Highly oriented stretched polytetrafluoroethylene with excellent rigidity

Abstract

To provide a method for forming a self-supporting uniaxially stretched polytetrafluoroethylene membrane having high intrinsic strength, high matrix elastic modulus, and high crystallinity.SOLUTION: A method for forming a uniaxially oriented ePTFE membrane, comprising steps of: (1) cutting at least a first piece from a first stretched polytetrafluoroethylene (ePTFE) membrane;(2) obtaining a second stretched polytetrafluoroethylene membrane by biaxially stretching the first piece; (3) cutting at least a second piece from the second stretched membrane; (4) positioning the at least one first piece and the at least one second piece in a stacked orientation to form a stacked sample; (5) biaxially stretching the stacked sample; (6) repeating steps (1) to (5) until a desired biaxially oriented ePTFE membrane is obtained; and (7) uniaxially stretching the biaxially oriented ePTFE membrane, thereby forming a uniaxially oriented ePTFE membrane.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to microporous fluoropolymer membranes, and more particularly to self-supporting, highly expanded polytetrafluoroethylene (ePTFE) membranes having high intrinsic strength, high matrix modulus, high crystallinity, and aligned fibrils. [Background technology]

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

[0003] According to one embodiment (“Embodiment 1”), an expanded polytetrafluoroethylene (ePTFE) membrane comprises a matrix tensile strength in the machine direction of at least about 1000 MPa, a matrix modulus at a temperature of 20° C. of at least about 100 GPa, and a crystallinity of at least about 94%.

[0004] According to another embodiment ("Embodiment 2") in addition to Embodiment 1, the ePTFE membrane has an areal density of about 30 mg / m 2 is less than.

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

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

[0007] According to another embodiment ("Embodiment 5") added to any one of the preceding embodiments, the ePTFE membrane has a tenacity of greater than about 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") in addition to any one of the preceding embodiments, the ePTFE membrane is uniaxially oriented.

[0010] According to another embodiment ("Embodiment 8") added to any one of the preceding embodiments, the ePTFE membrane is at least partially coated with a polymer, at least partially imbibed 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 diced fiber, a diced sheet, a diced tube, or a diced three-dimensional self-supporting structure.

[0012] According to another embodiment ("embodiment 10") in addition to any one of the preceding embodiments, the ePTFE membrane further comprises a spacer layer.

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

[0014] According to another embodiment (“embodiment 12”), a composite comprises the expanded polytetrafluoroethylene membrane of any one of the preceding embodiments.

[0015] According to another embodiment (“embodiment 13”), a laminate includes the expanded polytetrafluoroethylene membrane of any one of the preceding embodiments.

[0016] According to another embodiment (“embodiment 14”), an article comprises the expanded polytetrafluoroethylene membrane of embodiments 1-11, the composite of embodiment 12, or the laminate of embodiment 13.

[0017] According to another embodiment ("Embodiment 15"), there is provided a method of forming a uniaxially oriented ePTFE membrane, the method comprising: (1) cutting at least a first piece from a first expanded polytetrafluoroethylene (ePTFE) membrane; (2) biaxially stretching the at least first piece to obtain a second expanded polytetrafluoroethylene membrane; (3) cutting at least a second piece from the second stretched membrane; (4) positioning the at least one first piece and the at least one second piece in a stacked orientation to form a stacked sample; (5) repeating steps (1) to (4) until the desired biaxially oriented ePTFE membrane is obtained; and (6) uniaxially stretching the biaxially oriented ePTFE membrane This includes:

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

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

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

[0021] The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated in and constitute a part of this specification, illustrating embodiments and, together with the description, serving to explain the principles of the disclosure.

[0022] [Figure 1] FIG. 1 is a scanning transmission electron microscope (STEM) image of sample E1G of Example 1 according to an embodiment described herein, taken at 2,000x magnification with a total horizontal field width of approximately 63 microns.

[0023] [Figure 2] FIG. 2 is a STEM image of sample E1G of Example 1 according to an embodiment described herein, taken at 5,000x magnification with a total horizontal field width of about 25 microns.

[0024] [Figure 3] FIG. 3 is a STEM image of sample E1G of Example 1 according to an embodiment described herein, taken at 10,000x magnification with a total horizontal field width of about 12 microns.

[0025] [Figure 4] FIG. 4 is a STEM image of sample E1H of Example 1 according to an embodiment described herein, taken at 20,000x magnification with a total horizontal field width of about 6 microns.

[0026] [Figure 5] FIG. 5 is a STEM image of sample E1I of Example 1 according to an embodiment described herein, taken at 2,000x magnification with a total horizontal field width of about 63 microns.

[0027] [Figure 6] FIG. 6 is a STEM image of sample E2E of Example 2 according to an embodiment described herein, taken at 5,000x magnification with a total horizontal field width of about 25 microns.

[0028] [Figure 7] FIG. 7 is a STEM image of sample E2F of Example 2 according to an embodiment described herein, taken at 5,000x magnification with a total horizontal field width of about 25 microns.

[0029] [Figure 8] FIG. 8 is a STEM image of sample E2G of Example 2 according to an embodiment described herein, taken at 5,000x magnification with a total horizontal field width of about 25 microns.

[0030] [Figure 9] FIG. 9 is a STEM image of sample E3A of Example 3 according to an embodiment described herein, taken at 100,000x magnification with a total horizontal field width of about 1.27 microns.

[0031] [Figure 10] FIG. 10 is a STEM image of sample E3B of Example 3 according to an embodiment described herein, taken at 20,000x magnification with a total horizontal field width of about 6 microns.

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

[0033] [Figure 12] FIG. 12 is a histogram and log-normal distribution fit of fibril width data (nanometers) from manual image analysis of FIG. 11 of Example 5 according to an embodiment described herein.

[0034] [Figure 13] FIG. 13 is a STEM image of sample E5A of Example 5 according to an embodiment described herein, taken at 6,000x magnification with a total horizontal field width of about 21 microns.

[0035] [Figure 14] FIG. 14 is a STEM image of sample E5B of Example 5 according to an embodiment described herein, taken at 6,000x magnification with a total horizontal field width of about 21 microns.

[0036] [Figure 15] FIG. 15 is a STEM image of sample E5C of Example 5 according to an embodiment described herein, taken at 10,000× magnification with a total horizontal field width of about 12 microns.

[0037] [Figure 16] FIG. 16 is a STEM image of sample E5D of Example 5 according to an embodiment described herein, taken at 10,000× magnification with a total horizontal field width of about 12 microns.

[0038] [Figure 17] FIG. 17 is a STEM image of sample E5E of Example 5 according to an embodiment described herein, taken at 6,000x magnification with a total horizontal field width of about 21 microns.

[0039] [Figure 18] FIG. 18 is a STEM image of sample E5F of Example 5 according to an embodiment described herein, taken at 10,000x magnification with a total horizontal field width of about 12 microns.

[0040] [Figure 19] FIG. 19 is a STEM image of sample E5G of Example 5 according to an embodiment described herein, taken at 10,000x magnification with a total horizontal field width of about 12 microns.

[0041] [Figure 20] FIG. 20 is a scanning transmission electron microscope (STEM) image of sample E5H of Example 5 according to an embodiment described herein, taken at 10,000x magnification with a total horizontal field width of about 21 microns.

[0042] [Figure 21] FIG. 21 is a STEM image of sample E5I of Example 5 according to an embodiment described herein, taken at 20,000x magnification with a total horizontal field width of about 6 microns.

[0043] [Figure 22] FIG. 22 is a STEM image of sample E5H of Example 5 according to an embodiment described herein, taken at 5,000x magnification with a total horizontal field width of about 25 microns.

[0044] [Figure 23] FIG. 23 is a STEM image of sample E5I of Example 5 according to an embodiment described herein, taken at 5,000x magnification with a total horizontal field width of about 25 microns.

[0045] [Figure 24] FIG. 24 is a graph showing quality factor versus particle size for Samples E6A, E6B, E6D, and E6E of Example 6 according to embodiments described herein.

[0046] [Figure 25] FIG. 25 is a STEM image of sample E6A of Example 6 according to an embodiment described herein, taken at 10,000x magnification with a total horizontal field width of about 12 microns.

[0047] [Figure 26] FIG. 26 is a STEM image of sample E6B of Example 6 according to an embodiment described herein, taken at 10,000x magnification with a total horizontal field width of about 12 microns.

[0048] [Figure 27] FIG. 27 is a STEM image of sample E6A of Example 6 according to an embodiment described herein, taken at 1,500x magnification with a total horizontal field width of about 84 microns.

[0049] [Figure 28] FIG. 28 is a STEM image of sample E6B of Example 6 according to an embodiment described herein, taken at 1,500x magnification with a total horizontal field width of about 84 microns.

[0050] [Figure 29] FIG. 29 is a graph showing % transmittance versus wavelength for Sample E7A (gray line, 48 layers) and Sample E7B (black line, 3 layers) according to embodiments described herein.

[0051] [Figure 30] FIG. 30 is an X-ray diffraction pattern (XRD) of Sample E8C of Example 8 according to an embodiment described herein.

[0052] [Figure 31] FIG. 31 is an X-ray diffraction pattern (XRD) of Sample E8D of Example 8 (heat-treated) according to an embodiment described herein.

[0053] [Figure 32] FIG. 32 is a graph showing q (nm) versus intensity (10-45 nm) for Samples E8C (bottom trace—non-thermal treated) and E8D (top trace—thermal treated) of Example 8 according to an embodiment described herein.

[0054] [Figure 33] FIG. 33 is a graph showing q (nm) versus intensity (focused on the 10-20 nm range) for Samples E8C (bottom trace—non-thermal treated) and E8D (top trace—thermal treated) of Example 8 according to an embodiment described herein.

