WO2024095080A1

WO2024095080A1 - Porous fibrous nonwoven webs and methods of making same

Info

Publication number: WO2024095080A1
Application number: PCT/IB2023/059631
Authority: WO
Inventors: Jinsheng Zhou; Jacob J. THELEN; John D. Stelter; Michael R. Berrigan
Original assignee: Solventum Intellectual Properties Company
Priority date: 2022-11-03
Filing date: 2023-09-27
Publication date: 2024-05-10

Abstract

The present disclosure provides nonwoven fibrous webs including randomly arranged continuous fibers bonded together. At least some of the continuous fibers include an open celled porous structure. Also provided are methods of making nonwoven fibrous webs including extruding filaments of fiber-forming material from an extrusion head into a gas stream, directing the filaments through a processing chamber in which gaseous currents apply a longitudinal stress to the filaments, and subjecting the filaments to turbulent flow conditions after they exit the processing chamber. At least some of the filaments solidify while in the turbulent field to form fibers that along their length are of uniform diameter but vary in morphology. The method further includes collecting the processed fibers on a collector as a nonwoven fibrous web, subjecting the collected nonwoven fibrous web to a bonding operation, and stretching the nonwoven fibrous web to fracture at least a portion of the fibers to generate an open celled porous structure in the fractured fibers.

Description

POROUS FIBROUS NONWOVEN WEBS AND METHODS OF MAKING SAME

BACKGROUND

Porous fibers offer one or more advantages of light weight, soft feeling, high liquid absorbency, good acoustic and insulation properties, and readiness to functionalize. Some current processes to produce porous fiber materials include spinning fibers with an extractable filler, including a filler (including an immiscible polymer) within the fibers, or nonsolvent precipitation of fibers to generate pore microstructures. By these processes, fibers tend to be costly to produce and/or have limited porosity.

SUMMARY

In a first aspect, a nonwoven fibrous web is provided. The nonwoven fibrous web comprises a plurality of randomly arranged continuous fibers bonded together, wherein at least some of the continuous fibers comprise an open celled porous structure.

In a second aspect, a method of making a nonwoven fibrous web is provided. The method comprises extruding filaments of fiber-forming material from an extrusion head into a gas stream; directing the filaments through a processing chamber in which gaseous currents apply a longitudinal stress to the filaments; and subjecting the filaments to turbulent flow conditions after they exit the processing chamber, the temperature of the filaments being controlled so that at least some of the filaments solidify while in the turbulent field to form fibers that along their length are of uniform diameter but vary in morphology, wherein the fibers exhibit a draw down ratio of 50 or greater. The method further comprises collecting the processed fibers on a collector as a nonwoven fibrous web; subjecting the collected nonwoven fibrous web to a bonding operation; and stretching the nonwoven fibrous web to fracture at least a portion of the fibers to generate an open celled porous structure in the fractured fibers.

At least certain embodiments of the present disclosure provide a simplified process to prepare a porous fiber nonwoven by stretching a bonded nonwoven web. Bonded nonwoven webs may be produced by a conventional spunbond process. Stretching is then applied to the bonded nonwoven web. Unexpectedly, good fiber porosity has been achieved by such a process, which has the potential to significantly reduce costs of manufacturing porous fibrous nonwoven webs. For instance, in an alternative method, a typical air-laid process would require several more total steps: fiber spinning, fiber stretching, crimping, fiber cutting, fiber opening, air laying, and calendaring, to form a porous fibrous nonwoven web. The above summary of the present disclosure is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The description that follows more particularly exemplifies illustrative embodiments. In several places throughout the application, guidance is provided through lists of examples, which examples can be used in various combinations. In each instance, the recited list serves only as a representative group and should not be interpreted as an exclusive list.

Brief Description of the Drawings

FIG. 1A is a scanning electron microscopy (SEM) image of a portion of an exemplary nonwoven fibrous web, prepared according to Example 3 (E3).

FIG. IB is an SEM image of a portion of a fiber of the exemplary nonwoven fibrous web of FIG. 1A.

FIG. 2A is an SEM image of a portion of another exemplary nonwoven fibrous web, prepared according to Example 4 (E4).

FIG. 2B is an SEM image of a portion of a fiber of the exemplary nonwoven fibrous web of FIG. 2A.

FIG. 3 is an SEM image of a portion of a further exemplary nonwoven fibrous web, prepared according to Example 2 (E2).

FIG. 4 is an SEM image of a portion of a fiber of the exemplary nonwoven fibrous web of FIG. 3.

FIG. 5 is an SEM image of a portion of a fiber having row-ordered lamella microstructures, prepared according to Example 5 (E5).

FIG. 6A is a schematic view of a cross-section of a fiber having a shape of a circle.

FIG. 6B is a schematic view of a cross-section of a fiber having a shape of a bar.

FIG. 6C is a schematic view of a cross-section of a fiber having a shape of an oval.

FIG. 6D is a schematic view of a cross-section of a fiber having a shape of a plus sign.

FIG. 7 is a photograph of a top view of a disc of nonwoven fibrous web following stretching in one direction, prepared according to Example 3 (E3).

While the above-identified figures set forth several embodiments of the disclosure other embodiments are also contemplated, as noted in the description. The figures are not necessarily drawn to scale. In all cases, this disclosure presents the invention by way of representation and not limitation. Detailed Description of Illustrative Embodiments

As used herein, the term “filament” refers to a continuous elongated strand of material, typically longer than 6 inches.

As used herein, the term “fiber” refers to a monocomponent fiber; a bicomponent or conjugate fiber (for convenience, the term “bicomponent” will often be used to mean fibers that consist of two components as well as fibers that consist of more than two components); and a fiber section of a bicomponent fiber, i.e., a section occupying part of the cross-section of and extending over the length of the bicomponent fiber. Monocomponent fibrous webs are often preferred, and the combination of orientation and bondability offered by the invention makes possible high- strength bondable webs using monocomponent fibers. A fiber (i.e., fiber section) as described can perform bonding functions as part of a multicomponent fiber as well as providing high strength properties. Fibers have two ends and are separable, and typically 6 inches or shorter.

As used herein, the term “fracture” with respect to a fiber means to generate a void in a portion of the polymeric material of the fiber.

As used herein, the term “open celled porous structure” with respect to a fiber’s structure refers to a fiber that has a plurality of pores, at least some of which are connected to adjacent pores such that a fluid can pass from one major surface of a portion of the fiber to an opposing major surface of the fiber.

As used herein, the term “microfibril” refers to a portion of a porous structure of a fiber having a fibril in which each dimension is less than 1 micrometer in size.

As used herein, the term “lamellae” refer to crystal portions of semicrystalline polymeric material of a fiber.

As used herein, the term “continuous” with respect to a fiber refers to a fiber having a longest dimension that has a length of greater than 1 centimeter.

As used herein, the term “meltblown” or “melt-blown” refers to fibers prepared by extruding molten fiber component through orifices in a die into a high-velocity gaseous stream, wherein the extruded material is first attenuated and then solidifies as a mass of fibers.

