The SEM of sample E9A is shown in Figure 37 .

Table 1

Table 2

[0203] Example 10 The following examples disclose the manufacture of very low mass multilayer ePTFE membranes having high intrinsic strength and nanoparticle retention measurements. The nanoparticle retention is tested using the bead test disclosed in the section on the method for measuring the transmittance and bead retention of membrane samples.

[0204] PTFE fine powder (E.I. DuPont de Nemours) was blended with ISOPAR® K isoparaffinic hydrocarbon lubricant at a target ratio of 110 mL per pound (approx. 0.454 kg) of fine powder (0.156 g of lubricant / total g) (grams of lubricant / total mass of mixture). The lubricated powder was compressed into a cylindrical shape and then tape was provided by ram extrusion at 49 °C. The tape was 16.2 cm wide and 0.762 mm thick. ISOPAR® K was removed by heating to approximately 200 °C. 98 square mm was cut from the dried tape. A summary of the process parameters used in Example 10 is shown in Table 21.

[0205] First pass Using a pantograph machine, four square tapes were heated in a furnace set at approximately 300 °C for a target of 120 (E10A - C) seconds, then simultaneously in the longitudinal and transverse directions at selected target ratios (λ sp ) It was stretched at a ratio of about 7:1 (E10A and E10C) or 2:1 (E10B) while maintaining a temperature of about 300 °C. The average engineering strain rate target was set at 36% / second. The pantograph opened at a constant speed target over approximately 16.6 (E10A and E10C) or about 2.8 (E10B) seconds based on the target ratio. The stretched membrane was cooled to room temperature (approximately 22 °C) while being constrained by the pantograph. The first pass was repeated until 64 (E10A) layers, or 16 (E10B) layers, or 32 (E10C) layers became available for the second pass.

[0206] Second pass A specific number, 64 (E10A), 16 (E10B) or 32 (E10C) layers, were loaded for the second pass under the writing conditions shown in Table 21. Using the same pantograph machine, the ePTFE layer stack was heated in a furnace set at 300 °C for 240 (E10A and B) or 120 (E10C) seconds, and then simultaneously in the longitudinal and transverse directions at a selected target ratio of 7:1 (E10A) or 10:1 (E10B) or 6:1 (E10C) while maintaining a temperature of about 300 °C. The average engineering strain rate target was 5% / second (E10A and E10C) or 18% / s (E10B) (Table 21). The pantograph opened at a constant target speed over approximately 120 (E10A), 50 (E10B) and 100 (E10C) seconds. The stretched membrane was cooled to room temperature (approximately 22 °C) while being constrained by the pantograph.

[0207] Third pass Samples were recovered from the cooled ePTFE membranes and laminated if further stretching, i.e., a third pass, was required. A specific number of layers, 256 (E10A), 120 (E10B), or 128 (E10C), were loaded for the second pass of each condition shown in Table 21. Using the same pantograph machine, the membranes were reheated in an oven set at 300 °C for a targeted 120 (E10A–C) seconds and then stretched simultaneously in both the longitudinal and transverse directions at a targeted ratio of approximately 8 (E10A), 10 (E10B), or 6:1 (E10C) in both the longitudinal and transverse directions while maintaining a temperature of approximately 300 °C. The average constant acceleration strain rate set point was 1% / s. The pantograph opened at a constant acceleration set point target for approximately 221 (E10A), 261 (E10B), or 179 (E10C) seconds. The stretched membranes were cooled to room temperature (approximately 22 °C) while being restrained by the pantograph.

[0208] Samples were removed from the machine and placed on a frame (152.4 x 152.4 mm) with adhesive applied to the back side for further testing (E10A and E10B) or further stretching (E10C).

[0209] Fourth pass Samples were recovered from the cooled ePTFE membranes and laminated if further stretching, i.e., a fourth pass, was required. A specific number of layers, 2056, (E10C), were loaded for the fourth pass of each condition shown in Table 21. Using the same pantograph machine, the membranes were reheated in an oven set at 300 °C for a targeted 120 (E10C) seconds and then stretched simultaneously in both the longitudinal and transverse directions at a targeted ratio of 4.75:1 (E10C) in both the longitudinal and transverse directions while maintaining a temperature of approximately 300 °C. The constant acceleration strain rate set point was 1% / second. The pantograph opened at a constant acceleration target for approximately 156 (E10C) seconds. The stretched membranes were cooled to room temperature (approximately 22 °C) while being restrained by the pantograph.

[0210] Densification Isopropyl alcohol (IPA) was gently poured onto the constrained membrane and allowed to evaporate, thereby densifying the samples (E10A - C) while constraining them in the MD and TD planes.

[0211] In accordance with the determination of the transmittance and retention rate by the bead test as described above in the test method section, the average filtrate transmittance (see the above equation (9)) and the bead retention rate (see the above equation (10)) of each membrane sample (Samples E10A, E10B, and E10C) were evaluated. The results are shown in Table 22 and Figure 38.

[0212] Comparative Examples 5 - 7 Three comparative liquid filtration samples were prepared as follows.

