Highly oriented expanded polytetrafluoroethylene having excellent stiffness

Abstract

The present application provides self-supporting, uniaxially expanded polytetrafluoroethylene (ePTFE) films having high intrinsic strength, high matrix modulus, and high crystallinity index. In some embodiments, the ePTFE films are stretched in the machine direction. The uniaxially oriented ePTFE films have a matrix tensile strength in the machine direction of at least about 1000 MPa, a matrix modulus at ambient temperature (i.e., about 20°C) of at least about 100 GPa, and a crystallinity index of at least about 94%. In some embodiments, the ePTFE films have a tenacity greater than or equal to about 5 gf / d and a denier less than or equal to about 750 g / 9000 m. Further, the uniaxially oriented ePTFE films have a Gurley number of at least about 0.98 <p2>Orientation. In addition, the fibrils in ePTFE films are nearly perfectly aligned in parallel. ePTFE films can be used to form composites, laminates, fibers, tapes, sheets, tubes, or other three-dimensional objects.< / p2>

Description

Technical Field

[0001] This invention relates to microporous fluoropolymer membranes, and more specifically, to self-supporting, highly expandable polytetrafluoroethylene (ePTFE) membranes, said ePTFE membranes having high inherent strength, high matrix modulus, high crystallinity index, and aligned fibrils. Background Technology

[0002] Polytetrafluoroethylene (PTFE) is an attractive material due to 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 forms, such as films, fibers, and tubes. Expanded PTFE (ePTFE) can be used alone or in composites and / or laminates to produce articles for a wide range of applications. Many of these applications may benefit from the use of lighter, thinner, stronger materials with / or improved optical properties. Therefore, there has been a ongoing need to provide ePTFE articles with improved performance. Summary of the Invention

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

[0004] According to another aspect of aspect 1 (“Aspect 2”), the ePTFE membrane has a density of less than about 30 g / m³. 2 Surface density.

[0005] According to another aspect of aspects 1 and 2 (“Aspect 3”), the ePTFE membrane has a strength greater than or equal to 0.98. <p2>orientation.

[0006] According to any one of the foregoing aspects ("Aspect 4"), the ePTFE membrane has a volume denier of less than about 750 g / 9000 m.

[0007] According to another aspect of any of the foregoing aspects ("Aspect 5"), the ePTFE membrane has a toughness greater than about 5 gf / d.

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

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

[0010] According to another aspect of any of the foregoing aspects ("Aspect 8"), the ePTFE membrane is at least partially coated with a polymer, at least partially absorbed with a polymer, or a combination of the foregoing.

[0011] According to another aspect of any of the foregoing aspects ("Aspect 9"), the ePTFE membrane is in the form of fibers, sheets, tubes, three-dimensional self-supporting structures, cut fibers, cut sheets, cut tubes, or cut three-dimensional self-supporting structures.

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

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

[0014] According to another aspect ("Aspect 12"), a composite material includes an expanded polytetrafluoroethylene film of any of the foregoing aspects.

[0015] According to another aspect ("Aspect 13"), a laminate includes an expanded polytetrafluoroethylene film of any of the foregoing aspects.

[0016] According to another aspect ("Aspect 14"), an article comprises an expanded polytetrafluoroethylene film of aspects 1-11, a composite material of aspect 12, or a laminate of aspect 13.

[0017] According to another aspect ("Aspect 15"), a method for forming a uniaxially oriented ePTFE film includes (1) cutting at least a first piece from a first expanded polytetrafluoroethylene (ePTFE) film, (2) biaxially stretching the at least first piece to obtain a second expanded polytetrafluoroethylene film, (3) cutting at least a second piece from the second expanded film, (4) placing the at least one first piece and the at least one second piece in a stacking orientation to form a stacked sample, (5) repeating steps (1) to (4) until the desired biaxially oriented ePTFE film is obtained, and (6) uniaxially stretching the biaxially oriented ePTFE film.

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

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

[0020] According to another aspect of aspects 15 to 17 ("Aspect 18"), the ePTFE membrane is uniaxially stretched in the machine direction.

[0021] Brief description of the attached figures

[0022] The accompanying drawings, which are incorporated in and form part of this specification, are used to aid in a further understanding of this disclosure and illustrate embodiments thereof. Together with the specification, they serve to explain the principles of this disclosure.

[0023] Figure 1 The image is a scanning transmission electron microscope (STEM) image of sample E1G from Example 1, taken at 2,000X magnification with a full horizontal field width of approximately 63 micrometers, according to the embodiments described herein.

[0024] Figure 2 This is a STEM image of sample E1G from Example 1, taken at 5,000X magnification with a full horizontal field width of approximately 25 micrometers, according to the embodiments described herein.

[0025] Figure 3 This is a STEM image of sample E1G from Example 1, taken at 10,000X magnification with a full horizontal field width of approximately 12 micrometers, according to the embodiments described herein.

[0026] Figure 4 This is a STEM image of sample E1H from Example 1, taken at 20,000X magnification with a full horizontal field width of approximately 6 micrometers, according to the embodiments described herein.

[0027] Figure 5 This is a STEM image of sample E1I from Example 1, taken at 2,000X magnification with a full horizontal field width of approximately 63 micrometers, according to the embodiments described herein.

[0028] Figure 6 The image is a STEM image of sample E2E from Example 2, taken at 5,000X magnification with a full horizontal field width of approximately 25 micrometers, according to the embodiments described herein.

[0029] Figure 7 This is a STEM image of sample E2F from Example 2, taken at 5,000X magnification with a full horizontal field width of approximately 25 micrometers, according to the embodiments described herein.

[0030] Figure 8 The image is a STEM image of a sample E2G from Example 2, taken at 5,000X magnification with a full horizontal field width of approximately 25 micrometers, according to the embodiments described herein.

[0031] Figure 9 The image is a STEM image of sample E3A from Example 3, taken at 100,000X magnification with a full horizontal field width of approximately 1.27 micrometers, according to the embodiments described herein.

[0032] Figure 10 This is a STEM image of sample E3B from Example 3, taken at 20,000X magnification with a full horizontal field width of approximately 6 micrometers, according to the embodiments described herein.

[0033] Figure 11 The images are STEM images of sample E1H from Example 5 (taken at 20,000X magnification with a full horizontal field width of approximately 6 micrometers) according to the embodiments described herein, wherein manual image analysis was used to measure the fibril width.

[0034] Figure 12 This is a bar chart of fibril width data in nanometers based on Example 5 described herein. Figure 11 The fitting of the log-normal distribution to the manual image analysis.

[0035] Figure 13 This is a STEM image of sample E5A from Example 5, taken at 6,000X magnification with a full horizontal field width of approximately 21 micrometers, according to the embodiments described herein.

[0036] Figure 14 This is a STEM image of sample E5B from Example 5, taken at 6,000X magnification with a full horizontal field width of approximately 21 micrometers, according to the embodiments described herein.

[0037] Figure 15 This is a STEM image of a sample E5C from Example 5, taken at 10,000X magnification with a full horizontal field width of approximately 12 micrometers, according to the embodiments described herein.

[0038] Figure 16 This is a STEM image of a sample E5D from Example 5, taken at 10,000X magnification with a full horizontal field width of approximately 12 micrometers, according to the embodiments described herein.

[0039] Figure 17 This is a STEM image of sample E5E from Example 5, taken at 6,000X magnification with a full horizontal field width of approximately 21 micrometers, according to the embodiments described herein.

[0040] Figure 18 This is a STEM image of sample E5F from Example 5, taken at 10,000X magnification with a full horizontal field width of approximately 12 micrometers, according to the embodiments described herein.

[0041] Figure 19 This is a STEM image of a sample E5G from Example 5, taken at 10,000X magnification with a full horizontal field width of approximately 12 micrometers, according to the embodiments described herein.

[0042] Figure 20 The image is a scanning electron microscope (SEM) image of sample E5H from Example 5, taken at 10,000X magnification with a full horizontal field width of approximately 21 micrometers, according to the embodiments described herein.

[0043] Figure 21 The image is a SEM image of sample E5I from Example 5, taken at 20,000X magnification with a full horizontal field width of approximately 6 micrometers, according to the embodiments described herein.

[0044] Figure 22 The image is a SEM image of sample E5H from Example 5, taken at 5,000X magnification with a full horizontal field width of approximately 25 micrometers, according to the embodiments described herein.

[0045] Figure 23 The image is a SEM image of sample E5I from Example 5, taken at 5,000X magnification with a full horizontal field width of approximately 25 micrometers, according to the embodiments described herein.

[0046] Figure 24 This is a graphical illustration of the quality factor vs. particle size of samples E6A, E6B, E6D and E6E from Example 6, according to the embodiments described herein;

[0047] Figure 25 This is a STEM image of sample E6A from Example 6, taken at 10,000X magnification with a full horizontal field width of approximately 12 micrometers, according to the embodiments described herein.

[0048] Figure 26 This is a STEM image of sample E6B from Example 6, taken at 10,000X magnification with a full horizontal field width of approximately 12 micrometers, according to the embodiments described herein.

[0049] Figure 27 This is a STEM image of sample E6A from Example 6, taken at 1500X magnification with a full horizontal field width of approximately 84 micrometers, according to the embodiments described herein.

[0050] Figure 28 This is a STEM image of sample E6B from Example 6, taken at 1500X magnification with a full horizontal field width of approximately 84 micrometers, according to the embodiments described herein.

[0051] Figure 29 This is a graphical illustration of the % transmittance vs. wavelength for samples E7A (gray line; 48 layers) and E7B (black line; 3 layers) according to the embodiments described herein.

[0052] Figure 30 The X-ray diffraction (XRD) pattern of sample E8C from Example 8 according to the embodiments described herein;

[0053] Figure 31 This is an X-ray diffraction (XRD) pattern of sample E8D (heat-treated) from Example 8 according to the embodiments described herein;

[0054] Figure 32 The q (nm) of samples E8C (bottom trace - untreated) and E8D (top trace - treated) from Example 8 according to the described embodiment. -1 ) vs. Intensity (10-45nm) -1 A diagrammatic explanation of ( );

[0055] Figure 33 The q (nm) of samples E8C (bottom trace - untreated) and E8D (top trace - treated) from Example 8 according to the described embodiment. -1 ) vs. Intensity (focusing on 10-20nm) -1 A diagrammatic explanation of the scope;

[0056] Figure 34 This is a graphical illustration of the matrix storage modulus vs. temperature of sample E9A from Example 9, according to the embodiments described herein;

[0057] Figure 35 The X-ray diffraction (XRD) pattern of sample E9A from Example 9 according to the embodiments described herein;

[0058] Figure 36 This is a graphical illustration of the intensity vs. 2θ of sample E9A from Example 9 according to the embodiments described herein; and

[0059] Figure 37 The image is a SEM image of sample E9A from Example 9, according to the embodiments described herein, taken at 5,000X magnification with a full horizontal field width of approximately 23 micrometers.

[0060] Figure 38 This is a graphical illustration of nanoparticles vs. filtrate permeability retention from the sample of Example 10, according to the embodiments described herein; and

[0061] Figure 39 A method for manufacturing a biaxial expansion film according to the embodiments described herein is generally described.

[0062] the term

[0063] Average fibril width:

[0064] Median fibril width: w m (nm).

[0065] Area-weighted fibril width:

[0066] The area-weighted fibril width is calculated using the following equation:

[0067]

[0068] Specific surface area (SSA) (m 2 / g) is calculated using the following formula:

[0069]

[0070] in:

[0071] Surface area: A(m²) 2 );

[0072] Volume: V(m) 3 );as well as

[0073] Crystal density: PTFEρ x (g / m 3 ).

[0074] Specific surface area (based on w) m (m) 2 / g) is calculated using the following formula:

[0075]

[0076] Specific surface area (based on) (m) 2 / g) is calculated using the following formula:

[0077]

[0078] areal density (mass per unit area) (g / m³) 2 ):

[0079] Areal density (initial): MPa o ,and

[0080] Areal density (final): MPa f .

[0081] Number of layers (n).

[0082] The area ratio (AR) is calculated by the following formula:

[0083] Detailed Implementation

[0084] Those skilled in the art will understand that various aspects of this disclosure can be implemented by any number of methods and apparatuses constructed to carry out the desired effects. It should also be noted that the accompanying drawings referenced herein are not necessarily drawn to scale, but may be enlarged to illustrate various aspects of this disclosure, and in this regard, the drawings should not be considered limiting.

[0085] Furthermore, the terms "adjacent" and "adjacent to" as used herein are intended to mean that when one element is "adjacent" to another element, the element may be directly adjacent to the other element, or there may be an intermediate element present. Unless otherwise expressly stated herein, the singular forms "an," "a," and "described" as used herein include the plural referent. The term "on" as used herein is intended to mean that when one element is "on" another element, it may be directly on the other element, or there may be an intermediate element present. It is understood that the terms "fine powder" and "powder" are used interchangeably herein. Furthermore, the terms "ePTFE membrane" and "membrane" are used interchangeably herein. Additionally, in this application, the term "ePTFE membrane" is intended to include single-layer or multi-layer ePTFE membranes. It should be understood that the machine orientation and longitudinal direction are the same and are used interchangeably herein. Furthermore, the terms "microporous ePTFE membrane" and "ePTFE membrane" are used interchangeably herein.

[0086] In one aspect, the present invention relates to a thin, self-supporting, biaxially oriented polytetrafluoroethylene (ePTFE) membrane having a high crystallinity index, high intrinsic strength, low areal density (i.e., light weight), and high optical transparency. Specifically, the ePTFE membrane may have a crystallinity index 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 also have a tensile strength of less than about 100 mg / m³. 2 It has a high areal density and a total light transmittance of at least 98%. Furthermore, ePTFE membranes are transparent or invisible to the naked eye. Additionally, ePTFE membranes are stackable and can be used to control permeability, pore size, and / or overall mechanical properties. ePTFE membranes can be used to form composites, laminates, fibers, sheets, tubes, or other three-dimensional objects that may or may not be cut or otherwise diced or segmented into multiple smaller parts. Furthermore, biaxially oriented ePTFE membranes can be used in filtration applications. On the other hand, biaxially oriented ePTFE membranes can be further uniaxially expanded, which aligns the fibrils in one direction (hereinafter referred to as uniaxially oriented ePTFE membranes). Such ePTFE membranes can have a toughness greater than about 5 gf / denier (gf / d) and a volume denier less than about 750 g / 9000 m (g / 9000 m).

