Porous fibrous nonwoven webs and methods of making same

Abstract

The present disclosure provides a nonwoven fibrous web comprising randomly arranged continuous fibers bonded together. At least some of the continuous fibers include an open-cell porous structure. Also provided is a method of manufacturing a non-woven fibrous web, the method comprising: extruding filaments of a fiber-forming material from an extrusion head into a gas stream; directing the filament through a process chamber in which a gas stream applies a longitudinal stress to the filament; and placing the filament in a turbulent flow condition after the filament exits the process chamber. At least some of the filaments solidify in a turbulent field to form fibers that are uniform in diameter but varied in form along their length. The method further includes collecting the treated fibers on a collector as a non-woven fibrous web; the collected non-woven fiber webs are subjected to bonding operation; and stretching the nonwoven fibrous web to break at least a portion of the fibers to create an open-cell porous structure in the broken fibers.

Description

Background Art

[0001] Porous fibers offer one or more advantages of being lightweight, having a soft handfeel, high liquid absorbency, good acoustic and insulating properties, and being easily functionalized. Some current processes for producing porous fiber materials include spinning fibers with extractable fillers (including fillers within the fibers (including immiscible polymers)), or non-solvent precipitation of the fibers to generate a pore microstructure. Through these processes, the fibers tend to be costly to produce and / or have limited porosity. Summary of the Invention

[0002] In a first aspect, a nonwoven fibrous web is provided. The nonwoven fibrous web includes a plurality of randomly arranged continuous fibers bonded together, wherein at least some of the continuous fibers include an open-celled porous structure.

[0003] In a second aspect, a method of manufacturing a nonwoven fibrous web is provided. The method includes: extruding filaments of a fiber-forming material from an extrusion head into a gas stream; guiding the filaments through a treatment chamber in which the gas flow applies longitudinal stress to the filaments; and subjecting the filaments to turbulent conditions after they leave the treatment chamber, controlling the temperature of the filaments such that at least some of the filaments solidify in the turbulent field to form fibers that are uniform in diameter along their length but vary in morphology, wherein the fibers exhibit a draw ratio of 50 or greater. The method further includes: collecting the treated fibers on a collector as a nonwoven fibrous web; performing a bonding operation on the collected nonwoven fibrous web; and stretching the nonwoven fibrous web to break at least a portion of the fibers, thereby generating an open-celled porous structure in the broken fibers.

[0004] At least certain embodiments of the present disclosure provide a simplified process for preparing a porous fiber nonwoven fabric by stretching a bonded nonwoven web. The bonded nonwoven web can be produced by a conventional spunbond process. Then, stretching is applied to the bonded nonwoven web. Unexpectedly, good fiber porosity has been achieved by such a process, which has the potential to significantly reduce the cost of manufacturing a porous fiber nonwoven web. For example, in an alternative method, a typical air-laying process would require several more total steps: fiber spinning, fiber stretching, crimping, fiber cutting, fiber opening, air-laying, and calendering, to form a porous fiber nonwoven web.

[0005] The above summary of the present disclosure is not intended to describe every disclosed embodiment or every implementation of the present disclosure. The following description more specifically illustrates exemplary embodiments. Throughout the application, guidance is provided by way of lists of examples, which can be used in various combinations. In each case, the recited lists are only used as representative groups and should not be construed as exclusive lists. Brief Description of the Drawings

[0006] Figure 1A SEM image of a portion of an exemplary nonwoven fiber web prepared according to Example 3 (E3).

[0007] Figure 1B is Figure 1A SEM image of a portion of the fibers of an exemplary nonwoven fiber web of

[0008] Figure 2A SEM image of a portion of another exemplary nonwoven fiber web prepared according to Example 4 (E4).

[0009] Figure 2B is Figure 2A SEM image of a portion of the fibers of an exemplary nonwoven fiber web of

[0010] Figure 3 SEM image of a portion of another exemplary nonwoven fiber web prepared according to Example 2 (E2).

[0011] Figure 4 is Figure 3 SEM image of a portion of the fibers of an exemplary nonwoven fiber web of

[0012] Figure 5 SEM image of a portion of a fiber having a row-ordered lamellar microstructure prepared according to Example 5 (E5).

[0013] Figure 6A Schematic diagram of the cross-section of a fiber having a circular shape.

[0014] Figure 6B Schematic diagram of the cross-section of a fiber having a bar shape.

[0015] Figure 6C Schematic diagram of the cross-section of a fiber having an oval shape.

[0016] Figure 6D Schematic diagram of the cross-section of a fiber having a cross shape.

[0017] Figure 7 Photo of the top view of a disk of a nonwoven fiber web stretched in one direction prepared according to Example 3 (E3).

[0018] Although the above drawings illustrate several embodiments of the present disclosure, other embodiments are also contemplated as noted in the description. The drawings are not necessarily to scale. In all cases, the present disclosure presents the invention in an exemplary rather than a limiting manner. Detailed Description

[0019] As used herein, the term "filament" refers to a continuous, elongated strand of material, typically longer than 6 inches.

[0020] As used herein, the term "fiber" refers to a single-component fiber; a bicomponent or conjugate fiber (for convenience, the term "bicomponent" is generally used to mean a fiber composed of two components as well as a fiber composed of more than two components); and a fiber segment of a bicomponent fiber, i.e., a portion that occupies a cross-section of the bicomponent fiber and extends along the length of the bicomponent fiber. A single-component fiber web is generally preferred, and the combination of orientation and adhesiveness provided by the present invention makes it possible to use a high-strength, adhesive web of single-component fibers. The described fibers (i.e., fiber segments) can perform an adhesive function and provide high-strength properties as part of a multicomponent fiber. Fibers have two ends and are discrete, and are typically 6 inches or shorter.

[0021] As used herein, the term "rupture" with respect to a fiber means the formation of voids in a portion of the polymeric material of the fiber.

[0022] As used herein, the term "open-celled porous structure" with respect to a fiber structure refers to a fiber having a plurality of pores, at least some of which are connected to adjacent pores such that fluid can be transferred from one major surface of a portion of the fiber to the opposite major surface of the fiber.

[0023] As used herein, the term "microfibril" refers to a portion of the porous structure of a fiber having fibrils, where each dimension is less than 1 micron in size.

[0024] As used herein, the term "lamellar" refers to the crystalline portion of the semi-crystalline polymeric material of a fiber.

[0025] As used herein, the term "continuous" with respect to a fiber means a fiber having a longest dimension greater than 1 centimeter.

