Porous hollow fiber web and method for producing same

Abstract

The present disclosure provides a porous hollow fiber web comprising connected hollow fibers, at least some of which have an open porous structure comprising microfibrils connecting the lamellar microstructure. Also provided is a method for producing a porous hollow fiber web. The method includes obtaining a hollow fiber web having connected hollow fibers and stretching the hollow fiber web in a machine direction to break at least some of the hollow fibers and produce an open porous structure.

Description

[Background technology]

[0001] Webs of connected hollow strands have been formed, for example, using extrusion processes, however, such webs lack porosity. Summary of the Invention

[0002] In a first aspect, a porous hollow fiber web is provided, comprising a plurality of connected hollow fibers, at least some of which have an open porous structure comprising microfibrils connecting the lamellar microstructure.

[0003] In a second aspect, a method for producing a porous hollow fiber web is provided, the method comprising the steps of obtaining a hollow fiber web comprising a plurality of connected hollow fibers, and stretching the hollow fiber web in a machine direction to break at least some of the hollow fibers and produce an open porous structure comprising microfibrils connecting lamellar microstructures within the broken hollow fibers.

[0004] At least certain embodiments of the present disclosure provide a simplified process for producing porous hollow fiber webs by stretching the hollow fiber web to form an open, porous structure containing microfibrils connecting the lamellar microstructure. Hollow fiber webs can be produced by extrusion processes, such as those described in PCT Publication Nos. WO 2020 / 170115, WO 2021 / 028798, and WO 2021 / 250478 (all to Ausen et al.). The hollow fiber web is then stretched. Unexpectedly, this process achieves good fiber porosity, potentially significantly reducing the cost of producing porous hollow fiber webs. For example, as an alternative to forming porous hollow fiber webs, a typical airlaid process requires multiple steps: extruding hollow fibers, stretching the fibers to form pores, and braiding the individual porous hollow fibers together to form a web. Porous hollow fiber webs are useful, for example, for filtration and other separation applications.

[0005] The above summary of the present disclosure is not intended to describe all disclosed embodiments or all implementations of the present disclosure. The following description more particularly exemplifies specific examples. Throughout this specification, examples are presented in list form; these examples can be used in various combinations. In each instance, the recited list is intended to be representative and should not be interpreted as an exclusive list. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a schematic perspective cross-sectional view of a spliced ​​hollow fiber in which adjacent hollow fibers are joined at a junction region.

[0007] [Figure 2] FIG. 2 is a schematic perspective cross-sectional view of connecting hollow fibers in the form of individual hollow fibers with spacer segments between adjacent hollow fibers.

[0008] [Figure 3] FIG. 3 is a schematic perspective cross-sectional view of a connected hollow fiber in the form of individual hollow fibers arranged in two planes with spacer segments between adjacent hollow fibers.

[0009] [Figure 4] FIG. 4 is a schematic perspective cross-sectional view of a connected hollow fiber in which polymer strands are periodically bonded at bonding regions throughout the array to form a net with voids between adjacent strands, and in which at least a portion of the strands are in the form of hollow polymer strands.

[0010] [Figure 5] FIG. 5 is a scanning electron microscope (SEM) image of a portion of an example hollow fiber web.

[0011] [Figure 6A]FIG. 6A is an SEM image of a cross section of a portion of an example porous hollow fiber web.

[0012] [Figure 6B] FIG. 6B is an SEM image of a portion of a hollow fiber of the exemplary porous hollow fiber web shown in FIG. 6A.

[0013] [Figure 6C] FIG. 6C is an SEM image of a portion of a segment between two hollow fibers of the exemplary porous hollow fiber web shown in FIG. 6A.

[0014] [Figure 6D] FIG. 6D is an SEM image of a section of an example porous hollow fiber, showing the microfibrils connecting the lamellar microstructure.

[0015] [Figure 6E] FIG. 6E is an SEM image of a portion of an example porous hollow fiber, showing the open porous structure on the inner surface of the hollow fiber.

[0016] [Figure 7] FIG. 7 shows a photograph of a gas flux experiment using an example porous hollow fiber web.

[0017] While the above-described figures illustrate several embodiments of the present disclosure, other embodiments are contemplated, as noted in the description. The drawings are not necessarily drawn to scale. In any event, the present disclosure is intended to be illustrative and not limiting. DETAILED DESCRIPTION OF THE INVENTION

[0018] As used herein, the term "fracture" refers to the creation of a void in a portion of the polymer material of a hollow fiber.

[0019] As used herein, the term "open celled porous structure," with respect to the structure of a hollow fiber, refers to a hollow fiber having a plurality of pores, at least some of the pores being connected to adjacent pores, thereby allowing fluid to pass from one major surface of the hollow fiber to the opposing major surface.

[0020] As used herein, the term "microfibril" refers to fibrils that are part of the porous structure of a hollow fiber and have a size of less than 1 micrometer in each dimension.

[0021] As used herein, the term "lamellae" refers to the crystalline portion of the semi-crystalline polymer material of the hollow fiber.

[0022] As used herein, the term "continuous" refers to hollow fibers having a length in their longest dimension greater than one centimeter.

[0023] As used herein, the term "web," with respect to hollow fiber webs, refers to an array or network of integrally bonded hollow fibers (e.g., formed by coextrusion rather than braiding individual hollow fibers). Webs include strips or ribbons having a length in one planar axis that is substantially longer than the other, as well as webs having similar lengths in both planar axes.

[0024] As used herein, the term "netting" refers to a web having openings (eg, voids) between adjacent fibers.

[0025] As used herein, the term "amorphous" refers to a polymer that does not exhibit a melting point.

[0026] As used herein, the term "semicrystalline" refers to a polymer that forms crystalline domains upon solidification in addition to an amorphous phase and exhibits a melting peak upon heating and a crystallization peak upon solidification by dynamic scanning calorimetry (DSC).

[0027] As used herein, the term "porosity" refers to a measurement of the void space of a fiber having an open porous structure, as determined by gas flux measurements, an example of which is detailed in the Examples below.

