Highly oriented stretched polytetrafluoroethylene with excellent rigidity

Abstract

To provide self-supporting uniaxially expanded polytetrafluoroethylene (ePTFE) membranes that have high intrinsic strength, a high matrix modulus, and a high crystallinity index.SOLUTION: Uniaxially oriented ePTFE membranes have a matrix tensile strength of at least about 1000 MPa in a machine direction, a matrix modulus of at least about 100 GPa at ambient temperature (i.e., about 20°C), and a crystallinity index of at least about 94%. In some embodiments, the ePTFE membranes have a strength greater than or equal to about 5 gf / d, and a denier less than or equal to about 750 g / 9000 m. In addition, the uniaxially oriented ePTFE membranes have a <P2> orientation of at least about 0.98. In addition, the fibrils in the ePTFE membranes have a nearly perfect parallel alignment. The ePTFE membranes may be used to form composites, laminates, fibers, tapes, sheets, tubes, or other three-dimensional objects.SELECTED DRAWING: Figure 1

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 technology]

[0002] Polytetrafluoroethylene (ePTFE) 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 form 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 a variety of 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 constant need to provide ePTFE articles with improved properties. [Overview of the Initiative] [Means for solving the problem]

[0003] According to one embodiment ("Aspect 1"), the stretched polytetrafluoroethylene (ePTFE) membrane comprises a matrix tensile strength of at least about 1000 MPa in the mechanical 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 embodiment added to Embodiment 1 ("Embodiment 2"), the surface density of the ePTFE membrane is approximately 30 mg / m². 2 It is less than.

[0005] According to another embodiment added to Embodiment 1 ("Embodiment 3"), the ePTFE membrane <p2>The orientation is 0.98 or higher.

[0006] According to another embodiment added to any one of the preceding embodiments ("Embodiment 4"), the bulk denier of the ePTFE membrane is 750 g / 9000 m.

[0007] According to another embodiment ("Embodiment 5") added to any one of the preceding embodiments, the tenacity of the ePTFE membrane is greater than approximately 5 gf / d.

[0008] According to another embodiment ("Embodiment 6") added to any one of the preceding embodiments, the ePTFE membrane is self-supporting.

[0009] According to another embodiment ("Embodiment 7") added to any one of the preceding embodiments, the ePTFE membrane is uniaxially oriented.

[0010] According to another embodiment added to any one of the preceding embodiments ("Embodiment 8"), the ePTFE membrane is at least partially coated with a polymer, at least partially absorbed with a polymer, or a combination thereof.

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

[0012] According to another embodiment added to any one of the prior embodiments ("Embodiment 10"), the ePTFE membrane further includes a spacer layer.

[0013] According to another embodiment added to embodiment 10 ("embodiment 11"), the spacer layer is selected from porous polymers, non-porous polymers, fluoropolymers, porous polyolefins, and non-porous polyolefins.

[0014] In another embodiment ("Embodiment 12"), the composite comprises an extended polytetrafluoroethylene membrane of any one of the preceding embodiments.

[0015] In another embodiment ("Embodiment 13"), the laminate comprises an extended polytetrafluoroethylene membrane of any one of the preceding embodiments.

[0016] In another embodiment ("Embodiment 14"), the article comprises an stretched polytetrafluoroethylene membrane of embodiments 1 to 11, a composite of embodiment 12, or a laminate of embodiment 13.

[0017] According to another embodiment ("Embodiment 15"), a method for forming a uniaxially oriented ePTFE membrane, wherein the method is (1) Separate at least one piece from the first stretched polytetrafluoroethylene (ePTFE) membrane, (2) By biaxially stretching at least the first piece, a second stretched polytetrafluoroethylene membrane is obtained. (3) Separate at least a second piece from the second stretched membrane, (4) By positioning the at least one first piece and the at least one second piece in an overlapping orientation, an overlapping sample is formed. (5) Repeat steps (1) to (4) until the desired biaxially oriented ePTFE membrane is obtained, (6) The biaxially oriented ePTFE membrane is uniaxially stretched. This includes the following.

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

[0019] According to another embodiment added to embodiment 16 ("embodiment 17"), the spacer layer is selected from porous polymers, non-porous polymers, fluoropolymers, porous polyolefins, and non-porous polyolefins.

[0020] According to another embodiment added to embodiment 15 ("embodiment 18"), the ePTFE membrane is uniaxially stretched in the mechanical direction. [Brief explanation of the drawing]

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

[0022] [Figure 1] Figure 1 is a scanning transmission electron microscope (STEM) image of sample E1G of Example 1, based on the embodiments described herein, taken at a magnification of 2,000x with a full horizontal field width of approximately 63 microns.

[0023] [Figure 2] Figure 2 is a STEM image of sample E1G of Example 1, based on the embodiments described herein, taken at a magnification of 5,000x with a full horizontal field width of approximately 25 microns.

[0024] [Figure 3] Figure 3 is a STEM image of sample E1G from Example 1, based on the embodiments described herein, taken at a magnification of 10,000x with a full horizontal field width of approximately 12 microns.

[0025] [Figure 4] Figure 4 is a STEM image of sample E1H of Example 1, based on the embodiments described herein, taken at a magnification of 20,000x with a full horizontal field width of approximately 6 microns.

[0026] [Figure 5] Figure 5 is a STEM image of sample E1I of Example 1, based on the embodiments described herein, taken at a magnification of 2,000x with a full horizontal field width of approximately 63 microns.

[0027] [Figure 6] Figure 6 is a STEM image of sample E2E from Example 2, based on the embodiments described herein, taken at a magnification of 5,000x with a full horizontal field width of approximately 25 microns.

[0028] [Figure 7] Figure 7 is a STEM image of sample E2F from Example 2, based on the embodiments described herein, taken at a magnification of 5,000x with a full horizontal field width of approximately 25 microns.

[0029] [Figure 8] Figure 8 is a STEM image of sample E2G from Example 2, based on the embodiments described herein, taken at a magnification of 5,000x with a full horizontal field width of approximately 25 microns.

[0030] [Figure 9] Figure 9 is a STEM image of sample E3A from Example 3, based on the embodiments described herein, taken at a magnification of 100,000x with a full horizontal field width of approximately 1.27 microns.

[0031] [Figure 10] Figure 10 is a STEM image of sample E3B from Example 3, based on the embodiments described herein, taken at a magnification of 20,000x with a full horizontal field width of approximately 6 microns.

[0032] [Figure 11] Figure 11 is a STEM image of sample E1H from Example 5, based on an embodiment described herein (taken at a magnification of 20,000x with a full horizontal field width of approximately 6 microns), with manual image analysis used to measure the fibril width.

[0033] [Figure 12] Figure 12 shows the histogram of fibril width data (nanometers) from manual image analysis of Figure 11 for Example 5 based on the embodiments described herein, and a fit of the log-normal distribution.

[0034] [Figure 13] Figure 13 is a STEM image of sample E5A from Example 5, based on the embodiments described herein, taken at a magnification of 6,000x with a full horizontal field width of approximately 21 microns.

[0035] [Figure 14] Figure 14 is a STEM image of sample E5B from Example 5, based on the embodiments described herein, taken at a magnification of 6,000x with a full horizontal field width of approximately 21 microns.

[0036] [Figure 15] Figure 15 is a STEM image of sample E5C from Example 5, based on the embodiments described herein, taken at a magnification of 10,000x with a full horizontal field width of approximately 12 microns.

[0037] [Figure 16] Figure 16 is a STEM image of sample E5D of Example 5, based on the embodiments described herein, taken at a magnification of 10,000x with a full horizontal field width of approximately 12 microns.

[0038] [Figure 17] Figure 17 is a STEM image of sample E5E from Example 5, based on the embodiments described herein, taken at a magnification of 6,000x with a full horizontal field width of approximately 21 microns.

[0039] [Figure 18] Figure 18 is a STEM image of sample E5F from Example 5, based on the embodiments described herein, taken at a magnification of 10,000x with a full horizontal field width of approximately 12 microns.

[0040] [Figure 19] Figure 19 is a STEM image of sample E5G from Example 5, based on the embodiments described herein, taken at a magnification of 10,000x with a full horizontal field width of approximately 12 microns.

[0041] [Figure 20] Figure 20 is a scanning transmission electron microscope (STEM) image of sample E5H from Example 5, based on the embodiments described herein, taken at a magnification of 10,000x with a full horizontal field width of approximately 21 microns.

[0042] [Figure 21] Figure 21 is a STEM image of sample E5I from Example 5, based on the embodiments described herein, taken at a magnification of 20,000x with a full horizontal field width of approximately 6 microns.

[0043] [Figure 22] Figure 22 is a STEM image of sample E5H from Example 5, based on the embodiments described herein, taken at a magnification of 5,000x with a full horizontal field width of approximately 25 microns.

[0044] [Figure 23] Figure 23 is a STEM image of sample E5I from Example 5, based on the embodiments described herein, taken at a magnification of 5,000x with a full horizontal field width of approximately 25 microns.

[0045] [Figure 24] Figure 24 is a graph showing the quality factor versus particle size of samples E6A, E6B, E6D, and E6E of Example 6 based on the embodiments described herein.

[0046] [Figure 25] Figure 25 is a STEM image of sample E6A from Example 6, based on the embodiments described herein, taken at a magnification of 10,000x with a full horizontal field width of approximately 12 microns.

[0047] [Figure 26] Figure 26 is a STEM image of sample E6B from Example 6, based on the embodiments described herein, taken at a magnification of 10,000x with a full horizontal field width of approximately 12 microns.

[0048] [Figure 27] Figure 27 is a STEM image of sample E6A from Example 6, based on the embodiments described herein, taken at a magnification of 1,500x with a full horizontal field width of approximately 84 microns.

[0049] [Figure 28] Figure 28 is a STEM image of sample E6B of Example 6, based on the embodiments described herein, taken at a magnification of 1,500x with a full horizontal field width of approximately 84 microns.

[0050] [Figure 29] Figure 29 is a graph showing the % transmittance versus wavelength of sample E7A (gray line, 48 layers) and sample E7B (black line, 3 layers) based on the embodiments described herein.

[0051] [Figure 30] Figure 30 shows the X-ray diffraction pattern (XRD) of sample E8C from Example 8, based on the embodiments described herein.

[0052] [Figure 31] Figure 31 shows the X-ray diffraction pattern (XRD) of sample E8D (heat-treated) of Example 8, based on the embodiments described herein.

[0053] [Figure 32] Figure 32 is a graph showing the q (nm-1) versus intensity (10-45 nm-1) for samples E8C (bottom trace - unheated) and E8D (top trace - heat-treated) of Example 8 based on the embodiments described herein.

[0054] [Figure 33] Figure 33 is a graph showing the q (nm-1) versus intensity (focused in the 10-20 nm-1 range) for samples E8C (bottom trace - unheated) and E8D (top trace - heat-treated) of Example 8 based on the embodiments described herein.

[0055] [Figure 34] Figure 34 is a graph showing the matrix storage modulus versus temperature for sample E9A of Example 9, based on the embodiments described herein.

[0056] [Figure 35] Figure 35 shows the X-ray diffraction pattern (XRD) of sample E9A of Example 9, based on the embodiments described herein.

[0057] [Figure 36] Figure 36 is a graph showing the intensity versus 2-theta of sample E9A of Example 9 based on the embodiments described herein.

[0058] [Figure 37] Figure 37 is an SEM image of sample E9A of Example 9, based on the embodiments described herein, taken at a magnification of 5000x with a full horizontal field width of approximately 23 microns.

[0059] [Figure 38] Figure 38 is a graph showing the nanoparticle retention rate versus filtrate transmission rate of the sample from Example 10 based on the embodiments described herein.

[0060] [Figure 39] Figure 39 is a schematic diagram illustrating a method for manufacturing a biaxially oriented membrane based on the embodiments described herein.