[0087] For polytetrafluoroethylene (PTFE) polymers, particle size, shape, and distribution are important for obtaining the desired porous structure. These particle characteristics affect the packing density and bonding density, thus influencing the porous structure that can be produced from the particles. PTFE resin is supplied in granular form, such as as fine powder. PTFE fine powder is formed from primary particles.

[0088] In the formation of the ePTFE membrane, fine PTFE powder is first mixed with a lubricant (such as light mineral oil). A specific example of a suitable lubricant is an isoparaffin, such as ISOPAR. TM K (ExxonMobil Chemical, Spring, TX). Other suitable lubricants include aliphatic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, etc., selected based on flammability, evaporation rate, and economic considerations. It should be understood that the term "lubricant" as used herein describes a processing aid that includes incompressible fluids (or is composed of incompressible fluids), and is not a solvent for the polymer under processing conditions. Fluid-polymer surface interactions allow for the production of homogeneous mixtures. It should also be noted that there are no particular limitations on the choice of lubricant; the selection is primarily based on safety and convenience considerations. Lubricant can be added to the PTFE powder in amounts from approximately 242 mL / kg to approximately 340 mL / kg.

[0089] In at least one embodiment, fine PTFE powder and a lubricant are mixed to distribute the lubricant and PTFE powder uniformly or substantially uniformly. It should be understood that 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., a pellet). The pellets are then plunged through an extruder die (e.g., commonly referred to as paste extrusion or paste processing when a lubricant is present) to produce a cohesive, flexible PTFE strip. As used herein, the term "cohesive" is intended to describe a strip that is sufficiently robust for further processing. Plunger extrusion occurs at temperatures below the melting temperature of the PTFE polymer (e.g., below 327°C). The resulting strip has an indefinite length and a thickness 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 strip is referred to hereinafter simply as "strip material".

[0090] In the subsequent steps, lubricant is removed from the strip. (At ISOPAR) TM When K is a lubricant, the strip can be heated to approximately 200°C. In other embodiments, the lubricant can be removed by washing the strip in hexane or other suitable solvent. If the lubricant is sufficiently volatile, it can be removed without a washing step, or it can be removed by heating and / or vacuum. However, it should be understood that any conventional drying method can be used.

[0091] The strip then expands simultaneously in both the longitudinal and transverse directions (i.e., biaxial expansion). As used herein, the terms "biaxially expanded," "biaxially expanded," and "biaxially oriented" are intended to describe polymers, films, preforms, or articles that expand in at least two orthogonal directions such that the fibrils are substantially in-plane oriented. In one embodiment, the strip is subsequently expanded only in the machine direction (i.e., uniaxial expansion). As used herein, the terms "uniaxial," "uniaxially oriented," or "uniaxial expansion" are intended to describe polymers, films, preforms, or articles that expand in only one direction (e.g., the machine direction (MD) or the transverse direction (TD)). Expansion can be carried out with or without heating at strain rates up to about 10,000% / s, up to about 5,000% / s, up to about 2,500% / s, up to about 1,000% / s, up to about 750% / s, up to about 500% / s, up to about 250% / s, up to about 150% / s, up to about 100% / s, up to about 75% / s, up to about 50% / s, up to about 40% / s, up to about 35% / s, up to about 30% / s, up to about 20% / s, up to about 10% / s, or up to about 5% / s. Furthermore, the strip can range from approximately 1% / second to approximately 10,000% / second, from approximately 1% / second to approximately 5,000% / second, from approximately 1% / second to 2,500% / second, from approximately 1% / second to approximately 1,000% / second, from approximately 1% / second to approximately 750% / second, from approximately 1% / second to approximately 500% / second, from approximately 1% / second to approximately 250% / second, from approximately 1% / second to approximately 150% / second, and from approximately 1% / second to approximately Expansion is carried out at 100% / second, from approximately 1% / second to approximately 75% / second, from approximately 1% / second to approximately 50% / second, from approximately 1% / second to approximately 40% / second, from approximately 1% / second to approximately 35% / second, from approximately 1% / second to approximately 30% / second, from approximately 1% / second to approximately 20% / second, from approximately 1% / second to approximately 10% / second, or from approximately 1% / second to approximately 5% / second (with or without heating). It should be understood that an increase in inherent strength occurs simultaneously with expansion. The increase in the inherent strength of the PTFE polymer depends on the strength of the strip before expansion, the quality of the PTFE resin (e.g., particle size, molecular weight, particle size and / or molecular weight distribution, crystallinity, polymer composition, etc.), the temperature at which expansion is carried out, the expansion rate, and / or the total amount of expansion.

[0092] The tape is biaxially expanded, and in some embodiments, additionally uniaxially expanded to form an ePTFE membrane. The tape can be expanded 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" is intended to define articles having pores invisible to the naked eye, such as membranes. It has been found that ePTFE membranes produced in this manner, by efficiently and completely converting PTFE primary particles (i.e., PTFE fine powder) into fibrils, exhibit material properties exceeding those of conventional membranes. Advantageously, the ePTFE membranes discussed herein retain properties of conventional ePTFE membranes, such as, but not limited to, chemical inertness, thermal stability, low surface energy, low coefficient of friction, biocompatibility, and a wide operating temperature range. The ePTFE membrane can optionally be heat-treated at temperatures up to about 390°C. Uniaxially stretched ePTFE membranes produce ePTFE membranes with uniaxially oriented fibrils, a high crystallinity index, and high matrix tensile strength in the stretching direction (i.e., the machine direction (MD) or transverse direction (TD)). The following describes an ePTFE membrane that expands in the machine direction, but it should be understood that expansion in the transverse direction is also considered to be within the scope of the invention.

[0093] Biaxially oriented ePTFE films are very thin, and the total film thickness can be 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 indicate a range of + / - 10% of the described number or amount. Biaxially oriented ePTFE films can be formed to have a total film 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 nanometer to about 10 nanometers.

[0094] In at least one embodiment, the thickness of each layer of the biaxially oriented ePTFE film is less than about 100 nm, less than about 90 nm, less than about 80 nm, less than about 70 nm, less than about 60 nm, less than about 50 nm, or less than about 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 of each layer of the ePTFE film 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 nm, 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 traditional ePTFE membranes, biaxially oriented ePTFE membranes are extremely thin and invisible to the naked eye.

[0095] The "invisibility" of biaxially oriented ePTFE membranes is also at least partly attributed to the fibrillary microstructure of the ePTFE membrane. Typically, the fibrils are substantially cylindrical in shape. As used herein, the term "substantially cylindrical" is intended to indicate that the aspect ratio of the fibrils in the cross-section of a biaxially oriented ePTFE membrane is from about 1:1 to about 10:1. Furthermore, the fibrils in biaxially oriented ePTFE membranes are very fine and have a median fibril width of no more than about 80 nm. In some embodiments, the median fibril width is less than about 70 nm, less than about 60 nm, less than about 50 nm, less than about 40 nm, less than about 30 nm, less than about 20 nm, or less than about 10 nm. In some embodiments, the median fibril width is from about 10 nm to about 80 nm, from about 10 nm to about 70 nm, from about 10 nm to about 60 nm, from about 10 nm to about 50 nm, from about 10 nm to about 40 nm, from about 10 nm to about 30 nm, or from about 10 nm to about 20 nm. In some embodiments, the median fibril width is 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 "crossing point". In some embodiments, the thickness of the biaxially oriented ePTFE membrane can be the thickness of the crossing point of two fibrils.

[0096] Furthermore, biaxially oriented ePTFE membranes are very lightweight, with an areal density of less than approximately 100 mg / m³ per layer. 2 (0.1g / m 2 (less than approximately 90 mg / m³) 2 (0.09g / m 2 Less than approximately 80 mg / m 2 (0.08g / m 2 (less than approximately 70 mg / m³) 2 (0.07g / m 2 (), less than approximately 60 mg / m³ 2 (0.06g / m 2 (), less than approximately 50 mg / m 2 (0.05g / m 2 Less than approximately 40 mg / m³ 2 (0.04g / m 2 (less than approximately 30 mg / m³) 2 (0.03g / m 2 (less than approximately) 2 0mg / m 2 (0.02g / m 2 (less than approximately 15 mg / m³) 2 (0.015g / m 2 (less than approximately 10 mg / m³) 2 (0.01g / m 2 (less than approximately 5 mg / m³) 2 (0.005g / m 2 (less than approximately 4 mg / m³) 2 (0.004g / m 2 (less than approximately 3 mg / m³) 2 (0.003g / m 2 (less than approximately 2 mg / m³) 2 (0.002g / m 2 <1.0 mg / m 2 (0.001g / m 2 Less than approximately 0.50 mg / m³ 2 (0.0005g / m 2 Less than approximately 0.40 mg / m³ 2 (0.0004g / m 2 Less than approximately 0.30 mg / m³ 2 (0.0003g / m 2 (less than approximately 0.20 mg / m³) 2 (0.0002g / m 2 Less than approximately 0.10 mg / m³ 2 (0.0001g / m 2 (less than approximately 0.05 mg / m³) 2 (0.00005g / m 2 or less than approximately 0.003 mg / m³ 2 (0.000003 g / m 2 In some embodiments, the areal density of each layer is approximately 0.003 mg / m³. 2 (0.000003g / m 2 (approximately 100 mg / m²) 2 (0.1g / m 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 (approximately 90 mg / m³) 2 (0.09g / m 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 Up to approximately 80 mg / m 2 (0.08g / m 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 Up to approximately 70 mg / m 2 (0.07g / m 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 Up to approximately 60 mg / m 2 (0.06g / m 2 From approximately 0.003 mg / m³ 2 (0.000003g / m 2 Up to approximately 50 mg / m 2 (0.05g / m 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 Up to approximately 40 mg / m 2 (0.04g / m 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 Up to approximately 30 mg / m 2 (0.03g / m 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 Up to approximately 20 mg / m 2 (0.02g / m 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 Up to approximately 10 mg / m 2 (0.01g / m 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 Up to approximately 1.0 mg / m 2 (0.001g / m 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 Up to approximately 0.5 mg / m 2 (0.0005g / m 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 Up to approximately 0.4 mg / m 2 (0.0004g / m 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 Up to approximately 0.3 mg / m 2 (0.0003g / m 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 Up to approximately 0.2 mg / m 2 (0.0002g / m 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 (approximately 0.1 mg / m³) 2 (0.0001g / m 2 or approximately 0.003 mg / m³ 2 (0.000003g / m 2 (approximately 0.05 mg / m³) 2 (0.00005g / m 2 In some implementations, the areal density of each layer is approximately 5 mg / m³. 2 (0.005g / m 2 (approximately 100 mg / m²) 2 (0.1g / m 2 ), approximately 20 mg / m 2 (0.02g / m 2 (approximately 90 mg / m³) 2 (0.09g / m 2 ), or approximately 30 mg / m 2 (0.03g / m 2 (approximately 80 mg / m²) 2 (0.08g / m 2 ).

[0097] Furthermore, the biaxially oriented ePTFE film has an area ratio of about 2:000:1 to about 300,000,000:1. In some embodiments, the area ratio of the biaxially oriented ePTFE film 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 300,000,000,000:1, about 80,000:1 to about 300,000,000:1, about 100,000:1, or about 100,000:1. From about 1,000:1 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 from about 2,500,000:1 to about 300,000,000:1.

[0098] In addition, the total areal density of biaxially oriented ePTFE films can be less than about 100 g / m³. 2 Less than approximately 10g / m 2 Less than approximately 5g / m 2 Less than approximately 1g / m 2 Less than approximately 0.5 g / m 2 Less than approximately 0.1 g / m 2 Less than approximately 50 mg / m³ 2 (0.05g / m 2 (less than approximately 10 mg / m³) 2 (0.01g / m 2 (less than approximately 5.0 mg / m³) 2 (0.005g / m 2 Less than approximately 4.0 mg / m³ 2 (0.004g / m 2 (less than approximately 3.0 mg / m³) 2 (0.003g / m 2 (less than approximately 2.0 mg / m³) 2 (0.002g / m 2 (less than approximately 1.0 mg / m³) 2 (0.001g / m 2 Less than approximately 0.50 mg / m³ 2 (0.0005g / m 2 Less than approximately 0.40 mg / m³ 2 (0.0004g / m 2 Less than approximately 0.30 mg / m³ 2 (0.0003g / m 2 (less than approximately 0.20 mg / m³) 2 (0.0002g / m 2 Less than approximately 0.10 mg / m³ 2 (0.0001g / m 2 (less than approximately 0.07 mg / m³) 2 (0.00007g / m 2 (less than approximately 0.05 mg / m³) 2 (0.00005g / m 2 (less than approximately 0.03 mg / m³) 2 (0.00003g / m 2 (less than approximately 0.007 mg / m³) 2 (0.000007g / m 2 or less than approximately 0.003 mg / m³ 2 (0.000003g / m 2 In some embodiments, the total areal density of the biaxially oriented ePTFE film is approximately 0.003 mg / m³. 2 (0.000003g / m 2 (approximately 100g / m) 2 Approximately 0.003 mg / m 2 (0.000003g / m 2 (approximately 10 g / m) 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 Up to approximately 1.0 g / m 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 Up to approximately 0.5 g / m 2 From approximately 0.003 mg / m 2 (0.00000m 2 (approximately 0.1 g / m) 2 Approximately 0.003 mg / m 2 (0.000003g / m 2 (approximately 50 mg / m²) 2 (0.05g / m 2 ), approximately 0.003 mg / m 2 (0.000003g / m 2 (approximately 10 mg / m²) 2 (0.01g / m 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 Up to approximately 5 mg / m 2 (0.005g / m 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 Up to approximately 4.0 mg / m 2 (0.004g / m 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 Up to approximately 3.0 mg / m 2 (0.003g / m 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 Up to approximately 2.0 mg / m 2 (0.002g / m 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 Up to approximately 1.0 mg / m 2 (0.001g / m 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 Up to approximately 0.50 mg / m 2 (0.0005g / m 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 Up to approximately 0.40 mg / m 2 (0.0004g / m 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 Up to approximately 0.30 mg / m 2 (0.0003g / m 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 Up to approximately 0.20 mg / m³ 2 (0.0002g / m 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 Up to approximately 0.10 mg / m 2 (0.0001g / m 2 From approximately 0.003 mg / m 2 (0.000003g / m 2 Up to approximately 0.07 mg / m 2 (0.00007g / m 2 ), approximately 0.003 mg / m 2 (0.000003g / m 2 (approximately 0.05 mg / m³) 2 (0.00005g / m 2 or approximately 0.10 mg / m 2 (0.010g / m 2 (approximately 10 g / m) 2 .