[0028] As used herein, the term "filler" refers to solid particles contained in the fiber-forming material.

[0029] As used herein, the term "solid" refers to a state of matter in which the shape of a particle is stable and is not in a liquid or gaseous state.

[0030] As used herein, the term "thermoplastic" refers to a polymer that flows when heated sufficiently above its glass transition temperature and becomes solid when cooled. In contrast, the term "thermoset" refers to a polymer that becomes permanently solid when cured and does not flow upon subsequent heating. Thermoset polymers are typically crosslinked polymers.

[0031] As used herein, the term "glass transition temperature (Tg)" refers to the temperature at which a polymer transitions from a glassy state to a rubbery state and can be measured using differential scanning calorimetry (DSC) (e.g., at a heating rate of 10°C / min in a nitrogen stream). When referring to the Tg of a monomer, it refers to the Tg of the homopolymer of that monomer. The homopolymer must have a sufficiently high molecular weight so that the Tg reaches a constant value. It is generally understood that the Tg of a homopolymer increases with increasing molecular weight and converges to a constant value. Furthermore, the homopolymer should be substantially free of moisture, residual monomer, solvent, and other impurities that may affect the Tg. Suitable DSC measurement methods and analysis modes are described in Matsumoto, A. et al., J. Polym. Sci. A., Polym. Chem. 1993, 31, 2531-2539.

[0032] As used herein, "machine direction (MD)" refers to the direction in which a web of material runs during a manufacturing process. "Machine direction" and "longitudinal direction" are sometimes used synonymously. As used herein, "transverse direction (TD)" refers to the direction essentially perpendicular to the machine direction.

[0033] As used herein, the terms "preferred" and "preferably" refer to the fact that certain embodiments of the present disclosure may offer certain advantages, under particular circumstances. However, other embodiments may also be preferred, under the same or different circumstances. Furthermore, the description of a preferred embodiment does not imply that other embodiments are not useful, or are intended to exclude them from the scope of the present disclosure.

[0034] As used herein, the words "a," "an," and "the" are not intended to be limited to a single object but to include the entire general class for which a particular example is given for illustrative purposes. These words are used synonymously with "at least one." The phrases "at least one of" and "comprises at least one of," when followed by a list, refer to any one or more of the list in combination.

[0035] As used herein, the term "or" is to be construed in its ordinary sense as "and / or," unless expressly stated otherwise. "And / or" refers to one or all elements in a list, or a combination of any two or more elements.

[0036] Additionally, all numerical values ​​herein are modified by the word "about," and preferably by the word "exactly." The term "about" encompasses variations within the range expected by those skilled in the art depending on the objectivity of the measurements and the precision of the measuring equipment.

[0037] As used herein, when the term "generally" is used as a modifier for a certain characteristic or attribute, unless otherwise defined, it refers to a characteristic or attribute that would be readily recognizable by a person of ordinary skill in the art, but does not require absolute precision or perfect agreement (e.g., within ±20% for a quantifiable characteristic). As used herein, the term "substantially" means a high degree of approximation (e.g., within ±10% for a quantifiable characteristic), but does not require absolute precision or perfect agreement. As used herein, terms such as "same," "equal," "uniform," "constant," and "strictly" should be interpreted within normal tolerances and measurement errors in each situation, but do not imply absolute precision or perfect agreement.

[0038] In a first aspect, a porous hollow fiber web is provided. The porous hollow fiber web comprises: It comprises a plurality of connected hollow fibers, at least some of which have an open porous structure comprising microfibrils connecting the lamellar microstructure.

[0039] In a second aspect, a method for producing a porous hollow fiber web is provided, the method comprising: obtaining a hollow fiber web comprising a plurality of connected hollow fibers; stretching the hollow fiber web in the machine direction to break at least a portion of the hollow fibers and produce an open porous structure comprising microfibrils connecting the lamellar microstructure within the broken hollow fibers.

[0040] The following disclosure relates to both the first and second aspects.

[0041] A polymeric material is used to form the continuous hollow fibers of the hollow fiber web. Often, the hollow fibers comprise one or more semi-crystalline polymers. Suitable materials for the continuous fibers include, but are not limited to, at least one of polypropylene (PP), polyethylene (PE), polymethylpentene (PMP), polybutene-1, polyoxymethylene (POM), or copolymers thereof. Optionally, the continuous fibers can comprise a blend of at least two polymers. For example, a blend of a first PP and a second PP can be included. In some cases, one type of PP is preferred, and in other cases, two or more (e.g., different) types of PP are preferred. For example, the continuous fibers may have a number average molecular weight (Mn) of 250,000 grams per mole (g / mol) or more, such as 275,000 g / mol, 300,000 g / mol, 325,000 g / mol, 350,000 g / mol, 375,000 g / mol, 400,000 g / mol or more and 800,000 g / mol or less, such as 775,000 g / mol, 750,000 g / mol, 725,000 g / mol, 750 ... The continuous fiber may comprise PP having a number average molecular weight of 0 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 PP having a number average molecular weight of 250,000 g / mol to 800,000 g / mol (inclusive). The number average molecular weight can be measured using gel permeation chromatography. Specific examples of PP include polypropylenes commercially available from TotalEnergies Petrochemicals & Refining USA, Inc. (Houston, TX) under the tradenames "PPH3264" and "PPH3766."

[0042] Suitable crystalline thermoplastic polypropylene homopolymer resins are available from TotalEnergies Petrochemicals & Refining USA, Inc. (Houston, TX), including, for example, Homopolymer Polypropylene 3281, 3274, PPH3060, 3273, 3272, 3371, PPH4022, PPH4069, 3462, 3571, 3662, M3661, 3766, 3865, and 3860. Other suitable polypropylene homopolymers are available from LyondellBasell Industries (Pasadena, TX) under the "PRO-FAX" trade name, including, for example, PRO-FAX 1280, PRO-FAX 814, PRO-FAX 1282, and PRO-FAX 1283. It is also available under other trade names, such as ADFLUEX X500F, ADSYL 3C30F, HP403G, and TOPPYL SP 2103. Suitable polypropylene homopolymers are available from INEOS Olefins & Polymers, USA (Carson, CA), including, 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), including, for example, F008, F013M, FF026, and FF030F2. Suitable polypropylene homopolymers are available from ExxonMobil Chemical Co. (Spring, TX), including, for example, PP1024E4, PP2252E3, PP4292E1, PP4612E2, and PP4792.