[0061] Glossary

number

[0062] [Number]

[0063] [Number]

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

[0065] [Number] It is calculated by Surface area: A (m 2 ) Volume: V (m 3 ) and The density ρ of crystalline PTFE x (g / m 3 ) was

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

[0067] [Number] It is calculated by

[0068] The 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

[0071] As will be readily apparent to those skilled in the art, various aspects of this disclosure can be realized by any number of methods and apparatus configured to perform the desired functions. Furthermore, for the sake of clarity, the accompanying drawings referenced herein are not necessarily to scale and may be exaggerated to illustrate various aspects of this disclosure, and in that regard, the drawings should not be construed as restrictive.

[0072] In addition, as used herein, the terms “adjacent” and “adjacent to” mean that when one element is “adjacent” to another element, there may be elements that are directly adjacent to or intervening with the other element. As used herein, the singular forms “a,” “an,” and “the” include the plural form unless the context explicitly indicates otherwise. As used herein, the term “on” means that when one element is on another element, there may be elements that are directly on or intervening with the other element. Needless to say, the terms “fine powder” and “powder” are interchangeable as used herein. Similarly, the terms “ePTFE membrane” and “membrane” are interchangeable as used herein. Furthermore, in this application, the term “ePTFE membrane” includes a single layer or multiple layers of ePTFE membrane. Needless to say, the mechanical direction and the longitudinal direction are the same and are interchangeable as used herein. In addition, the terms “microporous ePTFE membrane” and “ePTFE membrane” are interchangeable as used herein.

[0073] In one embodiment, the present invention relates to a thin, self-supporting, biaxially oriented polytetrafluoroethylene (ePTFE) membrane having high crystallinity, high intrinsic strength, low surface 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 of at least about 600 MPa in both the longitudinal and transverse directions. The ePTFE membrane has a surface density of about 100 mg / m². 2 The total visible transmittance may be less than 98%. In addition, the ePTFE membrane is transparent or invisible to the naked eye. Furthermore, the ePTFE membrane is stackable, and this can be used to control transmittance, pore size, and / or bulk mechanical properties. Using the ePTFE membrane, composites, laminates, fibers, sheets, tubes, or other three-dimensional objects can be formed. These may be further divided into smaller parts by dicing or other cutting or cutting. In addition, biaxially oriented ePTFE membranes can be used for filtration applications. In another embodiment, the biaxially oriented ePTFE membrane can be uniaxially stretched. This aligns the film in one direction (hereafter, uniaxially oriented ePTFE membrane). Such an ePTFE membrane may have a tenacity (gf / d) of more than about 5 grams of weight per denier and a bulk denier (g / 9000m) of less than about 750 grams of weight per 9000 meters.

[0074] In the case of polytetrafluoroethylene (PTFE) polymers, particle size, shape, and distribution are important for obtaining the desired porous structure. These particle properties affect packing density and binding density, which in turn affect the porous structure that can be produced from the particles. PTFE resin is supplied in granular form, for example, in the form of fine powder. PTFE fine powder is formed from primary particles.

[0075] When forming an ePTFE membrane, the PTFE fine powder is first mixed with a lubricant, such as diesel fuel. One specific example of a suitable lubricant is isoparaffinic hydrocarbons, such as ISOPAR® K (ExxonMobil Chemical, Spring, TX). Other suitable lubricants include aliphatic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, and similar substances, selected based on flammability, evaporation rate, and economic considerations. Needless to say, the term “lubricant” as used herein refers to a processing aid containing (or consisting of) an incompressible fluid that is not a solvent for the polymer under process conditions. Fluid-polymer surface interactions occur to form a homogeneous mixture. The choice of lubricant is not particularly limited, and safety and convenience are the primary considerations in the selection of the lubricant. The lubricant can be added to the PTFE powder in an amount of approximately 242 mL / kg to approximately 340 mL / kg.

[0076] In at least one embodiment, the lubricant is distributed uniformly or nearly uniformly with the PTFE powder by mixing the PTFE powder with the lubricant. Needless to say, various times and mixing methods can be used to distribute the PTFE powder into the lubricant. Once the lubricant and PTFE powder are sufficiently distributed, the lubricated powder is compressed into a cylindrical shape (i.e., pellets). The pellets can then be extruded with a ram through an extruder die (typically called paste extrusion or paste processing, e.g., when lubricant is present) to produce a cohesive flexible PTFE tape. As used herein, “cohesive” means a tape that is strong enough for further processing. Ram extrusion is performed below the melting temperature of the PTFE polymer (e.g., below 327°C). The formed tape has an indeterminate 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 henceforth be simply referred to as “tape”.

[0077] In a subsequent step, the lubricant is removed from the tape. In cases where ISOPAR® K is the lubricant, the tape may be heated to approximately 200°C. In other embodiments, the lubricant can be removed by washing the tape in hexane or other suitable solvent. If the lubricant is sufficiently volatile, it may be removed without a washing step, or by heat and / or vacuum. Needless to say, however, any convenient drying method may be used.

[0078] The tape is then stretched simultaneously in the longitudinal and transverse directions (i.e., biaxial stretching). As used herein, the terms “biaxially expanded” and “biaxially oriented” refer to a polymer, membrane, preform, or article 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., uniaxial stretching). As used herein, the terms “uniaxial,” “uniaxial orientation,” or “uniaxial stretching” refer to a polymer, membrane, preform, or article stretched in only one direction (e.g., the machine direction (MD) or the transverse direction (TD)). Stretching may be carried out with or without heat at strain rates up to approximately 10,000% / second, 5,000% / second, 2,500% / second, 1,000% / second, 750% / second, 500% / second, 250% / second, 150% / second, 100% / second, 75% / second, 50% / second, 40% / second, 35% / second, 30% / second, 20% / second, 10% / second, or 5% / second. In addition, the tape has the following ranges: approximately 1% / sec to approximately 10,000% / sec, approximately 1% / sec to approximately 5,000% / sec, approximately 1% / sec to approximately 2,500% / sec, approximately 1% / sec to approximately 1,000% / sec, approximately 1% / sec to approximately 750% / sec, approximately 1% / sec to approximately 500% / sec, approximately 1% / sec to approximately 250% / sec, approximately 1% / sec to approximately 150% / sec, and approximately 1% / sec. The tape may be stretched (with or without heat) at rates of approximately 100% / second, 1% / second to 75% / second, 1% / second to 50% / second, 1% / second to 40% / second, 1% / second to 35% / second, 1% / second to 30% / second, 1% / second to 20% / second, 1% / second to 10% / second, or 1% / second to 5% / second. Needless to say, stretching simultaneously increases the intrinsic strength. 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, degree of crystallinity, polymer composition, and similar factors), the temperature at which stretching is performed, the stretching rate, and / or the total amount of stretching.

[0079] ePTFE membranes are formed by biaxial stretching of a tape, and in some embodiments, by additional uniaxial stretching. Microporous ePTFE membranes can be obtained by stretching the tape at the same or different strain rates and at the same or different temperatures. As used herein, the term “microporous” defines an article having pores invisible to the naked eye, such as a membrane. The material properties of ePTFE membranes thus produced have been found to surpass the comparative properties of conventional membranes by efficiently and completely converting ePTFE primary particles (i.e., PTFE fine powder) into fibrils. It is advantageous that the ePTFE membranes discussed herein maintain the properties of conventional ePTFE membranes, such as chemical inertness, thermal stability, low surface energy, low coefficient of friction, biocompatibility, and a wide operating temperature range. The ePTFE membranes can optionally be heat-treated at temperatures up to approximately 390°C. By uniaxially stretching an ePTFE membrane, an ePTFE membrane is formed that has uniaxially oriented fibrils in the direction of stretching (i.e., the mechanical direction (MD) or the transverse direction (TD)), high crystallinity, and high matrix tensile strength. Hereafter, the ePTFE membrane will be described in terms of stretching in the mechanical direction, but it goes without saying that stretching in the transverse direction is also considered to be within the scope of the present invention.

[0080] Biaxially oriented ePTFE membranes are extremely thin and may have a total membrane thickness of less than approximately 2 mm, less than approximately 1.5 mm, less than approximately 1.0 mm, less than approximately 0.5 mm, less than approximately 0.3 mm, less than approximately 0.1 mm, less than 0.05 mm, less than 0.005 mm, less than 0.001 mm, less than approximately 500 nm, less than approximately 400 nm, less than approximately 300 nm, less than approximately 200 nm, less than approximately 100 nm, less than approximately 50 nm, less than approximately 25 nm, less than approximately 10 nm, less than approximately 5 nm, or less than approximately 1 nm. The term "approximately" as used herein means within a range of ±10% of the number or quantity stated. The biaxially oriented ePTFE membrane may be formed to have a total membrane thickness of approximately 1 nm to 100 nm, approximately 1 nm to 90 nm, approximately 1 nm to 80 nm, approximately 1 nm to 70 nm, approximately 1 nm to 60 nm, approximately 1 nm to 50 nm, approximately 1 nm to 40 nm, approximately 1 nm to 30 nm, approximately 1 nm to 20 nm, or approximately 1 nm to 10 nm.

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

[0082] The “invisibility” of biaxially oriented ePTFE membranes is also at least partially attributable to the fibril microstructure of the ePTFE membrane. Roughly speaking, the fibrils are substantially cylindrical. As used herein, the term “substantially cylindrical” means that the aspect ratio in cross-section of the fibrils in the biaxially oriented ePTFE membrane is about 1:1 to about 10:1. In addition, the fibrils in the biaxially oriented ePTFE membrane are thin, with 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 widths are approximately 10 nm to 80 nm, 10 nm to 70 nm, 10 nm to 60 nm, 10 nm to 50 nm, 10 nm to 40 nm, 10 nm to 30 nm, or 10 nm to 20 nm. In some embodiments, the median fibril widths are approximately 20 nm to 70 nm, 30 nm to 60 nm, or 40 nm to 50 nm. In other embodiments, the median fibril widths are approximately 30 nm to 80 nm, 40 nm to 80 nm, 50 nm to 80 nm, 60 nm to 80 nm, or 70 nm to 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 of the crossover point of two fibrils.