[0055] [Figure 34] FIG. 34 is a graph showing matrix storage modulus versus temperature for Sample E9A of Example 9 according to an embodiment described herein.

[0056] [Figure 35] FIG. 35 is an X-ray diffraction pattern (XRD) of Sample E9A of Example 9 according to an embodiment described herein.

[0057] [Figure 36] FIG. 36 is a graph showing intensity versus 2-theta for Sample E9A of Example 9 according to an embodiment described herein.

[0058] [Figure 37] FIG. 37 is an SEM image of sample E9A of Example 9 according to an embodiment described herein, taken at 5000x magnification with a total horizontal field width of about 23 microns.

[0059] [Figure 38] FIG. 38 is a graph showing nanoparticle retention versus filtrate transmittance for samples of Example 10 according to embodiments described herein.

[0060] [Figure 39] FIG. 39 is a diagram that schematically illustrates a method for manufacturing a biaxially oriented membrane according to embodiments described herein.

[0061] Glossary

number

[0062]

number

[0063]

number

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

number

[0065]

number

[0066] Specific surface area (w m Based on (m 2 / g) is given by the following equation:

number

[0067]

number

[0068] Surface 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 the present disclosure may be implemented by any number of methods and apparatus configured to perform their intended functions. Further, for clarity, the accompanying drawings referred to herein are not necessarily drawn to scale and may be exaggerated to illustrate various aspects of the present disclosure, and in that regard, the drawings should not be construed as limiting.

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

[0073] In one aspect, the present invention relates to a thin, self-supporting, biaxially oriented polytetrafluoroethylene (ePTFE) membrane having high crystallinity, high intrinsic strength, low areal density (i.e., light weight), and high optical transparency. 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 may have an areal density of about 100 mg / m 2 The ePTFE membrane may have a total luminous transmittance of at least 98%. Additionally, the ePTFE membrane may be transparent or invisible to the naked eye. Furthermore, ePTFE membranes are stackable, which can be used to control the transmittance, pore size, and / or bulk mechanical properties. They may be used to form composites, laminates, fibers, sheets, tubes, or other three-dimensional objects, which may or may not be subsequently diced or otherwise cut or separated into smaller pieces. Additionally, biaxially oriented ePTFE membranes can be used in filtration applications. In another embodiment, biaxially oriented ePTFE membranes can be uniaxially stretched, which aligns the fibers in one direction (hereinafter, uniaxially oriented ePTFE membranes). Such ePTFE membranes may have a tenacity greater than about 5 grams force per denier (gf / d) and a bulk denier less than about 750 grams per 9000 meters (g / 9000m).

[0074] For polytetrafluoroethylene (PTFE) polymers, particle size, shape, and distribution are important to achieve the desired porous structure. These particle characteristics affect the packing density and bonding density, thereby affecting the porous structure that can be produced from the particles. PTFE resins are provided in granular form, e.g., in the form of a fine powder. PTFE fine powder is formed from primary particles.

[0075] To form the ePTFE membrane, the PTFE fine powder is first mixed with a lubricant, such as a light oil. One specific example of a suitable lubricant is an isoparaffinic hydrocarbon, such as ISOPAR® K (ExxonMobil Chemical, Spring, TX). Other suitable lubricants include aliphatic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, and the like, and are selected based on flammability, evaporation rate, and economic considerations. It should be understood that the term "lubricant" as used herein refers to a processing aid that includes (or consists of) an incompressible fluid that is not a solvent for the polymer under process conditions. Fluid-polymer surface interactions occur so that a homogeneous mixture can be formed. The choice of lubricant is not particularly critical, and the primary considerations are safety and convenience. The lubricant can be added to the PTFE powder in an amount of about 242 mL / kg to about 340 mL / kg.

[0076] In at least one embodiment, the PTFE fine powder and lubricant are mixed together to uniformly or nearly uniformly distribute the lubricant with the PTFE powder. Of course, various times and mixing methods can be used to distribute the PTFE powder in the lubricant. Once the lubricant and PTFE powder are sufficiently distributed, the lubricated powder is compressed into a cylindrical shape (i.e., pellets). A cohesive, flexible PTFE tape can then be produced by ram extruding the pellets through an extruder die (e.g., typically referred to as paste extrusion or paste processing when a lubricant is present). As used herein, "cohesive" refers to 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 indefinite length and a thickness of less than about 1.0 mm, less than about 0.8 mm, less than about 0.5 mm, or less than about 0.4 mm. The cohesive, flexible tape will hereinafter be referred to simply as "tape."

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

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

[0079] The tape is biaxially stretched, and in some embodiments, additionally uniaxially stretched, to form an ePTFE membrane. The tape can be stretched at the same or different strain rates and at the same or different temperatures to obtain a microporous ePTFE membrane. As used herein, the term "microporous" defines an article, e.g., a membrane, having pores that are not visible to the naked eye. The material properties of the ePTFE membranes produced in this manner have been found to exceed those of conventional membranes by efficiently and completely converting the ePTFE primary particles (i.e., PTFE fine powder) into fibrils. Advantageously, 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 about 390°C. Uniaxially stretching an ePTFE membrane results in an ePTFE membrane with uniaxially oriented fibrils in the direction of stretching (i.e., machine direction (MD) or transverse direction (TD)), high crystallinity, and high matrix tensile strength. Hereinafter, ePTFE membranes will be described with respect to stretching in the machine direction, although it should be understood that transverse stretching is also considered within the scope of the present invention.

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

[0081] In at least one embodiment, the biaxially oriented ePTFE membrane has a thickness per layer of less than about 100 nm, less than about 90 nm, less than about 80 nm, less than about 70 nm, less than about 60 nm, less than about 50 nm, or less than 40 nm, less than about 30 nm, less than about 20 nm, less than about 10 nm, less than about 5 nm, less than about 4 nm, less than about 3 nm, less than about 2 nm, or less than about 1 nm. In some embodiments, the thickness per layer of the ePTFE membrane is about 1 nm to about 100 nm, about 1 nm to about 90 nm, about 1 nm to about 80 nm, about 1 nm to about 70 nm, about 1 nm to about 60 nm, about 1 nm to about 50 nm, about 1 nm to about 40 nm, about 1 nm to about 30, about 1 nm to about 20 nm, about 1 nm to about 10 nm, about 1 nm to about 5 nm, about 1 nm to about 4 nm, about 1 nm to about 3 nm, or about 1 nm to about 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 due, at least in part, to the fibril microstructure of the ePTFE membrane. Broadly speaking, the fibrils are substantially cylindrical in shape. The term "substantially cylindrical" is used herein to mean that the cross-sectional aspect ratio of the fibrils in the biaxially oriented ePTFE membrane is from about 1:1 to about 10:1. In addition, the fibrils in the biaxially oriented ePTFE membrane are thin, having a median fibril width of about 80 nm or less. In some embodiments, the median fibril width is less than about 70 nm, less than about 60 nm, less than about 50 nm, less than about 40 nm, less than about 30 nm, less than about 20 nm, or less than about 10 nm. In some embodiments, the median fibril width is about 10 nm to about 80 nm, about 10 nm to about 70 nm, about 10 nm to about 60 nm, about 10 nm to about 50 nm, about 10 nm to about 40 nm, about 10 nm to about 30 nm, or about 10 nm to about 20 nm. In some embodiments, the median fibril width is about 20 nm to about 70 nm, about 30 nm to about 60 nm, or about 40 nm to about 50 nm. In other embodiments, the median fibril width is about 30 nm to about 80 nm, about 40 nm to about 80 nm, about 50 nm to about 80 nm, about 60 nm to about 80 nm, or about 70 nm to about 80 nm. The intersection or overlap of two or more fibrils is referred to herein as a "crossover point." In some embodiments, the thickness of the biaxially oriented ePTFE membrane can be the thickness at the crossover point of two fibrils.

[0083] In addition, the surface density per layer is approximately 100 mg / m 2 (0.1g / m 2 ) less than about 90 mg / m 2 (0.09g / m 2 ) less than about 80 mg / m 2 (0.08g / m 2 ) less than about 70 mg / m 2 (0.07g / m 2 ) less than about 60 mg / m 2 (0.06g / m 2 ) less than about 50 mg / m 2 (0.05g / m 2 ) less than about 40 mg / m 2 (0.04g / m 2 ) less than about 30 mg / m 2 (0.03g / m 2 ) less than about 20 mg / m 2 (0.02g / m 2 ) less than about 15 mg / m 2 (0.015g / m 2 ) less than about 10 mg / m 2 (0.01g / m 2 ) less than about 5 mg / m 2 (0.005g / m 2 ) less than about 4 mg / m 2 (0.004g / m 2 ) less than about 3 mg / m 2 (0.003g / m 2 ) less than about 2 mg / m 2 (0.002g / m 2 ), 1.0 mg / m 2 (0.001g / m 2 ) less than about 0.50 mg / m 2 (0.0005g / m 2 ) less than about 0.40 mg / m 2 (0.0004g / m 2 ) less than about 0.30 mg / m 2 (0.0003g / m 2 ) less than about 0.20 mg / m 2 (0.0002g / m 2 ) less than about 0.10 mg / m 2 (0.0001g / m 2 ) less than about 0.05 mg / m 2 (0.00005g / m 2 ), or about 0.003 mg / m 2 (0.000003g / m 2 ) are significantly lighter. In some embodiments, the areal density per layer is about 0.003 mg / m 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 ), about 0.003mg / m 2 (0.000003g / m 2 )~about 80mg / m 2 (0.08g / m 2 ), about 0.003mg / m 2 (0.000003g / m 2 )~about 70mg / m 2 (0.07g / m 2 ), about 0.003mg / m 2 (0.000003g / m 2 )~about 60mg / m 2 (0.06g / m 2 ), about 0.003mg / m 2 (0.000003g / m 2 )~about 50mg / m 2 (0.05g / m 2 ), about 0.003mg / m 2 (0.000003g / m 2 )~about 40mg / m 2 (0.04g / m 2 ), about 0.003mg / m 2 (0.000003g / m 2 ) ~ about 30mg / m 2 (0.03g / m 2 ), about 0.003mg / m 2 (0.000003g / m 2 )~about 20mg / m 2 (0.02g / m 2 ), about 0.003mg / m 2 (0.000003g / m 2 )~about 10mg / m 2 (0.01g / m 2 ), about 0.003mg / m 2 (0.000003g / m 2 )~about 1.0mg / m 2 (0.001g / m 2 ), about 0.003mg / m 2 (0.000003g / m 2 )~about 0.5mg / m 2 (0.0005g / m 2 ), about 0.003mg / 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 about 0.003 mg / m 2 (0.000003g / m 2 ) ~ approx. 0.05mg / m 2 (0.00005g / m 2 In some embodiments, the areal density per layer is about 5 mg / m 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 about 30 mg / m 2 (0.03g / m 2 ) ~ approx. 80mg / m 2 (0.08 g / m 2 )