[0043] Suitable crystalline thermoplastic polyethylene (PE) homopolymer resins are available from ExxonMobil 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) resins HDPE 56020, HDPE 55060, HDPE 5802, HDPE 51090, and HDPE 5502. Other suitable polyethylene homopolymers are available from Braskem Chemical and Plastics Company (LaPorte, TX), such as HF0144, HF0150, HF0147, and FH35. Additionally, suitable polyethylene polymers are available from NOVA Chemicals Corporation (Calgary, AB, Canada), including, for example, SUPRASS HPs167-AB, HPs267-AB, HPs667-AB, SCLAIR 19E, SCLAIR 99L, and NOVAPOL HB-L354-A.

[0044] In some embodiments, the resin may also comprise one or more poly(methyl)pentene (PMP) copolymer resins. Suitable grades of PMP copolymer resins containing low amounts of linear or branched α-olefin copolymers are available from Mitsui Chemicals (Minato-ku, Tokyo, Japan) under the general trade name "TPX," including resin grades such as DX470, RT18, DX820, and DX845.

[0045] Suitable crystalline thermoplastic polybutene-1 (PB-1) homopolymer resins are available from LyondellBasell Industries (Pasadena, TX), including, for example, Toppyl PB 0110M, Toppyl PB 8640M, Toppyl PB 8310, and Toppyl PB 8340M.

[0046] In some embodiments, the polymeric material includes a filler (e.g., aluminum oxide, aluminum nitride, aluminum trihydrate, boron nitride, aluminum, copper, graphite, graphene, magnesium oxide, zinc oxide), which can impart thermal conductivity to the hollow fiber web.

[0047] In some cases, a porous hollow fiber web comprises a continuous web of an array of connected hollow fibers, each having the form of an individual hollow fiber, with adjacent hollow fibers connected by bonded regions. Referring to FIG. 1, a suitable hollow fiber web 100 comprises an array of individual hollow fibers 102. The hollow fibers 102 have a hollow core 116 surrounded by a sheath 114. In some embodiments, the hollow cross-sectional area of ​​the fibers having a hollow cross-sectional area may exceed 50%, 60%, 70%, or 80% of the area between the top and bottom surfaces of the web. Adjacent hollow fibers 102 are connected by bonded regions 118. The length L of the bonded regions 118 is greater than 5% of the average diameter of the hollow fibers 102.

[0048] Generally, the longer the length L of the bonded region, the more linear the tubular shape formed by the openings of adjacent connected hollow fibers. A linear shape with rounded corners (e.g., a squircle shape) occupies a larger percentage of the hollow cross-sectional area in the area between the top and bottom surfaces of the web compared to a circular shape bonded only at tangent points. A shorter bond length L results in a more elliptical tubular shape. These squircle shapes can also be extruded onto a flat quenching surface to form flat segments at the top or bottom of the squircle shape. A linear squircle shape has a larger contact area with the planes of the top and bottom surfaces than a circular hollow fiber. This larger contact area is useful, for example, for heat transfer between the top and bottom surfaces. In some embodiments, the length L of the bonded region ranges from 0.1 millimeters (mm) to 5 mm. In some embodiments, the thickness T2 of the bonded region is substantially uniform along its length. In the example web 100 shown in FIG. 1, the cross-sectional shapes of the hollow fibers 102 are identical. In other embodiments, the cross-sectional shape of the hollow fibers 102 may vary. The cross-sectional shape of the hollow fibers 102 may be any suitable shape, such as squirrel-shaped, circular, or elliptical. The hollow fibers 102 typically have a wall thickness T1 (e.g., tubular wall thickness) ranging from 0.025 to 0.25 mm. Adjacent hollow fibers have first and second bond points 120 and 121, with bond points having radii greater than 0.1T1, 0.2T1, 0.3T1, 0.4T1, or 0.5T1. These bond points are the beginning and end of the bonded region between adjacent hollow fibers, represented as the bond length L shown in FIG. 1. The connection between the walls of adjacent hollow fibers and the bond points forms radii at both ends of the bond length. The bond points with radii improve crack propagation resistance between the hollow fibers. In some embodiments, the strength of the bond or weld between adjacent hollow fibers is greater than the strength of the wall thickness T1. As shown in Figure 1, web 100 is a continuous web, with hollow fibers 102 arranged in the same plane. As shown in Figure 1, each hollow fiber has a width W1 and a height H1. The squircle-shaped hollow fibers have flat surfaces on the top and bottom of the web.The dimensions W2 and t shown in Figure 1 can be used to calculate the contact area of ​​the squircle-shaped tubular web. The surface contact area percentage can be calculated by comparing the dimensions W1 and W2 shown in Figure 1.

[0049] In some embodiments, the contact area of ​​the upper and lower surfaces of the squircle-shaped web can reach up to 10%, up to 25%, up to 50%, or up to 95% of the planar surface area of ​​the upper or lower surface.

[0050] In some embodiments, the height H1 of the webs described herein is up to 5,000 micrometers (in some embodiments, up to 2,000 micrometers, up to 1,000 micrometers, up to 500 micrometers, or up to 100 micrometers), and may be in the range of 100 to 5,000 micrometers, 100 to 2,000 micrometers, 100 to 1,000 micrometers, or 100 to 500 micrometers.

[0051] In some embodiments, the average cross-sectional diameter of the hollow fiber ranges from 0.1 to 5 millimeters. In some embodiments, thickness T2 is twice thickness T1. In some embodiments, thickness T1 is uniform around the entire circumference of the hollow fiber. In some embodiments, thickness T1 varies to aid in the formation of a desired tubular shape.