[0083] In addition, the surface density per layer is approximately 100 mg / m². 2 (0.1g / m 2 ) less than approximately 90 mg / m² 2 (0.09g / m 2 ) less than approximately 80 mg / m² 2 (0.08g / m 2 ) less than approximately 70 mg / m² 2 (0.07g / m 2 ) less than approximately 60 mg / m² 2 (0.06g / m 2 ) less than approximately 50 mg / m² 2 (0.05g / m 2 ) less than approximately 40 mg / m² 2 (0.04g / m 2 ) less than approximately 30 mg / m² 2 (0.03g / m 2 ) less than approximately 20 mg / m² 2 (0.02g / m 2 ) less than approximately 15 mg / m² 2 (0.015g / m 2 ) less than approximately 10 mg / m² 2 (0.01g / m 2 ) less than approximately 5 mg / m² 2 (0.005g / m 2 ) less than approximately 4 mg / m² 2 (0.004g / m 2 ) less than approximately 3 mg / m² 2 (0.003g / m 2 ) less than approximately 2 mg / m² 2 (0.002g / m 2 ), 1.0 mg / m² 2 (0.001g / m 2 ) less than approximately 0.50 mg / m² 2 (0.0005g / m 2 ) less than approximately 0.40 mg / m² 2 (0.0004g / m 2 ) Less than approximately 0.30 mg / m² 2 (0.0003g / m 2 ) Less than approximately 0.20 mg / m² 2 (0.0002g / m 2 ) Less than approximately 0.10 mg / m² 2 (0.0001g / m 2 ) less than approximately 0.05 mg / m² 2 (0.00005g / m 2 ), or approximately 0.003 mg / m² 2 (0.000003g / m 2 Biaxially oriented ePTFE membranes with a density of less than 0.003 mg / m² are remarkably lightweight. In some embodiments, the surface density per layer is approximately 0.003 mg / m². 2 (0.000003g / m 2 ) ~ approx. 100mg / m 2 (0.1g / m 2 ), approximately 0.003mg / m 2 (0.000003g / m 2 ) ~ approx. 90mg / m 2 (0.09g / m 2 ), approximately 0.003 mg / m 2 (0.000003g / m 2 Approximately 80mg / m 2 (0.08g / m 2 ), approximately 0.003 mg / m 2 (0.000003g / m 2 Approximately 70mg / m 2 (0.07g / m 2 ), approximately 0.003 mg / m 2 (0.000003g / m 2 Approximately 60mg / m 2 (0.06g / m 2 ), approximately 0.003 mg / m 2 (0.000003g / m 2 Approximately 50mg / m 2 (0.05g / m 2 ), approximately 0.003 mg / m 2 (0.000003g / m 2 Approximately 40mg / m 2 (0.04g / m 2 ), approximately 0.003 mg / m 2 (0.000003g / m 2 Approximately 30mg / m 2 (0.03g / m 2 ), approximately 0.003 mg / m 2 (0.000003g / m 2 Approximately 20 mg / m³ 2 (0.02g / m 2 ), approximately 0.003 mg / m 2 (0.000003g / m 2 Approximately 10 mg / m³ 2 (0.01g / m 2 ), approximately 0.003 mg / m 2 (0.000003g / m 2 Approximately 1.0 mg / m³ 2 (0.001g / m 2 ), approximately 0.003 mg / m 2 (0.000003g / m 2 Approximately 0.5 mg / m³ 2 (0.0005g / m 2 ), approximately 0.003 mg / m 2 (0.000003g / m 2 ) ~ approx. 0.4mg / m 2 (0.0004g / m 2 ), approximately 0.003mg / m 2 (0.000003g / m 2 ) ~ approx. 0.3mg / m 2 (0.0003g / m 2 ), approximately 0.003mg / m 2 (0.000003g / m 2 ) ~ approx. 0.2mg / m 2 (0.0002g / m 2 ), approximately 0.003mg / m 2 (0.000003g / m 2 ) ~ approx. 0.1mg / m 2 (0.0001g / m 2 ), or approximately 0.003 mg / m² 2 (0.000003g / m 2 ) ~ approx. 0.05mg / m 2 (0.00005g / m 2 ) In some embodiments, the surface density per layer is approximately 5 mg / m². 2 (0.005g / m 2 ) ~ approx. 100mg / m 2 (0.1g / m 2 ), about 20mg / m 2 (0.02g / m 2 ) ~ approx. 90mg / m 2 (0.09g / m 2 ), or approximately 30 mg / m² 2 (0.03g / m 2 ) ~ approx. 80mg / m 2 (0.08 g / m 2 )

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

[0085] In addition, the total surface density of the biaxially oriented ePTFE membrane is approximately 100 g / m². 2 Less than approximately 10g / m 2 Less than approximately 5g / m 2 Less than approximately 1 g / m 2 Less than approximately 0.5 g / m 2 Less than approximately 0.1 g / m 2 Less than approximately 50 mg / m² 2 (0.05g / m 2 ) less than approximately 10 mg / m² 2 (0.01g / m 2 ) less than approximately 5.0 mg / m² 2 (0.005g / m 2 ) less than approximately 4.0 mg / m² 2 (0.004g / m 2 ) less than approximately 3.0 mg / m² 2 (0.003g / m 2 ) less than approximately 2.0 mg / m² 2 (0.002g / m 2 ) less than approximately 1.0 mg / m² 2 (0.001g / m 2 ) less than approximately 0.50 mg / m² 2 (0.0005g / m 2 ) less than approximately 0.40 mg / m² 2 (0.0004g / m 2 ) Less than approximately 0.30 mg / m² 2 (0.0003g / m 2 ) Less than approximately 0.20 mg / m² 2 (0.0002g / m 2 ) Less than approximately 0.10 mg / m² 2 (0.0001g / m 2 ) less than approximately 0.07 mg / m² 2 (0.00007g / m 2 ) less than approximately 0.05 mg / m² 2 (0.00005g / m 2 ) Less than approximately 0.03 mg / m² 2 (0.00003g / m 2 ) less than approximately 0.007 mg / m² 2 (0.000007g / m 2 ), or approximately 0.003 mg / m² 2 (0.000003g / m 2 ) may be less than ). In some embodiments, the total surface density of the biaxially oriented ePTFE membrane is approximately 0.003 mg / m². 2 (0.000003g / m 2 ) ~ approx. 100g / m 2 , about 0.003mg / m 2 (0.000003g / m 2 ) ~ approx. 10g / m 2 , about 0.003mg / m 2 (0.000003g / m 2 ) ~ approx. 1.0g / m 2 , about 0.003mg / m 2 (0.000003g / m 2 ) ~ approx. 0.5g / m 2 , about 0.003mg / m 2 (0.000003g / m 2 ) ~ approx. 0.1g / m 2 , about 0.003mg / m 2 (0.000003g / m 2 ) ~ approx. 50mg / m 2 (0.05g / m 2 ), approximately 0.003mg / m 2 (0.000003g / m 2 ) ~ approx. 10mg / m 2 (0.01g / m 2 ), approximately 0.003mg / m 2 (0.000003g / m 2 ) ~ approx. 5mg / m 2 (0.005g / m 2 ), approximately 0.003 mg / m 2 (0.000003g / m 2 Approximately 4.0 mg / m³ 2 (0.004g / m 2 ), approximately 0.003 mg / m 2 (0.000003g / m 2 Approximately 3.0 mg / m³ 2 (0.003g / m 2 ), approximately 0.003 mg / m 2 (0.000003g / m 2 Approximately 2.0 mg / m³ 2 (0.002g / m 2 ), approximately 0.003 mg / m 2 (0.000003g / m 2 Approximately 1.0 mg / m³ 2 (0.001g / m 2 ), approximately 0.003 mg / m 2 (0.000003g / m 2 Approximately 0.50 mg / m³ 2 (0.0005g / m 2 ), approximately 0.003 mg / m 2 (0.000003g / m 2 Approximately 0.40 mg / m³ 2 (0.0004g / m 2 ), approximately 0.003 mg / m 2 (0.000003g / m 2 Approximately 0.30 mg / m³ 2 (0.0003g / m 2 ), approximately 0.003 mg / m 2 (0.000003g / m 2 Approximately 0.20 mg / m³ 2 (0.0002g / m 2 ), approximately 0.003 mg / m 2 (0.000003g / m 2 Approximately 0.10 mg / m³ 2 (0.0001g / m 2 ), approximately 0.003 mg / m 2 (0.000003g / m 2 Approximately 0.07 mg / m³ 2 (0.00007g / m 2 ), approximately 0.003 mg / m 2 (0.000003g / m 2 ) ~ approx. 0.05mg / m 2 (0.00005g / m 2 ), or approximately 0.10 mg / m² 2 (0.010g / m 2 ) ~ approx. 10g / m 2 That is the case.

[0086] The surface density per layer is approximately 500 mg / m². 2 (0.5g / m 2 ) less than approximately 400 mg / m² 2 (0.4g / m 2 ) less than approximately 300 mg / m² 2 (0.3g / m 2 ) less than approximately 200 mg / m² 2 (0.2g / m 2 ) less than approximately 100 mg / m² 2 (0.1g / m 2 ) less than approximately 70 mg / m² 2 (0.07g / m 2 ) less than approximately 50 mg / m² 2 (0.05g / m 2 ) less than approximately 30 mg / m² 2 (0.03g / m 2 ) less than approximately 25 mg / m² 2 (0.025g / m 2 ) less than approximately 20 mg / m² 2 (0.02g / m 2 ) less than approximately 15 mg / m² 2 (0.015g / m 2 ) less than approximately 10 mg / m² 2 (0.01g / m 2 ) less than approximately 5 mg / m² 2 (0.005g / m 2 ) less than approximately 4 mg / m² 2 (0.004g / m 2 ) less than approximately 3 mg / m² 2 (0.003g / m 2 ) less than approximately 2 mg / m² 2 (0.002g / m 2 ) less than approximately 1.0 mg / m² 2 (0.001g / m 2 ) less than approximately 0.50 mg / m² 2 (0.0005g / m 2 ) less than approximately 0.40 mg / m² 2 (0.0004g / m 2 ) Less than approximately 0.30 mg / m² 2 (0.0003g / m 2 ) Less than approximately 0.20 mg / m² 2 (0.0002g / m 2 ), or approximately 0.10 mg / m² 2 (0.0001g / m 2 Uniaxially oriented ePTFE membranes with a density of less than 0.10 mg / m² are also remarkably lightweight. In some embodiments, the surface density is approximately 0.10 mg / m². 2 (0.0001g / m 2 ) ~ approx. 500mg / m 2 (0.5g / m 2 ), approx. 0.10mg / m 2 (0.0001g / m 2 ) ~ approx. 400mg / m 2 (0.4g / m 2 ), approx. 0.10mg / m 2 (0.0001g / m 2 ) ~ approx. 300mg / m 2 (0.3g / m 2 ), approx. 0.10mg / m 2 (0.0001g / m 2 ) ~ approx. 200mg / m 2 (0.2g / m 2 ), approx. 0.10mg / m 2 (0.0001g / m 2 ) ~ approx. 100mg / m 2 (0.1g / m 2 ), approx. 0.10mg / m 2 (0.0001g / m 2 ) ~ approx. 70mg / m 2 (0.07g / m 2 ), approx. 0.10mg / m 2 (0.0001g / m 2 ) ~ approx. 50mg / m 2 (0.05g / m 2 ), approx. 0.10mg / m 2 (0.0001g / m 2 ) ~ approx. 30mg / m 2 (0.03g / m 2 ), approx. 0.10mg / m 2 (0.0001g / m 2 ) ~ approx. 20mg / m 2 (0.02g / m 2 ), approx. 0.10mg / m 2 (0.0001g / m 2 ) ~ approx. 15mg / m 2 (0.015g / m 2 ), approx. 0.10mg / m 2 (0.0001g / m 2 ) ~ approx. 10mg / m 2 (0.01g / m 2 ), approx. 0.10mg / m 2 (0.0001g / m 2 ) ~ approx. 5mg / m 2 (0.005g / m 2 ), approx. 0.10mg / m 2 (0.0001g / m 2 ) ~ approx. 0.40mg / m 2 (0.0004g / m 2 ), approx. 0.10mg / m 2 (0.0001g / m 2 ) ~ approx. 0.30mg / m 2 (0.0003g / m 2 ), or approximately 0.10 mg / m² 2 (0.0001g / m 2 ) ~ approx. 0.20mg / m 2 (0.0002g / m 2 )

[0087] Despite being thin and lightweight, biaxially oriented ePTFE membranes possess high intrinsic strength characteristics. The matrix tensile strength (MTS) of ePTFE membranes 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 a biaxially oriented ePTFE membrane is about 600 MPa to about 1000 MPa, about 650 MPa to about 1000 MPa, about 700 MPa to about 1000 MPa, about 750 MPa to about 1000 MPa, about 800 MPa to about 1000 MPa, about 850 MPa to about 1000 MPa, or about 900 MPa to about 1000 MPa in both the longitudinal and transverse directions.

[0088] In addition, uniaxially stretched ePTFE membranes have higher intrinsic strength characteristics. In some embodiments, the matrix tensile strength (MTS) of the ePTFE membrane is greater than approximately 1000 MPa in the mechanical direction, greater than approximately 1100 MPa in the mechanical direction, greater than approximately 1200 MPa in the mechanical direction, greater than approximately 1200 MPa in the mechanical direction, greater than approximately 1300 MPa in the mechanical direction, or greater than approximately 1400 MPa in the mechanical direction. In some embodiments, the matrix tensile strength (MTS) of the uniaxially oriented ePTFE membrane is greater than approximately 1000 MPa to 1400 MPa in the mechanical direction, greater than approximately 1100 MPa to 1400 MPa in the mechanical direction, greater than approximately 1200 MPa to 1400 MPa in the mechanical direction, greater than approximately 1200 MPa to 1300 MPa in the mechanical direction, or greater than approximately 1300 MPa to 1400 MPa in the transverse direction. Needless to say, although matrix tensile strength is provided herein with respect to the mechanical direction, it can be equally applied to ePTFE membranes stretched transversely.