[0213] Comparative Example 5 Polytetrafluoroethylene polymer fine powder manufactured in accordance with the teachings of Baillie's U.S. Patent No. 6,541,589 was combined with 0.184 lb / lb of an isoparaffinic hydrocarbon lubricant (ISOPAR® K, located in Houston, Texas, Exxon). The resulting mixture was then blended and compressed into cylindrical pellets, and heat-conditioned at a temperature of 49°C for at least 8 hours. The cylindrical pellets were then extruded through a square orifice die at a reduction ratio of 72:1 to form a tape. The tape was then calendered between rolls at a calender ratio of 3:1. The calendered tape was then stretched horizontally at a ratio of 3.6:1 and dried at a temperature of 200°C.

[0214] The dried tape was then stretched in the machine direction at 330°C to a draw ratio of 7:1. The resulting material was subsequently stretched horizontally at a temperature of about 310°C to a draw ratio of 12:1.

[0215] This biaxially stretched membrane was compressed between rolls at a speed of 1 m / min with a compressive force of 10 N / mm (at 25°C).

[0216] Comparative Example 6 - Sample E10D2 The polytetrafluoroethylene polymer fine powder manufactured according to the teachings of Baillie's U.S. Patent No. 6,541,589 was combined with 0.151 lb / lb of a lubricant (ISOPAR® K, located in Houston, Texas, Exxon). Subsequently, the resulting mixture was blended and compressed into cylindrical pellets and heat-conditioned at a temperature of 49 °C for at least 8 hours. Then, the cylindrical pellets were extruded through a square orifice die at a reduction ratio of 72:1 to form a tape. Next, the tape was calendered between rolls at a calender ratio of 3:1. Then, the calendered tape was stretched horizontally at a ratio of 3.6:1 and dried at a temperature of 200 °C. Then, the dried tape was stretched in the machine direction to a draw ratio of 5:1 at 330 °C. The resulting material was subsequently stretched horizontally to a draw ratio of 10.8:1 at a temperature of approximately 310 °C. Then, the membrane was heat-treated at a temperature of approximately 380 °C for a target of 25 seconds. This biaxially stretched membrane was compressed between rolls at a speed of 1 m / min with a compressive force of 20 N / mm (at 25 °C).

[0217] Comparative Example 7 - Sample E10D3 The polytetrafluoroethylene polymer fine powder manufactured according to the teachings of Baillie's U.S. Patent No. 6,541,589 was combined with 0.145 lb / lb of a lubricant (ISOPAR® K, located in Houston, Texas, Exxon). Subsequently, the resulting mixture was blended and compressed into cylindrical pellets and heat-conditioned at a temperature of 49 °C for at least 8 hours. Then, the cylindrical pellets were extruded through a square orifice die at a reduction ratio of 72:1 to form a tape. Next, the tape was calendered between rolls at a calender ratio of 3:1. Then, the calendered tape was stretched horizontally at a ratio of 3.6:1 and dried at a temperature of 230 °C. Then, the dried tape was stretched in the machine direction to a draw ratio of 5:1 at 325 °C. The resulting material was subsequently stretched horizontally to a draw ratio of 12.3:1 at a temperature of approximately 300 °C. This biaxially stretched membrane was compressed between rolls at a speed of 5 m / min with a compressive force of 80 N / mm (at 90 °C).

[0218] Using the above test procedures, the average filtrate permeability (see the above equation (9)) and bead retention rate (see the above equation (10)) of each comparative example membrane sample (Sample E10D1, E10D2, and E10D3) were evaluated. The results are shown in Table 22 and Figure 38.