As used herein, the term “spunbond” or “spun-bond” herein refers to fibers prepared by extruding molten filament-forming material through orifices in a die into a low-velocity, optionally heated, gaseous stream, which then solidify as a mass of thermally-bondable fibers before being collected as a web.

As used herein, the term “amorphous” refers to a polymer that does not exhibit a melting point.

As used herein, the term “semicrystalline” refers to a polymer that beside an amorphous phase forms crystalline domains during solidification, plus exhibits a melting peak during heating and a crystallization peak during solidification as measured by dynamic scanning calorimetry (DSC).

As used herein, the term “porosity” with respect to fibers refers to a measurement of void spaces in a fiber that has an open celled porous structure, as determined by solvent absorption. One solvent absorption method is described in detail in the Examples below.

As used herein, the term “porosity” with respect to a nonwoven fibrous web refers to a total volume of the void spaces between individual fibers of the web, as determined by measuring the solidity of the nonwoven fibrous web and subtracting the solidity from 100. Accordingly, the solidity represents the proportion of the total volume of a nonwoven fibrous web that is occupied by the fibers. Solidity is determined by dividing the measured bulk density of the nonwoven fibrous web by the density of the fibers. Bulk density of a web can be determined by first measuring the weight (e.g., of a 10-cm-by-10-cm section) of a web. Dividing the measured weight of the web by the web area provides the basis weight of the web, which is reported in g/m². The thickness of the web can be measured by obtaining (e.g., by die cutting) a 135 mm diameter disk of the web and measuring the web thickness with a 230 g weight of 100 mm diameter centered atop the web. The bulk density of the web is determined by dividing the basis weight of the web by the thickness of the web and is reported as g/m³. The solidity is then determined by dividing the bulk density of the nonwoven fibrous web by the density of the material (e.g., polymer) comprising the fibers of the web. The density of a bulk polymer can be measured by standard means if the supplier does not specify the material density. Solidity is a dimensionless fraction which is usually reported as a percentage.

As used herein, the term “autogenous bonding” refers to as bonding between fibers at an elevated temperature as obtained in an oven or with a through-air bonder - sometimes known as a hot-air knife - without application of solid contact pressure such as in point-bonding or calendaring.

As used herein, “filler” refers to a solid particulate included in a fiber-forming material.

As used herein, “solid” with respect to a particulate refers to the state of matter that is stable in shape, as opposed to a state of matter that is liquid or gas.

As used herein, “thermoplastic” refers to a polymer that flows when heated sufficiently above its glass transition point and become solid when cooled. In contrast, “thermoset” refers to a polymer that permanently sets upon curing and does not flow upon subsequent heating. Thermoset polymers are typically crosslinked polymers.

As used herein, the term “glass transition temperature” (T_g), of a polymer refers to the transition of a polymer from a glassy state to a rubbery state and can be measured using Differential Scanning Calorimetry (DSC), such as at a heating rate of 10 °C per minute in a nitrogen stream. When the T_g of a monomer is mentioned, it is the T_g of a homopolymer of that monomer. The homopolymer must be sufficiently high molecular weight such that the T_g reaches a limiting value, as it is generally appreciated that a T_g of a homopolymer will increase with increasing molecular weight to a limiting value. The homopolymer is also understood to be substantially free of moisture, residual monomer, solvents, and other contaminants that may affect the T_g. A suitable DSC method and mode of analysis is as described in Matsumoto, A. et. al., J. Polym. Sci. A., Polym. Chem. 1993, 31, 2531-2539.

As used herein, “machine direction” (MD) as used herein denotes the direction of a running web of material during a manufacturing process. The terms “machine direction” and “longitudinal direction” may be used interchangeably. The terms “transverse direction” (TD) and “cross direction” (CD) as used herein each denotes the direction which is essentially perpendicular to the machine direction.

The words “preferred” and “preferably” refer to embodiments of the disclosure that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful and is not intended to exclude other embodiments from the scope of the disclosure.

In this application, terms such as “a”, “an”, and “the” are not intended to refer to only a singular entity, but include the general class of which a specific example may be used for illustration. The terms “a”, “an”, and “the” are used interchangeably with the term “at least one.” The phrases “at least one of’ and “comprises at least one of’ followed by a list refers to any one of the items in the list and any combination of two or more items in the list.

As used herein, the term “or” is generally employed in its usual sense including “and/or” unless the content clearly dictates otherwise. The term “and/or” means one or all of the listed elements or a combination of any two or more of the listed elements.

Also herein, all numbers are assumed to be modified by the term “about” and preferably by the term “exactly.” As used herein in connection with a measured quantity, the term “about” refers to that variation in the measured quantity as would be expected by the skilled artisan making the measurement and exercising a level of care commensurate with the objective of the measurement and the precision of the measuring equipment used.

As used herein as a modifier to a property or attribute, the term “generally”, unless otherwise specifically defined, means that the property or attribute would be readily recognizable by a person of ordinary skill but without requiring absolute precision or a perfect match (e.g., within +/- 20 % for quantifiable properties). The term “substantially”, unless otherwise specifically defined, means to a high degree of approximation (e.g., within +/- 10% for quantifiable properties) but again without requiring absolute precision or a perfect match. Terms such as same, equal, uniform, constant, strictly, and the like, are understood to be within the usual tolerances or measuring error applicable to the particular circumstance rather than requiring absolute precision or a perfect match.

In a first aspect, a nonwoven fibrous web is provided. The nonwoven fibrous web comprises: a plurality of randomly arranged continuous fibers bonded together, wherein at least some of the continuous fibers comprise an open celled porous structure.

In a second aspect, a method of making a nonwoven fibrous web is provided. The method comprises: extruding filaments of fiber-forming material from an extrusion head into a gas stream; directing the filaments through a processing chamber in which gaseous currents apply a longitudinal stress to the filaments; subjecting the filaments to turbulent flow conditions after they exit the processing chamber, the temperature of the filaments being controlled so that at least some of the filaments solidify while in the turbulent field to form fibers that along their length are of uniform diameter but vary in morphology, wherein the fibers exhibit a draw down ratio of 50 or greater; collecting the processed fibers on a collector as a nonwoven fibrous web; subjecting the collected nonwoven fibrous web to a bonding operation; and stretching the nonwoven fibrous web to fracture at least a portion of the fibers to generate an open celled porous structure in the fractured fibers.

The below disclosure relates to both the first and second aspects.

Fiber-forming material may be extruded by introducing a fiber-forming material into a hopper, melting the material in an extruder, and pumping the molten material into the extrusion head through a pump. Although solid polymeric material in pellet or other particulate form is most commonly used and melted to a liquid, pumpable state, other fiber-forming liquids such as polymer solutions could also be used.