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

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

[0086] The surface density per layer is approximately 500 mg / m 2 (0.5g / m 2 ) less than about 400 mg / m 2 (0.4g / m 2 ) less than about 300 mg / m 2 (0.3g / m 2 ) less than about 200 mg / m 2 (0.2g / m 2 ) less than about 100 mg / m 2 (0.1g / m 2 ) less than about 70 mg / m 2 (0.07g / m 2 ) less than about 50 mg / m 2 (0.05g / m 2 ) less than about 30 mg / m 2 (0.03g / m 2 ) less than about 25 mg / m 2 (0.025g / m 2 ) less than about 20 mg / m 2 (0.02g / m 2 ) less than about 15 mg / m 2 (0.015g / m 2 ) less than about 10 mg / m 2 (0.01g / m 2 ) less than about 5 mg / m 2 (0.005g / m 2 ) less than about 4 mg / m 2 (0.004g / m 2 ) less than about 3 mg / m 2 (0.003g / m 2 ) less than about 2 mg / m 2 (0.002g / m 2 ) less than approximately 1.0 mg / m 2 (0.001g / m 2 ) less than about 0.50 mg / m 2 (0.0005g / m 2 ) less than about 0.40 mg / m 2 (0.0004g / m 2 ) less than about 0.30 mg / m 2 (0.0003g / m 2 ) less than about 0.20 mg / m 2 (0.0002g / m 2 ), or about 0.10 mg / m 2 (0.0001g / m 2 ) areal densities of less than about 0.10 mg / m 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 about 0.10 mg / m 2 (0.0001g / m 2 ) ~ approx. 0.20mg / m 2 (0.0002g / m 2 )

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

[0088] Additionally, uniaxially expanded ePTFE membranes have higher intrinsic strength properties. In some embodiments, the matrix tensile strength (MTS) of the ePTFE membrane is greater than about 1000 MPa in the machine direction, greater than about 1100 MPa in the machine direction, greater than about 1200 MPa in the machine direction, greater than about 1200 MPa in the machine direction, greater than about 1300 MPa in the machine direction, or greater than about 1400 MPa in the machine direction. In some embodiments, the matrix tensile strength (MTS) of the uniaxially oriented ePTFE membrane is from about 1000 MPa to about 1400 MPa in the machine direction, from about 1100 MPa to about 1400 MPa in the machine direction, from about 1200 MPa to about 1400 MPa in the machine direction, from about 1200 MPa to about 1300 MPa in the machine direction, or from about 1300 MPa to about 1400 MPa in the transverse direction. Of course, although matrix tensile strength is provided herein with respect to the machine direction, it is equally applicable to ePTFE membranes expanded in the transverse direction.

[0089] Additionally, the uniaxially oriented ePTFE membrane has a matrix storage modulus of at least 100 GPa at ambient temperature (i.e., about 20°C). In some embodiments, the uniaxially oriented ePTFE membrane has a matrix storage modulus at ambient temperature (i.e., about 20°C) of 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 the uniaxially oriented ePTFE is from about 0.5 g / 9000 m to about 750 g / 9000 m, from about 0.5 g / 9000 m to about 650 g / 9000 m, from about 0.5 g / 9000 m to about 500 g / 9000 m, from about 100 g / 9000 m to about 450 g / 9000 m, from about 0.5 g / 9000 m to about 400 g / 9000 m, from about 0.5 g / 9000 m to about 350 g / 9000 m, from about 0.5 g / 9000 m to about 250 g / 9000 m, from about 0.5 g / 9000 m to about 200 g / 9000 m. / 9000m, about 0.5g / 9000m to about 150g / 9000m, about 0.5g / 9000m to about 100g / 9000m, about 0.5g / 9000m to about 50g / 9000m, 0.5g / 9000m to about 25g / 9000m, about 0.5g / 9000m to about 15g / 9000m, about 0.5g / 9000m to about 10g / 9000m, about 0.5g / 9000m to about 5g / 9000m, about 0.5g / 9000m to about 3g / 9000m, or about 0.5g / 9000m to about 1g / 9000m.

[0090] Additionally, the uniaxially oriented ePTFE membrane has a tenacity of at least about 5 gf / d. In some embodiments, the uniaxially oriented ePTFE membrane has a tenacity of 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 greater. <p2>It has an orientation.

[0091] Additionally, biaxially oriented ePTFE membranes have only a small air resistance. In some embodiments, the air resistance of the ePTFE membrane can 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 5000 Pa·s / m, less than about 2000 Pa·s / m, less than about 1500 Pa·s / m, less than about 1000 Pa·s / m, less than about 750 Pa·s / m, less than about 500 Pa·s / m, less than about 250 Pa·s / m, or less than about 150 Pa·s / m. In some embodiments, the air resistance is about 100 Pa·s / m to about 2000 Pa·s / m, about 100 Pa·s / m to about 1500 Pa·s / m, about 100 Pa·s / m to about 1000 Pa·s / m, about 100 Pa·s / m to about 750 Pa·s / m, about 100 Pa·s / m to about 500 Pa·s / m, about 100 Pa·s / m to about 250 Pa·s / m, or about 250 Pa·s / m to about 500 Pa·s / m. The low air resistance combined with the high surface area of ​​the ePTFE membrane allows for a high performance filtration device.

[0092] The biaxially oriented ePTFE membrane also has high light transmittance, with a total luminous transmittance (measured between 380 nm and 780 nm) of about 90% or greater, about 95% or greater, about 98% or greater, or about 99% or greater. In exemplary embodiments, the total luminous transmittance of the biaxially oriented ePTFE membrane can be about 90% to about 99%, about 95% to about 99%, or about 98% to about 99%. In some embodiments, the total luminous transmittance of the ePTFE membrane is nearly 100%.

[0093] The fibrils of the ePTFE membrane (biaxially and uniaxially oriented) may be optionally coated with at least one coating composition, such as a polymer or biological coating, so that the ePTFE is porous or so that the ePTFE is nonporous. The coating composition can be applied to the ePTFE membrane by any conventional coating method, such as solvent coating, spray coating, spin coating, vapor deposition, atomic layer deposition (ALD), or dip coating. In addition, coatings can be applied to the ePTFE membrane by compressing it between sheets of components, such as fluorinated ethylene propylene (FEP), polyfluoroacrylate (PFA), and silicone, while heating.

[0094] In some embodiments, the coating composition occupies or fills at least a portion of the through-thickness space of the biaxially or uniaxially oriented ePTFE membrane. Suitable polymeric and / or biological coatings for coating and / or imbibing onto or within the ePTFE membrane include, but are not limited to, 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 fluoride). Examples of coatings that can be applied include terpolymers of tetrafluoroethylene (TFE) and perfluoroalkyl vinyl ethers (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 coating (commercially available from W. L. Gore & Associates, Inc.), antimicrobial agents, antibodies, pharmaceuticals, biological entities, angiogenesis stimulants, and any combination thereof. The amount of coating applied depends on the initial application.

[0095] Biaxially or uniaxially oriented ePTFE membranes are self-supporting, and in some embodiments, ePTFE membranes are used to reinforce polymeric 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 at macroscale lengths. In other words, the integrity of the ePTFE membrane is maintained by constraining (e.g., "picture-framed") the membrane around its perimeter. The inherent strength of the membrane is related over various distances, holding it together without a backing or support layer behind or below it.

[0096] Biaxially and uniaxially oriented ePTFE membranes can be formed as a single ePTFE membrane layer. In other embodiments, biaxially and uniaxially oriented ePTFE membranes can have tens, hundreds, or thousands of ePTFE membrane layers within the ePTFE membrane. In some embodiments, there can be 2 to 4 layers. In other embodiments, there can be 2 to 16 layers within the ePTFE membrane. In further embodiments, there can 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, or 2 to 1,000,000 layers (or more) within the ePTFE membrane. Without wishing to be bound by theory, the only limiting factor on the number of ePTFE layers present in an ePTFE membrane is the time spent stacking and expanding the layers. Typically, the ePTFE membrane stack "grows" four times each time the ePTFE membrane is biaxially expanded. Of course, while adhesives or other bonding agents are typically not used to bond individual ePTFE membranes within a stack of ePTFE membranes, the inclusion of adhesives or other bonding materials is not excluded from use herein and is considered within the scope of the present invention.