[0099] Uniaxially oriented ePTFE membranes are also very lightweight, with an areal density of less than approximately 500 mg / m³ per layer. 2 (0.5g / m 2 Less than approximately 400 mg / m 2 (0.4g / m 2 Less than approximately 300 mg / m 2 (0.3g / m 2 Less than approximately 200 mg / m 2 (0.2g / m 2 Less than approximately 100 mg / m 2 (0.1g / m 2 (less than approximately 70 mg / m³) 2 (0.07g / m 2 (less than approximately 50 mg / m³) 2 (0.05g / m 2 (less than approximately 30 mg / m³) 2 (0.03g / m 2 (less than approximately 25 mg / m³) 2 (0.025g / m 2 (less than approximately 20 mg / m³) 2 (0.02g / m 2 (less than approximately 15 mg / m³) 2 (0.015g / m 2 (less than approximately 10 mg / m³) 2 (0.01g / m 2 (less than approximately 5 mg / m³) 2 (0.005g / m 2 (less than approximately 4 mg / m³) 2 (0.004g / m 2 (less than approximately 3 mg / m³) 2 (0.003g / m 2 (less than approximately 2 mg / m³) 2 (0.002g / m 2 <1.0 mg / m 2 (0.001g / m 2 Less than approximately 0.50 mg / m³ 2 (0.0005g / m 2 Less than approximately 0.40 mg / m³ 2 (0.0004g / m 2 Less than approximately 0.30 mg / m³ 2 (0.0003g / m 2 (less than approximately 0.20 mg / m³) 2 (0.0002g / m 2 ), or less than about 0.10 mg / m³ 2 (0.0001g / m 2 In some embodiments, the areal density is about 0.10 mg / m³. 2 (0.0001mg / m 2 (approximately 500 mg / m²) 2 (0.5g / m 2 (approximately 0.10 mg / m²) 2 (0.0001mg / m 2 (approximately 400 mg / m²) 2 (0.4g / m 2 (approximately 0.10 mg / m²) 2 (0.0001mg / m 2 Up to approximately 300 mg / m 2 (0.3g / m 2 (approximately 0.10 mg / m²) 2 (0.0001mg / m 2 Up to approximately 200 mg / m 2 (0.2g / m 2 (approximately 0.10 mg / m²) 2 (0.0001mg / m 2 Up to approximately 100 mg / m 2 (0.1g / m 2 (approximately 0.10 mg / m²) 2 (0.0001mg / m 2 Up to approximately 70 mg / m 2 (0.07g / m 2 (approximately 0.10 mg / m) 2 (0.0001mg / m 2 Up to approximately 50 mg / m 2 (0.06g / m 2 (approximately 0.10 mg / m) 2 (0.0001mg / m 2 Up to approximately 30 mg / m 2 (0.03g / m 2 (approximately 0.10 mg / m) 2 (0.0001mg / m 2 Up to approximately 20 mg / m 2 (0.02g / m 2 (approximately 0.10 mg / m²) 2 (0.0001mg / m 2 Up to approximately 15 mg / m 2 (0.015g / m 2 (approximately 0.10 mg / m²) 2 (0.0001mg / m 2 Up to approximately 10 mg / m 2 (0.01g / m 2 (approximately 0.10 mg / m) 2 (0.0001mg / m 2 Up to approximately 5 mg / m 2 (0.005g / m 2 (approximately 0.10 mg / m) 2 (0.0001mg / m 2 Up to approximately 0.40 mg / m³ 2 (0..0004g / m 2 (approximately 0.10 mg / m) 2 (0.0001mg / m 2 Up to approximately 0.30 mg / m 2 (0..0003g / m 2 (approximately 0.10 mg / m) 2 (0.0001mg / m 2 Up to approximately 0.20 mg / m³ 2 (0..0002g / m 2 ), ).

[0100] Despite being thin and lightweight, biaxially expanded ePTFE membranes possess high inherent strength. The ePTFE membranes have a matrix tensile strength (MTS) of at least about 600 MPa, 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 biaxially oriented ePTFE membrane has a matrix tensile strength (MTS) of about 600 MPa to about 1000 MPa, about 650 MPa to about 1000 MPa, about 700 MPa to about 1000 MPa, about 750 MPa to about 1000 MPa, about 800 MPa to about 1000 MPa, about 850 MPa to about 1000 MPa, or about 900 MPa to about 1000 MPa in both the longitudinal and transverse directions.

[0101] Furthermore, ePTFE membranes that undergo additional uniaxial expansion exhibit higher inherent strength. 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 uniaxially oriented ePTFE membrane has a matrix tensile strength of about 1000 MPa to about 1400 MPa in the machine direction, about 1100 MPa to about 1400 MPa in the machine direction, about 1200 MPa to about 1400 MPa in the machine direction, about 1200 MPa to about 1300 MPa in the machine direction, or about 1300 MPa to about 1400 MPa in the transverse direction. It should be understood that although the matrix tensile strength is given herein with respect to the machine direction, it also applies to ePTFE membranes expanded in the transverse direction.

[0102] Furthermore, 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 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 111 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 at ambient temperature (i.e., about 20°C). The uniaxially oriented ePTFE membrane also has a volume denier of less than about 750 g / 9000 m. In some embodiments, the uniaxially oriented ePTFE membrane has a density of about 0.5 g / 9000 m to about 750 g / 9000 m, about 0.5 g / 9000 m to about 650 g / 9000 m, about 0.5 g / 9000 m to about 500 g / 9000 m, about 100 g / 9000 m to about 450 g / 9000 m, about 0.5 g / 9000 m to about 400 g / 9000 m, about 0.5 g / 9000 m to about 350 g / 9000 m, about 0.5 g / 9000 m to about 250 g / 9000 m, and about 0.5 g / 9000 m to about 200 g / 9000 m. Approximately 0.5g / 9000m to approximately 150g / 9000m, approximately 0.5g / 9000m to approximately 100g / 9000m, approximately 0.5g / 9000m to approximately 50g / 9000m, approximately 0.5g / 9000m to approximately 25g / 9000m, approximately 0.5g / 9000m to approximately 15g / 9000m, approximately 0.5g / 9000m to approximately 10g / 9000m, approximately 0.5g / 9000m to approximately 5g / 9000m, approximately 0.5g / 9000m to approximately 3g / 9000m, or approximately 0.5g / 9000m to approximately 1g / 9000m in volumetric denier.

[0103] Furthermore, the uniaxially oriented ePTFE membrane has a toughness of at least about 5 gf / d. In some embodiments, the uniaxially oriented ePTFE membrane has a toughness 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. Additionally, the uniaxially oriented ePTFE membrane has a strength greater than or equal to 0.985. <p2>orientation.

[0104] Furthermore, the biaxially oriented ePTFE membrane exhibits very low 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 5,000 Pa·s / m, less than about 2,000 Pa·s / m, less than about 1,500 Pa·s / m, less than about 1,000 Pa·s / m, less than about 750 Pa·s / m, less than about 500 Pa·s / m, less than about 250 Pa·s / m, or less than about 150 Pa·s / m / 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 combination of low air resistance and the high surface area of ​​the ePTFE membrane provides a high-performance filtration device.

[0105] Biaxially oriented ePTFE films are also highly transparent, with a total transmittance (measured from 380 nm to 780 nm) greater than or equal to about 90%, greater than or equal to about 95%, greater than or equal to about 98%, and greater than or equal to about 99%. In exemplary embodiments, biaxially oriented ePTFE films may have a total transmittance of about 90% to about 99%, about 95% to about 99%, or about 98% to about 99%. In some embodiments, the ePTFE film has a total transmittance close to 100%.

[0106] The fibrils (biaxially oriented and uniaxially oriented) of the ePTFE membrane can optionally be coated with at least one coating composition (e.g., but not limited to polymers or bio-coatings) to make the ePTFE porous or non-porous. The coating composition can be applied to the ePTFE membrane by any conventional coating method such as solvent coating, spraying, spin coating, vapor deposition, atomic layer deposition (ALD), or dip coating. Alternatively, the coating can be applied to the ePTFE membrane by applying thermocompression between sheets of components (e.g., but not limited to fluorinated ethylene propylene (FEP), polyfluoroacrylate (PFA), and silicone).

[0107] In some embodiments, the coating composition occupies or fills at least a portion of the space through the thickness of the biaxially or uniaxially oriented ePTFE membrane. Suitable polymers and / or bio-coatings that can be coated and / or absorbed onto or into the ePTFE membrane include, but are not limited to, polyesters; polystyrene; polyamides; polyphthalamides; polyamide-imides; polycarbonates; polyethersulfones; polysulfones; polyphenylene sulfides; liquid crystal polymers; polyetherketones; polyetheretherketones; polysiloxanes; epoxy resins; polyurethanes; polyimides; polyetherimides; polyacrylates; poly(p-xylene); tetrafluoroethylene (TFE); VDF (vinylidene fluoride); and Terpolymers of HFP (hexafluoropropylene); copolymers of tetrafluoroethylene (TFE) and perfluoroalkyl vinyl ethers (PAVE); copolymers of tetrafluoroethylene and perfluoro-2,2-dimethyl-1,3-dioxolane; perfluoroalkyl vinyl ethers; perfluoroalkyl ethers; polyvinylidene fluoride (PVDF); ethylene tetrafluoroethylene (ETFE); polyvinyl chloride trifluoroethylene (PCTFE); fluorinated ethylene propylene (FEP); perfluoroalkoxyalkylene (PFA); polyvinyl alcohol (PVA). Heparin coating (available from WL Gore and Tongren Co., Ltd.), antimicrobial agents, antibodies, pharmaceuticals, biological entities, angiogenesis stimulants, and any combination thereof. The amount of coating applied will depend on the desired application.

[0108] Biaxially or uniaxially oriented ePTFE membranes are self-supporting, and in some embodiments, ePTFE membranes are used to reinforce polymer membranes, such as porous polymers, non-porous polymers, fluoropolymers, polyolefins, films, tapes, and other membranes. "Self-supporting" means that ePTFE membranes do not require a backing or support layer. However, because ePTFE membranes are very thin, their edges are typically limited in macroscopic length. In other words, the ePTFE membrane is confined to its perimeter (e.g., a "frame") to maintain its integrity. The inherent strength of the membrane binds across the distance and holds itself together, without a backing or support layer behind or beneath the membrane.

[0109] Biaxially oriented and uniaxially oriented ePTFE films can form a single-layer ePTFE film. In other embodiments, the biaxially and uniaxially oriented ePTFE films in the ePTFE film can have tens, hundreds, or thousands of ePTFE film layers. In some embodiments, there can be 2 to 4 layers. In other embodiments, there can be 2 to 16 layers in the ePTFE film. 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, 2 to 1,000,000 layers (or more) in the ePTFE film. While not wishing to be bound by theory, it is believed that the only limiting factor for the number of ePTFE layers present in the ePTFE film is the time spent stacking and expanding the layers. Typically, the ePTFE membrane stack "grows" four times each time the ePTFE membrane undergoes biaxial expansion. It should be understood that adhesives or other bonding agents are not typically used to connect the individual ePTFE membranes in the stack, although the inclusion of adhesives or other bonding materials is not excluded from the scope of use herein and is considered to be within the scope of the invention.

[0110] In another embodiment, the ePTFE membrane (biaxially oriented 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, non-porous polymers, fluoropolymers, porous polyolefins, or non-porous polyolefins). In other words, the ePTFE membrane can be designed to include different polymer layers and / or non-polymer layers within the ePTFE membrane. Furthermore, one ePTFE membrane layer may differ from another ePTFE layer in terms of expansion and / or strain rate, and / or the total work / total processing it has undergone. By varying the membrane type, expansion, and mechanical properties of any additional layers within the ePTFE membrane, ePTFE membranes can be formed to meet specific bulk phase characteristics while maintaining transport, filtration, or separation requirements.

[0111] Permeability, pore size, and overall mechanical properties can be controlled by the formation of ePTFE membranes (biaxial and uniaxial orientations) and / or optional additional spacers within the ePTFE membrane. As used herein, the term "permeability" refers to the ability of a fluid (i.e., liquid or gas) to pass through the pores of a membrane or filter material when subjected to a pressure differential thereon. In one example, ePTFE membranes allow for a range of pore sizes, such as pores with diameters less than about 6 micrometers. As used herein, the term "pore size" refers to the size of the pores in an ePTFE membrane. Pore sizes can range from about 2 nanometers to about 6 micrometers. In addition, the specific surface area (SSA) of ePTFE is about 35 m² / g to about 120 m² / g, about 45 m² / g to about 120 m² / g, about 55 m² / g to about 120 m² / g, about 65 m² / g to about 120 m² / g, about 75 m² / g to about 120 m² / g, about 80 m² / g to about 120 m² / g, about 90 m² / g to about 120 m² / g, about 100 m² / g to about 120 m² / g, or about 110 m² / g to about 120 m² / g, measured by area-weighted fibrillary width (AWFW).

[0112] In some implementations, biaxially oriented ePTFE membranes can be used in air filtration applications. In such applications, the ePTFE membrane exhibits a surface velocity of at least 65 kPa at 5.33 cm⁻¹ when using challenging particles with a diameter of 0.1 micrometers. -1 The quality factor is [not specified]. It should be understood that the strength-to-weight ratio (intrinsic strength) of ePTFE membranes is higher than that of conventional ePTFE membranes. A higher quality factor is associated with better filtration performance. In some embodiments, biaxially oriented ePTFE membranes may have a quality factor of approximately 65 kPa. -1 ) to approximately 180 (kPa) -1 ), about 70(kPa -1 ) to approximately 180 (kPa) -1 ), about 80(kPa -1 ) about 180(kPa -1 ), about 90(kPa -1 ) to approximately 180 (kPa) -1 ), about 100(kPa -1 ) to approximately 180 (kPa) -1 From approximately 110 kPa -1 ) to approximately 180 (kPa) -1 ), about 120(kPa -1 ) to approximately 180 (kPa) -1 ), about 130(kPa -1 ) to approximately 180 (kPa) -1 ), about 140(kPa -1 ) to approximately 180 (kPa) -1 ), about 150(kPa -1 ) to approximately 180 (kPa) -1 ), about 160(kPa -1 ) to approximately 180 (kPa) -1 ) or approximately 170 (kPa) -1 ) to approximately 180 (kPa) -1 The quality factor of ).