Fiber-forming materials are employed to form continuous fibers of the nonwoven fibrous web. Often, the continuous fibers comprise one or more semicrystalline polymers. At least one amorphous polymer may optionally be included in a blend with at least one semicrystalline polymer. In some cases, the continuous fibers comprise a polymer having a polydispersity index (PDI) of 3 or greater, 4 or greater, 5 or greater, 6 or greater, 7 or greater, 8 or greater, 9 or greater, or 10 or greater.

Typically, the continuous fibers comprise a polypropylene polymer from Total Petrochemicals (Houston, TX) having a melt flow index of 0.5 to 100, inclusive. For instance, the polymer may have a melt flow index of 0.5 grams per 10 minutes (g/10 min) or greater, 1 g/10 min, 2 g/10 min, 5 g/10 min, 7 g/10 min, 10 g/10 min, 15 g/10 min, 20 g/10 min, 25 g/10 min, 30 g/10 min, 35 g/10 min, 40 g/10 min, 45 g/10 min, or g/10 min or greater; and 100 g/10 min or less, 95 g/10 min, 90 g/10 min, 85 g/10 min, 80 g/10 min, 75 g/10 min, 70 g/10 min, 65 g/10 min, 60 g/10 min, or 55 g/10 min or less.

Suitable materials for the continuous fibers include for instance and without limitation, at least one of a polypropylene (PP), a polyethylene (PE), a polymethyl pentene (PMP), a polyoxymethylene (POM), a polyvinylidene difluoride (PVDF), polybutene- 1, or copolymers thereof. Optionally, the continuous fibers include a blend of at least two polymers, e.g., a blend of a first PP and a second PP. In some cases, one PP is preferred or two or more (e.g., different) PPs are preferred. For instance, the continuous fibers may comprise a PP having a number average molecular weight (Mn) of 250,000 grams per mole (g/mol) or greater, 275,000 g/mol, 300,000 g/mol, 325,000 g/mol, 350,000 g/mol, 375,000 g/mol, or 400,000 g/mol or greater; and 800,000 g/mol or less, 775,000 g/mol, 750,000 g/mol, 725,000 g/mol, 700,000 g/mol, 675,000 g/mol, 650,000 g/mol, 625,000 g/mol, 600,000 g/mol, 575,000 g/mol, 550,000 g/mol, 525,000 g/mol, 500,000 g/mol, 475,000 g/mol, 450,000 g/mol, or 425,000 g/mol or less. The continuous fibers may comprise a PP having a number average molecular weight of 250,000 g/mol to 800,000 g/mol, inclusive. Exemplary PPs include for instance those polypropylenes commercially available under the trade designation “PPH3264” and “PPH3766” both from TotalEnergies Petrochemicals & Refining USA, Inc. (Houston, TX).

Suitable crystalline thermoplastic polypropylene homopolymer resins are available from TotalEnergies Petrochemicals & Refining USA, Inc. (Houston, TX) such as, for example Homopolymer Polypropylene 3281, 3274, PPH3060, 3273, 3272, 3371, PPH4022, PPH4069, 3462, 3571, 3662, M3661, 3766, 3865, 3860. Other suitable polypropylene homopolymers are available from Lyondel-Basell Industries (Pasadena, TX) under the trade designation PRO-FAX such as, for example, PRO-FAX 1280 PRO-FAX 814, PRO-FAX 1282, PROFAX 1283 or under other trade designation such as ADFLUEX X500F, ADSYL 3C30F, HP403G, TOPPYL SP 2103. Additional suitable polypropylene homopolymers are available from INEOS Olefins & Polymers, USA (Carson, CA), for example INEOS H01-00, INEOS H02C-00, INEOS H04G-00, and INEOS H12G-00. Other suitable polypropylene homopolymers are available from Braskem Chemical and Plastics Company (LaPorte, TX), for example, F008, F013M, FF026, FF030F2. Further suitable polypropylene homopolymers are available from Exxon-Mobil Chemical Co. (Spring, TX), for example, PP1024E4, PP2252E3, PP4292E1, and PP4612E2, PP 4792,

Suitable crystalline thermoplastic polyethylene (PE) homopolymer resins are available from Exxon-Mobil Chemical Co. Spring, TX), for example, HDPE 6908. Suitable polyethylene homopolymers are also available from TotalEnergies Petrochemicals& Refining USA, Inc. (Houston, TX), for example, High density polyethylene HDPE 56020, HDPE 55060, HDPE 5802, HDPE 51090, HDPE 5502. Other suitable polyethylene homopolymers are available from Braskem Chemical and Plastics Company (LaPorte, TX), for example, HF0144, HF0150, HF0147, and FH35; polyethylene polymer from NOVA Chemicals Corporation (Calgary, AB, Canada), for example, SUPRASS HPsl67-AB, HPs267-AB, HPs667-AB, SCLAIR 19E, SCLAIR99L, NOVAPOL HB-L354-A.

In some embodiments, the resin can also include one or more poly(methyl)pentene (PMP) copolymer resins. Suitable grades of PMP copolymer resin having a low content of linear or branched alpha olefin comonomers are available from Mitsui Chemical (Minato-Ku, Tokyo, Japan) under the general trade designation TPX, for example resin grades DX470, RT18, DX820, and DX845.

In some embodiments, the resin can also include one or more polyvinylidene difluoride (PVDF) homopolymer or copolymer resins. Suitable PVDF resins are available under the trade designations Dyneon Fluoroplsic PVDF 6008, 6010, and 6012 from 3M Company (St Paul, MN), and Solef 6008, Solef 6010, and Solef 6012 from Solvay Specialty Polymers, Alpharetta, GA.

In some embodiments, the resin can also include one or more polyoxymethylene (POM) homopolymer or copolymer resins. Suitable polyoxymethylene resins are available under the trade designations TENAC 2010 homopolymer acetal, TENAC 3010, TENAC4010, and TENAC4060 from Asahi Kasei, Delrin 511CPE NC010 acetal homopolymer, and Delrin 100CPE NC010 acetal homopolymer from DuPont Mobility and Materials, Wilmington, Delaware.

Suitable crystalline thermoplastic polybutene-1 (PB-1) homopolymer resins are available from Lyondel-Basell Industries (Pasadena, TX) for example Toppyl PB 0110M, Toppyl PB 8640M, Toppyl PB 8310, Toppyl PB 8340M.