[0026] As used herein, the term "meltblown" or "melt-blown" refers to fibers prepared by extruding a molten fiber-forming composition through spinneret holes in a die into a high-velocity gas stream, where the extruded material is first attenuated and then solidified into a fiber mat.

[0027] As used herein, the term "spunbond" or "spun-bond" refers to fibers prepared by extruding a molten filament-forming material through spinneret holes in a die into a low-velocity, optionally heated, gas stream, and the extruded material is then solidified into a thermally-bondable fiber mat before being collected as a web.

[0028] As used herein, the term "amorphous" refers to a polymer that does not exhibit a melting point.

[0029] As used herein, the term "semicrystalline" refers to a polymer that forms crystalline domains during curing in addition to an amorphous phase and exhibits a melting peak during heating and a crystallization peak during curing as measured by dynamic scanning calorimetry (DSC).

[0030] As used herein, the term "porosity" with respect to a fiber refers to the measurement of void space in a fiber having an open-cell porous structure as determined by solvent uptake. A solvent uptake method is described in detail in the following examples.

[0031] As used herein, the term "porosity" with respect to a nonwoven fibrous web refers to the total volume of void space between the individual fibers of the web as determined by measuring the density of the nonwoven fibrous web and subtracting that density from 100. Thus, the density represents the proportion of the total volume of the nonwoven fibrous web that is occupied by the fibers. The density is determined by dividing the measured bulk density of the nonwoven fibrous web by the density of the fibers. The bulk density of the web can be determined by first measuring the weight of the web (e.g., the weight of a 10 cm × 10 cm cross-section). Dividing the measured weight of the web by the area of the web gives the basis weight of the web reported in g / m 2 The reported basis weight. 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 thickness of the web with a 100 mm diameter, 230 g weight located at the center of the top of 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 in g / m 3 The reported. The density is then determined by dividing the bulk density of the nonwoven fibrous web by the density of the material (e.g., polymer) that comprises the fibers of the web. If the material density is not specified by the supplier, the density of the bulk polymer can be measured by standard means. The density is a dimensionless fraction and is typically reported as a percentage.

[0032] As used herein, the term "self-bonding" refers to the bonding between fibers at elevated temperatures, such as obtained in an oven or with a through-air bonder (sometimes referred to as a hot air knife) without the application of solid contact pressure (such as in spot bonding or calendering).

[0033] As used herein, "filler" refers to solid particles included in the fiber-forming material.

[0034] As used herein, "solid" with respect to a particle refers to a state of matter having a stable shape, as opposed to the state of matter of a liquid or a gas.

[0035] As used herein, "thermoplastic" refers to a polymer that flows when sufficiently heated above its glass transition temperature and becomes 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.

[0036] As used herein, the "glass transition temperature" (T g ) of a polymer refers to the transition of the polymer from the glassy state to the 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 gas stream. When referring to the T g of a monomer, it is the T g of the homopolymer of that monomer. The homopolymer must have a sufficiently high molecular weight such that the T g reaches a limiting value, as it is generally understood that the T g of a homopolymer will increase to a limiting value as the molecular weight increases. The homopolymer is also understood to be substantially free of moisture, residual monomers, solvents, and other contaminants that may affect the T g . Suitable DSC methods and analysis modes are described in Matsumoto, A. et al., Journal of Polymer Science A, Polymer Chemistry (J. Polym. Sci. A., Polym. Chem.) 1993, 31, 2531 - 2539.

[0037] As used herein, "machine direction" (MD) refers to the direction of the running web of material during the manufacturing process. The terms "machine direction" and "longitudinal direction" may be used interchangeably. As used herein, the terms "transverse direction" (TD) and "cross direction" (CD) each refer to a direction that is substantially perpendicular to the machine direction.

[0038] The terms "preferred" and "preferably" refer to embodiments of the present disclosure that may provide certain benefits in certain circumstances. However, in the same or other circumstances, other embodiments may also be preferred. Moreover, 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 present disclosure.

[0039] In the present application, terms such as "a", "an", and "the" are not intended to refer only to a singular entity, but include a general category for which a particular 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 "comprising at least one of... " followed by a list refer to any one of the items in the list and any combination of two or more of the items in the list.

[0040] As used herein, the term "or" is generally used in its ordinary sense, including "and / or", unless the context 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.

[0041] Also herein, it is assumed that all numbers are modified by the term "about" and preferably by the term "exactly". As used herein in connection with measured quantities, the term "about" refers to the variation in the measured quantity that would be expected by a person skilled in the art making the measurement and exercising a level of care commensurate with the purpose of the measurement and the precision of the measuring equipment used.

[0042] As used herein as a modifier of a property or attribute, unless otherwise specifically defined, the term "substantially" means that the property or attribute will be readily recognizable by a person of ordinary skill in the art but does not require absolute precision or perfect match (e.g., within + / - 20% for a quantifiable property). Unless otherwise specifically defined, the term "essentially" means highly approximate (e.g., within + / - 10% for a quantifiable property), but likewise does not require absolute precision or perfect match. Terms such as same, equal, consistent, constant, exact, etc. are understood to be within the normal tolerances or measurement errors applicable to a particular situation and do not require absolute precision or perfect match.

[0043] In a first aspect, there is provided a nonwoven fibrous web. The nonwoven fibrous web comprises:

[0044] a plurality of randomly arranged continuous fibers bonded together, wherein at least some of the continuous fibers comprise an open-celled porous structure.

[0045] In a second aspect, there is provided a method of manufacturing a nonwoven fibrous web. The method comprises:

[0046] extruding filaments of a fiber-forming material from an extrusion head into a gas stream;

[0047] guiding the filaments through a treatment chamber in which an air stream applies a longitudinal stress to the filaments;

[0048] After the filaments leave the treatment chamber, the filaments are subjected to turbulent conditions, and the temperature of the filaments is controlled such that at least some of the filaments in the filaments solidify in the turbulent field to form fibers having a uniform diameter along their length but a varying morphology, wherein the fibers exhibit a draw ratio of 50 or greater;

[0049] Collect the treated fibers on a collector as a nonwoven fiber web;

[0050] Perform a bonding operation on the collected nonwoven fiber web; and

[0051] Stretch the nonwoven fiber web to break at least a portion of the fibers, thereby creating an open-celled porous structure in the broken fibers.

[0052] The following disclosure relates to both a first aspect and a second aspect.

[0053] The fiber-forming material can be extruded by introducing the fiber-forming material into a hopper, melting the material in an extruder, and pumping the molten material to an extrusion head by a pump. Although solid polymer materials in pellet or other particulate form are most commonly used and melted into a liquid, pumpable state, other fiber-forming liquids, such as polymer solutions, can also be used.