[0052] In some embodiments, at least 25% of the hollow fibers (in some embodiments, at least 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100% of the hollow fibers) have an area of ​​0.1 to 10 square millimeters (mm 2 In some embodiments, the hollow cross-sectional area is in the range of 0.1 to 2 mm 2 or 0.1 to 5 mm 2 The range is.

[0053] In some embodiments, the array of hollow fibers has at least one cross-sectional opening that is circular, oval, or squircle shaped.

[0054] In some embodiments, the hollow fibers have a web direction (e.g., the t-direction shown in Figure 1) and a cross-web direction. The hollow fibers typically extend substantially in the web direction.

[0055] For example, a hollow fiber web such as that shown in Figure 1 may be produced by providing an extrusion die. The extrusion die defines a first cavity, a second cavity, and a distribution surface. The distribution surface has an array of alternating distribution orifices, and the extrusion die provides a first passageway extending from the first cavity to the first plurality of orifices. The extrusion die further provides a second passageway extending from the second cavity to the second plurality of orifices, providing an open passageway to the second cavity and the second distribution orifices. The method includes dispensing first hollow fibers from the first distribution orifices.

[0056] Additional information useful for making and using the hollow fibers described herein (e.g., those shown in FIG. 1 ), in combination with this disclosure, is set forth in WO 2020 / 003065 and WO 2021 / 250478 (both by Ausen et al.), the disclosures of which are incorporated herein by reference in their entireties.

[0057] In some cases, the porous hollow fiber web comprises a continuous web of an array of connected hollow fibers having the form of individual hollow fibers and a plurality of spacer segments disposed between at least a plurality of adjacent hollow fibers. Optionally, at least some of the spacer segments may have an open porous structure. The hollow fibers are disposed in one or more planes. For example, Figure 2 illustrates an embodiment in which the hollow fibers are disposed in one plane, and Figure 3 illustrates an embodiment in which the hollow fibers are disposed in two planes.

[0058] Referring to FIG. 2, a suitable hollow fiber web 200 includes an array of individual hollow fibers 202. Spacer segments 212 are disposed between adjacent hollow fibers 202. These spacer segments are formed simultaneously with the hollow fibers and are fused to the hollow fibers to form a continuous web. The spacer segments provide uniform tube placement and spacing. Regions 213 are formed between adjacent fibers. The hollow fibers 202 have a hollow core 216 surrounded by a sheath 214. As shown in FIG. 2, the hollow fiber web 200 is a continuous web. The hollow fibers 202 are also disposed in the same plane.

[0059] Referring to FIG. 3, another suitable hollow fiber web 300 includes an array of individual hollow fibers 302. Spacer segments 312 are disposed between adjacent hollow fibers 302. These spacer segments are formed simultaneously with the hollow fibers and are fused to the hollow fibers to form a continuous web. The spacer segments provide uniform fiber placement and spacing. Regions 313 are formed between adjacent hollow fibers. The hollow fibers 302 each have a hollow core 316 surrounded by a sheath 314. As shown in FIG. 3, the hollow fiber web 300 is a continuous web. The hollow fibers 302 are also disposed in two planes (e.g., on either side of the spacer segments). In other embodiments, the hollow fibers 302 may be disposed in more than two planes.

[0060] In some embodiments, the hollow fiber webs described herein have a thickness of up to 1000 micrometers (in some embodiments, up to 500 micrometers, up to 100 micrometers, up to 50 micrometers, or up to 25 micrometers). The thickness can also be in the following ranges: 10-750 micrometers, 10-500 micrometers, 10-100 micrometers, 10-50 micrometers, or 10-25 micrometers. In some embodiments, the average (e.g., tubular) wall thickness of the hollow fibers ranges from 5 to 100 micrometers. In some embodiments, the average spacer length ranges from 5 to 5000 micrometers.

[0061] In some embodiments, the hollow fibers have an average cross-sectional diameter in the range of 0.05 to 2 millimeters. In some embodiments, at least 25% of the hollow fibers (in some embodiments, at least 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100% of the fibers) have an average cross-sectional diameter in the range of 0.2 to 1 square millimeter (mm 2 In some embodiments, the hollow cross-sectional area may be in the following range: 0.1 mm 2 ~2mm 2 , 0.1mm 2 ~5mm 2 .

[0062] For example, hollow fiber webs such as those shown in Figures 2 and 3 may be produced by providing an extrusion die. The extrusion die defines a first cavity, a second cavity, and a third cavity, and a distribution surface. The distribution surface has an array of alternating distribution orifices. The extrusion die provides a fluid passageway between the second cavity and the second plurality of orifices, a fluid passageway between the first cavity and the first plurality of orifices, a third passageway extending from the third cavity to the third plurality of orifices, and an open air passageway to the third cavity and the third distribution orifices. The method includes dispensing first hollow fibers from the first distribution orifices and simultaneously dispensing spacer segments from the second distribution orifices.

[0063] The size of the hollow fibers (either the same or different sizes) can be adjusted, for example, by the composition of the extruded polymer, the speed at which the hollow fibers are extruded, and / or the orifice design (e.g., the cross-sectional area (height and / or width) of the orifice). Typically, hollow fibers are extruded in the direction of gravity. In some embodiments, it may be desirable to extrude the hollow fibers horizontally, especially when the extrusion orifices of the first and second polymers are not aligned with each other.

[0064] In practicing the methods described herein, the polymeric materials can be solidified simply by cooling. This cooling can be easily accomplished by passive cooling with ambient air, or it can be actively achieved, for example, by quenching the extruded first and second polymeric materials on a cooled surface (e.g., a chill roll). In some embodiments, the first and / or second polymeric materials may be low molecular weight polymers that require crosslinking to solidify. This crosslinking can be achieved, for example, by irradiation with electromagnetic waves or particle beams. In some embodiments, it may be desirable to maximize the time before quenching to improve weld strength.