The method includes extruding filaments of fiber-forming material from an extrusion head into a gas stream. The extrusion head may be a conventional spinneret or spin pack, generally including multiple orifices arranged in a regular pattern, e.g., straight-line rows. The method further includes directing the filaments through a processing chamber in which gaseous currents apply a longitudinal (e.g., orienting) stress to the filaments. In select embodiments, the fiberforming material comprises a PP and the filaments are extruded through a hole die at a temperature of 190°C to 270°C and at a melt output of less than 2 gram per hole per minute (e.g., 1.8 gram per hole per minute or less, 1.6 gram per hole per minute, 1.4 gram per hole per minute, 1.2 gram per hole per minute, 1 gram per hole per minute, 0.9 gram per hole per minute, 0.8 gram per hole per minute, 0.7 gram per hole per minute, 0.6 gram per hole per minute, 0.5 gram per hole per minute, 0.4 gram per hole per minute, or 0.3 gram per hole per minute). The filaments are subjected to turbulent flow conditions after they exit the processing chamber and the temperature of the filaments is controlled so that at least some of the filaments solidify while in the turbulent field to form fibers that along their length are of uniform diameter but vary in morphology. The continuous fibers exhibit a draw down ratio of 50 or greater, such as 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 180, 200, 220, 240, 260, 280, 300, 320, 340, 360, 380, 400, 420, 440, 460, 480, or 500 or greater. As used herein, the “draw down ratio” refers to the ratio of a cross-sectional area of the extrusion head to a cross-sectional area of the final fiber.

The turbulent flow conditions are provided by turbulent currents of air or other fluid. Turbulence occurs as the currents passing through, e.g., an attenuator, reach an unconfmed space at the end of the attenuator, where the pressure that existed within the attenuator is released. The current stream widens as it exits the attenuator, and eddies develop within the widened stream. These eddies - whirlpools of currents running in different directions from the main stream - subject filaments within them to forces different from the straight-line forces the filaments are generally subjected to within and above the attenuator. For example, filaments can undergo a to- and-fro flapping within the eddies and be subjected to forces that have a vector component transverse to the length of the fiber. The processed filaments are long and travel a tortuous and random path through the turbulent field. Different portions of the filaments experience different forces within the turbulent field. To some extent the lengthwise stresses on portions of at least some filaments are relaxed, and those portions consequently become less oriented than those portions that experience a longer application of the lengthwise stress.

In some embodiments, the filaments are subjected to the turbulent flow conditions by subjection to air flow of 150 meters per second (m/s) air flow or greater, 160 m/s, 171 m/s, 182 m/s, 192 m/s, 203 m/s, 214 m/s, 226 m/s, or 237 m/s or greater. Typically, higher air flow gives a more uniform fiber size. In some cases, 294 m/s is a suitable maximum air flow to which the filaments may be subjected to during the turbulent flow.

The temperature of the filaments within the turbulent field can be controlled, for example, by controlling the temperature of the filaments as they enter the attenuator (e.g., by controlling the temperature of the extruded fiber-forming material, the distance between the extrusion head and the attenuator, and the amount and nature of the quenching streams), the length of the attenuator, the velocity and temperature of the filaments as they move through the attenuator, and the distance of the attenuator from a collector. By causing some or all of the filaments and segments thereof to cool within the turbulent field to the temperature at which the filaments or segments solidify, the differences in orientation experienced by different portions of the filaments, and the consequent morphology of the fibers, become frozen in; i.e., the molecules are thermally trapped in their aligned position. The different orientations that different fibers and different segments experienced as they passed through the turbulent field are retained to at least some extent in the fibers as collected on the collector.

The method further comprises collecting the processed fibers on a collector as a nonwoven fibrous web and subjecting the collected nonwoven fibrous web to a bonding operation. In some embodiments, the nonwoven fibrous web comprises fibers of uniform diameter that vary in morphology over their length so as to provide longitudinal segments that differ from one another in softening characteristics during a selected bonding operation. Some of these longitudinal segments soften under the conditions of the bonding operation, i.e., are active during the selected bonding operation and become bonded to other fibers of the web; and others of the segments are passive during the bonding operation. By “uniform diameter” it is meant that the fibers have essentially the same diameter (varying by 10 percent or less) over a significant length (i.e., 5 centimeters or more) within which there can be and typically is variation in morphology.

In select embodiments, the bonding operation comprises an autogenous bonding operation comprising heating the collected web without application of calendaring pressure, some longitudinal segments softening under the conditions of the autogenous bonding operation and bonding to other adjacent fibers, and other longitudinal segments being passive during the autogenous bonding operation. Alternatively, the boding operation may include a different type of bonding operation, such as calendaring or point-bonding, which are well-known to the skilled practitioner.

The (e.g., individual) fibers are preferably oriented in microstructures; i.e., the fibers preferably comprise molecules that are aligned lengthwise of the fibers and are locked into (i.e., are thermally trapped into) that alignment. As such, the polymeric material used for the fibers has the ability to develop a row lamellar crystal structure, such as noted in US Patent No 4,541,981 (Lowery et al.). In preferred embodiments, the passive longitudinal segments of the fibers are oriented to a degree exhibited by typical spunbond fibrous webs. More details regarding spunbond webs may be found, for instance, in US Patent Nos. 6,916,752 and 7,279,440 (both to Berrigan et al.). In crystalline or semicrystalline polymers, such segments preferably exhibit strain-induced or chain-extended crystallization (i.e., molecular chains within the fiber have a crystalline order aligned generally along the fiber axis). As a whole, the web can exhibit strength properties like those obtained in spunbond webs, while being strongly bondable in ways that a typical spunbond web cannot be bonded. And autogenously bonded webs of the invention tend to have a loft and uniformity through the web that are not available with the point-bonding or calendaring generally used with spunbond webs. Further details regarding nonwoven fibrous webs having autogenous bonding and how to make them are described in US Patent No. 7,695,660 (Berrigan et al.), incorporated herein by reference.

The method further comprises stretching the nonwoven fibrous web to fracture at least a portion of the fibers to generate an open celled porous structure in the fractured fibers. Optionally, the nonwoven fibrous web may first be folded, particularly if the equipment used to stretch the web is configured for a greater thickness than one layer of the nonwoven fibrous web. Surprisingly, the nonwoven fibrous webs structurally survive being stretched despite some of the fibers completely breaking during the stretching process. Without wishing to be bound by theory, is believed that either some of fiber bonds survive the stretching process and/or many fibers remain well entangled as continuous fibers. The stretched webs are generally thicker and loftier due to an increased fiber length and a reduced bonding density, as compared to the nonwoven fibrous webs prior to stretching.

Referring to FIG. 7, a photograph is provided of a top view of a disc of nonwoven fibrous web 700 following stretching in one (e.g., horizontal) direction indicated by the double arrows, prepared according to Example 3 (E3) described below. As can be seen in the figure, the nonwoven fibrous web is opaque following stretching, plus maintains good web integrity, e.g., a majority of fiber bonding points remain.

Often, the stretching of the nonwoven fibrous web is performed in a machine direction to impart the open celled porous structure to the fibers (i.e., fracture the fibers). Typically, at least some minority of the individual fibers break and/or at least some minority of the bonds between adjacent fibers come apart, as additional result(s) of the stretching of the web. The method optionally further comprises stretching the nonwoven fibrous web in a transverse direction to disperse the broken and/or unbonded fibers. Alternatively, the initial stretching of the nonwoven fibrous web is performed in the transverse direction to impart the open celled porous structure to the fibers (i.e., fracture the fibers), and optionally the nonwoven fibrous web is further stretched in the machine direction to disperse the broken and/or unbonded fibers. In some cases, the stretching of the nonwoven fibrous web is performed in biaxial directions (i.e., stretched in both the machine and the transverse directions simultaneously) to fracture the fibers. In some cases, a suitable stretching ratio in the machine direction is different from that in the transverse directions.