[0113] Biaxially oriented ePTFE membranes can be used in applications where it is desirable to filter nanoparticles (e.g., from about 1 nm to about 200 nm) from a liquid medium, even if the liquid medium travels at high flow rates. Therefore, ePTFE membranes can be used as filter materials, and due to the properties of polytetrafluoroethylene, ePTFE membranes are chemically resistant, biocompatible, and have high matrix tensile strength (MTS). The filterable matrix can be selected from solutions, suspensions, colloids, biofluids, biofluid components, 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 percentage of nanoparticles retained (%) of the biaxially oriented ePTFE membrane is equal to or greater than the line defined by formula (1).

[0114] y>=9.70-10.76*ln(x) Formula (1)

[0115] in

[0116] y = % retention of nanoparticles; and

[0117] x = Filtrate permeability [g / cm³] 2 / s / MPa).

[0118] Test methods

[0119] Non-contact thickness testing

[0120] The non-contact thickness of the membrane was measured using a KEYENCE LS-7600 laser system (KEYENCE America).

[0121] Membrane density calculation

[0122] The samples were cut into 15.2cm × 15.2cm square slices. Each sample was weighed using a Mettler Toledo AT20 balance. The density of the sample was calculated using the thickness calculated by the KEYENCE laser, and then calculated using the following formula (2):

[0123] ρ=m / (w*|*t) Formula (2).

[0124] in:

[0125] ρ = density (g / cm³) 3 );

[0126] m = mass (g);

[0127] w = width (cm);

[0128] l = length (cm); and

[0129] t = thickness (cm).

[0130] Matrix tensile strength (MTS) (Method 1)

[0131] To determine the MTS of biaxial ePTFE membranes, sample ePTFE composite membranes were cut along both the longitudinal and transverse directions using an ASTM D412-Dogbone Die Type F (D412F). To determine the MTS of uniaxial membranes, sample ePTFE membranes were loaded longitudinally. A load cell equipped with a flat-faced grip and a "22 lb" (~100 N) was used. A 5567R (Illinois ToolWorks Inc., Norwood, MA) tensile testing machine was used to measure the tensile fracture load. The gauge length of the fixture was set to 8.26 cm, and the strain rate was 0.847 cm / s. After placing the sample in the fixture, the sample was retracted 1.27 cm to obtain a baseline, and then a tensile test was performed at the strain rate mentioned above. The peak force measurement was used for MTS calculation. The longitudinal and transverse MTS were calculated using the following formula (3):

[0132] MTS = (maximum load / cross-sectional area) × (resin density / film density) Formula (3).

[0133] Matrix tensile strength (MTS) (Method 2)

[0134] To determine the MTS of a uniaxial ePTFE membrane, a sample of ePTFE was loaded longitudinally using a rope and yarn clamp. A load cell equipped with a rope and yarn clamp and a "22 lb" (~100 N) was used. A 5567R (Illinois Tool Works Inc., Norwood, MA) tensile testing machine was used to measure the tensile fracture load. The gauge length of the fixture was set to 15.24 cm, and the strain rate was 0.254 cm / s. After placing the sample in the fixture, the sample was retracted 1.27 cm to obtain a baseline, and then a tensile test was performed at the strain rate described above. The peak force measurement was used for MTS calculation.

[0135] Scanning transmission electron microscopy (STEM)

[0136] Low-voltage STEM (scanning transmission electron microscopy) is a technique for visualizing thin samples by accelerating a focused electron beam through them and collecting the transmitted electrons with a suitable detector. Low voltage refers to the use of a beam acceleration voltage of less than 100 kV (<30 kV, as exemplified in this article). Image contrast varies depending on the composition or thickness of the film due to electron absorption.

[0137] A scanning electron microscope (STEM) with a transfer adapter (Hitachi, SU8000; Hitachi Ltd., Tokyo, Japan) was used and operated at an accelerating voltage not exceeding 30 kV. No prior or additional treatment (staining) was performed on the samples. Samples used for analyzing porous films were laid on a copper mesh with a carbon support layer (carbon type-B, 300 mesh, copper, product number 01813, Ted Pella, Inc.). Prepared on a 400-mesh, copper, center-marked grid, product number #1GC400, Ted Pera Corporation, Redding, CA.

[0138] X-ray diffraction pattern of biaxial sample

[0139] Two-dimensional (2-d) X-ray diffraction patterns were obtained using the X27C beamline of the National Synchrotron Light Source at Brookhaven National Laboratory (Upton, NY). The beamline provided a well-calibrated monochromatic X-ray beam with a wavelength of 0.1371 nm, a nominal flux of 10¹² photons / s, and a diameter of 0.39 mm. The detector was a Rayonix MAR-CCD 2-d imaging system (Rayonix LLC, Evanston, IL). The sample-detector distance of the system was set to 67.97 mm and calibrated using an Al₂O₃ powder standard. The sample was mounted between the beam and the detector, and transmission geometry scattering / diffraction X-ray images were collected between 480 and 540 seconds. Additionally, a background image was recorded immediately after each sample image for the absence of the sample within the same time period. The background image was then subtracted from the sample image to remove the effects of air scattering and obtain the desired diffraction pattern.

[0140] X-ray scattering method for uniaxial samples

[0141] Wide-angle X-ray scattering experiments were performed on a Xenocs Xeuss 2.0 SAXS / WAXS laboratory beam system (Xenocs SAS, Sassenage, France). The instrument used a GeniX3DCu ka source (0.154 nm wavelength) operating at 50 kV and 0.6 mA and a Dectris Pilatus 300K detector (Dectris Ltd., Baden-Daettwil, Switzerland). The beam was calibrated through two coaxial slits, each with an opening area of ​​0.5 mm x 0.5 mm. The sample-detector distance was 71.0 mm (calibrated using the lanthanum hexaboride standard). The Xeuss 2.0 system's "virtual detector" function was used to eliminate blind spots in the detector and expand its angular range. This was achieved by horizontally translating the detector and then averaging multiple scans. Here, four scans were performed with different horizontal detector offsets, each with an exposure time of 15 minutes.

[0142] The average of these four scans provides the scattering spectrum. Using formula (4) from I and Quantization orientation in azimuth scanning.

[0143]

[0144] when <p2>When it approaches 1, as determined by formula (5), a near-perfect orientation is achieved in the machine direction.

[0145]

[0146] Crystallinity Index

[0147] Crystallinity index is used The values ​​were obtained by fitting the intensity to the peak values ​​of the q-scan using statistical analysis software (SAS Research). The integration range was limited to q = 8.74–15.4 nm. -1 The linear background is defined as approximately q = 8.74 - 10 (nm). -1 The measured intensities (nm) are consistent with those for q = 14.1-15.4. -1 After subtracting the linear background, the two peaks are fitted using the Pearson VII function.

[0148] As defined in U.S. Patent Publication No. 2004 / 0173978 by Bowen et al., the crystallinity index is calculated by the area under the fitted 100 crystallization peak (A100) and the area under the fitted amorphous peak according to the following formula (6).

[0149] Crystallinity index (%) = {A 100 / (A 100 +A 无定形峰 Formula (6) for x 100.

[0150] Bubble

[0151] Bubble point was measured using a capillary orifice meter (CFP 1500AE model from Porous Materials, Inc., Ithaca, NY) according to the general teachings of ASTM F31 6-03. The sample film was placed in the sample chamber and wetted with SilWick silicone fluid (available from Porous Materials, Inc.) with a surface tension of 19.1 dynes / cm. The bottom clamp of the sample chamber consisted of a 40-micron porous metal disc insert (Mott Metallurgical, Fannington, Conn.) with the following dimensions (diameter 2.54 cm, thickness 3.175 mm). The top clamp of the sample chamber consisted of an opening with a diameter of 12.7 mm. Capwin software version 6.74.70 was used with the following parameters and settings:

[0152] Parameter settings

[0153] Maximum flow rate: 200,000 cc / m³

[0154] Bubble flow: 10-127 cc / m

[0155] F / PT 50

[0156] Minbppres 0.1 (psi)

[0157] Zero time (1 second)

[0158] V2incr 10(cts)

[0159] Preginc 1(cts)

[0160] Pulse delay 2 (seconds)

[0161] Maximum pressure 500 psi

[0162] Pulse width: 0.2 seconds

[0163] Mineqtime 30 (seconds)

[0164] Presslew 10 (cts)

[0165] Flowslew 50 (cts)

[0166] Eqiter (0.1 sec) 3

[0167] Aveiter (0.1 sec) 20

[0168] Maxpdif 0.1 (psi)

[0169] Maxfdif 50 (cc / m)

[0170] Start 1 (psi).

[0171] The bubble point value is the average of two measurements.

[0172] ATEQ airflow

[0173] ATEQ airflow testing measures the laminar volumetric flow rate of air passing through a membrane sample. Each membrane sample is tested at a flow channel of 2.99 cm⁻¹, sealing the entire flow channel. 2 The area is sandwiched between two plates. The (ATEQ Corp., Livonia, MI) PremierD miniature flow meter is used to measure the gas flow rate (L / hr) through each membrane sample by challenging it with a pressure difference of 1.2 kPa (12 mbar) through the membrane.

[0174] airflow resistance

[0175] Airflow resistance was tested using a Textest FX 3300 permeability tester apparatus manufactured by Textest AG (Zurich, Switzerland). Frazier permeability readings are the airflow velocity per cubic feet per square foot per minute of sample area at a pressure drop of 12.7 mm water column. It should be noted that the pressure drop is reduced for characterizing lightweight, unsupported membranes. Permeability was measured by clamping the test sample in a circular flange clamp with a diameter of 7 cm (area 38.5 cm²). 2 The sample holder has a circular opening. The upstream side is connected to a flow meter that is connected to a source of dry compressed air.

[0176] Light transmittance measurement

[0177] Light transmittance measurements were performed using a spectrophotometer (Jasco V-670; JASCO Deutschland GmbH, Pfungstadt, Germany) with a dual-beam integrating sphere attachment (150 mm diameter, ILN-725). The spectrophotometer consisted of a deuterium lamp and a halogen tungsten lamp, a single Czerny-Turner monochromator (1200 lines / mm diffraction 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 mounted at the entrance of the integrating sphere in a perpendicular manner; the reference beam passed through an open end of the integrating sphere. The sample and reference beams were alternately incident on the PMT detector and converted into digital signals after synchronous rectification.

[0178] The monochromator bandwidth was set to 10 nm, the grating wavelength was scanned in the range of 250 nm to 800 nm, and the scan rate was 2000 nm / min. The light source was changed from a deuterium lamp to a 340 nm halogen tungsten lamp. The signal was recorded at 2 nm intervals. "Dark correction" spectra (blocking the sample beam) and "baseline correction" spectra (passing through the aperture end) were collected: these spectra were used to record the transmission spectrum expressed as a percentage of incident light.

[0179] Total transmittance was calculated by weighting the transmission spectra using a CIE standard illuminant and a CIE standard colorimeter (see ASTM D1003-13: Standard Test Method for Haze and Transmittance of Transparent Plastics). A D65 illuminant and a 1931 2-deg standard observer were used in the calculations described herein. Transmittance percentages in the UVA and UVB ranges were calculated by calculating the average transmittance percentages in the 315–400 nm and 280–315 nm wavelength ranges, respectively.

[0180] Average fibril width measurement:

[0181] The selected samples were imaged by STEM and manually characterized by 50 measurements of the fibril projection width (e.g., Figure 11 Uniform sampling is facilitated by highlighting 50 regions using a random number generator, and the operator then traces the outline of the nearest fibril – preferably a fragment of fibril that has not yet been characterized. Typically, the marked fibril shape is rectangular with an aspect ratio greater than 1. The nominal projected width of the fibril is calculated by dividing the area by the length of the object. This is considered more representative and informative than a single width measurement because it naturally forces the projected width measurement to be perpendicular to the principal axis of the rectangle. To confirm the method, a line orthogonal to the principal axis is drawn through the manually identified centroid of the region at the calculated width calculated according to formula (7).

[0182]

[0183] Dynamic Mechanical Analyzer (DMA) Matrix Storage Modulus and Loss Modulus

[0184] The matrix storage modulus and loss modulus were measured using a TA Instruments Q800 system (TA Instruments, Newcastle, DE) equipped with a tension sample clamp. The DMA was calibrated according to standard TA Instruments procedures. Sample dimensions were obtained using a KEYENCE LS7010 high-precision non-contact micrometer (Keyence Corp., Itasca, IL) with 0.1 mm wide graduations and a 10x microscope for thickness measurement. Sample mass was measured using a Mettler-Toledo A120 microbalance (Mettler-Toledo, LLC, Columbus, OH). The sample was then mounted 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 was applied at a true strain amplitude of 0.001 and a frequency of 1 Hz, with an additional constant load just sufficient to keep the sample under tension throughout the applied sinusoidal strain. The sample was equilibrated at -50°C for 10 minutes, and then the temperature was increased to 150°C at a rate of 2°C / min. The magnitude and phase angle of the resulting sinusoidal force acting on the sample were measured once per second throughout the heating process to calculate the storage modulus and loss modulus. The desired matrix modulus was obtained by multiplying the storage modulus and loss modulus by the ratio ρtrue / ρsample. ρtrue was assumed to be the modulus of crystalline poly(tetrafluoroethylene), 2.3 g / cm2. 3 ρ_sample is calculated based on the measured sample size and mass.

[0185] Air filtration performance measurement

[0186] Particulate filtration efficiency and membrane filtration efficiency were tested using dioctyl phthalate (DOP) aerosol in TSI. Model 8160 Automatic Filter Tester (TSI Incorporated, St. Paul, Minnesota) according to The procedure specified in the operation and service manual of the 8160 automatic testing instrument was followed. The sample testing area was 77.8 cm², and the surface velocity was 5.32 cm / s.

[0187] The quality factor Qf is determined using formula (8).

[0188] Q f =Ln(1 / P) / Δp Formula (8).

[0189] Penetration power P is the proportion of particles that penetrate or pass through the sample, and Δp is the pressure drop at an air velocity of 5.33 cm / s, expressed in kPa. A higher quality factor is associated with better filtration performance (see William C. Hinds). Aerosol technology: air Properties, behavior, and measurement of particles in the air , 2nd edition, John Wiley & Sons; Hoboken, NJ (1994)). Quality factors were compared using the same surface velocity and test aerosol particle size. Quality factors are expressed as the reciprocal of pressure (kPa⁻¹). Efficiency, E(%) = 100 * (1 - P).

[0190] Liquid permeability and retention were determined using the bead test.