[0065] Additional information useful for making and using the hollow fibers described herein (e.g., those shown in Figures 2 and 3) is set forth in U.S. Patent Publication Nos. 2014 / 0220328 and WO 2021 / 028798 (both to Ausen et al.), the disclosures of which are incorporated herein by reference in their entireties, in combination with this disclosure.

[0066] In some cases, the porous hollow fiber web comprises a net-like structure comprised of an array of polymeric strands. In this net-like structure, the polymeric strands are periodically bonded at bonded regions throughout the array, with spaces between adjacent strands. At least some of the strands are hollow polymeric strands (i.e., strands having a hollow core surrounded by a sheath). At least 50% of the strands do not cross each other. In some cases, at least some of the polymeric strands are solid strands, and at least some of the solid strands have an open porous structure. Referring to FIG. 4, a suitable hollow fiber web has a net-like structure 400 comprising an array 401 of polymeric strands 402. The polymeric strands 402 are periodically bonded at bonded regions 405 throughout the array 401, with openings 403 between adjacent strands (i.e., bonded strands are separated from each other between each bonded region). At least a plurality (i.e., at least two) of the strands 402 are hollow polymeric strands (i.e., strands having a hollow core 406 surrounded by a sheath 407). The strands 402 are substantially non-intersecting (i.e., at least 50% of the strands are non-intersecting), and the net-like structure 400 includes openings 403. In some embodiments, the openings 403 have at least one of a hexagonal shape or a diamond shape.

[0067] The strands produced using the methods described herein are substantially non-crossing (i.e., at least 50% (in some embodiments, at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99%, or 100%) of the strands are non-crossing).

[0068] In some embodiments, the strands are arranged in the same plane.

[0069] In some embodiments, hollow strands and solid strands are alternately arranged. The solid strands are designed to provide uniform spacing between the hollow strands. In some embodiments, the diameter of the solid strands may be in the following ranges: small: 0.05 mm to 0.2 mm, large: 0.2 mm to 2 mm. The distance between bonds of the solid strands may be in the following ranges: short: 0.1 mm to 1 mm, long: 1 mm to 10 mm. This design ensures the desired spacing between the hollow strands.

[0070] In some embodiments, the thicknesses of the strands (i.e., the first and second strands), bond regions, and other optional strands are substantially the same. In some embodiments, the average largest dimension of the bond region is defined as the dimension perpendicular to the strand thickness. The average largest dimension of the bond region is at least 2 times (in some embodiments, at least 3 times, 4 times, 5 times, 10 times, or at least 15 times) greater than the average width of at least either the first strand or the second strand.

[0071] In some embodiments, the net-like structures described herein have a thickness of up to 5,000 micrometers (in some embodiments, up to 2,000 micrometers, up to 1,000 micrometers, up to 500 micrometers, up to 100 micrometers, up to 50 micrometers, or up to 25 micrometers). The thickness may also be in the following ranges: 10 to 5,000 micrometers, 10 to 2,000 micrometers, 10 to 1,000 micrometers, 10 to 500 micrometers, 10 to 100 micrometers, 10 to 50 micrometers, or 10 to 25 micrometers.

[0072] In some embodiments, the average width of the polymeric strands is within the following ranges: 10 to 500 micrometers, 10 to 400 micrometers, or 10 to 250 micrometers. In some embodiments, the average width of the first polymeric strands is within the following ranges: 10 to 500 micrometers, 10 to 400 micrometers, or 10 to 250 micrometers. The average width of the second strands is also within the following ranges: 10 to 500 micrometers, 10 to 400 micrometers, or 10 to 250 micrometers.

[0073] In some embodiments, the basis weight of the netted structures described herein ranges from 5 to 1000 grams per square meter (g / m 2 ), 10~400g / m 2 (In some embodiments). For example, the net-like structure produced using the extrusion die described herein may have a basis weight in the above range. In some embodiments, the strand pitch (machine direction) of the net-like structure described herein is in the following range: 0.5 to 20 mm, 0.5 to 10 mm (in some embodiments).

[0074] In some embodiments, at least 25% of the hollow polymeric strands (in some embodiments, at least 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100% of the hollow polymeric strands) are between 0.2 and 1 square millimeter (mm 2 In some embodiments, the hollow cross-sectional area may be in the following range: 0.1 to 2 mm 2 , 0.1~5mm 2 .

[0075] Often, the solid strands comprise a first polymeric material and the hollow polymeric strands comprise a second polymeric material that is different from the first polymeric material.

[0076] For example, a hollow fiber web as shown in Figure 4 may be produced by providing an extrusion die. The extrusion die defines a first cavity, a second cavity, a third cavity, and a distribution surface. The distribution surface has an array of alternating distribution orifices. The extrusion die provides a second passageway extending from the second cavity to the second plurality of orifices, a third passageway extending from the third cavity to the third plurality of orifices, and an open passageway to the third cavity and the third distribution orifices. The method includes dispensing first polymeric strands from the first distribution orifices at a first strand velocity and simultaneously dispensing second polymeric strands from the second distribution orifices at a second strand velocity, wherein the first strand velocity is at least twice the second strand velocity, thereby forming a net-like structure.

[0077] As used herein, the term "bonded region" refers to the boundary where two strands are bonded. The boundary or bonded region can be detected using differential scanning calorimetry (DSC). The bond is formed by the collision of adjacent molten polymer strands with each other. Because adjacent strands are extruded at alternating speeds, adjacent molten strands continuously collide, form bonds, and then separate to form a net-like opening. Because the strands are extruded in the same direction, these bonds are all parallel bonds formed in the same direction. Furthermore, the bonds are coplanar and do not cross. For a given strand, on one side there is a first strand that is intermittently bonded, and on the other side there is a second strand that is also intermittently bonded. The bonded region is a continuous portion of the two strands, and therefore, the bonded region is composed of the sum of the two adjacent strands. Typically, the strands are continuous and can be tracked continuously through the bonded region.