In some cases, a stretched nonwoven fibrous web exhibits a basis weight of no more than 300 grams per square meter (g/m²), 275 g/m², 250 g/m², 225 g/m², 200 g/m², 175 g/m², 150 g/m², 125 g/m², 100 g/m², 75 g/m², or no more than 50 g/m²; and 20 g/m² or greater, 25 g/m², 30 g/m², 35 g/m², 40 g/m², 45 g/m², or 50 g/m² or greater. Such a basis weight advantageously provides a lighter weight article than nonwoven fibrous webs having a basis weight above 300 g/m². In select embodiments, the method further comprises annealing the nonwoven fibrous web prior to stretching the nonwoven web. Preferably, any annealing is performed at a temperature below a melting point of the fiber-forming material, for example, a nonwoven fibrous web formed of PP is preferably annealed at 120-150°C. The annealing time could be from one second to hours; preferably 1-60 minutes; more preferably 5-30 minutes.

Stretching can be advantageously performed using single or multi-stage cold stretching, optionally followed by single or multi-stage hot stretching. Preferably, the cold stretching temperature is selected to be between 5°C and 70°C above the glass transition temperature (T_g) of the polymer of the nonwoven fibrous web, more preferably between 10°C to 50°C (for example, it is noted that the glass transition temperature of PP is -10°C and PP is preferably stretched at 20°C to 30°C). Preferably, the hot stretching temperature is selected to be between 10°C and 120°C below the melt temperature of the polymer, more preferably between 20°C to 60°C, for example PP is preferably stretched at 100°C to 150°C.

A nonwoven fibrous web may be advantageously stretched to form an open porous structure in fibers by uniaxial extension of at least 5%, and up to 500%, more preferably at least 10% and up to 300%.

A nonwoven web after stretching may advantageously be exposed to a step of heat-setting to reduce the stress inside the individual fibers. The heat-setting temperature is typically selected to be higher than the hot stretching temperature by at least 5°C, at least 10°C, or even at least 15 °C. The heating setting duration is typically selected to be at least 30 seconds, or at least one minute.

Alternatively, a nonwoven web after stretching may advantageously be exposed to a relaxation step by allowing fiber lengths to shrink to a certain extent, which is at least 2%, or even at least 5%. Heating setting and relaxation can be used alone or combination.

Unexpectedly, good fiber porosity has been achieved by such “dry” stretching of a nonporous nonwoven fibrous web. In some cases, 30% or more of the continuous fibers comprise the open celled porous structure, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90% or more of the continuous fibers comprise the open celled porous structure. It is noted that in some cases, at least some fibers at a major surface of the nonwoven fibrous web lack an open celled porous surface. This typically occurs when there is greater bonding of individual fibers at the major surface of the nonwoven fibrous web than in the interior of the web, especially if there has been any calendaring of the nonwoven fibrous web or if the fibers are over exposed to high temperature and the fiber microstructure is changed.

The continuous fibers having an open celled porous structure comprise a plurality of pores. The plurality of pores results in the fibers having a higher surface area. For example, in one embodiment, the porous polymeric fibers have an average surface area of at least 5, 10, 15, 20, 35, 30, or even at least 40 m²/g as determined by BET (Brunauer Emmet Teller) nitrogen adsorption.

The continuous fibers having an open celled porous structure typically exhibit a (fiber) porosity of 5 volume percent (vol %) or greater, 10 vol %, 12 vol %, 15 vol %, 17 vol %, 20 vol %, 25 vol %, 30 vol %, 35 vol %, 40 vol %, 45 vol %, or 50 vol %; and 80 vol % or less, 75 vol %, 70 vol %, 65 vol %, 60 vol %, 55 vol %, or 50 vol % or less. The porosity advantageously imparts at least one of improved (e.g., fluid) absorbency, acoustic properties, insulation properties, or functionalization capability.

Additionally, the porosity of the nonwoven fibrous web may be greater than 90%, 91%, 92%, 93%, 94%, or greater than 95%. As the porosity of the nonwoven fibrous web is determined by measuring solidity and subtracting from 100, the measured solidity of the nonwoven fibrous web may be less than 10%, 9%, 8%, 7%, 6%, or less than 5%.

Referring to FIG. 1 A, a scanning electron microscopy (SEM) image of a portion of an exemplary nonwoven fibrous web 100, prepared according to Example 3 (E3) described below. In FIG. 1A, numerous individual fibers 110a of the web 100 are visible. Referring now to FIG. IB, an SEM image of a portion of a fiber 110b of the exemplary nonwoven fibrous web of FIG. 1A is provided. The greater magnification used for the image of FIG. IB allows visualization of the open celled porous structure 120b of the fiber 110b.

Similar to FIG. 1 A, FIG. 2A provides an SEM image of a portion of another exemplary nonwoven fibrous web 200, prepared according to Example 4 (E4) described below. In FIG. 2A, numerous individual fibers 210a of the web 200 are visible.

Referring now to FIG. 2B, an SEM image of a portion of a few adjacent fibers 210b of the exemplary nonwoven fibrous web of FIG. 2A is provided. The greater magnification used for the image of FIG. 2B allows visualization of the open celled porous structure 220b of the fibers 210b.

As noted above, the fibers of the nonwoven fibrous web exhibit a draw down ratio of 50 or greater. It has been discovered that fibers with higher draw down ratios tend to have a more uniform diameter down the length of the fiber, whereas fibers with lower draw down ratios tend to have a less uniform diameter down the length of the fiber. This can be seen in the SEM images of FIGS. 3-4. FIG. 3 is an SEM image of a portion of an exemplary nonwoven fibrous web 300 that includes fibers 310 having a draw down ratio of 68, made according to Example 2 (E2) described below. FIG. 4 is an SEM image showing a few fibers 410, including one with clear necking such that the fiber 410 includes at least a portion of its length having a diameter DI that is significantly larger than another portion of its length that has a diameter D2. Depending on the application of the nonwoven fibrous web, the inclusion of fibers having a lower draw down ratio and some amount of necking is acceptable, for example, less than 50% of the total fibers have a necked fiber segment, preferably less than 10%. In other applications it is preferred to use a higher draw down ratio, for instance 100 or greater, 120, 140, or 160 or greater, to minimize the occurrence of necking in fibers of the nonwoven fibrous web, for instance with webs used as absorbent media, acoustic media, insulation media, etc.