[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 about 100 GPa to about 111 GPa, about 101 GPa to about 111 GPa, about 102 GPa to about 111 GPa, about 103 GPa to about GPa, about 104 GPa to about 111 GPa, about 105 GPa to about 111 GPa, about 106 GPa to about 111 GPa, about 107 GPa to about 111 GPa, about 108 GPa to about 111 GPa, about 109 GPa to about 111 GPa, or about 110 GPa to about 111 GPa. Furthermore, the bulk denier of the uniaxially oriented ePTFE is about 750 g / 9000 m. In some embodiments, the bulk denier of uniaxially oriented ePTFE is approximately 0.5g / 9000m to 750g / 9000m, approximately 0.5g / 9000m to 650g / 9000m, approximately 0.5g / 9000m to 500g / 9000m, approximately 100g / 9000m to 450g / 9000m, approximately 0.5g / 9000m to 400g / 9000m, approximately 0.5g / 9000m to 350g / 9000m, approximately 0.5g / 9000m to 250g / 9000m, and approximately 0.5g / 9000m to 200g The values ​​are approximately 0.5g / 9000m to 150g / 9000m, 0.5g / 9000m to 100g / 9000m, 0.5g / 9000m to 50g / 9000m, 0.5g / 9000m to 25g / 9000m, 0.5g / 9000m to 15g / 9000m, 0.5g / 9000m to 10g / 9000m, 0.5g / 9000m to 5g / 9000m, 0.5g / 9000m to 3g / 9000m, or 0.5g / 9000m to 1g / 9000m.

[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 about 5 gf / d to about 8 gf / d, about 6 gf / d to about 8 gf / d, or about 6 gf / d to about 7 gf / d. Furthermore, the uniaxially oriented ePTFE membrane has a tenacity of 0.985 or higher. <p2>It has orientation.

[0091] In addition, the air resistance of the biaxially oriented ePTFE membrane is minimal. In some embodiments, the air resistance of the ePTFE membrane may be 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 5,000 Pa·s / m, less than about 2,000 Pa·s / m, less than about 1,500 Pa·s / m, less than about 1,000 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 approximately 100 Pa·s / m to 2000 Pa·s / m, approximately 100 Pa·s / m to 1500 Pa·s / m, approximately 100 Pa·s / m to 1000 Pa·s / m, approximately 100 Pa·s / m to 750 Pa·s / m, approximately 100 Pa·s / m to 500 Pa·s / m, approximately 100 Pa·s / m to 250 Pa·s / m, or approximately 250 Pa·s / m to 500 Pa·s / m. The low air resistance, combined with the high surface area of ​​the ePTFE membrane, enables a high-performance filtration device.

[0092] The biaxially oriented ePTFE membrane also exhibits high light transmittance, with total luminous transmittance (measured at 380 nm to 780 nm) of approximately 90%, 95%, 98%, and 99% or higher. In exemplary embodiments, the total luminous transmittance of the biaxially oriented ePTFE membrane may be approximately 90% to 99%, 95% to 99%, or 98% to 99%. In some embodiments, the total luminous transmittance of the ePTFE membrane is nearly 100%.

[0093] The fibrils of the (biaxially oriented and uniaxially oriented) ePTFE membrane may be optionally coated with at least one coating composition, such as a polymer or biological coating, so that the ePTFE is porous or non-porous. The coating composition can be applied to the ePTFE membrane by any conventional coating method, such as solvent coating, spray coating, rotational coating, vapor deposition, atomic layer volume (ALD), or immersion coating. In addition, a coating can also be applied to the ePTFE membrane by heating and compressing 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 penetrating the thickness of the biaxially or uniaxially oriented ePTFE membrane. Examples of polymers and / or biological coatings suitable for coating and / or absorbing onto or inside the ePTFE membrane include polyester, polystyrene, polyamide, polyphthalamide, polyamide-imide, polycarbonate, polyethersulfone, polysulfone, polyphenylene sulfide, liquid crystal polymer, polyetherketone, polyetheretherketone, polysiloxane, epoxy, polyurethane, polyimide, polyetherimide, polyacrylate, polyparaxylylene, tetrafluoroethylene (TFE), VDF (vinylidene fluoride), and HFP (hexafluoropropyl alcohol). Examples include copolymers of tetrafluoroethylene (TFE) and perfluoroalkyl vinyl ether (PAVE), copolymers of tetrafluoroethylene and perfluoro-2,2-dimethyl-1,3-dioxole, perfluoroalkyl vinyl ethers, perfluoroalkyl ethers, polyvinylidene fluoride (PVDF), ethylene tetrafluoroethylene (ETFE), polychlorotrifluoroethylene (PCTFE), fluorinated ethylene propylene (FEP), perfluoroalkoxyalkanes (PFA), polyvinyl alcohol (PVA), CBAS® / heparin coatings (commercially available from WL Gore & Associates, Inc.), antimicrobial agents, antibodies, pharmaceuticals, biological entities, angiogenic stimulants, and any combination thereof. The amount of coating applied depends on the initial application.

[0095] Biaxial or uniaxially oriented ePTFE membranes are self-supporting, and in some embodiments, ePTFE membranes are used to reinforce polymer films, such as porous polymers, non-porous polymers, fluoropolymers, polyolefins, films, tapes, and other membranes. "Self-supporting" means that the ePTFE membrane does not require a backing or carrier layer. However, because ePTFE membranes are extremely thin, their edges are often constrained over macroscopic lengths. In other words, the integrity of the ePTFE membrane is maintained by constraining it around its periphery (e.g., "picture-framed"). The inherent strength of the membrane is associated with various distances, holding the membrane together without the need for a backing or support layer behind or beneath it.

[0096] Biaxially oriented and uniaxially oriented ePTFE membranes can be formed as single ePTFE membrane layers. In other embodiments, biaxially oriented and uniaxially oriented ePTFE membranes may have tens, 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. While we do not wish to be bound by theory, the only limiting factor to the number of ePTFE layers present within an ePTFE membrane is the time spent stacking and stretching the layers. Typically, an ePTFE membrane stack "grows" four times each time the ePTFE membrane is biaxially stretched. Needless to say, while adhesives or other binders are typically not used to bond individual ePTFE membranes within a stacked ePTFE membrane, the inclusion of adhesives or other binders is not excluded from use herein and is considered to fall 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, e.g., 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. In addition, one ePTFE membrane layer may differ from another ePTFE layer in terms of the amount of stretching and / or strain rate and / or the overall work performed on the layer. By mutating the membrane type, stretching, 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] The transmittance, pore size, and bulk mechanical properties can be controlled by forming ePTFE membranes (biaxially oriented and uniaxially oriented) and / or any additional spacer layers within the ePTFE membrane. As used herein, the term “transmittance” refers to the ability of a material to pass a fluid (i.e., liquid or gas) through the pores of the membrane or filter material when exposed to a differential pressure across it. In one example, an ePTFE membrane allows for a variety of pore sizes, e.g., pore sizes less than approximately 6 microns in diameter. As used herein, “pore size” refers to the size of the pores within the ePTFE membrane. Pore sizes may range from 2 nm to approximately 6 microns. In addition, the specific surface area (SSA) of ePTFE is measured by the area-weighted fibril width (AWFW) and is approximately 35 m². 2 / g ~ approx. 120m 2 / g, approx. 45m 2 / g ~ approx. 120m 2 / g, approx. 55m 2 / g ~ approx. 120m 2 / g, approx. 65m 2 / g ~ approx. 120m 2 / g, approx. 75m 2 / g ~ approx. 120m 2 / g, approx. 80m 2 / g ~ approx. 120m 2 / g, approx. 90m 2 / g ~ approx. 120m 2 / g, about 100m 2 / g ~ approx. 120m 2 / g, or approximately 110m 2 / g ~ approx. 120m 2 / g is acceptable.

[0099] In some embodiments, biaxially oriented ePTFE membranes can be used for air filtration applications. In such applications, the quality factor of the ePTFE membrane is at least 65 (kPa) when the challenge particles have a diameter of 0.1 microns and a face velocity of 5.33 cm. -1 ). Needless to say, the strength-to-weight ratio (intrinsic strength) of ePTFE membranes 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 a biaxially oriented ePTFE membrane is approximately 65 (kPa). -1 ) ~ approximately 180 (kPa) -1 ), approximately 70 (kPa) -1 ) ~ approximately 180 (kPa) -1 ), approximately 80 (kPa) -1 ) ~ approximately 180 (kPa) -1 ), approximately 90 (kPa) -1 ) ~ approximately 180 (kPa) -1 ), approximately 100 (kPa) -1 ) ~ approximately 180 (kPa) -1 ), approximately 110 (kPa) -1 ) ~ approximately 180 (kPa) -1 ), approximately 120 (kPa) -1 ) ~ approximately 180 (kPa) -1 ), approximately 130 (kPa) -1 ) ~ approximately 180 (kPa) -1 ), approximately 140 (kPa) -1 ) ~ approximately 180 (kPa) -1 ), approximately 150 (kPa) -1 ) ~ approximately 180 (kPa) -1 ), approximately 160 (kPa) -1 ) ~ approximately 180 (kPa) -1 ), or approximately 170 (kPa) -1 ) to approximately 180 (kPa -1 ) may be.

[0100] Biaxially oriented ePTFE membranes 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 virtue of the properties of polytetrafluoroethylene, has chemical attack resistance, biocompatibility, and exhibits a high matrix tensile strength (MTS). The filtration matrix can be selected from solutions, suspensions, colloids, biological fluids, components of biological fluids, aqueous materials, or non-aqueous materials. To filter the filtration matrix, the matrix is passed through the ePTFE membrane and the resulting filtrate is collected. In one embodiment, the biaxially oriented ePTFE membrane contains a nanoparticle retention percentage (%) above the line defined by Equation (1). [Number] (In the above formula, y = nanoparticle retention rate %, and x = filtrate permeability [g / cm 2 / s / MPa])

[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 The sample was cut to form a square section 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] (In the above formula, ρ=density(g / cm 3 ); m=mass(g); w=width(cm); l = length (cm); and t = thickness (cm)

[0103] Matrix tensile strength (MTS) (Method 1) To determine the MTS of biaxial ePTFE membranes, sample ePTFE membranes were cut longitudinally and transversely using an ASTM D412-Dogbone Die Type F (D412F). To determine the MTS of uniaxial membranes, sample ePTFE membranes were loaded longitudinally. Tensile breaking load was measured using an INSTRON® 5567 tensile testing machine (Illinois Tool Works Inc., Norwood, Massachusetts) equipped with a flat-faced grip and a "22 lb" (approximately 100 N) load cell. The gauge length for the grip was set to 8.26 cm, and the strain rate was 0.847 cm / s. The sample was placed in the grip, a baseline was obtained by retracting the sample 1.27 cm, and then a tensile test was performed at the aforementioned rate. Peak force measurements were used for MTS calculations. Equation (3):

number

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

[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 passing 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 herein). Image contrast is based on the difference in electron absorption by the membrane due to its composition or thickness.

[0106] A scanning electron microscope (Hitachi, SU8000, Hitachi, Ltd., Tokyo, Japan) equipped with a transmission adapter (STEM) was used and operated at an acceleration voltage of 30kV or less. No pretreatment or additional treatment (staining) was performed on the samples. Samples for the analysis of thin porous films were prepared on a copper grid (PELCO® centrally marked grid, 400 mesh, copper, product # 1GC400, Ted Pella Inc., Redding, California) equipped with a carbon support layer (carbon type-B, 300 mesh, copper, product # 01813, Ted Pella, Inc.).