[0191] The bead test measures the permeability and bead retention of the membrane sample. The membrane sample is fixed in a 25 mm filter holder. The membrane is first wetted with an isopropanol (IPA)-DI aqueous solution (70:30 v / v IPA:water). The solution is forced through the membrane using air pressure. 7 g of the solution is passed through the sample, followed by 10 g of a solution containing 1% (v / v) of the nonionic surfactant TRITON. TM X-100CAS9002-93-1; Sigma Aldrich, St. Louis, MO, prepared an aqueous solution in deionized water. Then, polystyrene latex beads (Fluoro-Max R25 red fluorescent polymer microspheres; Thermo Fisher Scientific, Waltham, MA) with a diameter of 0.025 μm were dispersed in 1 vol% TRITON. TM The X-100 solution was challenged in a deionized aqueous solution to expose the membrane to a sufficient number of beads, thereby covering the membrane surface area with a monolayer of beads. The concentration of beads in the challenge solution and filtrate was determined using an Agilent Technologies Cary Eclipse fluorescence spectrophotometer (Agilent Technologies, Santa Clara, CA).

[0192] Calculate the membrane permeability using formula (9):

[0193]

[0194] In formula (9), k is the membrane permeability, g is the mass of the filtrate sample, A is the physical area of ​​the membrane sample in the filter holder, t is the time required to collect the filtrate sample, and P is the pressure difference across the membrane. In formula (9), g / t is the mass flow rate through the membrane, and g / At is the mass flux through the membrane.

[0195] Calculate the percentage of beads retained by the membrane in the solution using formula (10):

[0196]

[0197] In formula (10), C 挑战 It challenges the concentration of beads in the solution, C 滤液 It is the concentration of beads in the filtrate.

[0198] Example

[0199] Unless otherwise stated, all technical terms used herein have the same meaning as understood by one of ordinary skill in the art to which this invention pertains. The invention is further defined by the following embodiments. It should be understood that these embodiments, while illustrating preferred embodiments of the invention, are given by way of illustration only. Through the foregoing discussion and these embodiments, those skilled in the art can determine the essential features of the invention, and various changes and modifications can be made to the invention to suit various uses and conditions without departing from the spirit and scope of the invention.

[0200] Example 1

[0201] The following examples disclose a method with extremely low areal density (e.g., areal density less than 10 mg / m³). 2 Preparation of a single-layer PTFE membrane.

[0202] Polytetrafluoroethylene (PTFE) fine powder (DuPont de Nemours; Wilmington, DE) and ISOPAR TM K-isoparaffin lubricant (ExxonMobil Chemical; Spring, TX) was mixed at a target ratio of 110 ml / lb (approximately 0.454 kg) fine powder (0.156 g lubricant / g total) (g lubricant / total mass of mixture). The lubricated powder was compressed into cylinders and plunger-extruded at 49°C to provide a strip. The strip was 16.2 cm wide and 0.762 mm thick. ISOPAR was removed by heating to approximately 200°C. TM K is used to form dried strip ("initial strip"). A 98 mm square is cut from the initial strip. The areal density of the initial strip (before expansion in the scaler) is determined to be 1130 g / m². 2 In this paper, all initial strip areal densities are expressed as 1150 + / - 100 g / m. 2 Table 1 provides a summary of the process parameters used in Example 1.

[0203] Round 1

[0204] Using a scaling device, a 98mm dry strip block was heated in an oven set to 300°C (setpoint) for 120 seconds, then simultaneously expanded (biaxial expansion) in both the longitudinal (machine direction (MD)) and transverse (TD) directions at a target ratio of approximately 4:1, while maintaining a temperature of approximately 300°C. The average engineering strain rate was set to a target of 36% / second. The scaling device was then opened at a constant speed for approximately 8 seconds. Under the constraint of the scaling device, the ePTFE membrane was cooled to room temperature (approximately 22°C).

[0205] Second round

[0206] The cooled ePTFE membrane block collected from the first round is further expanded, known as the "second round." Using the same expander, the selected membrane is heated in an oven set to 300°C for 120 seconds, and then expanded simultaneously in both the longitudinal and transverse directions at a target ratio of 10:1, while maintaining a temperature of approximately 300°C. The average engineered strain rate is target-set at 9% / second. The expander is expanded at a constant target speed for approximately 100 seconds. Under the constraint of the expander, the second round ePTFE membrane is cooled to room temperature (approximately 22°C).

[0207] Third round

[0208] The cooled ePTFE membrane block collected from the second round is further expanded, i.e., the "third round". Using the same expander, the selected membrane is heated again in an oven set to 300°C for 120 seconds, and then expanded simultaneously in both the longitudinal and transverse directions at a target ratio of 10:1, while maintaining a temperature of approximately 300°C. The constant acceleration setpoint is 1% / second. The expander is opened at the constant acceleration setpoint for approximately 230 seconds.

[0209] Under the constraint of the scaling device, the ePTFE membrane was cooled to room temperature (approximately 22°C). Table 1 provides a summary of the process parameters for Example 1.

[0210] The expanded ePTFE membrane, cooled for the third round, was removed from the scaling device and placed on a (152.4m x 152.4mm) adhesive-backed frame. The frame was used to guide the cutting process, and the ePTFE membrane was weighed, yielding an average areal density of 4.3 mg / m³. 2 The lightest sample weighed 2.4 mg / m³. 2 (Table 2). The area ratio is defined as the ratio of the area density before and after a series of expansion operations. The area ratio of the ePTFE membrane in the third round ranged from 122,690:1 to 459,273:1, depending on the process conditions (Table 2). Figure 1-3 For the same sample (2.40 mg / m³) at 3 different magnifications 2 (Sample E1G). No remaining primary particles were observed. Figure 4 For the second film block using the same strain path, the oven was set to 322℃ (sample E1H). STEM images of sample E1I are shown below. Figure 5 As shown in Table 1, the process parameters are summarized.

[0211]

[0212] Table 2

[0213] Single-layer sample data after three rounds

[0214]

[0215] Example 2

[0216] The following examples disclose the preparation of ePTFE films with extremely low areal density per layer, stacked up to 256 layers, with an area ratio of approximately 34 million to 1.

[0217] PTFE fine powder (DuPont de Nemours and ISOPAR) TM K-isoparaffin lubricant was mixed at a target ratio of 110 ml / lb (approximately 0.454 kg) fine powder (0.156 g lubricant / g total weight) (g lubricant / total mass of mixture). The lubricating powder was compressed into cylinders and plunger-extruded at 49°C to provide a strip. The strip was 16.2 cm wide and 0.762 mm thick. ISOPAR was removed by heating the strip to approximately 200°C. TM K. Cut a 98 mm square from the dried strip. Table 3 provides a summary of the process parameters used in Example 2.

[0218] Round 1

[0219] Using a scaling apparatus, four rectangular strips were heated in an oven set to 300°C for 240 seconds, then expanded simultaneously in both the longitudinal and transverse directions at a target ratio of approximately 7:1, while maintaining the temperature at approximately 300°C. The target average engineering strain rate was set at 36% / second. The scaling apparatus was opened at a constant target speed for approximately 16.7 seconds. Under the constraint of the scaling apparatus, the ePTFE membrane was cooled to room temperature (approximately 22°C). Four sheets (4 layers each) were harvested from the cooled ePTFE membrane and used for further expansion, i.e., the second round. The first round process was repeated once more to produce another 16 layers. The two 16-layer samples were combined to create a 32-layer sample.

[0220] Second round

[0221] Using the same scaling apparatus, two stacks of 16 layers (32 layers in total) were heated in an oven set to 300°C for 240 seconds, then expanded simultaneously in both the longitudinal and transverse directions at a target ratio of 7:1, while maintaining the temperature at approximately 300°C. The target average engineering strain rate was set at 5% / second. The scaling apparatus was then expanded at a constant target speed for approximately 120 seconds. Under the constraint of the scaling apparatus, the ePTFE membrane was cooled to room temperature (approximately 22°C).

[0222] Third round

[0223] Four samples (32 layers each) were harvested from the cooled ePTFE membrane and stacked (128 layers total) for further expansion, i.e., the third round. Using the same scaling apparatus, the membrane was reheated in an oven set to 300°C for 240 seconds, and then expanded simultaneously in both the longitudinal and transverse directions at a target ratio of 8:1, while maintaining a temperature of approximately 300°C. Simultaneous expansion was performed at a constant acceleration setpoint of 1% / s, with a target ratio of 8:1 in each direction. The scaling apparatus was opened for approximately 208 seconds in the third round. Under the constraint of the scaling apparatus, the ePTFE membrane was cooled to room temperature (approximately 22°C).

[0224] Fourth round

[0225] Samples (128 layers) were harvested from the cooled ePTFE membrane and stacked (128 layers total) for further expansion, i.e., the fourth round. Using the same scaling apparatus, the membrane was reheated in an oven set to 300°C for 120 seconds, and then expanded simultaneously in both the longitudinal and transverse directions at a target ratio of 3:1, while maintaining the temperature at approximately 300°C. Simultaneous expansion was performed at a constant acceleration setpoint of 1% / s, with a target ratio of 3:1 in each direction. The scaling apparatus was opened for approximately 110 seconds in the fourth round. Under the constraint of the scaling apparatus, the expanded ePTFE membrane was cooled to room temperature (approximately 22°C).

[0226] The ePTFE membrane was collected from the machine onto a (152.4 mm x 152.4 mm) adhesive backing frame. Using the frame as a guide for cutting, the ePTFE membrane was weighed, and the areal density was calculated to be 0.00047 g / m³. 2 / layer, while the weight of the ePTFE membrane is 0.0605g / m 2 (Sample E2A; Table 4). The area ratio and areal density of other ePTFE membranes (for ePTFE membranes and laminated ePTFE membranes) are set and listed in Table 4.

[0227] Additionally, three more ePTFE membranes (E2B-D) of Example 2 were produced using the first three rounds described above, each consisting of 128 layers. Each ePTFE membrane was individually loaded for a fourth and final expansion. Using the same scaling device, the membranes were reheated in an oven set to 300°C for 120 seconds, and then expanded simultaneously in both the longitudinal and transverse directions at target ratios of 4:1 (E2B), 5:1 (E2C), or 6:1 (E2D), while maintaining a temperature of approximately 300°C. For Examples E2B-D, simultaneous expansion was performed at a constant acceleration setpoint of 1% / s. The scaling device was opened for approximately 139 (E2B), 161 (E2C), or 179 (E2D) seconds in the fourth round. At the end of each expansion (E2B-E2D), the expanded ePTFE membranes were cooled to room temperature (approximately 22°C) under the constraint of the scaling device. Collect the ePTFE membrane from the machine onto a (152.4mm x 152.4mm) adhesive backing frame. Use the frame to guide the cutting and weigh the ePTFE membrane. Table 4 includes the fourth round throughput settings, area ratio, areal density of the laminated ePTFE membrane, areal density of each layer, and translation time for the final round.

[0228] In addition, Example 2 produced three more ePTFE films (E2E-G), primarily for observing STEM images. Figure 6-8 ).

[0229] Example E2E was processed using the same steps as Example E2D, but with the following two differences. The dwell time before expansion in the third round was reduced from 240 (E2D) seconds to 120 (E2E) seconds, and the target ratio in the fourth round was increased from a two-way setpoint of 6:1 (E2D) to a two-way area ratio setpoint of 8:1 (E2E) in the final round. The scaler opened for approximately 208 seconds (E2E) in the fourth round. Under the constraint of the scaler, the expanded ePTFE membrane was cooled to room temperature (approximately 22°C). The ePTFE membrane was collected from the machine onto a (152.4 mm x 152.4 mm) adhesive backing frame.

[0230] Example E2F was processed using the same steps as Example E2E, but with the following two differences. The number of layers in the fourth expansion loading increased from 128 (E2E) to 256 (E2F), and the target ratio for the fourth round increased from 8:1 per direction (E2E) to 9:1 per direction (E2F). The expanded ePTFE membrane was cooled to room temperature (approximately 22°C) under the constraint of the scaling device. The ePTFE membrane was collected from the machine onto a (152.4 mm x 152.4 mm) adhesive backing frame.

[0231] Example E2G was processed using the same steps as Example E2E, but with the following two differences: The number of layers in the second expansion loading was reduced from 32 (E2E) to 16 (E2G), and a fourth round was not performed. The expanded ePTFE membrane was cooled to room temperature (approximately 22°C) under the constraint of a scaling device. The ePTFE membrane was collected from the machine onto a (152.4 mm x 152.4 mm) adhesive backing frame. Using the frame as a guide for cutting, the ePTFE membrane was weighed, and the areal density was calculated to be 0.009 g / m³. 2 / layer, while the weight of the ePTFE membrane is 1.175g / m³. 2 (Sample E2G; Table 4). The area ratio and areal density of these and other ePTFE membranes (for ePTFE membranes and laminated ePTFE membranes) were calculated and listed in Table 4.

[0232]

[0233] Table 4

[0234] Fourth round of ratio setpoints, area ratios, and areal density data for 128-layer samples

[0235]

[0236] Example 3

[0237] The following examples disclose the preparation of ePTFE films with extremely low areal density per layer, with up to 1024 ePTFE layers stacked, resulting in an area ratio of nearly 300 million to 1.

[0238] PTFE fine powder (DuPont de Nemours and ISOPAR) TM K-isoparaffin lubricant was mixed at a target ratio of 110 ml / lb (approximately 0.454 kg) fine powder (0.156 g lubricant / g total weight) (g lubricant / total mass of mixture). The lubricating powder was compressed into cylinders and plunger-extruded at 49°C to provide a strip. The strip was 16.2 cm wide and 0.762 mm thick. ISOPAR was removed by heating the strip to approximately 200°C. TM K. Cut a 98 mm square from the dried strip. Table 5 provides a summary of the process parameters used in Example 3.

[0239] Round 1

[0240] Using a scaling device, four rectangular strips were heated in an oven set to 322°C (setpoint) for 240 seconds, then expanded simultaneously in both the longitudinal and transverse directions at a target ratio of approximately 10:1, while maintaining the temperature at approximately 322°C. The target average engineered strain rate was set at 36% / second. The scaling device was then expanded at a constant target speed for approximately 25 seconds. Under the constraint of the scaling device, the ePTFE film was cooled to room temperature (approximately 22°C). The first round of the process was repeated once more to produce an additional 32 layers.