Referring to FIG. 5, an SEM image is provided of a portion of a surface of a fiber 510 of an exemplary nonwoven fibrous web prepared according to the Example 5 (E5) showing that, in some cases, the open celled porous structure comprises microfibrils that connect lamellae microstructures. FIG. 5 shows a fiber 510 that includes a plurality of microfibrils 512 extending between opposing lamellae microstructures 514. The microfibrils 512 and lamella microstructures 514 together define voids 524 of the open celled porous structure of the fiber 510. The size of the microfibrils 512 can vary, as evident in FIG. 5, typically including at least one dimension that has a length of 1 micrometer or smaller. In some cases, the lamella microstructures tend to have a non-row ordered configuration, but rather have been deformed during stretching to result in curved lamella microstructures.

In other cases, as visible in FIG. 5, the lamellae are not present in perfectly parallel rows but rather overall form adjacent rows attached by microfibrils 512.

It is clear from FIG. 5 that the open celled porous structure lacks filler particles present at least partially in the voids of the porous structure. This is in direct contrast to some prior methods for forming porous structure in fibers by including additives such as filler material (e.g., particulate fillers and nanoinclusion additives), for instance as described in US Patent Nos. 5,766,760 (Tsai et al.) and 11,001,944 (Topolkaraev et al.), respectively. Although a filler may be a suitable optional additive to include in nonwoven fibrous webs according to some embodiments of the present disclosure, such fillers do not significantly contribute to pore formation. This is evidenced at least by less than 20% of the total open celled pores of a fiber comprising a filler visible in the void, less than 15%, less than 10%, or less than 5% of the total open celled pores of a fiber comprising a filler visible in the void.

Often, continuous fibers have an average diameter of 5 micrometers or greater, 10 micrometers, 15 micrometers, 20 micrometers, 25 micrometers, 30 micrometers, 40 micrometers, 50 micrometers, 60 micrometers, 70 micrometers, 80 micrometers, 90 micrometers, or 10 micrometers or greater; and 200 micrometers or less, 190 micrometers, 180 micrometers, 170 micrometers, 160 micrometers, 150 micrometers, 140 micrometers, 130 micrometers, 120 micrometers, 110 micrometers, 100 micrometers, 90 micrometers, 80 micrometers, 70 micrometers, 60 micrometers, or 50 micrometers or less. In some cases, a small distribution of fiber diameters is advantageously achieved, e.g., such that the average diameter of the fibers varies by ± 30 micrometers or less, ± 25 micrometers, ± 20 micrometers, or ± 15 micrometers or less. A cross-sectional shape of fibers of exemplary nonwoven fibrous webs is not particularly limited. Referring to FIGS. 6A-6D, in some cases at least some of the fibers have a cross-section having a shape selected from a circle (i.e., FIG. 6A), a (e.g., rectangular) bar (i.e., FIG. 6B), an oval (i.e., FIG. 6C), or a plus sign (i.e., FIG. 6D). Various other shapes may be useful, such as multilobal (e.g., trilobal) cross-sectional fibers, or hollow cross-sectional fibers. In addition to shape, the cross-section of a fiber also includes cross-sectional distances. Cross-sectional distances are equivalent to the lengths of chords that could join points on the perimeter of the cross-section. The term “longest cross-sectional distance” refers to the greatest length of a chord that can be drawn through the cross-section of a fiber, at a given location along its axis. In cases where the shape of the fibers is not a circle, “longest cross-sectional shape” may be substituted for “diameter”.

Exemplary Embodiments

In a first embodiment, the present disclosure provides a nonwoven fibrous web. The nonwoven fibrous web comprises a plurality of randomly arranged continuous fibers bonded together, wherein at least some of the continuous fibers comprise an open celled porous structure.

In a second embodiment, the present disclosure provides a nonwoven fibrous web according to the first embodiment, wherein the open celled porous structure comprises microfibrils that connect lamellae microstructures.

In a third embodiment, the present disclosure provides a nonwoven fibrous web according to the first embodiment or the second embodiment, wherein the continuous fibers comprise one or more semicrystalline polymers.

In a fourth embodiment, the present disclosure provides a nonwoven fibrous web according to any of the first through third embodiments, wherein the continuous fibers comprise at least one of a polypropylene (PP), a polyethylene (PE), a polymethyl pentene (PMP), a polyoxymethylene (POM), a polyvinylidene difluoride (PVDF), polybutene- 1, or copolymers thereof.

In a fifth embodiment, the present disclosure provides a nonwoven fibrous web according to any of the first through fourth embodiments, wherein the continuous fibers comprise a PP.

In a sixth embodiment, the present disclosure provides a nonwoven fibrous web according to the fifth embodiment, wherein the continuous fibers comprise a PP having a number average molecular weight of 250,000 grams per mole or greater to 800,000 grams per mole or less.

In a seventh embodiment, the present disclosure provides a nonwoven fibrous web according to any of the first through sixth embodiments, wherein the continuous fibers comprise a blend of at least two polymers. In an eighth embodiment, the present disclosure provides a nonwoven fibrous web according to any of the first through seventh embodiments, wherein the continuous fibers comprise a blend of a first PP and a second PP.

In a ninth embodiment, the present disclosure provides a nonwoven fibrous web according to any of the first through eighth embodiments, wherein the continuous fibers comprise a blend of at least one amorphous polymer and at least one semicrystalline polymer.

In a tenth embodiment, the present disclosure provides a nonwoven fibrous web according to any of the first through ninth embodiments, wherein the continuous fibers comprise a polymer having a polydispersity index (PDI) of 3 or greater, 5 or greater, or 10 or greater.

In an eleventh embodiment, the present disclosure provides a nonwoven fibrous web according to any of the first through tenth embodiments, wherein the continuous fibers comprise a polymer having a melt flow index of 0.5 to 100, inclusive.

In a twelfth embodiment, the present disclosure provides a nonwoven fibrous web according to any of the first through eleventh embodiments, wherein 30% or more of the continuous fibers comprise the open celled porous structure.

In a thirteenth embodiment, the present disclosure provides a nonwoven fibrous web according to any of the first through twelfth embodiments, exhibiting a basis weight of no more than 300 grams per square meter.

In a fourteenth embodiment, the present disclosure provides a nonwoven fibrous web according to any of the first through thirteenth embodiments, wherein the continuous fibers have an average diameter of 5 micrometers to 200 micrometers.

In a fifteenth embodiment, the present disclosure provides a nonwoven fibrous web according to any of the first through fourteenth embodiments, wherein the continuous fibers exhibit a porosity of 5 volume percent to 80 volume percent.

In a sixteenth embodiment, the present disclosure provides a nonwoven fibrous web according to any of the first through fifteenth embodiments, wherein the continuous fibers exhibit an average surface area of at least 5, 10, 15, 20, 35, 30, or at least 40 m²/g as determined by BET (Brunauer Emmet Teller) nitrogen adsorption.