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

[0098] The permeability, pore size, and bulk mechanical properties can be controlled by forming ePTFE membranes (biaxially and uniaxially oriented) and / or optional additional spacer layers within the ePTFE membrane. As used herein, the term "permeability" refers to the ability of a membrane or filter material to transmit a fluid (i.e., liquid or gas) through the pores of the membrane or filter material when the material is subjected to a differential pressure across it. In one instance, the ePTFE membrane allows for a variety of pore sizes, e.g., pore sizes less than about 6 microns in diameter. As used herein, "pore size" refers to the size of the pores within the ePTFE membrane. The pore size can range from 2 nm to about 6 microns. Additionally, the specific surface area (SSA) of ePTFE, as measured by area-weighted fibril width (AWFW), is approximately 35 m. 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.

[0099] In some embodiments, the biaxially oriented ePTFE membrane can be used in air filtration applications. In such applications, the quality factor of the ePTFE membrane is at least 65 (kPa) when the challenge particle is 0.1 micron in diameter and the face velocity is 5.33 cm. -1 ). Needless to say, the strength-to-weight (intrinsic strength) of ePTFE membranes is higher than that of conventional ePTFE membranes. Higher quality factor values ​​correlate with better filtration performance. In certain embodiments, the quality factor of a biaxially oriented ePTFE membrane is about 65 (kPa -1 ) to approximately 180 (kPa -1 ), approximately 70 (kPa -1 ) to approximately 180 (kPa -1 ), approximately 80 (kPa -1 ) to approximately 180 (kPa -1 ), approximately 90 (kPa -1 ) to approximately 180 (kPa -1 ), approximately 100 (kPa -1 ) to approximately 180 (kPa -1 ), approximately 110 (kPa -1 ) to approximately 180 (kPa -1 ), approximately 120 (kPa -1 ) to approximately 180 (kPa -1 ), approximately 130 (kPa -1 ) to approximately 180 (kPa -1 ), approximately 140 (kPa -1 ) to approximately 180 (kPa -1 ), approximately 150 (kPa -1 ) to approximately 180 (kPa -1 ), approximately 160 (kPa -1 ) to approximately 180 (kPa -1 ), or about 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., about 1 nm to about 200 nm) from a liquid medium, even when the liquid medium is moving at a high flow rate. Thus, ePTFE membranes can be used as filtration materials, and due to the properties of polytetrafluoroethylene, they are resistant to chemical attack, biocompatible, and exhibit high matrix tensile strength (MTS). The filterable matrix can be selected from solutions, suspensions, colloids, biological fluids, components of biological fluids, aqueous materials, or non-aqueous materials. To filter the filterable matrix, the matrix is ​​passed through the ePTFE membrane, and the resulting filtrate is collected. In one embodiment, the biaxially oriented ePTFE membrane has a nanoparticle retention percentage (%) equal to or greater than the line defined by equation (1):

number

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

[0102] Membrane Density Calculation The samples were cut to form square sections 15.2 cm x 15.2 cm. Each sample was weighed using a Mettler Toledo AT20 balance. The thickness calculated by the KEYENCE laser was used to calculate the density of the sample using equation (2).

number

[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. The tensile break load was measured using an INSTRON® 5567 (Illinois Tool Works Inc., Norwood, MA) tensile testing machine equipped with flat-faced grips and a 22 lb (approximately 100 N) load cell. The gauge length for the grips was set at 8.26 cm, and the strain rate was 0.847 cm / s. A baseline was obtained by placing the sample in the grips and retracting the sample 1.27 cm, followed by tensile testing at the rates described above. The peak force measurement was used for MTS calculations. Equation (3):

number

[0104] Matrix Tensile Strength (MTS) (Method 2) To determine the MTS of uniaxial ePTFE membranes, sample ePTFE membranes were loaded longitudinally using string and thread grips. Tensile break loads were measured using an INSTRON® 5567 (Illinois Tool Works Inc., Norwood, Massachusetts) tensile testing machine equipped with string and thread grips and a 22 lb (approximately 100 N) load cell. The gauge length for the grips was set at 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 tensile testing at the rates described above. The peak force measurement was 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 through the sample and collecting the transmitted electrons with a suitable detector. Low voltage means using a beam acceleration voltage of less than 100 kV (<30 kV as exemplified herein). Image contrast is based on differences in electron absorption by the membrane due to composition or thickness.

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

[0107] X-ray diffractogram of biaxial sample Two-dimensional (2-d) X-ray diffractograms were obtained using the X27C beamline at the National Synchrotron Light Source at Brookhaven National Laboratory (Upton, NY). The beamline had a wavelength of 0.1371 nm and a nominal flux of 10 photons. 12 A well-collimated, monochromatic X-ray beam with a velocities of 1 / s and a diameter of 0.39 mm was provided. The detector was a Rayonix MAR-CCD 2-d imaging system (Rayonix LLC, Evanston, IL). The system was set at a sample-to-detector distance of 67.97 mm and calibrated using an Al2O3 powder standard. The sample was placed between the beam and the detector, and transmission geometry scattered / diffuse X-ray images were collected for 480–540 seconds. In addition, immediately after each sample was imaged, a sample-free background image was recorded for the same time period. The background image was subtracted from the sample image to remove the effects of air scattering and generate the desired diffractogram.

[0108] X-ray scattering methods for uniaxial samples Wide-angle X-ray scattering experiments were carried out on a Xenocs brand Xeuss 2.0 SAXS / WAXS Laboratory Beamline system (Xenocs SAS, Sassenage, France). The instrument was a GeniX3D Cu k a A Dectris-brand Pilatus 300K detector (Dectris Ltd., Baden-Daettwil, Switzerland) was used. The beam was collimated with two in-line slits, each opening to an area of ​​0.5 mm x 0.5 mm. The sample-to-detector distance was 71.0 mm (calibrated with a 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 with various horizontal detector offsets, each with a 15-minute exposure time. Averaging these four scans provided a scattering profile. Orientation was quantified from the I vs. φ azimuthal angle using equation (4):

number

[0109] As determined by equation (5), <p2>As approaches 1, nearly perfect orientation in the machine direction is achieved.

number

[0110] Crystallinity Crystallinity was obtained by peak fitting of the intensity versus q scan using JMP® 14.1.0 statistical analysis software (SAS Institute). The range of integration was q = 8.74 to 15.4 (nm -1 ), and the linear background is limited to the measured intensity of approximately q = 8.74 ~ 10 (nm -1 ) and q = 14.1 to 15.4 (nm -1 ) After the linear background was subtracted, both peaks were fitted using the Pearson VII function.

[0111] As defined in U.S. Patent Application Publication No. 2004 / 0173978 to Bowen, the fitted 100 crystal peaks (A 100 ) and the area under the fitted amorphous peak (A amorphous The crystallinity was calculated from the area under the

number

[0112] Bubble point Bubble points were 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 into the sample chamber and wetted 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 disk insert (Mott Metallurgical, Fannington, Conn.) with the following dimensions: 2.54 cm diameter, 3.175 mm thick. The upper clamp of the sample chamber consisted of a 12.7 mm diameter opening. The following parameters and set points were used using Capwin software version 6.74.70: Parameter Setpoint Maxflow 200000 (cc / m) Bubflow 10-127 (cc / m) F / PT 50 Minbppres 0.1 (psi) Zerotime 1 (sec) V2incr 10 (cts) Pregnancy 1 (cts) Pulse Delay 2 (sec) Maxpressure 500 (psi) Pulse Width 0.2 (sec) Mineqtime 30 (sec) Presslew 10 (cts) Flowslew 50 (cts) Eqiter (0.1 sec) 3 Aveiter (0.1 sec) 20 Maxpdif 0.1 (psi) Maxfdif 50 (cc / m) Startp 1 (psi) The value given for bubble point was the average of two measurements.

[0113] ATEQ Air Flow The laminar volumetric flow rate of air through the membrane sample is measured across a channel with an area of ​​2.99 cm. 2 Each membrane sample was clamped between two plates in a manner that created a seal. An ATEQ® (ATEQ Corp., Livonia, MI) Premier D miniature flow tester was used to measure the air flow rate (L / hr) through each membrane sample by challenging it with a differential air pressure of 1.2 kPa (12 mbar) across the membrane.

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

[0115] Light transmittance measurement Optical 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 consisted of a deuterium-tungsten-halogen lamp, a single Czerny-Turner-type monochromator (1200 lines / mm grating), and a photomultiplier tube (PMT) detector. Light from the monochromator was split into a sample beam and a reference beam before entering the integrating sphere. The integrating sphere was configured for unidirectional illumination and diffuse detection. The sample beam illuminated a 20 mm x 20 mm sample placed on the steep integrating incidence port at normal incidence, while the reference beam passed through an open port on the integrating sphere. The sample and reference beams alternately impinged on the PMT detector and were converted to digital signals after synchronous rectification.

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

[0117] Total luminous transmittance was calculated by weighting the transmission spectrum by the CIE Standard Illuminant and CIE Colorimetric Standard Observer (see ASTM D1003-13: Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics). The D65 illuminant and 1931 2-deg Standard Observer were used in the calculations presented here. The % transmittance in the UVA and UVB ranges was calculated by calculating the % transmittance average values ​​in the 315-400 nm and 280-315 nm wavelength ranges, respectively.