[0078] The size of the strands (same or different sizes) can be adjusted by the following factors: the composition of the polymeric material being extruded, the speed of the extruded strands, and the orifice design (e.g., the cross-sectional area (height and / or width) of the orifice). For example, if the orifice of the first polymer has three times the area of ​​the orifice of the second polymer, a net-like structure can be produced with strands of the same size while satisfying the speed difference between adjacent strands.

[0079] In general, it has been observed that the strand bond rate is proportional to a faster strand extrusion rate. Furthermore, the bond rate can be increased by: increasing the polymer flow rate for a given orifice size; or decreasing the orifice area for a given polymer flow rate. It has also been observed that the inter-bond distance (i.e., strand pitch) is inversely proportional to the strand bond rate and proportional to the net take-up speed from the die. Therefore, it is believed that the bond pitch and net structure basis weight can be independently controlled by the orifice cross-sectional area design, take-up speed, and polymer extrusion rate. For example, to obtain a net structure with a relatively high basis weight and a relatively short bond pitch, the following conditions can be used: extrude at a relatively high polymer flow rate, use a relatively low net take-up speed, and use a die with a relatively small strand orifice area.

[0080] Typically, the polymer strands are extruded in the direction of gravity, which allows collinear strands to collide and form bonds before they can move away from each other. In some embodiments, it may be desirable to extrude the strands horizontally, especially when the extrusion orifices of the first and second polymers are not aligned with each other.

[0081] Additional information useful for making and using the net-like structures described herein, in combination with this disclosure, is set forth in U.S. Patent Publication Nos. 2014 / 0220328 and WO 2020 / 170115 (both by Ausen et al.), the disclosures of which are incorporated herein by reference in their entireties.

[0082] As mentioned above, suitable hollow fiber webs can be produced by the extrusion process described in WO 2020 / 170115, WO 2021 / 028798, and WO 2021 / 250478 (all by Ausen et al.). WO 2020 / 170115 further discloses the option of stretching the net-like structure immediately after production, which has been observed to orient the strands and improve the tensile strength properties of the net-like structure. It also discloses that stretching can reduce the overall strand size. Additionally, WO 2020 / 170115 suggests that by selecting the appropriate material and the appropriate degree of stretching, some strands may yield while others do not, resulting in the formation of loft (bulging). However, WO 2020 / 170115 does not disclose specific stretching conditions or describe stretching to form an open-pore porous structure. Furthermore, WO 2020 / 170115 describes that the net-like structure can contain a fluid (e.g., a gas, liquid, or viscous fluid) within the core of the hollow strand, suggesting that in hollow strands having a porous structure, the fluid within the core can migrate to the outside through the strand wall.

[0083] A method for producing a porous hollow fiber web includes obtaining a hollow fiber web comprising a plurality of connected hollow fibers (e.g., a suitable hollow fiber web as described above), stretching the hollow fiber web in the machine direction, and breaking at least a portion of the hollow fibers to produce an open porous structure comprising microfibrils connecting the lamellar microstructure within the broken hollow fibers.

[0084] In certain embodiments, the method further includes a step of annealing the hollow fiber web before stretching. Annealing is carried out at a temperature below the melting point of the polymeric material. For example, a hollow fiber web made of PP (polypropylene) is preferably annealed at 100 to 140°C. The annealing time ranges from 1 second to several hours, preferably 1 to 60 minutes, and more preferably 5 to 30 minutes. An example of a suitable stretching process is a method in which stretching at room temperature, stretching at a high temperature, and web relaxation are performed in that order.

[0085] The stretching process can be advantageously carried out using single-stage or multi-stage low-temperature stretching, and optionally, single-stage or multi-stage high-temperature stretching can be carried out successively. The low-temperature stretching temperature (cold stretching) is preferably set to a temperature 5°C to 70°C higher than the glass transition temperature (Tg) of the polymer, more preferably 10°C to 50°C higher. For example, the glass transition temperature of PP (polypropylene) is -10°C, and PP is preferably stretched at 20°C to 30°C. The high-temperature stretching temperature (hot stretching) is preferably set to a temperature 10°C to 120°C lower than the melting point temperature of the polymer, more preferably 20°C to 60°C lower. For example, PP is preferably stretched at 100°C to 140°C.

[0086] To form an open porous structure by uniaxial stretching, the hollow fiber web is advantageously stretched by at least 20% up to 500%, more preferably by at least 50% up to 300%.

[0087] The hollow fiber web after stretching is advantageously subjected to heat setting to reduce stress within each fiber. The heat setting temperature is typically set at a temperature 5°C or higher, 10°C or higher, or 15°C or higher than the high-temperature stretching temperature. The heat setting time is typically 30 seconds or longer, or 1 minute or longer.

[0088] The drawn hollow fiber web is advantageously subjected to a relaxation treatment to reduce the fiber length to a certain extent. The shrinkage is at least 2%, or at least 5%. The heat setting and relaxation treatments can be used alone or in combination.

[0089] Contrary to expectations, good fiber porosity was achieved by "dry" stretching a non-porous hollow fiber web. Hollow fibers with an open porous structure exhibit porosities (volume %, vol %) in the following ranges: 5 vol % or more (e.g., 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 (e.g., 75 vol %, 70 vol %, 65 vol %, 60 vol %, 55 vol %, or 50 vol %). The porosity contributes to improved properties, such as absorbency (e.g., improved fluid absorption), filtration, gas separation, thermal insulation, and functionalization.

[0090] 5, there is shown a scanning electron microscope (SEM) image of a cross section of a portion of a porous hollow fiber web 500 prepared according to Example 1 herein. Adjacent hollow fibers 502 and spacer segments 512 are visible.

[0091] Referring to Figure 6A, an SEM image of a cross section of a porous hollow fiber web 650 is shown. It can be seen that the hollow fibers 602 are connected by spacer segments 612. Referring to Figure 6B, an SEM image of the inner surface of the hollow fibers 602 is shown. The open porous structure 652 can be seen at a higher magnification than in Figure 6A.