In a seventeenth embodiment, the present disclosure provides a method of making a nonwoven fibrous web. The method comprises extruding filaments of fiber-forming material from an extrusion head into a gas stream; directing the filaments through a processing chamber in which gaseous currents apply a longitudinal stress to the filaments; and subjecting the filaments to turbulent flow conditions after they exit the processing chamber, the temperature of the filaments being controlled so that at least some of the filaments solidify while in the turbulent field to form fibers that along their length are of uniform diameter but vary in morphology, wherein the fibers exhibit a draw down ratio of 50 or greater. The method further comprises collecting the processed fibers on a collector as a nonwoven fibrous web; subjecting the collected nonwoven fibrous web to a bonding operation; and stretching the nonwoven fibrous web to fracture at least a portion of the fibers to generate an open celled porous structure in the fractured fibers.

In an eighteenth embodiment, the present disclosure provides a method according to the seventeenth embodiment, further comprising annealing the nonwoven fibrous web prior to stretching the nonwoven web; wherein the annealing is performed at a temperature below a melting point of the fiber-forming material.

In a nineteenth embodiment, the present disclosure provides a method according to the seventeenth embodiment or the eighteenth embodiment, wherein the stretching was in a machine direction and wherein the method further comprises stretching the nonwoven fibrous web in a transverse direction to disperse the fractured fibers.

In a twentieth embodiment, the present disclosure provides a method according to any of the seventeenth through nineteenth embodiments, wherein the fiber-forming material comprises a PP and the filaments are extruded through a hole die at a temperature of 190°C to 250°C and at a melt output of less than 1.

In a twenty-first embodiment, the present disclosure provides a method according to the twentieth embodiment, wherein the filaments are subjected to the turbulent flow conditions at an air flow of 150 meters per second (m/s) or greater.

In a twenty-second embodiment, the present disclosure provides a method according to any of the seventeenth through twenty-first embodiments, wherein the fiber-forming material comprises a blend of a first PP and a second PP.

In a twenty-third embodiment, the present disclosure provides a method according to any of the seventeenth through twenty-second embodiments, wherein the bonding operation comprises an autogenous bonding operation comprising heating the collected web without application of calendering pressure, some longitudinal segments softening under the conditions of the autogenous bonding operation and bonding to other adjacent fibers, and other longitudinal segments being passive during the autogenous bonding operation.

In a twenty-fourth embodiment, the present disclosure provides a method according to any of the seventeenth through twenty-third embodiments, wherein at least some fibers at a major surface of the nonwoven fibrous web lack an open celled porous surface.

In a twenty-fifth embodiment, the present disclosure provides a method according to any of the seventeenth through twenty-fourth embodiments, wherein at least some of the fibers have a cross-section having a shape selected from a circle, a bar, an oval, or a plus sign. Examples

Objects and advantages of this disclosure are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this disclosure. Unless otherwise noted or otherwise apparent from the context, all parts, percentages, ratios, etc. in the Examples and the rest of the specification are by weight. A materials table (below) lists materials used in the examples and their sources.

Materials Used in the Examples

Test Methods:

PE1-PE6 web precursors and E1-E6 porous fiber webs were characterized using the test methods described below.

For web thickness and web solidity, a web disc with 135 mm diameter was cut and weighed. Its thickness was measured using a testing gauge at an applied pressure of 150 pascals (Pa). The web solidity was calculated from web disc volume, polymer density (0.91 grams per cubic centimeter (g/cc) for polypropylene) and its weight.

The web pressure drop was tested using an air permeation test in which air was passed through the web at a face velocity of 14 centimeters per second (cm/sec) under room temperature. The Effective Fiber Diameter (EFD) of the web was evaluated according to the method set forth in Davies, C. N., “The Separation of Airborne Dust and Particles,” Institution of Mechanical Engineers, London, Proceedings IB, 1952. The test was run at a face velocity of 14 cm/sec.

To determine the melt draw down ratio (DDR) for preparing the PE1-PE6 web precursors, fiber bundles were collected in an unbonded condition after the attenuator. They were cross-cut and actual fiber sizes (AFD) were measured by using an optical microscope. Melt draw down ratio (DDR) was calculated from cross-sectional surface area of actual fibers and the hole of the spinneret as follows:

Do is the hole size of spinneret and Di is AFD of fibers in web precursors.

To determine the fiber porosity of E1-E6 samples, a 135 mm or 47 mm disc was cut from a stretched web sample from each of E1-E6 and weighed as the initial mass (mO). Then, the disc was soaked in MPrOH for about 2 min to allow the web to fully saturate. The soaked web was drained and sandwiched between two cleanroom wipers to absorb the excess solvent. Some pressure was applied to the sandwich for a fast solvent absorption by wipers. Wipers were changed until no more solvent was visually seen after damping. The saturated disc web was weighed again in as the final mass (ml). Fiber porosity was calculated based on weight change, polypropylene density (dO), and MPrOH density (dl).

(ml — m0)/dl Porosity = — _n , _ln — - — - — — — ^x 100% mO/dO + (ml — m0)/dl

It was found that the web precursors of PE1-PE6 showed some MPrOH absorption, which is attributed to solvent adsorption onto fiber exterior surface. MPrOH absorption by the corresponding web precursor was measured as described above. Corrected fiber porosity was obtained by subtracting this surface contribution from the above measured porosity.

SEM was used to image fiber surface microstructure. Low magnification images were obtained using a table SEM (Model Hitachi TM4000 plus II, obtained from Hitachi High-Tech Corporations, Japan); high magnification images were obtained using a field emission SEM(FE- SEM), (Model Hitachi S-4700, obtained from Hitachi High-Tech Corporations, Japan); Preparatory Examples 1-6 (PE1-PE6) Preparation ofw eb precursors:

PE1-PE6 web precursors were prepared using an apparatus as disclosed in US Patents US 6,824,372, US 6,916,752, and US 7,695,660 (each to Berrigan et al.) incorporated herein by reference, from various grades of polypropylene homopolymers under process conditions summarized in Table 1. If a mixture of polymers were used, the polymer resin mixture was made by drying blending. A 2.5 inch (50 mm) diameter single-screw extruder was used to extrude polymer and melts were fed into a spinneret with 780 orifices. The hole diameter was 0.014 inch (0.355 mm) and the length to diameter (L/D) ratio was 4. Average melt output per hole (gram per hole per min, ghm) was calculated from the total hole count and the total output from melt pump. The formulation and the process conditions utilized for preparing PE1-PE6 such as melt output, polymer melt pressure existing from melt pump, total volume of air passed through the attenuators, and through-air bond temperature are shown in Table 1. PE1-PE6 web precursors were collected as web rolls.

The characteristics of PE1-PE6 web precursors determined above are summarized in Table 2, below.

Examples 1-6 (E1-E6) Cold/hot stretching ofPEl-PE6 web precursor to form porous fiber nonwoven:

PE1-PE6 web precursor samples (about 203 mm in machine direction by 305 mm in cross-web direction) were cut and thermally treated (i.e., annealed) in a convective oven for 10 min. The oven temperature was set at 140°C. For cold/hot stretching, annealed samples were folded along machine direction to form about linch- (25 mm) wide strips, which were firmly clamped by Instron grips in a temperature-controlled environmental chamber of an Instron Mechanical Tester (Model 5969, from Instron Corporation, Norwood, MA). 127mm (5inch) long web samples between grips were cold stretched to 40% at a stretching rate 600 mm/minute at 25 °C and subsequently hot-stretched with stretching rate 30 mm/min at 120°C. Total extension ratios after 10% relaxation were 100%. Stretched webs were manually stretched to de-orient fibers in crossweb direction and the resulting webs had about 215 mm width.