[0054] The fiber-forming material is used to form continuous fibers of a nonwoven fiber web. Generally, the continuous fibers comprise one or more semi-crystalline polymers. At least one amorphous polymer can optionally be included in a blend with at least one semi-crystalline 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.

[0055] Generally, the continuous fibers comprise a polypropylene polymer having a melt flow index of 0.5 to 100 (including the end values) from Total Petrochemicals (Houston, TX). For example, the melt flow index of the polymer can be 0.5 grams per 10 minutes (g / 10min) or greater, 1 g / 10min, 2 g / 10min, 5 g / 10min, 7 g / 10min, 10 g / 10min, 15 g / 10min, 20 g / 10min, 25 g / 10min, 30 g / 10min, 35 g / 10min, 40 g / 10min, 45 g / 10min, or g / 10min or greater; and 100 g / 10min or less, 95 g / 10min, 90 g / 10min, 85 g / 10min, 80 g / 10min, 75 g / 10min, 70 g / 10min, 65 g / 10min, 60 g / 10min, or 55 g / 10min or less.

[0056] Suitable materials for continuous fibers include, for example but not limited to, at least one of polypropylene (PP), polyethylene (PE), poly-4-methyl-1-pentene (PMP), polyoxymethylene (POM), polyvinylidene fluoride (PVDF), polybutene-1, or copolymers thereof. Optionally, the continuous fiber comprises a blend of at least two polymers, such as 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 example, the continuous fiber 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 fiber may comprise a PP having a number average molecular weight of from 250,000 g / mol to 800,000 g / mol (including the end values). Exemplary PPs include, for example, those polypropylenes that are commercially available under the trade names “PPH3264” and “PPH3766” from TotalEnergies Petrochemicals & Refining USA, Inc., Houston, TX.

[0057] Suitable crystalline thermoplastic polypropylene homopolymer resins are available from TotalEnergies Petrochemicals & Refining USA, Inc., Houston, TX, such as, for example, homopolymer polypropylenes 3281, 3274, PPH3060, 3273, 3272, 3371, PPH4022, PPH4069, 3462, 3571, 3662, M3661, 3766, 3865, 3860. Other suitable polypropylene homopolymers are available under the trade name PRO-FAX, such as, for example, PRO-FAX 1280, PRO-FAX 814, PRO-FAX 1282, PROFAX 1283, or under other trade names, such as ADFLUEXX 500F, ADSYL 3C30F, HP403G, TOPPYL SP 2103 from Lyondel-Basell Industries (Pasadena, TX). Additional suitable polypropylene homopolymers are available from INEOS Olefins & Polymers, USA (Carson, CA), such as, 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), such as, for example, F008, F013M, FF026, FF030F2. Further suitable polypropylene homopolymers are available from Exxon-Mobil Chemical Co. (Spring, TX), such as, for example, PP1024E4, PP2252E3, PP4292E1, and PP4612E2, PP 4792.

[0058] Suitable crystalline thermoplastic polyethylene (PE) homopolymer resins are available from Exxon-Mobil Chemical Co. (Spring, TX), such as HDPE 6908. Suitable polyethylene homopolymers are also available from TotalEnergies Petrochemicals & Refining USA, Inc., Houston, TX, such as 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), such as HF0144, HF0150, HF0147, and FH35; polyethylene polymers are from NOVA Chemicals Corporation (Calgary, AB, Canada), such as SUPRASS HPs167-AB, HPs267-AB, HPs667-AB, SCLAIR 19E, SCLAIR99L, NOVAPOL HB-L354-A.

[0059] In some embodiments, the resin may also include one or more poly(methyl)pentene (PMP) copolymer resins. Suitable grades of PMP copolymer resins with low levels of linear or branched α-olefin comonomers are available under the trade name TPX from Mitsui Chemicals (Minato-Ku, Tokyo, Japan), such as resin grades DX470, RT18, DX820, and DX845.

[0060] In some embodiments, the resin may also include one or more polyvinylidene fluoride (PVDF) homopolymer or copolymer resins. Suitable PVDF resins are available under the trade names Dyneon Fluoroplsic PVDF 6008, 6010, and 6012 from 3M Company (St Paul, MN), and under the trade names Solef 6008, Solef 6010, and Solef 6012 from Solvay Specialty Polymers (Alpharetta, GA).

[0061] In some embodiments, the resin may also include one or more polyoxymethylene (POM) homopolymers or copolymer resins. Suitable polyoxymethylene resins are available from Asahi Kasei under the trade names TENAC 2010 homopolymer acetal, TENAC 3010, TENAC 4010, and TENAC 4060, and Delrin 511CPE NC010 acetal homopolymer and 100CPE NC010 acetal homopolymer are available from DuPont Mobility and Materials (Wilmington, Delaware).

[0062] Suitable crystalline thermoplastic polybutene-1 (PB-1) homopolymer resins are available from Lyondel-Basell Industries (Pasadena, TX), such as Toppyl PB 0110M, Toppyl PB 8640M, Toppyl PB 8310, and Toppyl PB 8340M.

[0063] The method includes extruding filaments of the fiber-forming material from an extrusion head into a gas stream. The extrusion head can be a conventional spinneret or spinning assembly, which typically includes a plurality of spinneret holes arranged in a regular pattern (e.g., a straight line). The method also includes guiding the filaments through a treatment chamber in which the gas stream applies a longitudinal (e.g., orienting) stress to the filaments. In an alternative embodiment, the fiber-forming material includes PP, and the filaments are extruded through a die at a temperature of 190 °C to 270 °C and at a melt output of less than 2 grams per hole per minute (e.g., 1.8 grams per hole per minute or less, 1.6 grams per hole per minute, 1.4 grams per hole per minute, 1.2 grams per hole per minute, 1 gram per hole per minute, 0.9 grams per hole per minute, 0.8 grams per hole per minute, 0.7 grams per hole per minute, 0.6 grams per hole per minute, 0.5 grams per hole per minute, 0.4 grams per hole per minute, or 0.3 grams per hole per minute).

[0064] After the filaments leave the treatment chamber, the filaments are placed in turbulent conditions, and the temperature of the filaments is controlled such that at least some of the filaments in the filaments are solidified in the turbulent field to form fibers with a uniform diameter along their length but with morphological variations. The continuous fibers exhibit a draw 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, "draw ratio" refers to the ratio of the cross-sectional area of the extrusion head to the cross-sectional area of the final fiber.