[0118] Determining the average fibril width Selected samples were imaged by STEM and manually characterized by 50 measurements of the projected width of the fibrils (e.g., Figure 11). A random number generator was used to highlight 50 regions to facilitate uniform sampling, and the operator then traced the outline of the nearest fibril, preferably a previously uncharacterized fibril fragment. Generally, the marked fibrils were rectangular, with an aspect ratio greater than 1. The nominal projected width of the fibrils was calculated from the ratio of the object's area divided by its length. This is more representative and informative than a single width measurement, since it necessarily forces the projected width measurement to be perpendicular to the major axis of the rectangular shape. To validate this method, a line was drawn through the centroid of the manually identified region, perpendicular to the major axis, at the calculated width calculated according to Equation (7).

number

[0119] Dynamic Mechanical Analyzer (DMA) matrix storage and loss moduli Matrix storage and loss modulus measurements were performed using a TA Instruments Q800 system (TA Instruments, New Castle, Delaware) equipped with tension sample clamps. The DMA was calibrated according to standard TA Instruments procedures. Sample dimensions were obtained using a 10x microscope equipped 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 microbalance (Mettler-Toledo, LLC, Columbus, Ohio). The sample was then placed in the instrument, and a 5 mN preload 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 in tension throughout the application of the sinusoidal strain. The sample was equilibrated at -50°C for 10 minutes, then the temperature was ramped to 150°C at 2°C / min. The magnitude and phase angle of the resultant sinusoidal force acting on the sample was measured once per second throughout the heating ramp and used to calculate the storage and loss moduli. The storage and loss moduli were determined by the ratio ρ true / ρ sample The desired matrix modulus was obtained by multiplying by ρ true is 2.3 g / cm of crystalline poly(tetrafluoroethylene). 3 While assuming that ρ sample was calculated from the measured dimensions and mass of the sample.

[0120] Air filtration performance measurement Particle Filtration Efficiency Membrane Filtration Efficiency testing was performed using a dioctyl phthalate (DOP) aerosol on a TSI CERTITEST® Model 8160 Automated Filter Tester (TSI Incorporated, St. Paul, MN) according to the procedures specified in the TSI CERTITEST® Model 8160 Automated Filter Tester Operation and Service Manual. The sample test area was 77.8 cm and the face velocity was 5.32 cm / sec.

[0121] Using equation (8), the quality factor Q f We figured out the answer.

number

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

number

[0123] Determining Liquid Permeability and Retention Through Bead Testing The bead test measures the permeability and bead retention of a membrane sample. The membrane sample was restrained in a 25 mm filter holder. The membrane was first wetted with an isopropyl alcohol (IPA)-DI water solution (70:30 v / v IPA:water). Air pressure was used to force this solution through the membrane. Seven grams of the solution was allowed to flow through the sample, followed by 10 grams of an aqueous solution consisting of 1% by volume of the nonionic surfactant TRITON® X-100 (CAS 9002-93-1; Sigma-Aldrich, St. Louis, MO) 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, MA) dispersed in an aqueous solution consisting of 1% by volume of TRITON® X-100 in DI water. In this case, the membrane was challenged with a sufficient amount of beads to cover the membrane surface area with a single monolayer of beads. The concentrations of beads in the challenge solution and filtrate were determined using an Agilent Technologies Cary Eclipse Fluorescence Spectrophotometer (Agilent Technologies, Santa Clara, CA).

[0124] The membrane permeability was calculated using equation (9).

number

[0125] In equation (9), k is the permeability of the membrane, g is the mass of the filtrate aliquot, A is the physical area of ​​the membrane sample in the filter holder, t is the time required to collect the filtrate aliquot, 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 rate through the membrane.

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

number

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

[0128] Unless otherwise defined herein, all scientific and technical terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention belongs. The present invention is further defined in the following examples. It should be understood that these examples, while indicating preferred embodiments of the present invention, are intended for illustrative purposes only. From the above discussion and these examples, one skilled in the art will be able to ascertain the essential features of the present invention, and will be able to make various changes and modifications to the present invention to adapt it to various uses and conditions without departing from the spirit and scope of the present invention.

[0129] Example 1 The following examples demonstrate the use of extremely low areal densities (e.g., 10 mg / m 2 This application discloses the production of a single layer PTFE membrane having an areal density of less than 1000 nm.

[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 (0.156 g lubricant / g total) (grams of lubricant / total mixture mass) per pound (approximately 0.454 kg) of fine powder. The lubricated powder was compressed into a cylindrical shape and ram extruded at 49°C to provide a tape. The tape was 16.2 cm wide and 0.762 mm thick. The ISOPAR® K was removed by heating to approximately 200°C, thereby forming a dried tape ("initial tape"). A 98 mm square was cut from the initial tape. The areal density of the initial tape (before pantographic stretching) was 1130 grams per square meter (g / m 2 All initial tape areal densities used herein were determined to be 1150±100 g / m 2 A summary of the process parameters used in Example 1 is shown in Table 1.

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

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

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

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

[0135] The cooled expanded ePTFE membrane from the third pass was retrieved from the pantograph and placed on an adhesive-backed frame (152.4 mm x 152.4 mm). Using the frame as a cutting guide, the ePTFE membrane was weighed and found to have an average areal density of 4.3 mg / m². 2 The lightest sample was calculated to be 2.4 mg / m 2 The area ratio was defined as the ratio of the areal density before and after a series of stretching operations. The ePTFE membranes obtained from the third pass exhibited area ratios ranging from 122,690:1 to 459,273:1, depending on the process conditions (Table 2). Figures 1 to 3 show the same sample (2.40 mg / m 2 , sample E1G) are shown at three different magnifications. No residual primary particles are observed. Figure 4 is from a second piece where the same strain path was used, but the furnace was set to 322 °C (sample E1H). A 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 the use of extremely low areal densities per layer (e.g., 10 mg / m 2 The present invention discloses the fabrication of ePTFE membranes with an areal density of up to 256 layers, resulting in an area ratio of up to about 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 (0.156 g lubricant / g total) per pound (approximately 0.454 kg) of fine powder (grams of lubricant / total mixture mass). The lubricated powder was compressed into a cylindrical shape and ram extruded at 49°C to provide a tape. The tape was 16.2 cm wide and 0.762 mm thick. The ISOPAR® K was removed by heating the tape to approximately 200°C. 98 mm squares were 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, the four square tapes were heated in an oven set at 300°C for 240 seconds and then stretched simultaneously in the longitudinal and transverse directions at a target ratio of approximately 7:1 in each direction while maintaining a temperature of approximately 300°C. The average engineering strain rate target was set at 36% / sec. The pantograph opened at a constant rate target for approximately 16.7 seconds. The ePTFE membrane was allowed to cool to room temperature (approximately 22°C) while restrained by the pantograph. Four pieces (each with four layers) were collected from the cooled ePTFE membrane piece and set aside for further stretching, i.e., the second pass. Another 16 layers were created by repeating the first-pass process once more. Both 16-layer specimens were combined to form a 32-layer specimen.

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

[0140] Third Pass Four samples (32 layers each) were collected from the cooled ePTFE membrane piece and layered (128 layers total) for further stretching, or "third pass." Using the same pantograph machine, the membrane was reheated in an oven set at 300°C for a target time of 240 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. The simultaneous stretching was performed at a constant acceleration setpoint of 1% / sec for a target ratio of 8:1 in each direction. The pantograph was opened for approximately 208 seconds for the third pass. The ePTFE membrane was allowed to cool to room temperature (approximately 22°C) while restrained by the pantograph.

[0141] 4th pass Four samples (128 layers) were collected from the cooled ePTFE membrane piece and layered (128 layers total) for further stretching, i.e., "fourth pass." Using the same pantograph machine, the membrane was reheated in an oven set at 300°C for a target time of 120 seconds and then stretched simultaneously in the longitudinal and transverse directions at a target ratio of approximately 3:1 in each direction while maintaining a temperature of approximately 300°C. The simultaneous stretching was performed at a constant acceleration set point of 1% / sec for a target ratio of 3:1 in each direction. The pantograph was opened for approximately 110 seconds on the fourth pass. The expanded ePTFE membrane was allowed to cool to room temperature (approximately 22°C) while restrained by the pantograph.

[0142] The ePTFE membrane was removed from the machine and placed on an adhesive-backed frame (152.4 mm x 152.4 mm). Using the frame as a cutting guide, the ePTFE membrane was weighed and determined to have an areal density of 0.00047 g / m 2 / layer, and the ePTFE membrane is 0.0605g / m 2 (Sample E2A, Table 4). The area ratios and areal densities of other ePTFE membranes (both ePTFE membranes and stacks of ePTFE membranes) were established and are listed in Table 4.

[0143] In addition, three more ePTFE membranes consisting of 128 layers were produced for Example 2 using the first three passes described above (E2B–D). Each ePTFE membrane was individually loaded for the fourth and fifth stretches. Using the same pantograph machine, the membrane was heated in an oven set at 300°C for a target time of 120 seconds and then stretched simultaneously in the longitudinal and transverse directions at a target ratio of approximately 4:1 (E2B), 5:1 (E2C), or 6:1 (E2D) in each direction while maintaining the temperature at approximately 300°C. Simultaneous stretching was performed at a constant acceleration setpoint of 1% / sec for Examples E2B–D. The pantograph was opened for approximately 139 (E2B), 161 (E2C), or 179 (E2D) seconds on the fourth pass. At the end of each stretch (E2B–E2D), the expanded ePTFE membrane was allowed to cool to room temperature (approximately 22°C) while restrained by the pantograph. The ePTFE membrane was removed from the machine and placed on an adhesive-backed frame (152.4 mm x 152.4 mm). Using the frame as a cutting guide, the ePTFE membrane was weighed. Table 4 includes the ratio setting for the fourth pass, the area ratio, the areal density of the ePTFE membrane stack, the areal density of each layer, and the translation time for the final pass.

[0144] Additionally, three more ePTFE membranes were produced for Example 2 (E2E-G), primarily for observing STEM (Figs. 6-8) images.