[0241] Second round

[0242] Using the same scaling device, two stacks of 32 layers (64 layers in total) were heated in an oven set to 322°C for 240 seconds, and then expanded simultaneously in both the longitudinal and transverse directions at a target ratio of 10:1, while maintaining the temperature at approximately 322°C. The target average engineering strain rate was set at 3.6% / second. The scaling device was then allowed to expand at a constant speed for approximately 250 seconds. Under the constraint of the scaling device, the expanded film was allowed to cool to room temperature (approximately 22°C).

[0243] Third round

[0244] Four samples (64 layers each) were harvested from the cooled ePTFE membrane and stacked (256 layers total) for further expansion, i.e., the third round. Using the same scaling device, the stacked ePTFE membrane layers were reheated in an oven set to 322°C for 240 seconds, and then expanded simultaneously in both the longitudinal and transverse directions at a target ratio of 8:1 (E3B) or 10:1 (E3A), while maintaining the temperature at approximately 322°C. Simultaneous expansion was performed at a constant target acceleration of 1% / s until the scaling device reached a target velocity of 3.5 mm / s, achieving 400% strain (λ in both directions). sp =5:1), and expansion is completed at a constant setpoint of 5% / s (3.5mm / s in this specific case, based on an initial length input of 70mm ("r / s" rate mode)). The expander opens for approximately 221 (E3B) or 261 (E3A) seconds in the third round. Under the constraint of the expander, the expanded film is allowed to cool to room temperature (approximately 22°C).

[0245] Fourth round

[0246] Samples (256 layers) were harvested from the cooled ePTFE membrane and stacked (total 1024 layers) for further expansion, i.e., the fourth round. Using the same expander, the membrane was reheated in an oven set to 322°C for 120 seconds, and then expanded simultaneously in both the longitudinal and transverse directions at a target ratio of 7:1, while maintaining the temperature at approximately 322°C. Simultaneous expansion was carried out at a constant target acceleration of 1% / s until the expander accelerated to a target velocity of 3.5 mm / s to achieve a strain of 400% (λ in both directions). sp =5:1), and completes the expansion at a constant speed setpoint of 5% / s (3.5mm / s in this specific case, based on an original length input of 70mm ("r / s" rate mode)). The scaler expands in the fourth round approximately 201 seconds to a (λ in both directions). sp =7:1). Under the constraint of the scaling device, the expanded film was cooled to room temperature (approximately 22°C).

[0247] Collect the ePTFE membrane from the machine onto a (152.4 mm x 152.4 mm) adhesive backing frame. Use the frame to guide the cutting, weigh the ePTFE membrane, and calculate its areal density to be between 0.005 and 0.016 mg / m³. 2 / layer, while the areal density (MPa) of ePTFE membrane ranges from 3.88 mg / m³. 2 Up to 16.6 mg / m 2 (Table 6). Measurements were taken at two different locations (E3A-1 and E3A-2) for sample E3A and three different locations (E3B-1, E3B-2, and E3B-3) for sample E3B. For sample E3A ( Figure 9 ) and E3B ( Figure 10 STEM imaging was performed.

[0248] An area ratio as high as 298,611,016:1 can be achieved (Table 6). The minimum areal density of a complete laminated ePTFE membrane is approximately 3.9 mg / m³. 2 .

[0249]

[0250] Table 6

[0251] Area ratio, areal density, and density per layer of Example 3

[0252]

[0253] Example 4

[0254] The following examples disclose areal densities of 0.6-2.0 g / m³. 2 The production of ePTFE membranes to facilitate the measurement of membrane thickness (per layer).

[0255] PTFE fine powder (DuPont de Nemours and ISOPAR) TM K isoparaffin lubricant was mixed at a target ratio of 110 ml / lb (approximately 0.454 kg) fine powder (0.156 g lubricant / g total weight) (g lubricant / total mass of mixture). The lubricated powder was compressed into cylinders and plunger-extruded at 49°C to provide a strip. The strip was 16.2 cm wide and 0.762 mm thick. ISOPAR was removed by heating to approximately 200°C. TM K. Cut a 98 mm square from the dried strip. Table 7 provides a summary of the process parameters used in Example 4.

[0256] Round 1

[0257] Using a scaling apparatus, four rectangular strips were heated in an oven set to 300°C for 120 seconds (setpoint) (sample E4B) or 240 seconds (setpoint) (E4A, E4C, and E4D), and then expanded simultaneously in both the longitudinal and transverse directions at a target ratio of approximately 7:1, while maintaining a temperature of approximately 300°C. The target average engineering strain rate was set at 36% / second. The scaling apparatus was then opened at a constant target speed for approximately 16.6 seconds. Under the constraint of the scaling apparatus, the ePTFE membrane was cooled to room temperature (approximately 22°C).

[0258] Second round

[0259] Using the same scaling apparatus, the laminate (totaling 16, 32, or 48 layers – see Table 7) was heated in an oven set to 300°C for 120 seconds (E4B) or 240 seconds (E4A, E4C, and E4D), then expanded simultaneously in both the longitudinal and transverse directions at a target ratio of 7:1, while maintaining a temperature of approximately 300°C. The target average engineered strain rate was set to 5% / second. The scaling apparatus was then expanded at a constant speed for approximately 120 seconds. Under the constraint of the scaling apparatus, the expanded film was allowed to cool to room temperature (approximately 22°C).

[0260] Third round

[0261] Four samples were harvested from the cooled ePTFE membrane and stacked in total 128 layers (E4A-C) or 192 layers (E4D) for further expansion, i.e., the third round. Using the same scaler, the 128-layer or 192-layer stacks were loaded. The ePTFE membrane was reheated to the target in an oven set to 300°C for 120 seconds (E4A-C) or 180 seconds (E4D), and then expanded simultaneously in both the longitudinal and transverse directions at a target ratio of 8:1 while maintaining the temperature at approximately 300°C. Simultaneous expansion was performed at a constant acceleration of 1% / s until the scaler reached a target velocity of 3.5 mm / s, achieving 400% strain (λ in both directions). sp = 5:1), and expansion was completed at a constant speed setpoint of 5% / s (3.5mm / s in this specific case, based on an initial length input of 70mm) (E4A, E4C-D). During the expansion of E4A and E4C-D, the scaler opened for approximately 221 seconds. Simultaneously, expansion was carried out at a constant acceleration target of 1% / s, with a target ratio of 8:1 in each direction. For Example E4B, the entire third round of translation took approximately 210 seconds. Under the constraint of the scaler, the ePTFE membrane was cooled to room temperature (approximately 22°C). The ePTFE membrane was collected from the machine onto a (152.4mm x 152.4mm) adhesive backing frame.

[0262] The ePTFE membranes E4A-E4D were weighed and measured using a frame-guided cutting method. The ePTFE membrane E4A was weighed to calculate its weight as 0.0076 g / m³. 2 The areal density of the membrane layer is 0.974 g / m³. 2 The average total thickness of the 128-layer ePTFE membrane was measured to be 7.76 micrometers, equivalent to approximately 60 nanometers per layer. Table 7 includes process details for this sample and similar samples, which were exposed to approximately 350°C for 5 minutes (i.e., "heat treatment") to improve dimensional stability. The ePTFE membrane E4B was weighed to calculate 0.0049 g / m³. 2 The areal density of the membrane layer is 0.632 g / m³. 2 The average total thickness of the 128-layer ePTFE membrane was measured to be 4.95 micrometers, equivalent to approximately 39 nanometers per layer. Table 7 includes process details for two additional similar samples that were compressed using the methods described herein to reduce thickness. ePTFE membrane E4C is the compression region of ePTFE membrane E4A. ePTFE membrane E4C was placed in a laboratory press at a pressure of 2.07 MPa (300 psi) and a temperature of approximately 22°C for approximately 30 minutes. ePTFE membrane E4D was placed in an autoclave at a pressure of 1.73 MPa (250 psi) and held at approximately 200°C for 40 minutes. ePTFE membrane E4C was weighed to calculate 0.0076 g / m³. 2 The areal density of the membrane layer is 0.974 g / m³. 2 The average total thickness of the 128-layer ePTFE membrane was measured to be 1.50 micrometers, equivalent to approximately 11.7 nanometers per layer. The ePTFE membrane E4D was weighed to calculate 0.016 g / m³. 2 The areal density of the membrane layer is 2.038 g / m³. 2 The average total thickness of the 192-layer ePTFE membrane was measured to be 3.50 micrometers, which is equivalent to approximately 18.2 nanometers per layer.

[0263] Table 8 shows that the 128 and 192-layer ePTFE membranes are sufficiently heavy and thick for wall thickness measurements. The calculated thickness per layer of each uncompressed ePTFE membrane is approximately twice the typical fibril width measured by STEM microscopy, approximately 20–30 nm. The solids volume fraction and porosity were calculated as the density of PTFE using 2.2 g / cc. Compressed ePTFE membranes show a decrease in porosity and thickness per layer.

[0264] densification methods

[0265] Method 1: Laboratory Compression

[0266] The ePTFE membrane E4C was placed in a Caver laboratory compressor model M (Fred S. Carver Inc., Menomonee Falls, WI). The laboratory compressor operated at room temperature (approximately 22°C) with a 3" (approximately 0.0762m) diameter anvil at the top, generating approximately 300 psi (approximately 2.07MPa) of pressure for approximately 30 minutes.

[0267] Method 2: Laboratory autoclave

[0268] The ePTFE membrane E4D was placed in a container made of... The assembly is placed in an autoclave bag containing a polyimide membrane (DuPont Nemoir, Wilmington, DE). TM In a 3ft x 5ft laboratory autoclave (ASC Process Systems; Valencia, CA), using a temperature setpoint of 200°C, apply a pressure of 250 psi (approximately 1.72 MPa) for approximately 70 minutes.

[0269]

[0270] Example 5

[0271] The following examples disclose the preparation of stacked ePTFE membranes (up to 192 layers can be stacked through lamination and co-expansion) and the measurement of various membrane parameters, including: average fibril width, area-weighted fibril width (AWFW), median fibril width, specific surface area, bubble point, airflow resistance, and areal density.

[0272] High permeability manifests as a relatively high airflow rate at a given pressure, or in other words, a higher flow rate requires a lower pressure. Airflow resistance varies with structure, with the simplest models using the solids volume fraction and representative fibril radius as primary factors. More complex models resolve slip as the fibril radius decreases, thus representing a fraction of the mean free path of air under standard conditions (taken here as 65 nm). Other factors influencing the production of membranes with high airflow are the uniformity of fibril distribution, fibril shape, and orientation. A uniform distribution of fibrils is maximized if each fibril is spaced at equal intervals, where a less uniform distribution will be represented by clumps or aggregates of fibrils, the latter exhibiting higher permeability. Fibril shape can also alter airflow resistance.

[0273] One method to determine the average fibril width is to manually measure the width of the fibrils within an exemplary sample. Figure 4 (ePTFE membrane E1H) is used for manual measurement of fibril width (measurement of 50 fibrils) to calculate average width and median width. Figure 11 ). Fiber measurements are in nanometers (nm). Figure 11 As can be seen in (ePTFE membrane E1H), it is obvious that the projected width is oversimplified due to the variation in gray intensity across the fibril width, because smaller fibrils are observed to aggregate or clump on larger fibrils. Figure 11 The bar chart of fibril measurements is shown in Figure 12 The data fits a log-normal distribution.

[0274] PTFE fine powder (DuPont de Nemours and ISOPAR) TM K isoparaffin lubricant was mixed at a target ratio of 110 ml / lb (approximately 0.454 kg) fine powder (0.156 g lubricant / g total weight) (g lubricant / total mass of mixture). The lubricated powder was compressed into cylinders and plunger-extruded at 49°C to provide a strip. The strip was 16.2 cm wide and 0.762 mm thick. ISOPAR was removed by heating to approximately 200°C. TM K. The dried strip was cut into 98mm squares. Table 9 provides a summary of the process parameters used in Example 5.

[0275] Round 1

[0276] Using a scaling machine, heat up to four strip blocks in an oven set to 300°C (setpoint) for 120 seconds (E5A-G) or 240 seconds (E5H-J), then simultaneously in the longitudinal and transverse directions at a target ratio (λ) of 4:1, 7:1, or 9:1 (Table 9). sp The membrane expands while maintaining a temperature of approximately 300°C. The target average engineering strain rate is set at 36% / second. Depending on the target rate, the expander is opened at a constant speed for approximately 8.3, 16.6, or 22 seconds (Table 9). Under the constraint of the expander, the expanded ePTFE membrane is cooled to room temperature (approximately 22°C).

[0277] Second round

[0278] Samples were collected from the cooled ePTFE membrane for further expansion, i.e., the second round. The specific number of stacked layers for the second round is provided in Table 9 for each sample. Using the same scaling apparatus, the stacked ePTFE layers were heated in an oven set to 300°C for 120 seconds (E5A-G) or 240 seconds (E5H-J), and then expanded simultaneously in both the longitudinal and transverse directions at target ratios of 6.35:1 (E5J), 7:1 (E5H-I), or 10:1 (E5A-G), while maintaining a temperature of approximately 300°C. The target range for the average engineered strain rate was 4% / s–9% / s (Table 9). The scaling apparatus was opened at a constant target speed for approximately 100 seconds (E5A-BG), 150 seconds (E5H), 120 seconds (E5I), and 134 seconds (E5J) (Table 9). Under the constraint of the scaling apparatus, the ePTFE membrane was cooled to room temperature (approximately 22°C).

[0279] Third round

[0280] Samples were collected from the cooled ePTFE membrane and stacked (if necessary) for further expansion, i.e., a third round. Using the same scaler, the membrane was reheated in an oven set to 300°C for 120 seconds (E5A-G), 180 seconds (E5I), or 240 seconds (E5H and E5J), and then expanded simultaneously in both the longitudinal and transverse directions at target ratios of 7:1 (E5H and E5J), 8:1 seconds (E5I), or 10:1 seconds (E5A-G) (Table 9), while maintaining a temperature of approximately 300°C. Biaxial expansion was performed at a constant acceleration setpoint of 1% / s (E5A-E5H and E5J). For Example E5I, biaxial expansion was performed at a constant acceleration target of 1% / s until the scaler accelerated to a velocity target of 3.5 mm / s, reaching 400% strain (λ in both directions). sp =5:1), and completes the expansion in both directions at a constant speed setpoint of 5% / s (3.5mm / s in this specific case, based on an original length input of 70mm ("r / s" rate mode)). sp =8:1. The scaler is opened for approximately 221 seconds (E5I), 230 seconds (E5A-G), and 195 seconds (E5H and E5J). Under the scaler's constraint, the selected samples (E5E-G and E5I) are heat-conditioned (heat-treated) in an oven at a set point of 350°C for a target time of 300 seconds. Under the scaler's constraint, the ePTFE film is cooled to room temperature (approximately 22°C).