[0065] Turbulent conditions are provided by the turbulence of air or other fluids. Turbulence occurs when an air stream flowing through, for example, an attenuator reaches an unconstrained space at the end of the attenuator, where the pressure existing within the attenuator is released. The air stream widens as it exits the attenuator, and vortices form within the widened stream. These vortices - swirls of air flow running in a direction different from the main stream - subject the filaments within the vortices to forces different from the straight-line forces that the filaments typically experience within and above the attenuator. For example, the filaments can flutter back and forth within the vortices and are subject to forces having a vector component transverse to the fiber length. The processed filaments are long and travel a tortuous and random path within the turbulent field. Different portions of the filaments experience different forces within the turbulent field. To some extent, the longitudinal stress on at least some portions of the filaments is relaxed, and those portions thus become less oriented than those portions that have experienced a longitudinally applied stress for a longer time.

[0066] In some embodiments, the filaments are placed under turbulent conditions by subjecting the filaments to an air stream of 150 meters per second (m / s) 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 rates impart more uniform fiber sizes. In some cases, 294 m / s is a suitable maximum air flow rate that the filaments may experience during turbulence.

[0067] 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 quench stream), the length of the attenuator, the speed and temperature of the filaments as they travel through the attenuator, and the distance between the attenuator and the collector. By cooling some or all of the filaments and their segments within the turbulent field to a temperature at which the filaments or segments solidify, the orientation differences experienced by different portions of the filaments and the subsequent morphology of the fibers become frozen; that is, the molecules are thermally trapped in their aligned positions. The different orientations experienced by different fibers and different segments as they pass through the turbulent field are at least to some extent retained in the fibers collected on the collector.

[0068] The method also includes collecting the processed fibers on a collector as a nonwoven fibrous web, and performing a bonding operation on the collected nonwoven fibrous web. In some embodiments, the nonwoven fibrous web includes fibers having a uniform diameter in the direction, and the fibers vary in morphology along their length so as to provide longitudinally segmented portions that are different from each other in softening characteristics during a selected bonding operation. Some of these longitudinally segmented portions 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 other segmented portions in the segment are passive during the bonding operation. "Uniform diameter" means that the fibers have substantially the same diameter (varying 10% or less) over a significant length (i.e., 5 cm or longer), and morphological variations can and typically do exist within this significant length.

[0069] In an alternative embodiment, the bonding operation includes a self-bonding operation that includes heating the collected web without applying calendering pressure, and some longitudinally segmented portions soften and bond to other adjacent fibers under the conditions of the self-bonding operation, while other longitudinally segmented portions are passive during the self-bonding operation. Alternatively, the bonding operation can include different types of bonding operations, such as calendering or dot bonding, which are well known to those skilled in the art.

[0070] (For example, each) fiber is preferably oriented in the microstructure; that is, the fibers preferably include molecules that are aligned along the longitudinal direction of the fiber and are locked into (i.e., thermally trapped into) this alignment. Thus, the polymeric material used for the fibers has the ability to form a row-layered crystal structure, as pointed out in U.S. Patent No. 4,541,981 (Lowery et al.). In a preferred embodiment, the passive longitudinally segmented portions of the fibers are oriented to the extent exhibited by a typical spunbond fibrous web. More details regarding spunbond fibrous webs can be found, for example, in U.S. Patent Nos. 6,916,752 and 7,279,440 (both assigned to Berrigan et al.). In a crystalline or semi-crystalline polymer, such segmented portions preferably exhibit strain-induced or chain-extended crystallization (i.e., the molecular chains within the fiber have a crystal grade that is generally aligned along the fiber axis). As a whole, the web can exhibit strength properties similar to those obtained in a spunbond web, while being strongly bonded in a manner that a typical spunbond web cannot be bonded. And the self-bonding web of the present invention tends to have a bulkiness and uniformity in the web that are not achievable by dot bonding or calendering typically used with spunbond webs.

[0071] Additional details regarding nonwoven fibrous webs having self-bonding and how to manufacture such nonwoven fibrous webs are described in U.S. Patent No. 7,695,660 (Berrigan et al.), which is incorporated herein by reference.

[0072] The method also includes stretching the nonwoven fibrous web to break at least a portion of the fibers, thereby creating an open-celled porous structure in the broken fibers. Optionally, the nonwoven fibrous web may first be folded, particularly in cases where the apparatus for stretching the web is configured for a greater thickness than a single layer of the nonwoven fibrous web. Surprisingly, although some of the fibers in the web completely break during the stretching process, the nonwoven fibrous web structurally withstands the stretching. Without being bound by theory, it is believed that some of the fiber bonds in the fiber bonding withstand the stretching process and / or many of the fibers remain well-entangled as continuous fibers. The stretched web is generally thicker and fluffier compared to the nonwoven fibrous web prior to stretching due to the increased fiber length and reduced bond density.

[0073] See Figure 7 , which provides a top view photograph of a disc of the nonwoven fibrous web 700 after stretching in one (e.g., horizontal) direction indicated by the double arrows, prepared according to Example 3 (E3) described below. As can be seen from the figure, the nonwoven fibrous web is opaque after stretching and maintains good web integrity, e.g., retaining most of the fiber bond points.

[0074] Typically, the stretching of the nonwoven fibrous web is performed longitudinally to impart an open-celled porous structure to the fibers (i.e., break the fibers). Typically, at least some individual fibers break and / or at least some of the bonds between adjacent fibers separate as an additional result of the stretching of the web. The method optionally further includes stretching the nonwoven fibrous web transversely to disperse the broken and / or unbonded fibers. Alternatively, an initial stretching of the nonwoven fibrous web is performed transversely to impart an open-celled porous structure to the fibers (i.e., break the fibers), and optionally the nonwoven fibrous web is further stretched longitudinally to disperse the broken and / or unbonded fibers. In some cases, the stretching of the nonwoven fibrous web is performed in a biaxial direction (i.e., simultaneously longitudinally and transversely) to break the fibers. In some cases, the appropriate draw ratio in the longitudinal direction is different from the draw ratio in the transverse direction.

[0075] In some cases, the stretched nonwoven fibrous web exhibits a basis weight of no more than 300 grams per square meter (g / m 2 ), 275 g / m 2 , 250 g / m 2 , 225 g / m 2 , 200 g / m 2 , 175 g / m 2 , 150 g / m 2 , 125 g / m 2 , 100 g / m 2 , 75 g / m 2 or no more than 50 g / m 2; and having a basis weight of 20 g / m 2 or greater, 25 g / m 2 , 30 g / m 2 , 35 g / m 2 , 40 g / m 2 , 45 g / m 2 or 50 g / m 2 or greater. Such basis weights advantageously provide articles that are lighter in weight than nonwoven fiber webs having a basis weight above 300 g / m 2 .