[0145] Example E2E was processed using the same process as Example E2D, with two exceptions: the residence time before expansion was reduced from 240 seconds (E2D) to 120 seconds (E2E) before the third pass, and the fourth-pass target ratio was increased from a setpoint of 6:1 in both directions (E2D) to a setpoint of 8:1 in both directions (E2E) for the area ratio setpoint of the final pass. The pantograph was open for approximately 208 seconds (E2E) for the fourth pass. The expanded ePTFE membrane was allowed to cool to room temperature (approximately 22°C) while restrained by the pantograph. The ePTFE membrane was removed from the machine and placed on an adhesive-backed frame (152.4 mm x 152.4 mm).

[0146] Example E2F was processed using the same process as Example E2E, with two exceptions: 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 a set point of 8:1 in each direction (E2E) to a set point of 9:1 in both directions (E2F). The expanded ePTFE membrane was allowed to cool to room temperature (approximately 22°C) while restrained by a pantograph. The ePTFE membrane was removed from the machine and placed on an adhesive-backed frame (152.4 mm x 152.4 mm).

[0147] Example E2G was processed using the same process as Example E2E, with two exceptions: the number of layers applied for the second stretch was reduced from 32 (E2E) to 16 (E2G), and the fourth pass was not used. The expanded ePTFE membrane was allowed to cool to room temperature (approximately 22°C) while restrained by a pantograph. The ePTFE membrane was removed from the machine and placed on an adhesive-backed frame (152.4 mm x 152.4 mm). Using the frame as a cutting guide, the ePTFE membrane was weighed and cut to a thickness of 0.009 g / m². 2 / layer, and the ePTFE membrane is 1.175g / m 2 (Sample E2G, Table 4). The area ratios and areal densities of these and other ePTFE membranes (both ePTFE membranes and stacks of ePTFE membranes) were calculated and are listed in Table 4. [Table 3] [Table 4]

[0148] Example 3 The following examples disclose the production of PTFE membranes with extremely low areal density per layer, up to 1024 ePTFE layers, with area ratios 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 (0.156 g lubricant / g total) per pound (approximately 0.454 kg) of fine powder (grams of lubricant / total mixture mass). The lubricated powder was compressed into a cylindrical shape and ram extruded at 49°C to provide a tape. The tape was 16.2 cm wide and 0.762 mm thick. The ISOPAR® K was removed by heating the tape to approximately 200°C. 98 mm squares were 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, the four square tapes were heated in an oven set at approximately 322°C (set point) for a target time of 240 seconds, then stretched simultaneously in the longitudinal and transverse directions at a target ratio of approximately 10:1 in each direction while maintaining a temperature of approximately 322°C. The average engineering strain rate target was set at 36% / sec. The pantograph was opened at a constant rate target for approximately 25 seconds. The ePTFE membrane was allowed to cool to room temperature (approximately 22°C) while restrained 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 total) were heated in an oven set at approximately 322°C for a target time of 240 seconds, and then stretched simultaneously in the longitudinal and transverse directions at a target ratio of approximately 10:1 in each direction while maintaining a temperature of approximately 322°C. The average engineering strain rate target was set at 3.6% / sec. The pantograph was opened at a constant rate target for approximately 250 seconds. The stretched membrane was allowed to cool to room temperature (approximately 22°C) while restrained by the pantograph.

[0152] Third Pass Four samples (64 layers each) were collected from the cooled ePTFE membrane pieces and layered (256 layers total) for further stretching, or "third pass." Using the same pantograph machine, the stacked ePTFE membrane was reheated in the oven to about 322°C for a target time of 240 seconds and then stretched simultaneously in the longitudinal and transverse directions at a target ratio of about 8:1 (E3B) or 10:1 (E3A) in each direction while maintaining a temperature of about 322°C. A 400% strain (λ in both directions) was achieved as the pantograph accelerated to a speed target of 3.5 mm / s. sp Simultaneous stretching was performed at a constant acceleration target of 1% / s to a maximum of 1000 kJ / s (ratio = 5:1) and a constant speed setpoint of 5% / s (3.5 mm / s ("r / s" speed mode) in this specific case based on an original length input of 70 mm) to complete the stretch. The pantograph was opened for approximately 221 seconds (E3B) or 261 seconds (E3A) on the third pass. The stretched membrane was allowed to cool to room temperature (approximately 22°C) while restrained by the pantograph.

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

[0154] The ePTFE membrane was removed from the machine and placed on a frame (152.4 mm x 152.4 mm) with an adhesive backing. Using the frame as a cutting guide, the ePTFE membrane was weighed and cut to a thickness of 0.005-0.016 g / m. 2 / layer, and the mass per area (MPA, areal density) of the ePTFE membrane is 0.005 to 0.016 mg / m 2 (Table 6). Two different locations were measured for sample E3A (i.e., E3A-1 and E3A-2), while three different locations were measured for sample E3B (i.e., E3B-1, E3B-2, and E3b-3). Samples E3A (Figure 9) and E3B (Figure 10) were STEM imaged.

[0155] A maximum areal density of 298,611,016:1 was possible (Table 6). The lowest areal density of the completed ePTFE membrane stack was approximately 3.9 mg / m 2 It was. [Table 5] [Table 6]

[0156] Example 4 The following examples are based on membrane thickness (per layer) of 0.6 to 2.0 grams / m² for ease of measurement. 2 The production of ePTFE membranes with custom areal densities is disclosed.

[0157] PTFE fine powder (EI DuPont de Nemours) was blended with ISOPAR® K isoparaffinic hydrocarbon lubricant at a target ratio of 110 mL (0.156 g lubricant / g total) per pound (approximately 0.454 kg) of fine powder (grams of lubricant / total mixture mass). The lubricated powder was compressed into a cylindrical shape and ram extruded at 49°C to provide a tape. The tape was 16.2 cm wide and 0.762 mm thick. The ISOPAR® K was removed by heating to approximately 200°C. 98 mm squares were 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 an oven set at approximately 300°C for a target time of 120 (setpoint) (sample E4B) or 240 (setpoint) seconds (E4A, E4C, and E4D), and then stretched simultaneously in the longitudinal and transverse directions at a target ratio of approximately 7:1 in each direction while maintaining a temperature of approximately 300°C. The average engineering strain rate target was set at 36% / sec. The pantograph opened at a constant rate target over approximately 16.6 seconds. The ePTFE membrane was allowed to cool to room temperature (approximately 22°C) while restrained by the pantograph.

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

[0160] Third Pass Four samples were collected from the cooled ePTFE membrane pieces and stacked for further stretching, i.e., a total of 128 layers (E4A-C) or 192 layers (E4D), for a third pass. The same pantograph machine was used to add the 128-layer or 192-layer stack. The ePTFE membrane was reheated in an oven set at approximately 300°C for a target time of 120 (E4A-C) 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. A 400% strain (λ in both directions) was achieved as the pantograph accelerated to a speed set point of 3.5 mm / s. sp Simultaneous stretching was performed at a constant acceleration setpoint of 1% / s to a target ratio of 8:1 in each direction, and stretches (E4A, E4C-D) were completed at a constant speed setpoint of 5% / s (3.5 mm / s in this specific case based on an original length input of 70 mm). The pantograph was open for approximately 221 seconds during stretching of E4A and E4C-D. Simultaneous stretching of Example (E4B) was performed at a constant acceleration target of 1% / s to a target ratio of 8:1 in each direction. The entire third-pass translation took approximately 210 seconds for Example E4B. The stretched membrane was allowed to cool to room temperature (approximately 22°C) while restrained by the pantograph. The ePTFE membrane was removed from the machine and placed on an adhesive-backed frame (152.4 mm x 152.4 mm).

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

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

[0163] Densification method Method 1: Laboratory Press The ePTFE membrane E4C was placed in a Carver 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 on top to generate approximately 300 psi (~2.07 MPa) for approximately 30 minutes.

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

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

[0166] A relatively high air flow rate at a given pressure indicates a high permeability; in other words, a lower pressure is required for a higher flow rate. Airflow resistance is a function of structure, and most simple models use the solid volume fraction and representative fibril radius as key factors. More sophisticated models address slippage as a reduction in fibril radius, in this case, making these a small fraction of the mean free path of air at 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. A uniform distribution of fibrils will be maximized if each fibril is separated by the same distance. A less uniform distribution, represented by aggregated fibril aggregates, will subsequently exhibit higher permeability. Fibril shape can also alter airflow resistance.

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

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

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

[0170] Second Pass Samples were collected from the cooled ePTFE membrane pieces for further stretching, or "second pass." The specific number of layers stacked for each sample's second pass is shown in Table 9. Using the same pantograph machine, the ePTFE layer stack was heated in an oven set at 300°C for a target of 120 (E5A-G) or 240 (E5H-J) seconds and then stretched simultaneously in the longitudinal and transverse directions at target ratios of 6.35:1 (E5J), 7:1 (E5H-I), or 10:1 (E5A-G) in each direction while maintaining a temperature of approximately 300°C. The average engineering strain rate target was 4% / s to 9% / s (Table 9). The pantograph was opened at a constant rate target of 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 restrained in a pantograph.

[0171] Third Pass Samples were collected 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 an oven set at 300°C for a target of 120 (E5A-G), 180 (E5I), or 240 (E5H and E5J) seconds and then stretched simultaneously in the longitudinal and transverse directions at a target ratio of about 7:1 (E5H and E5J), 8:1 (E5I), or 10:1 (E5A-G) in each direction (Table 9), while maintaining a temperature of about 300°C. Biaxial stretching was performed at a constant acceleration set point of 1% / s (E5A-E5H and E5J). For Example E5I, the membrane was stretched to 400% strain (λ in both directions) as the pantograph accelerated to a speed set point of 3.5 mm / s. sp =5:1), biaxial stretching was performed at a constant acceleration set point of 1% / s and a constant velocity set point of 5% / s (3.5 mm / s in this specific case based on an original length input of 70 mm) ("r / s" velocity mode) to a target ratio λ in both directions. sp Stretching was completed at a ratio of 8:1. The pantograph was opened for approximately 221 (E5I), 230 (E5A-G), and 195 (E5H and E5J) seconds. Selected samples (E5E-G and E5I) were thermally conditioned in an oven setpoint of 350°C for a target time of 300 seconds while restrained on the pantograph. The ePTFE membrane was allowed to cool to room temperature (approximately 22°C) while restrained in the pantograph.