[0107] X-ray diffractogram of a biaxial sample A two-dimensional (2-d) X-ray diffractogram was obtained using the X27C beamline of the National Synchrotron Light Source at Brookhaven National Laboratory (Upton, New York). The beamline has a wavelength of 0.1371 nm and a nominal photon flux of 10⁻¹⁰ photons. 12 A well-collimated monochromatic X-ray beam with a speed of 0.39 mm and a diameter was provided. The detector was a Rayonix MAR-CCD 2-d imaging system (Rayonix LLC, Evanston, Illinois). The system was set up with 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 scattering / diffuse X-ray images were collected over 480–540 seconds. In addition, immediately after imaging each sample, a background image without the sample was recorded for the same amount of time. By subtracting the background image from the sample image, the effect of air scattering was removed, and the desired diffractogram was created.

[0108] X-ray scattering method for uniaxial samples Wide-angle X-ray scattering tests were conducted on a Xenocs brand Xeuss 2.0 SAXS / WAXS Laboratory Beamline system (Xenocs SAS, Sassenage, France). The instrument used was a GeniX3D Cu k operating at 50kV and 0.6mA. 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 through two in-line slits, each with an area of ​​0.5 mm x 0.5 mm. The sample-detector distance was 71.0 mm (calibrated by lanthanum hexaboride standard). The "virtual detector" feature of the Xeuss 2.0 system was used to eliminate blind spots in the detector and extend its angular range. This was achieved by translating the detector horizontally and then averaging multiple scans. Four scans were performed here with various horizontal detector offsets, each scan with a 15-minute exposure time. By averaging these four scans, a scattering profile was provided. Orientation was quantified from the I vs. φ azimuthal angle using equation (4).

number

[0109] As can be 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 crystal peak (A 100 ) and the area under the fitted amorphous peak (A amorphous ) according to the following equation (6). [Number]

[0112] Foaming point The foaming point was measured using a capillary flow porometer (Model CFP 1500 AE, Porous Materials, Inc., Ithaca, NY) according to the general teachings of ASTM F31 6-03. The sample membrane was placed in the sample chamber and moistened with SilWick silicone fluid (commercially available from Porous Materials, Inc.) with a surface tension of 19.1 dynes / cm. The lower clamp of the sample chamber consisted of a 40-micron porous metal disc insert (Mott Metallurgical, Fannington, Conn) with 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 setpoints. Parameter setting points Maxflow 200,000 (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) Equiter (0.1 sec) 3 Aveiter (0.1 sec) 20 Maxpdif 0.1 (psi) Maxfdif 50 (cc / m) Startp 1 (psi) The value shown for the foaming point was the average of two measurements.

[0113] ATEQ Airflow The laminar volumetric flow rate of air passing through the membrane sample is measured. A 2.99 cm² area is measured across the flow path. 2 Each membrane sample was clamped between two plates in a way that sealed the membrane. The airflow rate (L / hr) through each membrane sample was measured by challenging it with an air differential pressure of 1.2 kPa (12 mbar) using an ATEQ® (ATEQ Corp., Livonia, MI) Premier D miniature flow tester.

[0114] Airflow resistance Airflow resistance was tested using a Textest FX 3300 air permeability tester device manufactured by Textest AG (Zurich, Switzerland). Fragile permeability measurements are expressed as airflow in cubic feet per minute per square foot of sample area as the differential pressure across a 12.7 mm water column sample decreases. Air permeability was measured by clamping the sample into a circular flanged fixture. The fixture had a circular opening with a diameter of 7 cm (area 38.5 cm²). 2 The sample holder was provided. The upstream side of the sample holder was connected to a flow meter alongside the dry compressed air source.

[0115] Light transmittance measurement Light transmittance measurements were performed using a spectrophotometer (Jasco V-670; JASCO Deutschland GmbH, Pfungstadt, Germany) equipped with a dual-beam integrating sphere attachment (150 mm diameter, ILN-725). The spectrophotometer consists of a deuterium-tungsten halogen lamp, a single Czerny-Turner type monochromatic spectrometer (1200 lines / mm diffraction grating), and a photomultiplier tube (PMT) detector. Light from the monochromatic spectrometer is split into a sample beam and a reference beam before entering the integrating sphere. The integrating sphere is shaped for unidirectional illumination and diffuse detection. The sample beam, upon normal incidence, illuminates a 20 mm x 20 mm sample placed on the integrating rapid incidence port, while the reference beam passes through an open port on the integrating sphere. The sample beam and reference beam are alternately incident on the PMT detector, synchronously rectified, and then converted into digital signals.

[0116] The bandwidth of the monochromatic spectrometer 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 (allowing the sample beam to pass through the open port) were collected. These spectra were used to report the transmittance spectra, expressed as a percentage of incident light.

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

[0118] Calculation of the average fibril width Selected samples were imaged by STEM and manually characterized by 50 measurements of the fibril projection width (e.g., Figure 11). A random number generator was used to highlight the 50 regions, facilitating uniform sampling, after which the operator traced the contours of the nearest fibrils, preferably fibril fragments that had not yet been characterized. Generally, the marked fibrils were rectangular with an aspect ratio greater than 1. The nominal projection width of the fibril was calculated from the ratio obtained by dividing the object's area by its length. This is more representative and informative than a single width measurement, because it inevitably forces the projection width measurement to be perpendicular to the principal axis of the rectangular shape. To verify this method, lines were drawn passing through the centroids of the manually identified regions, perpendicular to the principal axis in the calculated width calculated according to equation (7).

number

[0119] Dynamic Mechanical Analyzer (DMA) Matrix Storage Modulus and Loss Modulus Matrix storage modulus and loss modulus measurements were performed using a TA Instruments Q800 system (TA Instruments, New Castle, Delaware) equipped with a tensioned sample clamp. The DMA was calibrated according to standard TA Instruments procedures. Sample dimensions were obtained using a 10x microscope with a 0.1 mm graduated reticle for width and a KEYENCE LS7010 high-precision non-contact micrometer (Keyence Corp., Itasca, Illinois) for thickness. Sample mass was measured using a Mettler-Toledo A120 microscale (Mettler-Toledo, LLC, Columbus, Ohio). The sample was then placed in the instrument and a preload of 5 mN was applied. Sample length was obtained at 25°C from the calibrated DMA clamp position. A sinusoidal strain with a true strain amplitude of 0.001 and a frequency of 1 Hz was applied along with an additional constant load. This constant load was just sufficient to keep the sample under tension while the sinusoidal strain was applied. The sample was equilibrated at -50°C for 10 minutes, and then the temperature was gradually increased at a rate of 2°C / min up to 150°C. The magnitude and phase angle of the combined sinusoidal force acting on the sample were measured once per second throughout the entire heating gradient, and the storage modulus and loss modulus were calculated using these values. The ratio of the storage modulus and loss modulus was ρ. true / ρ sample By multiplying by ρ, the desired matrix elastic modulus was obtained. true This is crystalline poly(tetrafluoroethylene) at 2.3 g / cm³. 3 While assuming that, ρ sample This was calculated from the dimensions and mass of the measured sample.

[0120] Air filtration performance measurement Following the procedures specified in the TSI CERTITEST® Model 8160 Automatic Filter Tester Operation and Service Manual, particle filtration efficiency and membrane filtration efficiency tests were performed using dioctyl phthalate (DOP) aerosol on a TSI CERTITEST® Model 8160 Automatic Filter Tester (TSI Incorporated, St. Paul, Minnesota). The sample test area was 77.8 cm², and the face velocity was 5.32 cm / sec.

[0121] Using equation (8), the quality factor Q f We determined that.

number

[0122] Penetration P is the percentage 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)). Quality factors are compared using the same face velocity and test aerosol particle size. The quality factor is compared against the pressure (kPa). -1 It is defined in units of ).

number

[0123] Determination of liquid permeability and retention rate by bead testing The bead test measures the transmittance and bead retention of the membrane sample. The membrane sample was confined in a 25 mm filter holder. The membrane was first moistened with an isopropyl alcohol (IPA)-DI aqueous solution (70:30 v / v IPA:water). This solution was forced through the membrane using air pressure. 7 grams of the solution was allowed to pass through the sample, followed by 10 grams of an aqueous solution consisting of 1 vol% TRITON® X-100 (CAS 9002-93-1; Sigma Aldrich, St. Louis, Missouri) 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; Thermo Fisher Scientific, Waltham, Massachusetts) dispersed in an aqueous solution consisting of 1 vol% TRITON® X-100 in DI water. In this case, the membrane was challenged with a sufficient amount of bead to cover the membrane surface area with a single monolayer of bead. The concentrations of bead and filtrate in the challenge solution were determined using an Agilent Technologies Cary Eclipse fluorescence spectrophotometer (Agilent Technologies, Santa Clara, California).

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

number

[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 in 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 flow 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 This is the concentration of the bead in the challenge solution, and C filtrate This represents the concentration of bead in the filtrate. [Examples]

[0128] Unless otherwise specified herein, all scientific and technical terms used herein have the same meaning as those widely understood by those skilled in the art to which the present invention pertains. The present invention is further defined in the following embodiments. Needless to say, these embodiments are illustrative, while they illustrate preferred embodiments of the present invention. From the above discussion and these embodiments, those skilled in the art will be able to identify the essential features of the present invention and make various changes and modifications to the present invention to suit various uses and conditions without departing from the spirit and scope of the present invention.

[0129] Example 1 The following examples demonstrate extremely low surface density (e.g., 10 mg / m²). 2 The invention discloses the manufacture of a single-layer PTFE membrane having a surface density of less than 1.

[0130] Polytetrafluoroethylene (PTFE) fine powder (EI DuPont de Nemours, Wilmington, Delaware) was blended with ISOPAR® K isoparaffinic hydrocarbon lubricant (ExxonMobil Chemical, Spring, Texas) at a target ratio of 110 mL per pound (approximately 0.454 kg) of fine powder (0.156 g lubricant / total g) (grams lubricant / total mixture mass). The lubricated powder was compressed into a cylinder and then ram-extruded at 49°C to produce the tape. The tape was 16.2 cm wide and 0.762 mm thick. ISOPAR® K was removed by heating to approximately 200°C, thereby forming the dried tape ("initial tape"). 98 square mm was cut from the initial tape. The surface density of the initial tape (before pantographic stretching) was 1130 grams per square meter (g / m²). 2 ) was determined. All initial tape surface densities used herein are 1150 ± 100 g / m². 2 This is what it means. A summary of the process parameters used in Example 1 is shown in Table 1.

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

[0132] Second Pass The cooled ePTFE membrane pieces from the first pass were collected for further stretching, i.e., the "second pass." Using the same pantograph machine, the selected membranes were heated in a furnace set to 300°C for a target of 120 seconds, and then stretched simultaneously in the longitudinal (machine direction (MD)) and transverse (TD) directions, maintaining a temperature of approximately 300°C at a target ratio of approximately 10:1 for each direction. The target average engineering strain rate was set to 9% / second. The pantograph was opened at a constant target rate for approximately 100 seconds. The second-pass ePTFE membranes were allowed to cool to room temperature (approximately 22°C) while constrained 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 to 300°C for 120 seconds, and then stretched simultaneously in the longitudinal (machine direction (MD)) and transverse (TD) directions, maintaining a temperature of approximately 300°C with a target ratio of approximately 10:1 for each direction. The constant acceleration setpoint was 1% / second. The pantograph was opened at a constant acceleration setpoint for approximately 230 seconds. The second-pass ePTFE membranes were allowed to cool to room temperature (approximately 22°C) while constrained by the pantograph.

[0134] The ePTFE membrane was allowed to cool to room temperature (approximately 22°C) while being restrained with a pantograph. A summary of the process parameters for Example 1 is shown in Table 1.

[0135] The cooled, stretched ePTFE membrane from the third pass was recovered from the pantograph and placed on a frame (152.4m x 152.4mm) with adhesive applied to the back. Using the frame as a cutting guide, the ePTFE membrane was weighed, and the average surface density was 4.3 mg / m². 2 This was calculated. The lightest sample was 2.4 mg / m². 2 (Table 2). The area ratio is defined as the ratio of surface densities before and after a series of stretching operations. The ePTFE membrane obtained from the third pass showed area ratios of 122,690:1 to 459,273:1 depending on the process conditions (Table 2). Figures 1-3 show the same sample (2.40 mg / m²). 2 The image shows sample E1G at three different magnifications. No residual primary particles are observed. Figure 4 is from a second sample using the same strain path, but the furnace was set to 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 examples demonstrate extremely low surface density per layer (e.g., 10 mg / m²). 2 The invention discloses the manufacture of a PTFE membrane having a surface density of less than 1.5%. The layering of this ePTFE membrane is limited to 256 layers, and the area ratio is up to approximately 34,000,000:1.