[0076] In an alternative embodiment, the method further comprises annealing the nonwoven fiber web prior to stretching the nonwoven web. Preferably, any annealing is carried out at a temperature below the melting point of the fiber-forming material. For example, a nonwoven fiber web formed from PP is preferably annealed at 120° C. to 150° C. The annealing time can be from one second to several hours; preferably from 1 minute to 60 minutes; more preferably from 5 minutes to 30 minutes.

[0077] The stretching can be carried out using single-stage or multi-stage cold stretching, optionally followed by single-stage or multi-stage hot stretching. Preferably, the cold stretching temperature is selected to be 5° C. to 70° C. higher than the glass transition temperature (T g ) of the polymer of the nonwoven fiber web, more preferably 10° C. to 50° C. (for example, it should be 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 10° C. to 120° C. lower than the melting temperature of the polymer, more preferably 20° C. to 60° C. For example, PP is preferably stretched at 100° C. to 150° C.

[0078] The nonwoven fiber web can be advantageously stretched by uniaxial extension of at least 5% and at most 500%, more preferably at least 10% and at most 300% to form an open porous structure in the fibers.

[0079] The nonwoven web after stretching can be advantageously exposed to a heat setting step to reduce the stress within each fiber. The heat setting temperature is typically selected to be at least 5° C., at least 10° C. or even at least 15° C. higher than the hot stretching temperature. The heat setting duration is typically selected to be at least 30 seconds or at least one minute.

[0080] Alternatively, the nonwoven web after stretching can be advantageously exposed to a relaxation step by allowing the fiber length to contract to some extent (which is at least 2% or even at least 5%). Heat setting and relaxation can be used alone or in combination.

[0081] Unexpectedly, such "dry" stretching of the non-porous nonwoven fiber web has achieved good fiber porosity. In some cases, 30% or more of the continuous fibers include an open-cell porous structure, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90% or more of the continuous fibers include an open-cell porous structure. It should be noted that in some cases, at least some of the fibers at the main surface of the nonwoven fiber web do not have an open-cell porous surface. This typically occurs when the adhesion of the individual fibers at the main surface of the nonwoven fiber web is greater than the adhesion inside the web, especially in cases where any calendering has been performed on the nonwoven fiber web or in cases where the fibers have been overly exposed to high temperatures and the fiber microstructure has changed.

[0082] Continuous fibers having an open-cell porous structure include a plurality of pores. The plurality of pores result in the fibers having a higher surface area. For example, in one embodiment, the porous polymer fibers have an average surface area of at least 5 m 2 / g, 10 m 2 / g, 15 m 2 / g, 20 m 2 / g, 35 m 2 / g, 30 m 2 / g or even at least 40 m 2 / g as measured by BET (Brunauer Emmet Teller) nitrogen adsorption.

[0083] Continuous fibers having an open-cell 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, insulating properties or functionalization ability.

[0084] In addition, the porosity of the nonwoven fiber web can be greater than 90%, 91%, 92%, 93%, 94% or greater than 95%. When the porosity of the nonwoven fiber web is determined by measuring the density and subtracting from 100, the measured density of the nonwoven fiber web can be less than 10%, 9%, 8%, 7%, 6% or less than 5%.

[0085] See Figure 1A, Scanning electron microscope (SEM) image of a portion of an exemplary nonwoven fiber web 100 prepared according to Example 3 (E3) described below. In Figure 1A , many individual fibers 110a of the web 100 are visible. Now refer to Figure 1B , and provide Figure 1A an SEM image of a portion of the fibers 110b of an exemplary nonwoven fiber web. The greater magnification for the Figure 1B image allows visualization of the open-celled porous structure 120b of the fibers 110b.

[0086] Similar to Figure 1A , Figure 2A provides an SEM image of a portion of another exemplary nonwoven fiber web 200 prepared according to Example 4 (E4) described below. In Figure 2A , many individual fibers 210a of the web 200 are visible.

[0087] Now refer to Figure 2B , and provide Figure 2A an SEM image of a portion of several adjacent fibers 210b of an exemplary nonwoven fiber web. The greater magnification for the Figure 2B image allows visualization of the open-celled porous structure 220b of the fibers 210b.

[0088] As noted above, the fibers of the nonwoven fiber web exhibit a draw ratio of 50 or greater. It has been found that fibers with a higher draw ratio tend to be more uniform in diameter along the fiber length direction, while fibers with a lower draw ratio tend to be less uniform in diameter along the fiber length direction. This can be seen in the Figures 3 to 4 SEM image. Figure 3 is an SEM image of a portion of an exemplary nonwoven fiber web 300 including fibers 310 with a draw ratio of 68, manufactured according to Example 2 (E2) described below. Figure 4 is an SEM image showing several fibers 410, including fibers with significant necking such that the fibers 410 include at least a portion of their length having a diameter D1 that is significantly greater than another portion of their length having a diameter D2. Depending on the application of the nonwoven fiber web, it may be acceptable to include fibers with a lower draw ratio and some amount of necking, for example, less than 50% of the total fibers have necked fiber segments, preferably less than 10%. In other applications, it is preferred to use a higher draw ratio, such as 100 or greater, 120, 140, or 160 or greater, to minimize the occurrence of necking in the fibers of the nonwoven fiber web, such as when the web is used as an absorbent medium, acoustic medium, insulating medium, etc.

[0089] Refer to Figure 5, provides a SEM image of a portion of the surface of the fibers 510 of an exemplary nonwoven fibrous web prepared according to Example 5 (E5), showing that in some cases, the open-cell porous structure includes microfibrils connecting the sheet-like microstructures. Figure 5 Shows the fiber 510, which includes a plurality of microfibrils 512 extending between opposing sheet-like microstructures 514. The microfibrils 512 and the sheet-like microstructures 514 together define the voids 524 of the open-cell porous structure of the fiber 510. The dimensions of the microfibrils 512 can vary, as Figure 5 confirmed, typically including at least one dimension with a length of 1 micron or less. In some cases, the sheet-like microstructures tend to have a non-row ordered configuration, but have been deformed during stretching to produce curved sheet-like microstructures.

[0090] In other cases, as Figure 5 visible, the sheet-like layers do not exist in completely parallel rows, but generally form adjacent rows attached by the microfibrils 512.