Table 3, below, summarizes the measured properties of porous fiber nonwovens of E2-E5.

FIG. 1A, FIG. 2A, and FIG. 3 are SEM images of a portion of an exemplary nonwoven fibrous web, prepared according to Examples 3 (E3), 4 (E4), and 2 (E2), respectively.

FIG. 5 is a high magnification scanning electron image of porous fiber nonwoven of E5. Porous microstructures were clearly seen with separated crystal lamellae (block) and microfibrils between them. Table 1.

Table 2. Properties of web precursors

Table 3.

BET Surface Area

BET Surface area was measured by gas sorption experiments performed using a Micromeritics Instrument Corporation (Norcross, GA) accelerated surface area and porosimetry (ASAP) 2020 Plus system instrument. In a Micromeritics half inch diameter sample tube, 50-250 milligrams of sample was degassed by first heating under high vacuum (500 micrometers of Hg) on the degas port for 3 hours at 80 °C. At the end of this degassing step, the sample tube was backfilled with nitrogen, and the sample tube was moved over to the analysis port. The sample was then further degassed by heating under ultra-high vacuum (3-7 micrometers Hg) on the analysis port of the instrument for 3 hours at 80 °C. Nitrogen sorption isotherms at 77 K were obtained using low pressure dosing (5 cm³/g) at a relative pressure (p/p°) less than 0. 1 and a pressure table of linearly spaced pressure points for a p/p° from 0.1 to 0.998. The method for all isotherms made use of the following equilibrium intervals: 90 seconds at p/p° less than 10-5, 40 seconds at p/p° in a range of 10-5 to 0. 1, and 20 seconds at p/p° greater than 0. 1. Helium was used for the free space determination, after nitrogen sorption analysis, both at ambient temperature and at 77 K. BET specific surface areas (SABET) were calculated from nitrogen adsorption data by multipoint Brunauer-Emmett-Teller (BET) analysis. Apparent micropore distributions were calculated from nitrogen adsorption data by density functional theory (DFT) analysis using the standard nitrogen at 77 K density functional theory (DFT) model. Total pore volume was calculated from the total amount of nitrogen adsorbed at a p/p° equal to approximately 0.98. BET, DFT, and total pore volume analyses were performed using Micromeritics MicroActive Version 5.02 software.

The BET surface area was measured and found to be 4.0 m²/g for PE5 and 48.2 m²/g for E5.

All of the patents and patent applications mentioned above are hereby expressly incorporated by reference. The embodiments described above are illustrative of the present invention and other constructions are also possible. Accordingly, the present invention should not be deemed limited to the embodiments described in detail above and shown in the accompanying drawings, but instead only by a fair scope of the claims that follow along with their equivalents.

Claims

CLAIMS:

1. A nonwoven fibrous web comprising: a plurality of randomly arranged continuous fibers bonded together, wherein at least some of the continuous fibers comprise an open celled porous structure.

2. The nonwoven fibrous web of claim 1, wherein the open celled porous structure comprises microfibrils that connect lamellae microstructures.

3. The nonwoven fibrous web of claim 1 or claim 2, wherein the continuous fibers comprise one or more semicrystalline polymers.

4. The nonwoven fibrous web of any of claims 1 to 3, wherein the continuous fibers comprise at least one of a polypropylene (PP), a polyethylene (PE), a polymethyl pentene (PMP), a polyoxymethylene (POM), a polyvinylidene difluoride (PVDF), polybutene- 1, or copolymers thereof.

5. The nonwoven fibrous web of any of claims 1 to 4, wherein the continuous fibers comprise a PP.

6. The nonwoven fibrous web of claim 5, wherein the continuous fibers comprise a PP having a number average molecular weight of 250,000 grams per mole or greater to 800,000 grams per mole or less.

7. The nonwoven fibrous web of any of claims 1 to 6, wherein the continuous fibers comprise a blend of at least two polymers.

8. The nonwoven fibrous web of any of claims 1 to 7, wherein the continuous fibers comprise a blend of a first PP and a second PP.

9. The nonwoven fibrous web of any of claims 1 to 8, wherein the continuous fibers comprise a blend of at least one amorphous polymer and at least one semicrystalline polymer.

10. The nonwoven fibrous web of any of claims 1 to 9, wherein 30% or more of the continuous fibers comprise the open celled porous structure.

11. The nonwoven fibrous web of any of claims 1 to 10, exhibiting a basis weight of no more than 300 grams per square meter.

12. The nonwoven fibrous web of any of claims 1 to 11, wherein the continuous fibers exhibit a porosity of 5 volume percent to 80 volume percent. The nonwoven fibrous web of any of claims 1 to 12, wherein the continuous fibers exhibit an average surface area of at least 5, 10, 15, 20, 35, 30, or at least 40 m²/g as determined by BET (Brunauer Emmet Teller) nitrogen adsorption. A method of making a nonwoven fibrous web, the method comprising: extruding filaments of fiber-forming material from an extrusion head into a gas stream; directing the filaments through a processing chamber in which gaseous currents apply a longitudinal stress to the filaments; subjecting the filaments to turbulent flow conditions after they exit the processing chamber, the temperature of the filaments being controlled so that at least some of the filaments solidify while in the turbulent field to form fibers that along their length are of uniform diameter but vary in morphology, wherein the fibers exhibit a draw down ratio of 50 or greater; collecting the processed fibers on a collector as a nonwoven fibrous web; subjecting the collected nonwoven fibrous web to a bonding operation; and stretching the nonwoven fibrous web to fracture at least a portion of the fibers to generate an open celled porous structure in the fractured fibers. The method of claim 14, further comprising annealing the nonwoven fibrous web prior to stretching the nonwoven web; wherein the annealing is performed at a temperature below a melting point of the fiber-forming material. The method of claim 14 or 15, wherein the stretching was in a machine direction and wherein the method further comprises stretching the nonwoven fibrous web in a transverse direction to disperse the fractured fibers. The method of any of claims 14 to 16, wherein the fiber-forming material comprises a blend of a first PP and a second PP. The method of any of claims 14 to 17, wherein the bonding operation comprises an autogenous bonding operation comprising heating the collected web without application of calendering pressure, some longitudinal segments softening under the conditions of the autogenous bonding operation and bonding to other adjacent fibers, and other longitudinal segments being passive during the autogenous bonding operation. The method of any of claims 14 to 18, wherein at least some fibers at a major surface of the nonwoven fibrous web lack an open celled porous surface.

20. The method of any of claims 14 to 19, wherein at least some of the fibers have a crosssection having a shape selected from a circle, a bar, an oval, or a plus sign.