[0137] PTFE fine powder (EI 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 lubricant / total g) (grams lubricant / total mixture mass). The lubricated powder was compressed into a cylindrical shape and then ram-extruded at 49°C to produce a tape. The tape was 16.2 cm wide and 0.762 mm thick. ISOPAR® K was removed by heating the tape to approximately 200°C. A 98 square mm section was cut from the dried tape. A summary of the process parameters used in Example 2 is shown in Table 3.

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

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

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

[0141] 4th Pass Four samples (128 layers) were collected from the cooled ePTFE membrane piece, and then layered (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 to 300°C for a target of 120 seconds, and then stretched simultaneously in the longitudinal and transverse directions, maintaining a temperature of approximately 300°C with a target ratio of approximately 3:1 in each direction. Simultaneous stretching was performed at a constant acceleration setpoint of 1% / second for 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 allowed to cool to room temperature (approximately 22°C) while constrained by the pantograph.

[0142] The ePTFE membrane was recovered from the machine and placed on a frame (152.4mm x 152.4mm) with adhesive applied to the back. Using the frame as a cutting guide, the ePTFE membrane was weighed and its surface density was found to be 0.00047 g / m². 2 The number of layers is calculated as / , and the ePTFE membrane is 0.0605 g / m². 2 (Sample E2A, Table 4). The area ratio and surface density (both ePTFE membrane and ePTFE membrane stack) of other ePTFE membranes were determined and listed in Table 4.

[0143] In addition, three more ePTFE membranes consisting of 128 layers were produced for Example 2 (E2B-D) using the first three passes described above. Each ePTFE membrane was loaded individually 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 120 seconds, and then stretched simultaneously in the longitudinal and transverse directions, maintaining a temperature of approximately 300°C at target ratios of approximately 4:1 (E2B), 5:1 (E2C), or 6:1 (E2D) in each direction. Simultaneous stretching was performed at a constant acceleration setpoint of 1% / second in Examples E2B-D. The pantograph was open for approximately 139 (E2B), 161 (E2C), or 179 (E2D) seconds in the fourth pass. At the end of each stretch (E2B-E2D), the stretched ePTFE membranes were allowed to cool to room temperature (approximately 22°C) while 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 adhesive applied to the back. The ePTFE membrane was weighed using the frame as a cutting guide. Table 4 includes the ratio setting value for the fourth pass, area ratio, surface density of the ePTFE membrane stack, surface density of each layer, and translation time in the final pass.

[0144] In addition, three more ePTFE membranes were created for Example 2 (E2E-G) primarily for observing STEM images (Figures 6-8).

[0145] Example E2E was processed using the same process 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 the target ratio for the fourth pass was increased from a bidirectional setting point of 6:1 (E2D) to a bidirectional setting point of 8:1 (E2E) for the final pass area ratio setting point. The pantograph was open for approximately 208 seconds (E2E) during the fourth pass. The stretched ePTFE membrane was allowed to cool to room temperature (approximately 22°C) while restrained by the pantograph. The ePTFE membrane was retrieved from the machine and placed on a frame (152.4mm x 152.4mm) with adhesive applied to the back.

[0146] Example E2F was processed using the same process as Example E2E, with the exception of the following two points: the number of layers loaded for the fourth stretch was increased from 128 (E2E) to 256 (E2F), and the fourth pass target ratio was increased from 8:1 (E2E) for the set points in each direction to 9:1 (E2F) for the set points in both directions. The stretched ePTFE membrane was allowed to cool to room temperature (approximately 22°C) while being restrained by a pantograph. The ePTFE membrane was recovered from the machine and placed on a frame (152.4mm x 152.4mm) with adhesive applied to the back surface.

[0147] Example E2G was processed using the same process as Example E2E, with the following two exceptions: the number of layers loaded for the second stretch was reduced from 32 (E2E) to 16 (E2G), and the fourth pass was omitted. The stretched ePTFE membrane was allowed to cool to room temperature (approximately 22°C) while restrained with a pantograph. The ePTFE membrane was recovered from the machine and placed on a frame (152.4 mm x 152.4 mm) with adhesive applied to the back. Using the frame as a cutting guide, the ePTFE membrane was weighed, and its surface density was found to be 0.009 g / m². 2 The number of layers is calculated as / , and the ePTFE membrane is 1.175 g / m². 2 (Sample E2G, Table 4). The area ratio and surface density (both ePTFE membrane and ePTFE membrane stack) of 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 a PTFE membrane having an extremely low surface density per layer, with an ePTFE layer of up to 10²⁴ and an area ratio of up to approximately 300,000,000:1.

[0149] PTFE fine powder (EI 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 lubricant / total g) (grams lubricant / total mixture mass). The lubricated powder was compressed into a cylindrical shape and then ram-extruded at 49°C to produce a tape. The tape was 16.2 cm wide and 0.762 mm thick. ISOPAR® K was removed by heating the tape to approximately 200°C. A 98 square mm section 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 to approximately 322°C (setpoint) for a target of 240 seconds, and then stretched simultaneously in the longitudinal and transverse directions, maintaining the temperature at approximately 322°C, with a target ratio of approximately 10:1 for each direction. The target average engineering strain rate was set to 36% / second. The pantograph was opened at a constant target rate for approximately 25 seconds. The ePTFE membrane was allowed to cool to room temperature (approximately 22°C) while constrained by the pantograph. Another 32 layers were created by repeating the first pass process once more.

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

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

[0153] 4th Pass Samples (256 layers) were collected from the cooled ePTFE membrane pieces and stacked for further stretching, i.e., the "fourth pass" (1024 layers in total). Using the same pantograph machine, the membrane was reheated in the furnace to approximately 322°C for a target 120 seconds, and then stretched simultaneously in the longitudinal and transverse directions, maintaining a temperature of approximately 322°C at a target ratio of approximately 7:1 for each direction. As the pantograph accelerated to the speed setpoint of 3.5 mm / s, a 400% strain (λ in both directions) was achieved. sp Simultaneous stretching was performed at a constant acceleration setpoint of 1% / s until the ratio was 5:1, and then the stretching was completed at a constant velocity setpoint of 5% / s (in this specific case, 3.5 mm / s ("r / s" velocity mode) based on the original length input of 70 mm). The pantograph was open for approximately 201 seconds in the fourth pass. The stretched membrane was allowed to cool to room temperature (approximately 22°C) while constrained by the pantograph.

[0154] The ePTFE membrane was recovered from the machine and placed on a frame (152.4mm x 152.4mm) with adhesive applied to the back. Using the frame as a cutting guide, the ePTFE membrane was weighed, and its surface density was 0.005–0.016 g / m². 2 The number of layers is calculated, and the mass per unit area (MPA, surface density) of the ePTFE membrane is 0.005~0.016 mg / m². 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 were formed from samples E3A (Figure 9) and E3B (Figure 10).

[0155] A maximum ratio of 298,611,016:1 was achievable (Table 6). The lowest surface density of the completed ePTFE membrane stack was approximately 3.9 mg / m². 2 That was the case. [Table 5] [Table 6]

[0156] Example 4 The following examples use a membrane thickness of 0.6 to 2.0 grams / m² to facilitate the measurement of the membrane thickness (per layer). 2 The invention discloses the manufacture of an ePTFE membrane having a surface density of the order of its type.

[0157] PTFE fine powder (EI 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 lubricant / total g) (grams lubricant / total mixture mass). The lubricated powder was compressed into a cylindrical shape and then ram-extruded at 49°C to produce a tape. The tape was 16.2 cm wide and 0.762 mm thick. ISOPAR® K was removed by heating to approximately 200°C. A 98 square mm section 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 to approximately 300°C for a target of 120 (setpoint) seconds (sample E4B) or 240 (setpoint) seconds (E4A, E4C, and E4D). They were then simultaneously stretched in the longitudinal and transverse directions, maintaining a temperature of approximately 300°C, at a target ratio of approximately 7:1 for each direction. The target average engineering strain rate was set to 36% / second. The pantograph was opened at a constant target speed for approximately 16.6 seconds. The ePTFE membrane was allowed to cool to room temperature (approximately 22°C) while constrained by the pantograph.

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

[0160] Third Pass Four samples were collected 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., a third pass. The same pantograph machine was used to add the 128-layer or 192-layer stack. 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. 400% strain (λ in both directions) was achieved as the pantograph accelerated to a speed setpoint of 3.5 mm / s. sp Simultaneous stretching was performed at a constant acceleration target of 1% / s until the ratio reached 5:1, and then the stretching (E4A, E4C~D) was completed at a constant velocity target of 5% / s (3.5 mm / s in this specific example based on the original length input of 70 mm). The pantograph was open for approximately 221 seconds during the stretching of E4A and E4C~D. Simultaneous stretching in Example (E4B) was performed at a constant acceleration target of 1% / s until the target ratio reached 8:1 in each direction. The entire third pass translation took approximately 210 seconds in Example E4B. The stretched membrane was allowed to cool to room temperature (approximately 22°C) while constrained by the pantograph. The ePTFE membrane was retrieved from the machine and placed on a frame (152.4 mm x 152.4 mm) with adhesive applied to the back.

[0161] The frame was used as a cutting guide to weigh and measure the ePTFE membranes E4A to E4D. The surface density of ePTFE membrane E4A was 0.0076 g / m². 2 The number of layers is calculated as / , and the ePTFE membrane is 0.974 g / m². 2 The average layer thickness measurement of the 128-layer ePTFE membrane was 7.76 microns. This corresponds to approximately 60 nm per layer. Table 7 includes process details for this sample and similar samples that were exposed to approximately 350°C for a target of 5 minutes to promote dimensional stability (i.e., “heat treated”). The surface density of the ePTFE membrane E4B was 0.0049 g / m². 2 The number of layers is calculated as / , and the membrane is 0.632 g / m². 2 The average layer thickness measurement of the 128-layer ePTFE membrane was 4.95 microns. This corresponds to approximately 39 nm per layer. Table 7 includes process details for two additional similar samples compressed to reduce thickness using the methods described herein. ePTFE membrane E4C was a compressed region of ePTFE membrane E4A. ePTFE membrane E4C was placed in a laboratory press at approximately 2.07 MPa (300 psi) for approximately 30 minutes at approximately 22°C. ePTFE membrane E4D was placed in an autoclave at approximately 2.73 MPa (250 psi) under pressure for 40 minutes at approximately 200°C. The surface density of ePTFE membrane E4C was 0.0076 g / m². 2 The number of layers is calculated as / , and the membrane is 0.974 g / m². 2 The average layer thickness of the 128-layer ePTFE membrane was measured at 1.50 microns. This corresponds to approximately 11.7 nm per layer. The surface density of the ePTFE membrane E4D was 0.016 g / m². 2 The number of layers is calculated as / , and the membrane is 2.038 g / m². 2 The average layer thickness of the 192-layer ePTFE membrane was measured at 3.50 microns. This corresponds 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 for each uncompressed ePTFE membrane was approximately twice the width of a typical fibril measured from STEM microscopy images, which was approximately 20–30 nm. Solid volume fraction and porosity were calculated using a PTFE density of 2.2 g / cc. 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 a Caver laboratory press model M (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, generating approximately 300 psi (~2.07 MPa) for approximately 30 minutes.