[0091] From Figure 5 it is clearly visible that the open-cell porous structure does not have filler particles that are at least partially present in the voids of the porous structure. This is directly contrary to some existing methods for forming porous structures in fibers by including additives such as filler materials (e.g., particulate fillers and nano-inclusion additives), as described in U.S. Patent Nos. 5,766,760 (Tsai et al.) and 11,001,944 (Topolkaraev et al.), respectively. Although fillers can be suitable optional additives included in the nonwoven fibrous webs of some embodiments according to the present disclosure, such fillers do not significantly contribute to pore formation. This is demonstrated by less than 20%, less than 15%, less than 10%, or less than 5% of the total open-cell pores of the fibers including fillers visible in the voids.

[0092] Typically, the average diameter of the continuous fibers is 5 microns or greater, 10 microns, 15 microns, 20 microns, 25 microns, 30 microns, 40 microns, 50 microns, 60 microns, 70 microns, 80 microns, 90 microns, or 100 microns or greater; and 200 microns or less, 190 microns, 180 microns, 170 microns, 160 microns, 150 microns, 140 microns, 130 microns, 120 microns, 110 microns, 100 microns, 90 microns, 80 microns, 70 microns, 60 microns, or 50 microns 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 microns or less, ±25 microns, ±20 microns, or ±15 microns or less.

[0093] The cross-sectional shape of the fibers of the exemplary nonwoven fibrous web is not particularly limited. Refer to Figures 6A to 6D , in some cases, at least some of the fibers have a cross-section selected from circular (i.e., Figure 6A ), (e.g., rectangular) bar-shaped (i.e., Figure 6B ), oval (i.e., Figure 6C ) or cross-shaped (i.e., Figure 6D ) shapes. A variety of other shapes can be useful, such as multi-lobed (e.g., three-lobed) cross-section fibers or hollow cross-section fibers. In addition to the shape, the cross-section of the fiber also includes a cross-sectional distance. The cross-sectional distance is equal to the length of the chord that can connect points on the perimeter of the cross-section. The term "longest cross-sectional distance" refers to the maximum length of the chord that can be drawn through the cross-section of the fiber at a given position along the fiber axis. In the case where the shape of the fiber is not circular, "longest cross-sectional shape" can be used instead of "diameter".

[0094] Exemplary embodiments

[0095] In a first embodiment, the present disclosure provides a nonwoven fibrous web. The nonwoven fibrous web includes a plurality of randomly arranged continuous fibers bonded together, wherein at least some of the continuous fibers include an open-celled porous structure.

[0096] In a second embodiment, the present disclosure provides the nonwoven fibrous web according to the first embodiment, wherein the open-celled porous structure includes microfibrils connecting sheet-like microstructures.

[0097] In a third embodiment, the present disclosure provides the nonwoven fibrous web according to the first or second embodiment, wherein the continuous fibers comprise one or more semi-crystalline polymers.

[0098] In a fourth embodiment, the present disclosure provides the nonwoven fibrous web according to any one of the first to third embodiments, wherein the continuous fibers comprise at least one of polypropylene (PP), polyethylene (PE), polymethylpentene (PMP), polyoxymethylene (POM), polyvinylidene fluoride (PVDF), polybutene-1 or a copolymer thereof.

[0099] In a fifth embodiment, the present disclosure provides the nonwoven fibrous web according to any one of the first to fourth embodiments, wherein the continuous fibers comprise PP.

[0100] In a sixth embodiment, the present disclosure provides the nonwoven fibrous web according to the fifth embodiment, wherein the continuous fibers comprise PP having a number average molecular weight of 250,000 g / mol or greater to 800,000 g / mol or less.

[0101] In a seventh embodiment, the present disclosure provides a nonwoven fibrous web according to any one of the first through sixth embodiments, wherein the continuous fibers comprise a blend of at least two polymers.

[0102] In an eighth embodiment, the present disclosure provides a nonwoven fibrous web according to any one of the first through seventh embodiments, wherein the continuous fibers comprise a blend of a first PP and a second PP.

[0103] In a ninth embodiment, the present disclosure provides a nonwoven fibrous web according to any one of the first through eighth embodiments, wherein the continuous fibers comprise a blend of at least one amorphous polymer and at least one semi-crystalline polymer.

[0104] In a tenth embodiment, the present disclosure provides a nonwoven fibrous web according to any one 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.

[0105] In an eleventh embodiment, the present disclosure provides a nonwoven fibrous web according to any one of the first through tenth embodiments, wherein the continuous fibers comprise a polymer having a melt flow index of 0.5 to 100 (including the end values).

[0106] In a twelfth embodiment, the present disclosure provides a nonwoven fibrous web according to any one of the first through eleventh embodiments, wherein 30% or more of the continuous fibers comprise an open-celled porous structure.

[0107] In a thirteenth embodiment, the present disclosure provides a nonwoven fibrous web according to any one of the first through twelfth embodiments, the nonwoven fibrous web exhibiting a basis weight of no more than 300 grams per square meter.

[0108] In a fourteenth embodiment, the present disclosure provides a nonwoven fibrous web according to any one of the first through thirteenth embodiments, wherein the continuous fibers have an average diameter of 5 micrometers to 200 micrometers.

[0109] In a fifteenth embodiment, the present disclosure provides a nonwoven fibrous web according to any one of the first through fourteenth embodiments, wherein the continuous fibers exhibit a porosity of 5 volume % to 80 volume %.

[0110] In a sixteenth embodiment, the present disclosure provides a nonwoven fibrous web according to any one of the first through fifteenth embodiments, wherein the continuous fibers exhibit at least 5 m 2 / g, 10 m 2 / g, 15 m 2 / g, 20 m 2 / g, 35 m 2 / g, 30 m 2 / g or at least 40 m 2 The average surface area per g.

[0111] In a seventeenth embodiment, the present disclosure provides a method of manufacturing a nonwoven fibrous web. The method includes: extruding filaments of a fiber-forming material from an extrusion head into a gas stream; guiding the filaments through a treatment chamber in which the gas stream applies a longitudinal stress to the filaments; and subjecting the filaments to turbulent conditions after they leave the treatment chamber, controlling the temperature of the filaments such that at least some of the filaments in the filament bundle solidify in the turbulent field to form fibers that are uniform in diameter along their length but vary in morphology, where the fibers exhibit a draw ratio of 50 or greater. The method further includes: collecting the treated fibers on a collector as a nonwoven fibrous web; performing a bonding operation on the collected nonwoven fibrous web; and stretching the nonwoven fibrous web to break at least a portion of the fibers, thereby creating an open-celled porous structure in the broken fibers.