[0281] The third-round cooled expanded ePTFE membrane was harvested from the scaling device and placed on a (152.4mm x 152.4mm) adhesive-backed frame. The average 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.

[0282]

[0283]

[0284] Example 6

[0285] 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 permeability. Air filtration performance was measured as described in the Test Methods section.

[0286] PTFE fine powder (DuPont de Nemours and ISOPAR) TM K isoparaffin lubricant was mixed at a target ratio of 110 ml / lb (approximately 0.454 kg) fine powder (0.156 g lubricant / g total weight) (g lubricant / total mass of mixture). The lubricated powder was compressed into cylinders and plunger-extruded at 49°C to provide a strip. The strip was 16.2 cm wide and 0.762 mm thick. ISOPAR was removed by heating to approximately 200°C. TM K. The dried strip was cut into 98mm squares. Table 11 provides a summary of the process parameters used in Example 6.

[0287] Round 1

[0288] Using a scaling machine, heat single-layer (E6A-C) or multi-size (E6D) strip blocks in an oven set to 300°C (set point) for 120 seconds (E6A-C) or 240 seconds (E5D), then simultaneously in both the longitudinal and transverse directions at a target ratio (λ) of 4:1, 7:1, or 9:1 (Table 11). sp The membrane expands while maintaining a temperature of approximately 300°C. The target average engineering strain rate is set at 36% / second. Depending on the target rate, the scaler expands at a constant speed for approximately 8.3, 16.6, or 22 seconds (Table 11). Under the constraint of the scaler, the ePTFE membrane is cooled to room temperature (approximately 22°C).

[0289] Second round

[0290] Samples were collected from the cooled membrane for further expansion, i.e., the second round. The specific number of ePTFE membranes loaded for the second round for each sample is provided in Table 11. Using the same scaling apparatus, the stacked ePTFE membranes were heated in an oven set to 300°C for 120 seconds (E6A-C) or 240 seconds (E6D), and then expanded simultaneously in both the longitudinal and transverse directions at target ratios of 7:1 or 10:1, while maintaining a temperature of approximately 300°C. The target average engineering strain rates were 5%, 9%, or 4% / s (Table 11). The scaling apparatus was opened at a constant target speed for approximately 120 seconds (E6A-B), 100 seconds (E6C), and 150 seconds (E6D). The expanded membranes were then allowed to cool to room temperature (approximately 22°C) under the constraint of the scaling apparatus.

[0291] Third round

[0292] Samples are collected from the cooled membrane and stacked (if necessary) for further expansion, i.e., a third round. Using the same expander, the membrane is reheated in an oven set to 300°C for 120 seconds (E6A-C) or 240 seconds (E6D), then expanded simultaneously in both the longitudinal and transverse directions at target ratios of 8:1 (E6A-B), 10:1 (E6C), or 7:1 (E6D), while maintaining a temperature of approximately 300°C. The target average strain rate is 1% / s. The expander is opened at a constant target speed for approximately 208 seconds (E6A-B), 230 seconds (E6C), or 195 seconds (E6D). Two samples, E6B and E6D, are exposed to heat (approximately 350°C) for 5 minutes. The expanded membrane is then cooled to room temperature (approximately 22°C) under the constraint of the expander.

[0293] The ePTFE membrane was collected from the machine onto a (152.4 mm x 152.4 mm) adhesive-backed frame for further testing. Airflow resistance and filtration efficiency of the samples were tested as described in the Test Methods section. Air filtration results are shown in Table 12. Figure 24 As shown, a graph of particle size vs. quality factor (Qf) for samples E6A, E6B, E6C, E6D and E6E (Comparative Example 1) is provided. Figure 24 The improvement in quality factor of samples E6A to E6D compared to comparative example E6E is shown.

[0294] ePTFE samples were cut from the strip and weighed on a Mettler-Toledo. The fibril widths of samples E6A and E6B were measured, such as... Figure 25 and 26 As shown. Figure 27 and 28 Samples E6A and E6B are shown at a lower magnification, respectively. The results of the fibril width measurement are shown in Table 13.

[0295] Comparative Example 1

[0296] The ePTFE membrane was manufactured according to the general teachings described in Gore's U.S. Patent No. 3,953,566. The ePTFE membrane (sample E6E) had a mass per unit area of ​​5.6 g / m³. 2 The airflow resistance was 6.68 mm H2O, and the particle capture efficiency of 0.1 μm DOP-excited particles was 98.344%, tested using a surface velocity of 5.33 cm / s (Table 12).

[0297]

[0298] Table 12

[0299] Air filtration data

[0300]

[0301] Table 13

[0302] fibril properties

[0303]

[0304] Example 7

[0305] The following examples disclose the preparation of ePTFE films for light transmission testing.

[0306] PTFE fine powder (DuPont de Nemours and ISOPAR) TM K isoparaffin lubricant was mixed at a target ratio of 110 ml / lb (approximately 0.454 kg) fine powder (0.156 g lubricant / g total weight) (g lubricant / total mass of mixture). The lubricated powder was compressed into cylinders and plunger-extruded at 49°C to provide a strip. The strip was 16.2 cm wide and 0.762 mm thick. ISOPAR was removed by heating to approximately 200°C. TM K. The dried strip is cut into 98mm squares. Table 14 provides a summary of the process parameters used in Example 7.

[0307] Round 1

[0308] Using a scaling apparatus, one or four strip squares were heated in an oven set to 300°C (setpoint) for 240 seconds (E7A) or 120 seconds (E7B), and then simultaneously expanded in the longitudinal and transverse directions at different target ratios (Table 13). The average engineering strain rate targets for samples E7A and E7B were determined (Table 13). The scaling apparatus was then opened at a constant target speed for approximately 16.6 seconds (E7A) or 8.4 seconds (E7B). The ePTFE membrane was then cooled to room temperature (approximately 22°C) under the constraint of the scaling apparatus.

[0309] Second round

[0310] Samples were collected from the cooled ePTFE membrane for further expansion, i.e., the second round. Using the same scaling apparatus, a single layer (E7B) or a stack of 16 layers (E7A) was heated in an oven set to 300°C for 120 seconds (E7B) or 240 seconds (E7A), and then expanded simultaneously in both the longitudinal and transverse directions at a target ratio of 7:1 (E7A) or 10:1 (E7B) while maintaining the temperature at approximately 300°C. The target average engineered strain rate was set at 5% / s (E7A) or 9% / s (E7B). The scaling apparatus was opened at a constant target speed for approximately 120 seconds (E7A) or 100 seconds (E7B). Under the constraint of the scaling apparatus, the ePTFE membrane was cooled to room temperature (approximately 22°C).

[0311] Third round

[0312] Samples are collected from the cooled ePTFE membrane and stacked (as needed) for further expansion, i.e., the third round. Using the same scaler, 3-layer (E7B) or 48-layer (E7A) samples are heated in an oven set to 300°C for 120 seconds, and then expanded simultaneously in both the longitudinal and transverse directions at a target ratio of 7:1 (E7B) or 8:1 (E7A) (Table 14), while maintaining the temperature at approximately 300°C. The target average strain rate is set to 1% / s. The scaler is opened at a constant target speed for approximately 208 seconds (E7A) or 195 seconds (E7B). Under the constraint of the scaler, the ePTFE membrane is cooled to room temperature (approximately 22°C).

[0313] The ePTFE membrane was collected from the machine onto a (152.4 mm x 152.4 mm) adhesive backing frame for further testing. The airflow resistance of the sample was tested as described in the Test Methods section. The ePTFE sample was cut from the strip and weighed on a Mettler-Toledo AT 20. Light transmittance testing was also performed on the selected sample as described in the Test Methods section. The light transmittance test results are shown in Table 15 and... Figure 29 middle. Figure 29 This is a graph showing the wavelength vs. transmittance percentage for a 3-layer sample (E7B; black line) and a 48-layer sample (E7A; gray line).

[0314]

[0315] Table 15

[0316] Optical testing in Example 7

[0317]

[0318] Example 8

[0319] This embodiment emphasizes the enhanced strength-to-weight ratio of a relatively balanced ePTFE membrane composed of extremely fine fibrils and similar fibrils, exhibiting an extremely high crystallinity index of at least 94%. Lamination and co-expansion were used to generate sufficient mass for bulk mechanical characterization and to reduce the time required for structural characterization in a synchrotron. Amorphous material content and relative intensity balance were determined using X-ray diffraction (XRD).

[0320] PTFE fine powder (DuPont and ISOPAR) TM K isoparaffin lubricant was mixed at a target ratio of 110 ml / lb (approximately 0.454 kg) fine powder (0.156 g lubricant / g total weight) (g lubricant / total mass of mixture). The lubricated powder was compressed into cylinders and plunger-extruded at 49°C to provide a strip. The strip was 16.2 cm wide and 0.762 mm thick. ISOPAR was removed by heating to approximately 200°C. TM K. The dried strip is cut into 98mm squares. Table 16 provides a summary of the process parameters used in this embodiment.

[0321] Round 1

[0322] Using a scaling apparatus, up to four strip squares were heated for 240 seconds in an oven set at 300°C (samples E8A and E8B) or 322°C (samples E8C and E8D), and then simultaneously expanded in both the longitudinal and transverse directions at a target ratio of 7:1 (E8C-D) or 9:1 (E8A-B) (Table 16). The average engineered strain rate target was set at 36% / second. The scaling apparatus was opened at a constant target speed for approximately 16.6 seconds (E8C-D) or 22.2 seconds (E8A-B). Under the constraint of the scaling apparatus, the ePTFE membrane was cooled to room temperature (approximately 22°C).

[0323] Second round

[0324] Samples were collected from the cooled ePTFE membrane for further expansion, i.e., the second round. Table 16 lists the specific number of layers for the second round loading under each condition. Using the same scaling apparatus, samples with 16 layers (E8B) or 32 layers (E8A and E8C-D) were heated for 240 seconds in an oven set to 300°C (E8A-B) or 322°C (E8C-D), and then expanded simultaneously in both the longitudinal and transverse directions at a ratio of 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 scaling apparatus was opened at a constant target speed for approximately 150 seconds (E8A-B) or 120 seconds (E8C-D). Under the constraint of the scaling apparatus, the expanded membrane was allowed to cool to room temperature (approximately 22°C).

[0325] Third round

[0326] Samples were collected from the ePTFE membranes and stacked (if necessary) for further expansion, i.e., a third round. Using the same scaling apparatus, ePTFE membranes with 64 layers (E8B) or 128 layers (E8A and E8C-D) were reheated in an oven set at 300°C (E8A-B) or 322°C (E8C-D) for 120 seconds (E8C-D) or 240 seconds (E8A-B), respectively, and then simultaneously expanded in both the longitudinal and transverse directions at a ratio of 7:1 (E8A-B) or 8:1 (E8C-D), maintaining the setpoint temperature (Table 16). The target average strain rate was 1% / s. The scaling apparatus was opened at a constant acceleration for approximately 195 seconds (E8A-B) or 208 seconds (E8C-D). Under the constraints of the scaling apparatus, samples E8B and E8D were heat-conditioned in an oven at a setpoint of 350°C for a target of 300 seconds. Under the constraint of the scaling device, the ePTFE membrane is cooled to room temperature (approximately 22°C).

[0327] The ePTFE membrane was collected from the machine onto a (152.4 mm x 152.4 mm) adhesive-backed frame for further testing. The tensile test results included in Table 17 show that the inherent strength to weight ratio exceeds values ​​previously reported in the art (see Comparative Examples - Table 18). Samples E8C and E8D were further characterized by X-ray diffraction (XRD). Figure 30 Sample E8C (untreated) and Figure 31 The sample underwent E8D (heat treatment), and the results are consistent with the isotropic orientation in the MD-TD plane. These results are consistent with the equilibrium strength results. Figure 32 The samples are heat-treated (sample E8D; top trace) and untreated (sample E8C; bottom trace) at 10-45 nm. -1 Within the range q(nm) -1 (vs. intensity curve) Figure 32 The samples are E8D (heat-treated, top trace) and E8C (untreated, bottom trace) at 10-20 nm. -1 Within the range q(nm) -1 ) vs. Intensity (10-20nm) -1 The curve graph of ). Figure 32 and 33 This indicates that the ePTFE film has a very high crystallinity index. Furthermore, with q = 12.8 nm... -1 The narrowness of the central peak ( Figure 33 This indicates that the crystallization of these ePTFE films is almost defect-free. Example E8C has a crystallinity index of 99%. Example E8D has a crystallinity index of 99.2%.

[0328]

[0329] Comparative Examples 2-4

[0330] Table 18 lists the matrix tensile strengths of ePTFE Examples 2-4 compared in the art.

[0331] Table 18

[0332] Strength-weight index - Comparative examples 2-4

[0333]

[0334] Example 9

[0335] The following examples describe the preparation and analysis of uniaxially oriented ePTFE membranes with low mass and high inherent strength in the original fiber direction.

[0336] PTFE fine powder (DuPont de Nemours and ISOPAR) TM K isoparaffin lubricant was mixed at a target ratio of 110 ml / lb (approximately 0.454 kg) fine powder (0.156 g lubricant / g total weight) (g lubricant / total mass of mixture). The lubricated powder was compressed into cylinders and plunger-extruded at 49°C to provide a strip. The strip was 16.2 cm wide and 0.762 mm thick. ISOPAR was removed by heating to approximately 200°C. TM K. Cut a series of 98 mm squares from the dried strip. Table 19 provides a summary of the process parameters used in Example 9.

[0337] Round 1

[0338] Using the same scaling apparatus, two different samples (each with four layers of tape) were heated in an oven set to 300°C (setpoint) for 240 seconds, and then expanded simultaneously in both the longitudinal (machine direction) and transverse directions at a target ratio of approximately 10:1, while maintaining the temperature at approximately 300°C. The target average engineering strain rate was set at 36% / second. The scaling apparatus was then opened at a constant target speed for approximately 25 seconds. Under the constraint of the scaling apparatus, the ePTFE membrane was cooled to room temperature (approximately 22°C).

[0339] Second round

[0340] Four sheets (four layers each) were collected from the cooled membrane and used for further expansion, i.e., the second round. Using the same scaling apparatus, the sample, comprising 16 layers, was heated in an oven set to 300°C for 240 seconds, and then expanded simultaneously in both the longitudinal and transverse directions at a target ratio of 10:1, while maintaining the temperature at approximately 300°C. The target average engineered strain rate was set at 3.6% / second. The scaling apparatus was opened at a constant target speed for approximately 250 seconds. Under the constraint of the scaling apparatus, the ePTFE membrane was cooled to room temperature (approximately 22°C).