[0092] Similarly, referring to Figure 6C, an SEM image of a portion of spacer segment 612 is shown. An open porous structure 652 is visible at a higher magnification than in Figure 6A. The porous hollow fiber web includes a lamellar microstructure 618 arranged in the row direction. As shown in Figure 6C, the lamellae do not form perfectly parallel rows, but rather form generally adjacent rows.

[0093] Referring to Figure 6D, an open porous structure containing microfibrils connecting the lamellar microstructures can be seen. Figure 6D shows an SEM image of the surface of a spacer segment 612, which contains multiple microfibrils 616 extending between opposing lamellar microstructures 618. The microfibrils 616 and lamellar microstructures 618 together constitute the open porous structure, forming voids 654. The size of the microfibrils 616 varies, and as shown in Figure 6D, at least one dimension may be less than 1 micrometer. This porous hollow fiber web has lamellar microstructures 618 arranged in a more curved row direction. As shown in Figure 6D, the lamellae collectively form adjacent rows connected by the microfibrils 616. Also, in some cases, the outer surface (e.g., skin layer) of the hollow fiber may exhibit lower orientation due to the extrusion process than the interior of the fiber wall. This is due to the quenching environment, which may result in more pronounced lamellar orientation deeper in the fiber wall than at the surface.

[0094] 6E, the open porous structure of the inner surface of hollow fiber 602 can be seen. Between voids 654, lamellar microstructures 618 arranged in the row direction are visible, but no microfibrils are visible.

[0095] As shown in all of Figures 6B-6E, the open porous structure is at least partially free of filler particles within the voids 654. This contrasts sharply with some prior art. For example, methods described in U.S. Patent No. 5,766,760 (Tsai et al.) and U.S. Patent No. 11,001,944 (Topolkaraev et al.) may form a porous structure by incorporating fillers (e.g., particulate fillers or nanoinclusion additives) into fibers. In some embodiments of the present disclosure, fillers may be optionally included, but the fillers do not essentially contribute significantly to the formation of the pore structure of the porous hollow fiber web. This is supported by the following evidence: even when fillers are included in the fibers, the proportion of the filler visible within the total voids of the open porous structure within the fibers is less than 20%, even less, less than 15%, less than 10%, or less than 5%. Therefore, it has been confirmed that the method of the present disclosure can form an open porous structure without relying on fillers.

[0096] [Example] In a first embodiment, the present disclosure provides a porous hollow fiber web comprising a plurality of connected hollow fibers, at least a portion of which have an open porous structure comprising microfibrils connecting a lamellar microstructure.

[0097] In a second embodiment, the present disclosure provides a porous hollow fiber web according to the first embodiment, wherein the porous hollow fiber web comprises an array of connected hollow fibers having the morphology of individual hollow fibers, adjacent hollow fibers being connected at bond regions, and the web is a continuous web.

[0098] In a third embodiment, the present disclosure provides a porous hollow fiber web according to the first embodiment, the porous hollow fiber web comprising an array of connected hollow fibers having the form of individual hollow fibers, and further comprising a plurality of spacer segments between at least a plurality of adjacent hollow fibers, the hollow fibers being arranged in one or more planes, and the web being a continuous web.

[0099] In a fourth embodiment, the present disclosure provides a porous hollow fiber web according to the third embodiment, wherein at least some of the spacer segments have an open porous structure.

[0100] In a fifth embodiment, the present disclosure provides a porous hollow fiber web according to the first embodiment. The porous hollow fiber web comprises a net-like structure consisting of an array of polymer strands. The polymer strands are periodically bonded at bonded regions throughout the array, with spaces between adjacent strands. At least a portion of the strands are connected hollow fibers in the form of hollow polymer strands. At least 50% of the strands do not cross each other.

[0101] In a sixth embodiment, the present disclosure provides a porous hollow fiber web according to the fifth embodiment, wherein at least some of the polymer strands are solid strands, and at least some of the solid strands have an open porous structure.

[0102] In a seventh embodiment, the present disclosure provides a porous hollow fiber web according to the sixth embodiment, wherein the solid strands comprise a first polymeric material and the hollow polymeric strands comprise a second polymeric material different from the first polymeric material.

[0103] In an eighth embodiment, the present disclosure provides a porous hollow fiber web according to any one of the first to seventh embodiments, wherein the hollow fibers comprise one or more semi-crystalline polymers.

[0104] In a ninth embodiment, the present disclosure provides a porous hollow fiber web according to any one of the first to eighth embodiments, wherein the hollow fibers comprise at least one of the following: polypropylene (PP), polyethylene (PE), polymethylpentene (PMP), polybutene-1, polyoxymethylene (POM), or copolymers thereof.

[0105] In a tenth embodiment, the present disclosure provides the porous hollow fiber web according to any one of the first to ninth embodiments, wherein the hollow fibers comprise PP (polypropylene).

[0106] In an eleventh embodiment, the present disclosure provides a porous hollow fiber web according to any one of the first to tenth embodiments, wherein the hollow fibers comprise a blend of at least two semi-crystalline polymers.

[0107] In a twelfth embodiment, the present disclosure provides the porous hollow fiber web according to any one of the first to eleventh embodiments, wherein the porosity of the hollow fibers is in the range of 5% to 80% by volume.

[0108] In a thirteenth embodiment, the present disclosure provides a method for producing a porous hollow fiber web, the method comprising: obtaining a hollow fiber web comprising a plurality of connected hollow fibers; and stretching the hollow fiber web in a machine direction to break at least a portion of the hollow fibers and form an open porous structure comprising microfibrils connecting the lamellar microstructure.

[0109] In a fourteenth embodiment, the present disclosure provides a method for producing a porous hollow fiber web according to the thirteenth embodiment, the method further comprising the step of annealing the hollow fiber web before stretching it.

[0110] In a fifteenth embodiment, the present disclosure provides a method for producing a porous hollow fiber web according to the thirteenth or fourteenth embodiment. Obtaining the hollow fiber web includes providing an extrusion die, the extrusion die defining a first cavity and a second cavity and a distribution surface, the distribution surface having an array of alternating distribution orifices, the extrusion die providing a first passageway extending from the first cavity to the first plurality of orifices, and the extrusion die providing a second passageway extending from the second cavity to the second plurality of orifices. Obtaining the hollow fiber web includes dispensing the first hollow fibers from the first distribution orifices and providing open passageways to the second cavity and the second distribution orifices.