[0112] In an eighteenth embodiment, the present disclosure provides the method according to the seventeenth embodiment, the method further including annealing the nonwoven fibrous web before stretching the nonwoven web; where the annealing is performed at a temperature below the melting point of the fiber-forming material.

[0113] In a nineteenth embodiment, the present disclosure provides the method according to the seventeenth or eighteenth embodiment, where the stretching is performed longitudinally, and where the method further includes stretching the nonwoven fibrous web transversely to disperse the broken fibers.

[0114] In a twentieth embodiment, the present disclosure provides the method according to any one of the seventeenth to nineteenth embodiments, where the fiber-forming material includes PP, and the filaments are extruded through a die at a temperature of 190 °C to 250 °C and at a melt output of less than 1.

[0115] In a twenty-first embodiment, the present disclosure provides the method according to the twentieth embodiment, where the filaments are subjected to turbulent conditions under an air flow of 150 meters per second (m / s) or greater.

[0116] In a twenty-second embodiment, the present disclosure provides the method according to any one of the seventeenth to twenty-first embodiments, where the fiber-forming material includes a blend of a first PP and a second PP.

[0117] In a twenty-third embodiment, the present disclosure provides a method according to any one of the seventeenth to twenty-second embodiments, wherein the bonding operation includes a self-bonding operation that includes heating the collected web without applying calendering pressure, and some of the longitudinal segments soften and bond to other adjacent fibers under the conditions of the self-bonding operation, and other longitudinal segments are passive during the self-bonding operation.

[0118] In a twenty-fourth embodiment, the present disclosure provides a method according to any one of the seventeenth to twenty-third embodiments, wherein at least some of the fibers at the main surface of the nonwoven fiber web do not have an open-celled porous surface.

[0119] In a twenty-fifth embodiment, the present disclosure provides a method according to any one of the seventeenth to twenty-fourth embodiments, wherein at least some of the fibers have a cross-section selected from the shapes of circular, bar-shaped, oval, or cross-shaped.

[0120] Examples

[0121] The following examples further illustrate the objects and advantages of the present disclosure, but the specific materials and their amounts, as well as other conditions and details listed in these examples should not be construed as unduly limiting the present disclosure. Unless otherwise specified or obvious from the context, all parts, percentages, ratios, etc. in the examples and the rest of the specification are by weight. The material table (below) lists the materials used in the examples and the sources of the materials.

[0122] Materials used in the examples

[0123]

[0124] Testing methods :

[0125] The PE1-PE6 web precursors and the E1-E6 porous fiber webs were characterized using the test methods described below.

[0126] For web thickness and web density, web disks with a diameter of 135 mm were cut and weighed. Their thickness was measured using a tester under an applied pressure of 150 Pascals (Pa). The web density was calculated based on the web disk volume, the polymer density (0.91 grams per cubic centimeter (g / cc) for polypropylene), and its weight.

[0127] An air permeability test was used to test the pressure drop across the web, where air passed through the web at a face velocity of 14 centimeters per second (cm / sec) at room temperature.

[0128] The effective fiber diameter (EFD) of the web is evaluated according to the method shown in Davies, C.N., “The Separation of Airborne Dust and Particles,” Institution of Mechanical Engineers, London, Proceedings 1B, 1952. The test is run at a face velocity of 14 cm / sec.

[0129] To determine the draw down ratio (DDR) for preparing the web precursors of PE1 - PE6, fiber bundles are collected after the attenuator under unbonded conditions. The fiber bundle is cross - sectioned and the actual fiber diameter (AFD) is measured by using an optical microscope. The draw down ratio (DDR) is calculated based on the cross - sectional surface area of the actual fiber and the orifice of the spinneret as follows:

[0130]

[0131] D 0 is the orifice size of the spinneret, and D 1 is the AFD of the fibers in the web precursor.

[0132] To determine the fiber porosity of the E1 - E6 samples, 135 mm or 47 mm discs are cut from the drawn web samples from each of E1 - E6 and weighed as the initial mass (m0). Then, the discs are soaked in MPrOH for about 2 minutes to fully saturate the web. The soaked web is drained and placed between two cleanroom wipes to absorb the excess solvent. Some pressure is applied to the sandwich to quickly absorb the solvent through the wipes. The wipes are replaced until no solvent is visually seen after damping. The saturated disc web is weighed again as the final mass (m1).

[0133] The fiber porosity is calculated based on the weight change, the density of polypropylene (d0), and the density of MPrOH (d1).

[0134]

[0135] It was found that the web precursors of PE1 - PE6 showed some MPrOH absorption, which was attributed to the adsorption of the solvent onto the outer surface of the fibers. The MPrOH absorption of the corresponding web precursors was measured as described above. The corrected fiber porosity is obtained by subtracting this surface contribution from the porosity measured above.

[0136] SEM was used to image the microstructure of the fiber surface. Low magnification images were obtained using a tabletop SEM (Model Hitachi TM4000 plus II, available from Hitachi High-Tech Corporations, Japan); high magnification images were obtained using a field emission SEM (FE-SEM) (Model Hitachi S-4700, available from Hitachi High-Tech Corporations, Japan).

[0137] Preparation of the precursors of the webs of Preparation Examples 1 - 6 (PE1 - PE6) :

[0138] The PE1 - PE6 web precursors were prepared from various grades of polypropylene homopolymers under the process conditions summarized in Table 1 using the equipment disclosed in U.S. Patents US 6,824,372, US 6,916,752, and US 7,695,660 (each granted to Berrigan et al.), which patents are incorporated herein by reference. If a mixture of polymers was used, the polymer resin mixture was prepared by dry blending. The polymer was extruded using a 2.5-inch (50 mm) diameter single screw extruder and the melt was fed into a spinneret having 780 spinneret holes. The hole diameter was 0.014 inches (0.355 mm) and the length to diameter ratio (L / D) was 4. The average melt output per hole (grams per hole per minute, ghm) was calculated based on the total number of holes and the total output from the melt pump. The formulations and process conditions used to prepare PE1 - PE6, such as melt output, polymer melt pressure from the melt pump, total volume of air through the attenuator, and the ventilation bonding temperature, are shown in Table 1. The PE1 - PE6 web precursors were collected as web rolls.

[0139] The properties of the PE1 - PE6 web precursors determined above are summarized in Table 2 below.