[0341] Third round

[0342] Four samples (16 layers each) were harvested from the cooled membrane and two 16-layer stacks (32 layers in total) were loaded for further expansion, i.e., the third round. Using the same scaling apparatus, the membrane was heated in an oven set to 300°C for 120 seconds, and then stretched simultaneously in both the longitudinal and transverse directions at a target ratio of 3:1 (Example E9A) or 5:1 (Example E9B) (details of each example are shown in Table 19), while maintaining the temperature at approximately 300°C. The target average strain rate was set at 1% / s. The scaling apparatus was opened at a constant acceleration for approximately 110 seconds (E9A) or 161 seconds (E9B). Under the constraint of the scaling apparatus, the ePTFE membrane was cooled to room temperature (approximately 22°C).

[0343] Optional fourth round

[0344] For sample E9B, using the same scaling apparatus, 32 layers of the sample were reheated to the target in an oven set to 300°C for 120 seconds, and then stretched simultaneously in both the longitudinal and transverse directions at a target ratio of 3:1 while maintaining the temperature at approximately 300°C. Simultaneous expansion was performed at a constant acceleration setpoint of 1% / s. The scaling apparatus was opened at a constant acceleration for approximately 110 seconds (E9B).

[0345] penultimate round

[0346] Using the same scaling device, the ePTFE membrane is unconstrained laterally while remaining fixed in the machine direction. The ePTFE membrane is heated to the target temperature in an oven set to 300°C for 120 seconds, then stretched only longitudinally at a target ratio of 6:1 (in the machine direction), while allowing the ePTFE membrane to freely neck (i.e., narrow) laterally. The scaling device is opened at a constant acceleration setpoint for approximately 170 seconds (E9A-B). Expansion is then performed at a constant acceleration setpoint of 1% / s.

[0347] final round

[0348] Using the same scaling apparatus, the 32-layer sample was heated to the target in an oven set to 350°C for 300 seconds, and then stretched only in the machine (longitudinal) direction at a target ratio of 1.5:1 (sample E9A) or 1.67:1 (sample E9B) while maintaining a temperature of approximately 350°C. Expansion was performed at a constant acceleration setpoint of 1% / s. The scaling apparatus was then opened at the constant acceleration setpoint for approximately 40 seconds (E9A) or 51 seconds (E9B).

[0349] The membrane was collected from the machine onto an adhesive-backed frame of known dimensions (152.4 mm x 152.4 mm). The ePTFE membrane was weighed using frame-guided cutting to calculate its linear density (bulk density), and mechanical data were collected using the matrix tensile test described in the above test method section. Sample E9A was also characterized using dynamic mechanical analysis (DMA), which indicated a matrix storage modulus of 100 GPa at ambient temperature (approximately 20 °C). Figure 34 Sample E9A was analyzed by XRD ( Figure 35 Further characterization showed that XRD patterns were consistent with extremely high crystallinity orientation. <p2>Orientation function was 0.989, where 1.0 indicates perfect parallel alignment Figure 36 ). Crystallinity index was determined to be 94.6%. SEM of sample E9A is shown in Figure 37 .

[0350] Table 19

[0351] Process parameters for Example 9 films

[0352]

[0353] 1 - "s" = constant velocity; "r" = constant acceleration set point; 2 - set point; 3 - final layer of last round

[0354]

[0355] Example 10

[0356] The following example discloses the preparation of multilayer ePTFE films with extremely low mass and high inherent strength as well as the measurement of nanoparticle retention. Nanoparticle retention was tested using the bead test disclosed in the Methods section, which measures the permeability and bead retention of a film sample.

[0357] PTFE fine powder (E. I. DuPont de Nemours) was mixed with ISOPAR TM K lubricant at a target ratio of 110 milliliters per pound of fine powder (0.156 g of lubricant per g of total) (grams of lubricant per total mass of mixture). The lubricated powder was compressed into a cylinder and plunger extruded at 49 °C to provide a tape. The tape was 16.2 centimeters wide and 0.762 millimeters thick. The ISOPAR TM 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 for Example 10 is provided in Table 21.

[0358] First round

[0359] Using the same scaling device, four square strips were stacked and heated in an oven set to 300°C for 120 seconds (E10A-C). They were then expanded simultaneously in both the longitudinal and transverse directions at a selected target ratio (λsp) of 7:1 (E10A and E10C) or 2:1 (E10B), while maintaining a temperature of approximately 300°C. The target average engineering strain rate was set at 36% / second. Depending on the target ratio, the scaling device was opened at a constant speed for approximately 16.6 seconds (E10A and E10C) or approximately 2.8 seconds (E10B) (Table 21). Under the constraint of the scaling device, the expanded film was allowed to cool to room temperature (approximately 22°C). The first round was repeated until 64 layers (E10A), 16 layers (E10B), or 32 layers (E10C) were available for the second round.

[0360] Second round

[0361] As shown in Table 21, the specific number of layers loaded under the second round of conditions was 64 layers (E10A), 16 layers (E10B), or 32 layers (E10C). Using the same scaling device, the laminate was heated in an oven set to 300°C for 240 seconds (E10A and B) or 120 seconds (E10C), and then expanded simultaneously in both the longitudinal and transverse directions at a target ratio of 7:1 (E10A), 10:1 (E10B), or 6:1 (E10C), while maintaining a temperature of approximately 300°C. The target average engineering strain rate was set at 5% / s (E10A and E10C) or 18% / s (E10B) (Table 21). The scaling device was opened at a constant target speed for approximately 120 seconds (E10A), 50 seconds (E10B), and 100 seconds (E10C). Under the constraint of the scaling device, the expanded film was cooled to room temperature (approximately 22°C).

[0362] Third round

[0363] Samples were collected from the cooled membrane and stacked (if necessary) for further expansion, i.e., the third round. As shown in Table 21, the specific number of layers loaded under the conditions of the second round were 256 layers (E10A), 120 layers (E10B), or 128 layers (E10C). Using the same scaling apparatus, the membrane was reheated in an oven set to 300°C for 120 seconds (E10A-C), and then expanded simultaneously in both the longitudinal and transverse directions at target ratios of 8:1 (E10A), 10:1 (E10B), or 6:1 (E10C), while maintaining a temperature of approximately 300°C. The average constant acceleration strain rate setpoint was 1% / s. The scaling apparatus was opened at a constant acceleration target for approximately 221 seconds (E10A), 261 seconds (E10B), and 179 seconds (E10C). Under the constraint of the scaling apparatus, the expanded membrane was allowed to cool to room temperature (approximately 22°C).

[0364] Samples were taken from the machine onto an adhesive backing frame (152.4 x 152.4 mm) for further testing (E10A and E10B) or further expansion (E10C).

[0365] Fourth round

[0366] Samples were collected from the cooled membrane and stacked (if necessary) for further expansion, i.e., the fourth round. As shown in Table 21, the specific number of layers loaded under each condition in the fourth round was 2056 (E10C). Using the same scaling apparatus, the membrane was reheated in an oven set to 300°C for 120 seconds (E10C), and then expanded simultaneously in both the longitudinal and transverse directions at a target ratio of 4.75:1 (E10C) while maintaining a temperature of approximately 300°C. The constant acceleration strain rate setpoint was 1% / s. The scaling apparatus was opened at a constant acceleration target for approximately 156 seconds (E10C). Under the constraint of the scaling apparatus, the expanded membrane was allowed to cool to room temperature (approximately 22°C).

[0367] densification

[0368] Under constrained conditions in the MD and TD planes, the sample (E10A-C) was densified by gently pouring isopropanol (IPA) onto the constrained membrane and allowing the IPA to evaporate.

[0369] According to the bead test described in the above test method section, the permeate permeability and retention were tested. The average filtrate permeability (see formula (9) above) and bead retention rate (see formula (10) above) of each membrane sample (samples E10A, E10B, and E10C) were evaluated. The results are shown in Table 22 and Figure 38 .

[0370] Comparative Examples 5-7

[0371] Three comparative liquid filtration samples were prepared as described below.

[0372] Comparative Example 5

[0373] Polytetrafluoroethylene polymer powder and isoalkane lubricant (ISOPAR) manufactured according to Baillie's U.S. Patent No. 6,541,589. TM K, ExxonMobil (Houston, Texas) was mixed at 0.184 lb / lb. The resulting mixture was then blended, compressed into cylindrical pellets, and heat-conditioned at 49°C for at least 8 hours. The cylindrical pellets were then extruded through a rectangular die at a compression ratio of 72:1 to form a strip. The strip was then calendered between rolls at a calendering ratio of 3:1. The calendered strip was then stretched laterally at a ratio of 3.6:1 and dried at 200°C.

[0374] The dried strip is then expanded at 330°C along the machine direction to an expansion ratio of 7:1. Subsequently, the resulting material is expanded laterally at approximately 310°C to an expansion ratio of 12:1.

[0375] The biaxially expanded film is compressed between rollers (at 25°C) at a speed of 1 m / min and a compressive force of 10 N / mm.

[0376] Comparative Example 6 - Sample E10D2

[0377] Polytetrafluoroethylene polymer powder and lubricant (ISOPAR) manufactured according to Baillie's U.S. Patent No. 6,541,589. TM K, ExxonMobil (Houston, Texas) was mixed at 0.151 lb / lb. The resulting mixture was then blended, compressed into cylindrical pellets, and heat-conditioned at 49°C for at least 8 hours. The cylindrical pellets were then extruded through a rectangular die at a compression ratio of 72:1 to form a strip. The strip was then calendered between rolls at a calendering ratio of 3:1. The calendered strip was then stretched laterally at a ratio of 3.6:1 and dried at 200°C.

[0378] The dried strip is then expanded along the machine direction at 330°C to an expansion ratio of 5:1. Subsequently, the resulting material is expanded laterally at approximately 310°C to an expansion ratio of 10.8:1. The film is then heat-treated at approximately 380°C for a target time of 25 seconds.

[0379] The biaxially expanded film was compressed between rollers (at 25°C) at a speed of 1 m / min and a compressive force of 20 N / mm.

[0380] Comparative Example 7 - Sample E10D3

[0381] Polytetrafluoroethylene polymer powder and lubricant (ISOPAR) manufactured according to Baillie's U.S. Patent No. 6,541,589. TM K, ExxonMobil (Houston, Texas) was mixed at 0.145 lb / lb. The resulting mixture was then blended, compressed into cylindrical pellets, and heat-conditioned at 49°C for at least 8 hours. The cylindrical pellets were then extruded through a rectangular die at a compression ratio of 72:1 to form a strip. The strip was then calendered between rolls at a calendering ratio of 3:1. The calendered strip was then stretched laterally at a ratio of 3.6:1 and dried at 230°C.

[0382] The dried strip is then expanded at 325°C along the machine direction to an expansion ratio of 5:1. Subsequently, the resulting material is expanded laterally at approximately 300°C to an expansion ratio of 12.3:1.

[0383] The biaxially expanded film is compressed between rollers (at 90°C) at a speed of 5 m / min and a compressive force of 80 N / mm.

[0384] The average filtrate permeability (see Equation (9)) and bead retention rate (see Equation (10)) of each comparative membrane sample (samples E10D1, E10D2, and E10D3) were evaluated using the above test methods. The results are shown in Table 22 and Figure 38 .

[0385] Table 21

[0386] Example 10 Process Parameters - Samples E10A-E10C

[0387]

[0388] 1 – "s" = constant velocity; "r" = constant acceleration setpoint; "r / s" – constant acceleration step, followed by a combination of constant velocity steps; 2 – setpoint; 3 – final layer number in the last round.

[0389] Table 22

[0390] Nanoparticle retention rate and filtrate permeability in Example 10

[0391]

[0392] The invention of this application has been described for brevity and in conjunction with specific embodiments above. It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the invention. Therefore, the embodiments are intended to cover these modifications and variations of the invention, provided that such modifications and variations are within the scope of the appended claims and their equivalents.

Claims

1. An expanded polytetrafluoroethylene (ePTFE) membrane, comprising: Multiple uniaxially oriented ePTFE layers; The tensile strength of the matrix in the machine direction or transverse direction is 1000 MPa to 1400 MPa; At least 94% crystallinity index; and The microstructure is composed of uniaxially oriented fibrils. The uniaxially oriented fibrils underwent biaxial expansion followed by uniaxial expansion.

2. The expanded polytetrafluoroethylene membrane as described in claim 1, wherein, The areal density of each layer of the ePTFE membrane is less than 500 mg / m³. 2 .

3. The expanded polytetrafluoroethylene membrane as described in claim 1, wherein, The specific surface area of ​​the ePTFE membrane is 35 m². 2 / g to 120 m 2 / g.

4. The expanded polytetrafluoroethylene membrane as described in claim 1, wherein, The ePTFE membrane is self-supporting.

5. The expanded polytetrafluoroethylene membrane as described in claim 1, wherein, The areal density of the ePTFE membrane is less than 0.5 g / m³. 2 .

6. The expanded polytetrafluoroethylene membrane according to any one of claims 1 to 5, wherein, The ePTFE membrane is at least partially coated with a polymer, at least partially absorbed with a polymer, or a combination of the above.

7. The expanded polytetrafluoroethylene membrane according to any one of claims 1 to 5, wherein, The ePTFE membrane has a matrix storage modulus of at least 100 GPa at 20°C.

8. The expanded polytetrafluoroethylene membrane according to any one of claims 1 to 5, wherein, The ePTFE membrane has a toughness of at least 5 gf / d.

9. The expanded polytetrafluoroethylene membrane as described in claim 7, wherein, The ePTFE membrane is at least partially coated with a polymer, at least partially absorbed with a polymer, or a combination of the above.

10. The expanded polytetrafluoroethylene membrane as described in claim 8, wherein, The ePTFE membrane is at least partially coated with a polymer, at least partially absorbed with a polymer, or a combination of the above.

11. The expanded polytetrafluoroethylene membrane according to any one of claims 1 to 5 and 9 to 10, wherein the expanded polytetrafluoroethylene membrane further comprises a spacer layer.

12. A composite material comprising an expanded polytetrafluoroethylene membrane as described in any one of claims 1 to 10.

13. A laminate comprising an expanded polytetrafluoroethylene film as claimed in any one of claims 1 to 10.

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