Table 21

Table 22

[0219] The invention of the present application has been described generally and in relation to specific embodiments as above. As will be apparent to those skilled in the art, various modifications and changes can be made to the embodiments without departing from the scope of the disclosure. Therefore, the embodiments are intended to cover these modifications and variations provided that they fall within the scope of the appended claims and their equivalents. The aspects of the present invention are listed below. (Aspect 1) An expanded polytetrafluoroethylene (ePTFE) membrane, having a matrix tensile strength of at least 1000 MPa in the machine direction, a matrix storage modulus of at least 100 GPa at a temperature of 20 °C, and a crystallinity of at least 94%, comprising an expanded polytetrafluoroethylene (ePTFE) membrane. (Aspect 2) The expanded polytetrafluoroethylene membrane according to Aspect 1, wherein the areal density of the ePTFE membrane is less than 30 mg / m 2 . (Aspect 3) of the ePTFE membrane <p2>The expanded polytetrafluoroethylene membrane according to Aspect 1 or 2, having an orientation of 0.98 or more. (Aspect 4) The expanded polytetrafluoroethylene membrane according to any one of Aspects 1 to 3, wherein the bulk denier of the ePTFE membrane is 750 g / 9000 m. (Aspect 5) The expanded polytetrafluoroethylene membrane according to any one of Aspects 1 to 4, wherein the strength of the ePTFE membrane exceeds 5 gf / d. (Aspect 6) The expanded polytetrafluoroethylene membrane according to any one of Aspects 1 to 5, wherein the ePTFE membrane is self-supporting. (Aspect 7) The expanded polytetrafluoroethylene membrane according to any one of Aspects 1 to 6, wherein the ePTFE membrane is uniaxially oriented. (Aspect 8) The expanded polytetrafluoroethylene membrane according to any one of Aspects 1 to 7, wherein the ePTFE membrane is at least partially coated with a polymer, at least partially absorbs a polymer, or a combination thereof is applied. (Aspect 9) The expanded polytetrafluoroethylene membrane according to any one of Aspects 1 to 8, which is in the form of a fiber, sheet, tube, three-dimensional self-supporting structure, die-shaped fiber, die-shaped sheet, die-shaped tube, or die-shaped three-dimensional self-supporting structure. (Aspect 10) The stretched polytetrafluoroethylene membrane according to any one of aspects 1 to 9, further comprising a spacer layer. (Aspect 11) The stretched polytetrafluoroethylene membrane according to aspect 10, wherein the spacer layer is selected from a porous polymer, a non-porous polymer, a fluoropolymer, a porous polyolefin, and a non-porous polyolefin. (Aspect 12) A composite comprising the stretched polytetrafluoroethylene membrane according to any one of aspects 1 to 11. (Aspect 13) A laminate comprising the stretched polytetrafluoroethylene membrane according to any one of aspects 1 to 11. (Aspect 14) An article comprising the stretched polytetrafluoroethylene membrane according to any one of aspects 1 to 11, the composite according to aspect 12, or the laminate according to aspect 13. (Aspect 15) A method for forming a uniaxially oriented ePTFE membrane, the method comprising: (1) cutting at least a first piece from a first stretched polytetrafluoroethylene (ePTFE) membrane; (2) obtaining a second stretched polytetrafluoroethylene membrane by biaxially stretching the at least first piece; (3) cutting at least a second piece from the second stretched membrane; (4) forming a stacked sample by positioning the at least one first piece and the at least one second piece in a stacked orientation; (4) biaxially stretching the stacked sample; (5) repeating steps (1) to (4) until a desired biaxially oriented ePTFE membrane is obtained; and (6) uniaxially stretching the biaxially oriented ePTFE membrane. A method for forming a uniaxially oriented ePTFE membrane, comprising the above steps. (Aspect 16) The method according to aspect 16, further comprising adding a spacer layer. (Aspect 17) The method according to aspect 15 or 16, wherein the spacer layer is selected from a porous polymer, a non-porous polymer, a fluoropolymer, a porous polyolefin, and a non-porous polyolefin. (Aspect 18) The method according to any one of aspects 15 to 17, wherein the ePTFE membrane is uniaxially stretched in the machine direction.

Claims

1. An expanded polytetrafluoroethylene (ePTFE) membrane, comprising: a matrix tensile strength of at least 1000 MPa in the machine direction; a matrix storage modulus of at least 100 GPa at a temperature of 20°C; a crystallinity of at least 94%; and an expanded polytetrafluoroethylene (ePTFE) membrane.

2. The areal density of the ePTFE membrane is less than 30 mg / m ２ The expanded polytetrafluoroethylene membrane according to claim 1, wherein the areal density is less than 30 mg / m.

3. The expanded polytetrafluoroethylene membrane according to claim 1 or 2, wherein the <P2> orientation of the ePTFE membrane is 0.98 or more.

4. The expanded polytetrafluoroethylene membrane according to any one of claims 1 to 3, wherein the bulk denier of the ePTFE membrane is 750 g / 9000 m.

5. The expanded polytetrafluoroethylene membrane according to any one of claims 1 to 4, wherein the strength of the ePTFE membrane is more than 5 gf / d.

6. The expanded polytetrafluoroethylene membrane according to any one of claims 1 to 5, wherein the ePTFE membrane is self-supporting.

7. The expanded polytetrafluoroethylene membrane according to any one of claims 1 to 6, wherein the ePTFE membrane is uniaxially oriented.

8. The expanded polytetrafluoroethylene membrane according to any one of claims 1 to 7, wherein at least a portion of the ePTFE membrane is coated with a polymer, at least a portion of the ePTFE membrane has absorbed a polymer, or a combination thereof is applied.

9. The expanded polytetrafluoroethylene membrane according to any one of claims 1 to 8, which is in the form of a sheet, a tube, or a three-dimensional self-supporting structure.

10. The expanded polytetrafluoroethylene membrane according to any one of claims 1 to 9, further comprising a spacer layer.

11. The expanded polytetrafluoroethylene membrane according to claim 10, wherein the spacer layer is selected from a porous polymer, a non-porous polymer, a fluoropolymer, a porous polyolefin, and a non-porous polyolefin.

12. A composite comprising the expanded polytetrafluoroethylene membrane according to any one of claims 1 to 11.

13. A laminate comprising the expanded polytetrafluoroethylene membrane according to any one of claims 1 to 11.

14. An article comprising the stretched polytetrafluoroethylene membrane according to any one of claims 1 to 11.

15. An article comprising the composite according to claim 12.

16. An article comprising the laminate according to claim 13.

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