[0140] Cold / hot stretching of the precursors of the webs of Examples 1 - 6 (E1 - E6) to form porous fibrous nonwovens :

[0141] PE1-PE6 web precursor samples (about 203 mm in longitudinal direction × about 305 mm in cross-web direction) were cut and heat treated (i.e., annealed) in a convection oven for 10 minutes. The oven temperature was set to 140°C. For cold / hot stretching, the annealed samples were folded longitudinally to form strips about 1 inch (25 mm) wide, which were firmly clamped in a temperature-controlled environmental chamber of an Instron mechanical tester (Model 5969, from Instron Corporation, Norwood, MA) by Instron fixtures. The 127 mm (5 inch) long web sample between the fixtures was cold stretched to 40% at a stretching rate of 600 mm / min at 25°C, and then hot stretched at a stretching rate of 30 mm / min at 120°C. The total elongation after 10% relaxation was 100%. The stretched web was manually stretched to de-orient the fibers in the cross-web direction, and the resulting web had a width of about 215 mm.

[0142] Table 3 below summarizes the measured properties of the porous fibrous nonwoven fabrics of E2-E5.

[0143] Figure 1A , Figure 2A and Figure 3 SEM images of a portion of exemplary nonwoven fibrous webs prepared according to Examples 3 (E3), 4 (E4), and 2 (E2), respectively.

[0144] Figure 5 is a high magnification scanning electron image of a porous fiber nonwoven fabric of E5. The porous microstructure is clearly seen with separated crystalline lamellae (blocks) and microfibrils between them.

[0145] Table 1 .

[0146]

[0147] Table 2. Properties of the web precursors

[0148]

[0149] Table 3.

[0150]

[0151] BET surface area

[0152] The BET surface area was measured by gas adsorption experiments using a Micromeritics Instrument Corporation (Norcross, GA) accelerated surface area and porosimetry (ASAP) 2020Plus system instrument. In a Micromeritics half-inch diameter sample tube, 50 mg to 250 mg of the sample was degassed by first heating at 80 °C for 3 hours under high vacuum (500 microns of mercury) at the degassing port. At the end of this degassing step, the sample tube was backfilled with nitrogen and moved to the analysis port. The sample was then further degassed by heating at 80 °C for 3 hours under ultra-high vacuum (3 microns to 7 microns of mercury) at the analysis port of the instrument. The nitrogen adsorption isotherm at 77 K was obtained using a low-pressure feed (5 cm 3 / g) and a manometer with linearly spaced pressure points from p / p° of 0.1 to 0.998 at a relative pressure (p / p°) of less than 0.1. The method for all isotherms utilized the following equilibration intervals: 90 seconds at p / p° less than 10-5, 40 seconds at p / p° in the range of 10-5 to 0.1, and 20 seconds at p / p° greater than 0.1. After nitrogen adsorption analysis at ambient temperature and 77 K, free space determination was performed using helium. The BET specific surface area (SA BET ) was calculated from the nitrogen adsorption data by multi-point Brunauer–Emmett–Teller (BET) analysis. The apparent micropore distribution was calculated from the nitrogen adsorption data using standard nitrogen in a 77 K density functional theory (DFT) model by density functional theory (DFT) analysis. The total pore volume was calculated based on 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.

[0153] The BET surface area was measured and found to be 4.0 m 2 / g for PE5 and 48.2 m 2 / g for E5.

[0154] All patents and patent applications mentioned above are hereby expressly incorporated by reference. The above-described embodiments are illustrative of the invention and may also be of other configurations. Accordingly, the invention should not be considered limited to the embodiments described in detail above and shown in the drawings, but only limited by the reasonable scope of the appended claims and their equivalents.

Claims

1. 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 include an open-celled porous structure.

2. The nonwoven fibrous web according to claim 1, wherein the open-celled porous structure comprises microfibrils connecting sheet-like microstructures.

3. The nonwoven fibrous web according to claim 1 or claim 2, wherein the continuous fibers comprise one or more semi-crystalline polymers.

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

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

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

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

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

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

11. The nonwoven fibrous web according to any one of claims 1 to 10, the nonwoven fibrous web exhibiting a basis weight of no more than 300 g / m².

12. The nonwoven fibrous web according to any one of claims 1 to 11, wherein the continuous fibers exhibit a porosity of 5% to 80% by volume.

13. The nonwoven fibrous web according to any one of claims 1 to 12, wherein the continuous fibers exhibit an average surface area of at least 5 m 2 / g, 10 m 2 / g, 15 m 2 / g, 20 m 2 / g, 35 m 2 / g, 30 m 2 / g, or at least 40 m 2 / g of average surface area as determined by BET (Brunauer Emmet Teller) nitrogen adsorption.

14. A method of manufacturing a nonwoven fibrous web, the method comprises: extruding filaments of a fiber-forming material from an extrusion head into a gas stream; guiding the filaments through a treatment chamber in which an air stream applies longitudinal stress to the filaments; subjecting the filaments to turbulent conditions after the filaments leave the treatment chamber, controlling the temperature of the filaments such that at least some of the filaments solidify in the turbulent field to form fibers having a uniform diameter along their length but a varying morphology, wherein the fibers exhibit a draw ratio of 50 or greater; collecting the treated fibers on a collector as a nonwoven fibrous web; performing a bonding operation on the collected nonwoven fibrous web; and stretching the nonwoven fibrous web to break at least a portion of the fibers, thereby generating an open-celled porous structure in the broken fibers.

15. The method according to claim 14, the method further comprising annealing the nonwoven fiber web before stretching the nonwoven web; wherein the annealing is performed at a temperature below the melting point of the fiber-forming material.

16. The method according to claim 14 or 15, wherein the stretching is performed longitudinally, and wherein the method further comprises stretching the nonwoven fiber web transversely to disperse the broken fibers.

17. The method according to any one of claims 14 to 16, wherein the fiber-forming material comprises a blend of a first PP and a second PP.

18. The method according to any one of claims 14 to 17, wherein the bonding operation comprises a self-bonding operation, the self-bonding operation comprising heating the collected web without applying calendering pressure, some longitudinal segments soften and bond to other adjacent fibers under the conditions of the self-bonding operation, and other longitudinal segments are passive during the self-bonding operation.

19. The method according to any one of claims 14 to 18, wherein at least some of the fibers at the main surface of the nonwoven fiber web do not have an open-cell porous surface.

20. The method according to any one of claims 14 to 19, wherein at least some of the fibers have a cross-section selected from the shapes of circular, strip, oval or cross-shaped.

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