[0172] The cooled expanded ePTFE membrane from the third pass was removed from the pantograph and placed on an adhesive-backed frame (152.4 mm x 152.4 mm). The mean fibril width, area-weighted fibril width (AWFW), median fibril width, specific surface area, bubble point, airflow resistance, and areal density are listed in Table 10. [Table 9] [Table 10]

[0173] Example 6 The following examples disclose the preparation of ePTFE membranes and the measurement of various membrane parameters, including quality factor, airflow resistance, areal 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 (0.156 g lubricant / g total) per pound (approximately 0.454 kg) of fine powder (grams of lubricant / total mixture mass). The lubricated powder was compressed into a cylindrical shape and ram extruded at 49°C to provide a tape. The tape was 16.2 cm wide and 0.762 mm thick. The ISOPAR® K was removed by heating to approximately 200°C. The dried tape was cut into 98 mm squares. 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 layered and heated in a furnace set at 300°C (set point) for 120 (E6A-C) or 240 seconds (E6D), then simultaneously in the longitudinal and transverse directions to the target ratio (λ sp The ePTFE membranes were stretched at a strain ratio of 4:1, 7:1, or 9:1 (Table 11) while maintaining a temperature of approximately 300°C. The average engineering strain rate target was set at 36% / sec. The pantograph was opened at a constant rate target for approximately 8.3, 16.6, or 22 seconds based on the target ratio (Table 11). The ePTFE membranes were allowed to cool to room temperature (approximately 22°C) while restrained by the pantograph.

[0176] Second Pass From the cooled membranes, samples were collected for further stretching, i.e., a second pass. The specific number of ePTFE membranes loaded for each sample's second pass is shown in Table 11. Using the same pantograph machine, the ePTFE layer stack was heated in an oven set at 300°C for a target of 120 (E6A-C) or 240 (E6D) seconds and then stretched simultaneously in the longitudinal and transverse directions at a target ratio of 7:1 or 10:1 in each direction while maintaining a temperature of approximately 300°C. The average engineering strain rate target was 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 restrained by the pantograph.

[0177] Third Pass Samples were collected 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 an oven set at 300°C for a target time of 120 (E6A-C) or 240 (E6D) seconds and then stretched simultaneously in the longitudinal and transverse directions at a target ratio of approximately 8:1 (E6A-B), 10:1 (E6C), or 7:1 (E6D) in each direction, while maintaining a temperature of approximately 300°C. The average strain rate target was 1% / s. The pantograph opened with a constant acceleration target for approximately 208 (E6A-B), 230 (E6C), or 195 (E6D) seconds. Two samples, E6B and E6D, were exposed to heat at approximately 350°C for 5 minutes. The expanded membrane was allowed to cool to room temperature (approximately 22°C) while restrained by the pantograph.

[0178] The ePTFE membranes were removed from the machine and placed on an adhesive-backed frame (152.4 mm x 152.4 mm) for further testing. The samples were tested for airflow resistance and filtration efficiency as described in the Test Methods section. The air filtration results are shown in Table 12. Particle diameter vs. quality factor (Q) for samples E6A, E6B, E6C, E6D, and E6E (Comparative Example 1) f ) is shown in Figure 24. Figure 24 shows the improvement in quality factor for Samples E6A-E6D over Comparative Example E6E.

[0179] The ePTFE samples were cut 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, respectively, at lower magnification. The fibril width measurement results are shown in Table 13.

[0180] Comparative Example 1 The ePTFE membrane was manufactured according to the general teachings of U.S. Patent No. 3,953,566 to Gore. The ePTFE membrane (sample E6E) had an areal weight of 5.6 g / m 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 example discloses the preparation of an ePTFE membrane that is subsequently used for light transmission measurements.

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

[0183] First pass Using a pantograph machine, one or four square tapes were heated in an oven set at 300°C (set point) for 240 (E7A) or 120 (E7B) seconds and then stretched simultaneously in the longitudinal and transverse directions 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 restrained by the pantograph.

[0184] Second Pass Samples were retrieved 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 an oven to approximately 300°C for a target time of 120 (E7B) or 240 (E7A) seconds and then stretched simultaneously in the longitudinal and transverse directions at a target ratio of approximately 7:1 (E7A) or 10:1 (E7B) in each direction, while maintaining a temperature of approximately 300°C. The average engineering strain rate target was set at 5% / s (E7A) or 9% / s (E7B). The pantograph 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 restrained by the pantograph.

[0185] Third Pass Samples were collected from the cooled ePTFE membrane 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 an oven set at approximately 300°C for a target time of 120 seconds and then stretched simultaneously in the longitudinal and transverse directions at a target ratio of approximately 7:1 (E7B) or 8:1 (E7A) in each direction (Table 14), while maintaining a temperature of approximately 300°C. The average strain rate target was set at 1% / s. The pantograph opened with 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 restrained by the pantograph.

[0186] The ePTFE membranes were removed from the machine and placed on an adhesive-backed frame (152.4 mm x 152.4 mm) for further testing. The samples were tested for airflow resistance as described in the Test Methods section. The ePTFE samples were cut from the tape and weighed on a Mettler Toledo AT 20. Selected samples were also tested for light transmittance as described in the Test Methods section. The results of the light transmittance tests are shown in Table 15 and Figure 29. Figure 29 is a plot of wavelength vs. % transmittance for both the 3-layer sample (E7B, black line) and the 48-layer sample (E7A, gray line). [Table 14] [Table 15]

[0187] Example 8 This example highlights the improved strength to weight ratio of a relatively balanced ePTFE membrane composed of extremely thin, similar fibrils, exhibiting exceptionally high crystallinity of at least 94%. Stacking and simultaneous stretching were employed to generate sample mass for bulk mechanical characterization and to reduce time at the synchrotron for structural characterization. Amorphous content and relative intensity 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 (0.156 g lubricant / g total) per pound (approximately 0.454 kg) of fine powder (grams of lubricant / total mixture mass). The lubricated powder was compressed into a cylindrical shape and ram extruded at 49°C to provide a tape. The tape was 16.2 cm wide and 0.762 mm thick. The ISOPAR® K was removed by heating to approximately 200°C. The dried tape was cut into 98 mm squares. A summary of the process parameters used in this example is shown in Table 16.

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

[0190] Second Pass From the cooled ePTFE membrane, samples were retrieved for further stretching, i.e., a second pass. Table 16 lists the specific number of layers loaded for each condition. Using the same pantograph machine, samples with 16 layers (E8B) or 32 layers (E8A and E8C-D) were heated in an oven to approximately 300°C (E8A-B) or 322°C (E8C-D) for 240 seconds and then stretched simultaneously in the longitudinal and transverse directions at a target ratio of approximately 7:1 in each direction while maintaining the set-point temperature. The average engineering strain rate target was set at 4% / s (E8A-B) or 5% / s (E8C-D) (Table 16). The pantograph 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 restrained 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, ePTFE membranes (using 64 layers (E8B) and 128 layers (E8A and E8C-D)) were reheated in an oven set at 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 at a target ratio of approximately 7:1 (E8A-B) or 8:1 (E8C-D) in each direction while maintaining the set-point temperatures (Table 16). The average strain rate target was 1% / s. The pantographs were opened at a constant acceleration rate for approximately 195 (E8A-B) or 208 (E8C-D) seconds. While restrained on the pantograph, samples E8B and E8D were thermally conditioned in an oven for a target time of 300 seconds at a set point of 350° C. The ePTFE membranes were allowed to cool to room temperature (approximately 22° C.) while restrained on the pantograph.

[0192] The ePTFE membranes were removed from the machine and placed on adhesive-backed frames (152.4 mm x 152.4 mm) for further testing. The tensile test results, contained in Table 17, demonstrate that the specific strength to weight metrics exceeds those previously reported in the art (see comparative examples—Table 18). Samples E8C and E8D were further characterized by X-ray diffraction (XRD) (Figure 30, Sample E8C (not heat-treated) and Figure 31, Sample E8D (heat-treated)), and the results are consistent with an isotropic orientation in the MD-TD plane. These results are consistent with the balanced strength results. Figure 32 shows the tensile strength distribution in the range 10–45 nm for both the heat-treated sample (Sample E8D, top trace) and the non-heat-treated sample (Sample E8C, bottom trace). -1 over q(nm -1 ) versus intensity in the range 10-20 nm for sample E8D (heat-treated, top trace) and sample E8C (non-heat-treated, bottom trace). -1 over q(nm -1 ) vs. intensity (10-20 nm -1 ) are plots of the crystallinity of the ePTFE membrane. Figures 32 and 33 demonstrate that the ePTFE membrane has a very high degree of crystallinity. In addition, q = 12.8 nm -1 The narrowness of the peak centered at (Figure 33) suggests that these ePTFE crystal packing defects are minimal. Example E8C had a crystallinity of 99%. Example E8D had a crystallinity of 99.2%. [Table 16] [Table 17]

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

[0194] Example 9 The following example describes the preparation and analysis of a low mass uniaxially oriented ePTFE membrane with 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 (0.156 g lubricant / g total) per pound (approximately 0.454 kg) of fine powder (grams of lubricant / total mixture mass). The lubricated powder was compressed into a cylindrical shape and ram extruded at 49°C to provide a tape. The tape was 16.2 cm wide and 0.762 mm thick. The ISOPAR® K was removed by heating to approximately 200°C. 98 mm squares were 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 with four tape layers, were heated in an oven set at approximately 300°C (set point) for 240 seconds and then stretched simultaneously in the longitudinal (machine) and transverse directions at a target ratio of approximately 10:1 in each direction while maintaining a temperature of approximately 300°C. The average engineering strain rate target was set at 36% / sec. The pantograph was opened at a constant rate target over approximately 25 seconds. The ePTFE membrane was allowed to cool to room temperature (approximately 22°C) while restrained by the pantograph.