[0164] Method 2: Laboratory autoclave An ePTFE membrane was placed in an autoclave bag assembled from KAPTON® polyimide film (EI DuPont de Nemours Inc., Wilmington, Delaware). The assembled body was placed in an Econoclave® 3ft x 5ft laboratory autoclave (ASC Process Systems, Valencia, California) for approximately 70 minutes at a set temperature of 200°C with an applied pressure of 250 psi (approximately 1.72 MPa). [Table 7] [Table 8]

[0165] Example 5 The following examples disclose the production of stacked ePTFE membranes (a stack of up to 192 layers by layer formation and simultaneous stretching), and the measurement of various membrane parameters, including average fibril width, area-weighted fibril width (AWFW), median fibril width, specific surface area, foaming point, airflow resistance, and surface density.

[0166] A relatively high airflow rate at a given pressure results in high transmittance; in other words, lower pressure is required for higher flow rates. Airflow resistance is a function of structure, and most simple models use solid volume fraction and representative fibril radius as the main factors. More sophisticated models address slip as a decrease in fibril radius, in which case these are set to a small portion of the mean free path of air under standard conditions, here 65 nm. Other contributing factors for producing membranes with high airflow rates are the uniformity of fibril distribution, fibril shape, and orientation. If each fibril is separated by the same distance, the uniform distribution of fibrils will be maximized. A less uniform distribution is represented by aggregated fibril aggregates, which lag behind and result in higher transmittance. Fibril shape can also change airflow resistance.

[0167] One method for determining the average fibril width is to manually measure the fibril width within a representative sample. Figure 4 (ePTFE membrane E1H) was used to calculate the average and median widths (Figure 11) by manually measuring the fibril width (50 fibrils were measured). Fibril measurements are expressed in nanometers (nm). From Figure 11 (ePTFE membrane E1H), it is clear that the projected width is oversimplified, as smaller fibrils are observed to aggregate on larger fibrils based on the grayscale intensity changes across the fibril width. A bar graph of the fibril measurements from Figure 11 is shown in Figure 12. The data are fitted to a log-normal distribution.

[0168] PTFE fine powder (EI 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 lubricant / total g) (grams lubricant / total mixture mass). The lubricated powder was compressed into a cylindrical shape and then ram-extruded at 49°C to produce a tape. 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 sections. 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 are heated in a furnace set to 300°C (setpoint) for a target of 120 (E5A~G) or 240 seconds (E5H~J), and then simultaneously in the longitudinal and transverse directions, according to the target ratio (λ). sp The ePTFE membranes were stretched at a ratio of 4:1, 7:1, or 9:1 (Table 9) while maintaining a temperature of approximately 300°C. The target average engineering strain rate was set at 36% / second. The pantograph was opened at a constant speed target for approximately 8.3, 16.6, or 22 seconds, based on the target ratio (Table 9). The stretched ePTFE membranes were allowed to cool to room temperature (approximately 22°C) while constrained by the pantograph.

[0170] Second Pass Samples were collected from the cooled ePTFE membrane pieces for further stretching, i.e., a “second pass.” The specific number of layers stacked for the second pass of each sample is shown in Table 9. Using the same pantograph machine, the ePTFE layer stacks were heated in a furnace set to 300°C for a target of 120 (E5A~G) or 240 (E5H~J) seconds, and then stretched simultaneously in the longitudinal and transverse directions, maintaining a temperature of approximately 300°C, with target ratios of 6.35:1 (E5J), 7:1 (E5H~I), or 10:1 (E5A~G) for each direction. The average engineering strain rate target was 4% / sec to 9% / sec (Table 9). The pantograph was opened at a constant rate target for approximately 100 (E5A~BG), 150 (E5H), 120 (E5I), and 134 (E5J) seconds (Table 9). The ePTFE membrane was allowed to cool to room temperature (approximately 22°C) while being restrained with a pantograph.

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

[0172] The cooled, 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 adhesive applied to the back surface. The average fibril width, area-weighted fibril width (AWFW), median fibril width, specific surface area, foaming point, airflow resistance, and surface density are listed in Table 10. [Table 9] [Table 10]

[0173] Example 6 The following examples disclose the manufacture of ePTFE membranes and the measurement of various membrane parameters, including quality factor, airflow resistance, surface density, particle capture efficiency, and penetration rate. Air filtration performance was measured as described in the Test Methods section.

[0174] PTFE fine powder (EI 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 lubricant / total g) (grams lubricant / total mixture mass). The lubricated powder was compressed into a cylindrical shape and then ram-extruded at 49°C to produce a tape. 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 sections. A summary of the process parameters used in Example 6 is shown in Table 11.

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

[0176] Second Pass The cooled membranes were collected for further stretching, i.e., a second pass. 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 stacks were heated in a furnace set to 300°C for a target of 120 (E6A-C) or 240 (E6D) seconds, and then stretched simultaneously in the longitudinal and transverse directions, maintaining a temperature of approximately 300°C, with target ratios of 7:1 or 10:1 for each direction. The average engineering strain rate targets were 5% / s, 9% / s, or 4% / s (Table 11). The pantograph was opened at a constant rate target for approximately 120 (E6A-B), 100 (E6C), and 150 (E6D) seconds. The stretched membranes were allowed to cool to room temperature (approximately 22°C) while constrained by the pantograph.

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

[0178] The ePTFE membrane was recovered from the machine and placed on a frame (152.4 mm x 152.4 mm) with adhesive applied to the back for further testing. The airflow resistance and filtration efficiency of the samples were tested as described in the Test Methods section. The results of air filtration are shown in Table 12. For samples E6A, E6B, E6C, E6D, and E6E (Comparative Example 1), the particle diameter versus quality factor (Q) was calculated. f The plot of ) is shown in Figure 24. Figure 24 shows the improvement in the quality factor of samples E6A to E6D compared to comparative example E6E.

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

[0180] Comparative Example 1 The ePTFE membrane was manufactured in accordance with 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 / m². 2 The airflow resistance was 6.68 mmH2O, 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 examples disclose the fabrication of an ePTFE membrane used subsequently for light transmittance measurement.

[0182] PTFE fine powder (EI 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 lubricant / total g) (grams lubricant / total mixture mass). The lubricated powder was compressed into a cylindrical shape and then ram-extruded at 49°C to produce a tape. 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 sections. A summary of the process parameters used in Example 7 is shown in Table 14.

[0183] First Pass Using a pantograph, one or four square tapes were heated in a furnace set to 300°C (setpoint) for 240 (E7A) or 120 (E7B) seconds, and then simultaneously stretched longitudinally and transversely at various target ratios (Table 13). Average engineering strain rate targets were determined for samples E7A and E7B (Table 13). The pantograph was opened at a constant rate target for approximately 16.6 (E7A) or 8.4 (E7B) seconds. The ePTFE membrane was allowed to cool to room temperature (approximately 22°C) while constrained by the pantograph.

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

[0185] Third Pass Samples were recovered from the cooled ePTFE membranes and stacked as needed for further stretching, i.e., a third pass. Using the same pantograph machine, 3-layer (E7B) and 48-layer (E7A) samples were heated in a furnace set to approximately 300°C for a target of 120 seconds, and then stretched simultaneously in the longitudinal and transverse directions, maintaining a temperature of approximately 300°C, with target ratios of approximately 7:1 (E7B) or 8:1 (E7A) in each direction (Table 14). The target mean strain rate was set to 1% / s. The pantograph was opened at a constant acceleration target for approximately 208 (E7A) or 195 (E7B) seconds. The ePTFE membranes were allowed to cool to room temperature (approximately 22°C) while constrained 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 adhesive applied to the back for further testing. The airflow resistance of the sample was tested as described in the Test Methods section. The ePTFE sample was detached from the tape and weighed on a Mettler Toledo AT 20. The selected sample was also tested for light transmittance as described in the Test Methods section. The results of the light transmittance test are shown in Table 15 and Figure 29. Figure 29 is a plot of wavelength versus % 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 highlights the improved strength-to-weight ratio of a relatively balanced ePTFE membrane composed of extremely fine, similar fibrils exhibiting an exceptionally high crystallinity of at least 94%. Stacking and simultaneous stretching were employed to generate sample mass for bulk mechanical characterization and to reduce synchrotron time for structural characterization. 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 lubricant / total g) (grams lubricant / total mixture mass). The lubricated powder was compressed into a cylindrical shape and then ram-extruded at 49°C to produce a tape. 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 this example is shown in Table 16.

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

[0190] Second Pass The sample was recovered from the cooled ePTFE membrane for further stretching, i.e., a 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 for 240 seconds to approximately 300°C (E8A-B) or 322°C (E8C-D), and then stretched simultaneously in the longitudinal and transverse directions, maintaining the setpoint temperature at a target ratio of approximately 7:1 for each direction. The average engineering strain rate target was set to 4% / s (E8A-B) or 5% / s (E8C-D) (Table 16). The pantograph was opened at a constant rate target for approximately 150 (E8A-B) or 120 (E8C-D) seconds. The ePTFE membrane was allowed to cool to room temperature (approximately 22°C) while constrained by the pantograph.

[0191] Third Pass Samples were collected from the cooled ePTFE membranes and stacked as needed for further stretching, i.e., a 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 to 300°C (E8A~B) or 322°C (E8C~D) for 120 (E8C~D) or 240 (E8A~B) seconds, and then stretched simultaneously in the longitudinal and transverse directions, maintaining the setpoint temperature at a target ratio of approximately 7:1 (E8A~B) or 8:1 (E8C~D) for each direction (Table 16). The target mean strain rate was 1% / s. The pantograph was opened at a constant acceleration for approximately 195 (E8A~B) or 208 (E8C~D) seconds. Samples E8B and E8D were thermally conditioned in a furnace at a set temperature of 350°C for a target of 300 seconds while constrained on a pantograph. The ePTFE membranes were then allowed to cool to room temperature (approximately 22°C) while still constrained on the pantograph.

[0192] The ePTFE membrane was recovered from the machine and placed on a frame (152.4 mm x 152.4 mm) with adhesive applied to the back for further testing. The tensile test results, included in Table 17, show that the intrinsic strength against the gravimetric exceeds 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 (unheat-treated) and Figure 31, sample E8D (heat-treated)), and the results are consistent with isotropic orientation in the MD-TD plane. These results are consistent with the balanced strength results. Figure 32 shows the range 10–45 nm for both the heat-treated sample (sample E8D, top trace) and the unheat-treated sample (sample E8C, bottom trace). -1 q(nm) -1 This is a plot of intensity against ). Figure 32 shows the range 10-20 nm for sample E8D (heat-treated, top trace) and sample E8C (unheat-treated sample, bottom trace). -1 q(nm) -1 ) against intensity (10~20nm -1 This is a plot of ). Figures 32 and 33 demonstrate that the ePTFE membrane has an extremely high degree of crystallinity. In addition, q = 12.8 nm -1 The narrowness of the peak centered at (Figure 33) suggests that there are few defects in the crystal packing of these ePTFE samples. The crystallinity of Example E8C was 99%. The crystallinity of Example E8D was 99.2%. [Table 16] [Table 17]

[0193] Comparative Examples 2-4 Table 18 shows the matrix tensile strengths of comparative ePTFE examples 2-4 using conventional technology. [Table 18]

[0194] Example 9 The following examples describe the preparation and analysis of low-mass uniaxially oriented ePTFE membranes having high intrinsic strength in the fibril direction.

[0195] PTFE fine powder (EI 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 lubricant / total g) (grams lubricant / total mixture mass). The lubricated powder was compressed into a cylindrical shape and then ram-extruded at 49°C to produce a tape. The tape was 16.2 cm wide and 0.762 mm thick. ISOPAR® K was removed by heating to approximately 200°C. A 98 square mm section was cut from the dried tape. 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 a furnace set to approximately 300°C (setpoint) for 240 seconds. They were then simultaneously stretched in the longitudinal (machine direction) and transverse directions, maintaining a temperature of approximately 300°C, at a target ratio of approximately 10:1 for each direction. The target average engineering strain rate was set to 36% / second. The pantograph was opened at a constant target rate for approximately 25 seconds. The ePTFE membrane was allowed to cool to room temperature (approximately 22°C) while constrained by the pantograph.