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

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

[0199] Optional 4th pass Using the same pantograph machine for sample E9B, the 32-layer sample was again heated in the oven to approximately 300°C for a target time of 120 seconds and then stretched simultaneously in the longitudinal and transverse directions at a target ratio of approximately 3:1 in each direction while maintaining a temperature of approximately 300°C. The simultaneous stretching was performed with a constant acceleration set point target of 1% / sec. The pantograph was opened at constant acceleration for approximately 110 (E9B) seconds.

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

[0201] Final Pass Using the same pantograph machine, the 32-layer specimens were heated in an oven set at approximately 350°C for a target time of 300 seconds and then stretched in the machine (longitudinal) direction only 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 point of 1% / sec. The pantograph was opened at constant acceleration for approximately 40 (E9A) or 51 (E9B) seconds.

[0202] The ePTFE membrane was removed from the machine and placed on an adhesive-backed frame (152.4 mm x 152.4 mm). Using the frame as a cutting guide, the ePTFE membrane was weighed to calculate the linear density (bulk denier), and mechanical data was collected using the matrix tensile test in the Test Methods section above. Sample E9A was further characterized using dynamic mechanical analysis (DMA) and showed a matrix modulus of 100 GPa at ambient temperature (i.e., approximately 20°C) (Figure 33). Sample E9A was further characterized by XRD (Figure 34). The XRD is consistent with a very high degree of crystalline orientation. <p2>The orientation function was 0.989, with 1.0 corresponding to a perfectly parallel alignment (Figure 35). The crystallinity was determined to be 94.6%. An SEM of sample E9A is shown in Figure 36. [Table 19] [Table 20]

[0203] Example 10 The following examples disclose the preparation of extremely low mass multi-layer ePTFE membranes with high intrinsic strength and nanoparticle retention measurements. Nanoparticle retention is tested using the bead test disclosed in the Methods for Measuring Permeability and Bead Retention of Membrane Samples section.

[0204] PTFE fine powder (EI DuPont de Nemours) was blended with ISOPAR® K isoparaffinic hydrocarbon lubricant at a target ratio of 110 mL (0.156 g lubricant / g total) per pound (approximately 0.454 kg) of fine powder (grams of lubricant / total mixture mass). The lubricated powder was compressed into a cylindrical shape and ram extruded at 49°C to provide a tape. The tape was 16.2 cm wide and 0.762 mm thick. The ISOPAR® K was removed by heating to approximately 200°C. 98 mm squares were 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, the four square tapes were heated in a furnace set at approximately 300°C for a target 120 (E10A-C) seconds, and then simultaneously rotated in the longitudinal and transverse directions at a selected target ratio (λ) in each direction. sp The stretched membrane was stretched at a strain ratio of approximately 7:1 (E10A and E10C) or 2:1 (E10B) while maintaining a temperature of approximately 300°C. The average engineering strain rate target was set at 36% / sec. The pantograph opened at a constant rate 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 restrained 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), was loaded for the second pass under the conditions shown in Table 21. Using the same pantograph machine, the ePTFE layer stack was heated in an oven set at 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 speed for approximately 120 (E10A), 50 (E10B), and 100 (E10C) seconds. The stretched membrane was allowed to cool to room temperature (approximately 22°C) while restrained in a pantograph.

[0207] Third Pass Samples were collected 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), was loaded for the second pass of each condition, as shown in Table 21. Using the same pantograph machine, the membrane was reheated in an oven set at 300°C for a target time of 120 (E10A-C) seconds and then stretched simultaneously in the longitudinal and transverse directions at a target ratio of approximately 8 (E10A), 10 (E10B), or 6:1 (E10C) in both the longitudinal and transverse directions, while maintaining a temperature of approximately 300°C. The average constant accelerated strain rate set point was 1% / s. The pantograph was opened at a constant acceleration set point for approximately 221 (E10A), 261 (E10B), or 179 (E10C) seconds. The stretched membrane was allowed to cool to room temperature (approximately 22°C) while restrained in a pantograph.

[0208] The samples were removed from the machine and placed on an adhesive backed frame (152.4 x 152.4 mm) for further testing (E10A and E10B) or further stretching (E10C).

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

[0210] densification The samples (E10A-C) were densified while being constrained in the MD and TD planes by gently pouring isopropyl alcohol (IPA) onto the constrained membrane and allowing the IPA to evaporate.

[0211] The average filtrate permeability (see equation (9) above) and bead retention (see equation (10) above) of each membrane sample (Samples E10A, E10B, and E10C) were evaluated according to the Bead Test Permeability and Retention Determination Method described above in the Test Methods section. The results are shown in Table 22 and Figure 38.

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

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

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

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

[0216] Comparative Example 6 - Sample E10D2 Fine polytetrafluoroethylene polymer powder, manufactured according to the teachings of U.S. Patent No. 6,541,589 to Baillie, 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 and heat conditioned at a temperature of 49°C for at least 8 hours. The cylindrical pellets were then extruded through a square orifice die at a reduction ratio of 72:1 to form a tape. The tape was then calendered between rolls at a calender ratio of 3:1. The calendered tape was then stretched in the transverse direction at a ratio of 3.6:1 and dried at a temperature of 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 in the transverse direction at a temperature of approximately 310°C to a stretch ratio of 10.8:1. The membrane was then heat-treated at a temperature of approximately 380°C for a target time of 25 seconds. The biaxially stretched membrane was compressed between rollers (at 25° C.) at a speed of 1 m / min with a compression force of 20 N / mm.

[0217] Comparative Example 7 - Sample E10D3 Fine polytetrafluoroethylene polymer powder, manufactured according to the teachings of U.S. Patent No. 6,541,589 to Baillie, 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 and heat conditioned at a temperature of 49°C for at least 8 hours. Tapes were then formed by extruding the cylindrical pellets through a square orifice die at a reduction ratio of 72:1. The tape was then calendered between rolls at a calender ratio of 3:1. The calendered tape was then stretched in the transverse direction at a ratio of 3.6:1 and dried at a temperature of 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 in the transverse direction at a temperature of approximately 300°C to a stretch ratio of 12.3:1. The biaxially stretched membrane was compressed between rollers (at 90° C.) with a compression force of 80 N / mm at a speed of 5 m / min.

[0218] Using the test procedures described above, the average filtrate permeability (see equation (9) above) and bead retention (see equation (10) above) of each comparative 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 generally and with reference to specific embodiments. It will be apparent to those skilled in the art that various modifications and variations can be made in the embodiments without departing from the scope of the disclosure. Accordingly, it is intended that the embodiments cover the modifications and variations of the present invention provided they fall within the scope of the appended claims and their equivalents.

Claims

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

2. The ePTFE membrane has an areal density of about 30 mg / m ２ The expanded polytetrafluoroethylene membrane of claim 1, wherein the expanded polytetrafluoroethylene membrane has a viscosity of less than 1000 MPa.

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

4. 4. The expanded polytetrafluoroethylene membrane of claim 1, wherein the ePTFE membrane has a bulk denier of less than about 750 g / 9000 m.

5. 5. The expanded polytetrafluoroethylene membrane of claim 1, wherein the ePTFE membrane has a strength greater than about 5 gf / d.

6. 6. The expanded polytetrafluoroethylene membrane of claim 1, wherein the ePTFE membrane is self-supporting.

7. 7. The expanded polytetrafluoroethylene membrane of claim 1, wherein the ePTFE membrane is uniaxially oriented.

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

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

10. 10. The expanded polytetrafluoroethylene membrane according to claim 1, further comprising a spacer layer.

11. 11. The expanded polytetrafluoroethylene membrane of 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 an expanded polytetrafluoroethylene membrane according to any one of claims 1 to 11.

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

14. 14. An article comprising the expanded polytetrafluoroethylene membrane of any one of claims 1 to 11, the composite of claim 12, or the laminate of claim 13.

15. 1. A method of forming a uniaxially oriented ePTFE membrane, said method comprising: (1) cutting at least a first piece from a first expanded polytetrafluoroethylene (ePTFE) membrane; (2) biaxially stretching the at least first piece to obtain a second expanded polytetrafluoroethylene membrane; (3) cutting at least a second piece from the second stretched membrane; (4) forming a stacked sample by positioning the at least one first piece and the at least one second piece in a stacked orientation; (4) biaxially stretching the stacked samples; (5) repeating steps (1) through (4) until the desired biaxially oriented ePTFE membrane is obtained; and (6) Uniaxially stretching the biaxially oriented ePTFE membrane 1. A method of forming a uniaxially oriented ePTFE membrane, comprising:

16. The method of claim 16 further comprising adding a spacer layer.

17. 17. The method of claim 15 or 16, wherein the spacer layer is selected from a porous polymer, a non-porous polymer, a fluoropolymer, a porous polyolefin, and a non-porous polyolefin.

18. 18. The method of any one of claims 15 to 17, wherein the ePTFE membrane is stretched uniaxially in the machine direction.

Images