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

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

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

[0200] The second to last pass Using the same pantograph machine, the ePTFE membrane was released from lateral constraints while remaining fixed in the machine direction. The ePTFE membrane was heated in a furnace set to approximately 300°C for a target of 120 seconds, and then stretched only in the longitudinal direction to a target ratio of 6:1 (machine direction), while the ePTFE membrane was allowed to freely neck down (i.e., narrow) in the lateral direction. The pantograph was opened at a constant acceleration setpoint for approximately 170 (E9A~B) seconds. Stretching was performed at a constant acceleration setpoint of 1% / s.

[0201] Final Pass Using the same pantograph machine, a 32-layer sample was heated in a furnace set to approximately 350°C for 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. Stretching was performed at a constant acceleration set at 1% / second. The pantograph was opened at a constant acceleration for 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 adhesive applied to the back. The linear density (bulk denier) was calculated by weighing the ePTFE membrane using the frame as a cutting guide, and mechanical data was collected using the matrix tensile test described in the test method section above. Sample E9A was further characterized using dynamic mechanical analysis (DMA) and matrix tensile testing at ambient temperature (i.e., approximately 20°C). storage The elastic modulus was 100 GPa (Figure) 34 Sample E9A was further characterized by XRD (Figure). 35 ). XRD results are consistent with an extremely high degree of crystal orientation. <p2>The orientation function is 0.989, and 1.0 is consistent with a perfectly parallel arrangement (Figure). 36 The degree of crystallinity was determined to be 94.6%. The SEM of sample E9A is shown in Figure. 37 It is shown here. [Table 1] [Table 2]

[0203] Example 10 The following examples disclose the production of extremely low-mass multilayer ePTFE membranes having high intrinsic strength and nanoparticle retention values. The nanoparticle retention rate is tested using the bead test disclosed in the section on methods for measuring the transmittance and bead retention rate of membrane samples.

[0204] PTFE fine powder (EI 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 lubricant / total g) (grams lubricant / total mixture mass). The lubricated powder was compressed into a cylindrical shape and then ram-extruded at 49°C to produce a tape. The tape was 16.2 cm wide and 0.762 mm thick. ISOPAR® K was removed by heating to approximately 200°C. A 98 square mm section 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 are heated in a furnace set to approximately 300°C for a target of 120 (E10A~C) seconds, and then simultaneously in the longitudinal and transverse directions, with a selected target ratio (λ) for each direction. sp The membrane was stretched at a ratio of approximately 7:1 (E10A and E10C) or 2:1 (E10B) while maintaining a temperature of approximately 300°C. The target average engineering strain rate was set to 36% / second. The pantograph was opened at a constant speed target for approximately 16.6 (E10A and E10C) or approximately 2.8 (E10B) seconds, based on the target ratio. The stretched membrane was allowed to cool to room temperature (approximately 22°C) while constrained by the pantograph. The first pass was repeated until 64 (E10A), 16 (E10B), or 32 (E10C) layers were available for the second pass.

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

[0207] Third Pass Samples were recovered from the cooled ePTFE membrane and layered if necessary for further stretching, i.e., a third pass. A specific number of layers, 256(E10A), 120(E10B), or 128(E10C), were loaded for the second pass under each condition shown in Table 21. Using the same pantograph machine, the membrane was reheated in a furnace set to 300°C for a target of 120(E10A-C) seconds, and then stretched simultaneously in the longitudinal and transverse directions, maintaining a temperature of approximately 300°C with target ratios of approximately 8(E10A), 10(E10B), or 6:1(E10C) in both directions. The average constant acceleration strain rate setpoint was 1% / s. The pantograph was opened at a constant acceleration target for approximately 221(E10A), 261(E10B), or 179(E10C) seconds. The stretched membrane was restrained with a pantograph and allowed to cool to room temperature (approximately 22°C).

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

[0209] 4th Pass Samples were recovered from the cooled ePTFE membrane and layered if necessary for further stretching, i.e., a fourth pass. A specific number of layers, 2056 (E10C), were loaded for the fourth pass under each condition shown in Table 21. Using the same pantograph machine, the membrane was reheated in a furnace set to 300°C for a target of 120 (E10C) seconds, and then stretched simultaneously in the longitudinal and transverse directions, maintaining a temperature of approximately 300°C at a target ratio of 4.75:1 (E10C) in both directions. The constant acceleration strain rate setpoint was 1% / second. The pantograph was opened at a constant acceleration target for approximately 156 (E10C) seconds. The stretched membrane was allowed to cool to room temperature (approximately 22°C) while constrained by the pantograph.

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

[0211] In accordance with the calculation of transmittance and retention rates by bead testing described above in the section on test methods, the average filtrate transmittance (see equation (9) above) and bead retention rate (see equation (10) above) 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 A polytetrafluoroethylene polymer fine powder, manufactured according to the instructions of Baillie's U.S. Patent No. 6,541,589, was combined with 0.184 lb / lb of isoparaffinic hydrocarbon lubricant (ISOPAR® K, Exxon, Houston, Texas). The resulting mixture was then blended and compressed into cylindrical pellets, which were heat-conditioned at 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 laterally at a ratio of 3.6:1 and dried at 200°C.

[0214] Next, the dried tape was stretched in the machine direction at 330°C to a stretch ratio of 7:1. The resulting material was then stretched laterally at a temperature of approximately 310°C to a stretch ratio of 12:1.

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

[0216] Comparative Example 6 - Sample E10D2 A polytetrafluoroethylene polymer fine powder, manufactured according to the instructions of Baillie's U.S. Patent No. 6,541,589, was combined with 0.151 lb / lb of lubricant (ISOPAR® K, Exxon, Houston, Texas). The resulting mixture was then blended and compressed into cylindrical pellets, which were heat-conditioned at 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 transversely at a ratio of 3.6:1 and dried at 200°C. The dried tape was then stretched in the machine direction at 330°C to a stretch ratio of 5:1. The resulting material was subsequently stretched transversely at approximately 310°C to a stretch ratio of 10.8:1. The membrane was then heat-treated at approximately 380°C for a target 25 seconds. This biaxially oriented membrane was compressed between rollers at a speed of 1 m / min with a compressive force of 20 N / mm (at 25°C).

[0217] Comparative Example 7 - Sample E10D3 A polytetrafluoroethylene polymer fine powder, manufactured according to the instructions of Baillie's U.S. Patent No. 6,541,589, was combined with 0.145 lb / lb of lubricant (ISOPAR® K, Exxon, Houston, Texas). The resulting mixture was then blended and compressed into cylindrical pellets, which were heat-conditioned at 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 transversely at a ratio of 3.6:1 and dried at 230°C. The dried tape was then stretched in the machine direction at 325°C to a stretch ratio of 5:1. The resulting material was subsequently stretched transversely at approximately 300°C to a stretch ratio of 12.3:1. This biaxially oriented membrane was compressed between rollers at a speed of 5 m / min with a compressive force of 80 N / mm (at 90°C).

[0218] Using the above test procedure, the average filtrate permeability (see equation (9) above) and bead retention rate (see equation (10) above) of each comparative example membrane sample (samples E10D1, E10D2, and E10D3) were evaluated. The results are shown in Table 22 and Figure 38. [Table 21] [Table 22]

[0219] The invention of this application has been described above in general terms and in relation to specific embodiments. 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. Accordingly, if modifications and changes to the invention fall within the scope of the appended claims and their equivalents, the embodiments shall extend to these modifications and changes. The following are aspects of the present invention. (Aspect 1) An extended polytetrafluoroethylene (ePTFE) membrane, Matrix tensile strength of at least 1000 MPa in the mechanical direction, A matrix storage modulus of at least 100 GPa at a temperature of 20°C, At least 94% crystallinity and An extended polytetrafluoroethylene (ePTFE) membrane containing this material. (Aspect 2) The surface density of the ePTFE membrane is 30 mg / m². 2 An extended polytetrafluoroethylene membrane according to Embodiment 1, wherein the value is less than [value missing]. (Aspect 3) The ePTFE membrane <p2> An extended polytetrafluoroethylene membrane according to embodiment 1 or 2, wherein the orientation is 0.98 or higher. (Aspect 4) The stretched polytetrafluoroethylene membrane according to any one of embodiments 1 to 3, wherein the bulk denier of the ePTFE membrane is 750 g / 9000 m. (Aspect 5) The stretched polytetrafluoroethylene membrane according to any one of embodiments 1 to 4, wherein the strength of the ePTFE membrane is greater than 5 gf / d. (Aspect 6) The stretched polytetrafluoroethylene membrane according to any one of embodiments 1 to 5, wherein the ePTFE membrane is self-supporting. (Aspect 7) The stretched polytetrafluoroethylene membrane according to any one of embodiments 1 to 6, wherein the ePTFE membrane is uniaxially oriented. (Pattern 8) The stretched polytetrafluoroethylene membrane according to any one of embodiments 1 to 7, wherein the ePTFE membrane is at least partially coated with a polymer, at least partially absorbed with a polymer, or a combination thereof. (Aspect 9) An extended polytetrafluoroethylene membrane according to any one of embodiments 1 to 8, which is in the form of a fiber, a sheet, a tube, a three-dimensional self-supporting structure, a die-shaped fiber, a die-shaped sheet, a die-shaped tube, or a die-shaped three-dimensional self-supporting structure. (Aspect 10) An extended polytetrafluoroethylene membrane according to any one of embodiments 1 to 9, further comprising a spacer layer. (Aspect 11) The stretched polytetrafluoroethylene membrane according to embodiment 10, wherein the spacer layer is selected from porous polymers, non-porous polymers, fluoropolymers, porous polyolefins, and non-porous polyolefins. (Aspect 12) A composite comprising an extended polytetrafluoroethylene membrane as described in any one of embodiments 1 to 11. (Aspect 13) A laminate comprising an extended polytetrafluoroethylene membrane as described in any one of embodiments 1 to 11. (Aspect 14) An article comprising an stretched polytetrafluoroethylene membrane as described in any one of embodiments 1 to 11, a composite as described in embodiment 12, or a laminate as described in embodiment 13. (Aspect 15) A method for forming a uniaxially oriented ePTFE membrane, wherein the method is (1) Separate at least one piece from the first stretched polytetrafluoroethylene (ePTFE) membrane, (2) By biaxially stretching at least the first piece, a second stretched polytetrafluoroethylene membrane is obtained. (3) Separate at least a second piece from the second stretched membrane, (4) By positioning the at least one first piece and the at least one second piece in an overlapping orientation, an overlapping sample is formed. (4) The stacked samples are biaxially stretched, (5) Repeat steps (1) to (4) until the desired biaxially oriented ePTFE membrane is obtained, (6) The biaxially oriented ePTFE membrane is uniaxially stretched. A method for forming a uniaxially oriented ePTFE membrane, including the following. (Aspect 16) The method according to embodiment 16, further comprising adding a spacer layer. (Aspect 17) The method according to embodiment 15 or 16, wherein the spacer layer is selected from porous polymers, non-porous polymers, fluoropolymers, porous polyolefins, and non-porous polyolefins. (Aspect 18) The method according to any one of embodiments 15 to 17, wherein the ePTFE membrane is uniaxially stretched in the mechanical direction.

Claims

1. An extended polytetrafluoroethylene (ePTFE) membrane, It comprises multiple ePTFE layers, and 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, At least 94% crystallinity and An extended polytetrafluoroethylene (ePTFE) membrane having [a certain characteristic].

2. The surface density of the ePTFE membrane is 30 mg / m². ２ The stretched polytetrafluoroethylene membrane according to claim 1, wherein the value is less than [value missing].

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

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

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

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

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

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

9. An stretched 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. An stretched polytetrafluoroethylene membrane according to any one of claims 1 to 9, further comprising a spacer layer.

11. The stretched polytetrafluoroethylene membrane according to claim 10, wherein the spacer layer is selected from porous polymers, non-porous polymers, fluoropolymers, porous polyolefins, and non-porous polyolefins.

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

13. A laminate comprising an stretched polytetrafluoroethylene membrane according to any one of claims 1 to 11.

14. An article comprising an 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 described in Claim 13.

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