[0111] In a sixteenth embodiment, the present disclosure provides a method for producing a porous hollow fiber web according to the thirteenth or fourteenth embodiment. The step of obtaining the hollow fiber web includes providing an extrusion die, the extrusion die defining a first cavity, a second cavity, and a third cavity, and a distribution surface, the distribution surface having an array of alternating distribution orifices, the extrusion die providing second passageways extending from the second cavity to the second plurality of orifices, and the extrusion die providing third passageways extending from the third cavity to the third plurality of orifices. The step of obtaining a hollow fiber web includes simultaneously dispensing first polymeric strands from a first dispensing orifice at a first strand speed and second polymeric strands from a second dispensing orifice at a second strand speed, providing an open air passage to the third cavity and the third dispensing orifice, wherein the first strand speed is at least twice the second strand speed, to provide a net-like structure.

[0112] In a seventeenth embodiment, the present disclosure provides a method for producing a porous hollow fiber web according to the thirteenth or fourteenth embodiment. Obtaining the hollow fiber web includes providing an extrusion die, the extrusion die defining a first cavity, a second cavity, and a third cavity, and a distribution surface, the distribution surface having an array of alternating distribution orifices, the extrusion die providing a fluid passageway between the second cavity and the second plurality of orifices, the extrusion die providing a fluid passageway between the first cavity and the first plurality of orifices, and the extrusion die providing a third passageway extending from the third cavity to the third plurality of orifices. Obtaining the hollow fiber web includes dispensing first hollow fibers from the first distribution orifices while simultaneously dispensing spacer segments from the second distribution orifices, and providing open passageways to the third cavity and the third distribution orifices.

[0113] [example] The objects and advantages of the present disclosure are further illustrated by the following examples. However, the specific materials, amounts used, and other conditions and details described in these examples should not be construed as unduly limiting the present disclosure. Unless otherwise specified or apparent from the context, all ingredients, proportions, ratios, etc. described in the examples and throughout the specification are by weight.

[0114] A hollow fiber web precursor with six hollow fibers was fabricated as follows. The hollow fibers and spacer segments were extruded from polypropylene resin (trade name "FF030F2" obtained from Braskem America, Inc., Philadelphia, PA) using a single-screw extruder. The temperature was set at 177-220°C, and the melt flow rate was approximately 2.6 pounds per hour (1.18 kg / hr). The melt was fed into two series of melt cavities within a web spinning die. The die temperature was set at 220°C. The melt cavity for the hollow fiber web precursor had an annular orifice and a central hole for the core air supply. The other series of cavities formed the spacer segments, connecting adjacent hollow fiber precursors. The hollow fiber web precursor was quenched by an air knife. The molten web precursor was pulled down by three sets of godet rolls at a pulldown speed of 100 meters per minute.

[0115] Porous hollow fiber webs were fabricated by annealing a hollow fiber web precursor and then dry stretching it. The hollow fiber web precursor was annealed for 20 minutes at a temperature set at 140°C in a convection oven. For dry (cold / hot) stretching, the precursor specimen was secured in a temperature-controlled environmental chamber attached to an Instron Mechanical Tester (Model 5969, obtained from Instron Corporation, Norwood, MA). A 127 mm (5 inch) long web was cold stretched at 25°C with a stretch rate of 600 mm / min, followed by hot stretching at 120°C with a stretch rate of 100 mm / min. The total stretch ratio after 10% relaxation was 100%.

[0116] Figure 5 shows an SEM image of a portion of the resulting porous hollow fiber web. The CO2 flux (GPU) of the resulting porous hollow fiber web was measured using a custom-designed test rig. The test rig was equipped with a cylinder of pure CO2 gas, a pressure gauge, and an in-line gas flow meter. The principle of the test was to supply pure gas into the lumen of the porous hollow fiber and measure the gas flow rate through the fiber wall and out into the surrounding environment. The gas pressure and gas flow rate were monitored by data acquisition software, and data were acquired once the pressure and gas flow rate stabilized.

[0117] Three replicate loop modules were fabricated by sealing the porous hollow fiber web within a 0.65 cm (1 / 4 inch) outer diameter nylon tube and securing it with epoxy adhesive. The lumen of each fiber was exposed by cutting the sealing tube with a razor. The loop module contained a porous hollow fiber web with an effective length of approximately 10.2 cm (4 inches). Referring to Figure 7, a photograph of a porous hollow fiber web 750 subjected to gas flux testing is shown. Air bubbles 760 are visible in the photograph, demonstrating that the porous hollow fiber web 750 is indeed porous. The gas permeability (GPU) of the porous hollow fiber web, 1 GPU = 10 -6 cm 3 (STP) / (cm2 s·cm Hg)) was calculated using the following formula:

number

[0118] The surface area of ​​the fibers was calculated based on their outer diameter (150 micrometers). This diameter was measured using the SEM images shown in Figure 5. When the test module was inserted into a water bath, bubbles formed along the entire hollow fiber web due to gas passing through the fiber walls. This suggests that the hollow fibers within the web have open, porous walls. Furthermore, the high-resolution SEM images shown in Figures 6A-6E clearly show the porous structure of the spacer segments and the inner surfaces of the hollow fibers.

[0119] The CO2 flow rate (i.e., flux) of the hollow fiber web module fabricated by the above method was 156±70 GPU.

[0120] All patents and patent applications referred to above are expressly incorporated herein by reference. The above-described embodiments are illustrative of the invention, and other configurations are possible. Accordingly, the invention should not be limited to the embodiments described in detail above and illustrated in the accompanying drawings, but should properly be limited only by the following claims and equivalents thereof.

Claims

1. 1. A porous hollow fiber web having a plurality of connected hollow fibers, at least some of the hollow fibers having an open porous structure comprising microfibrils connecting a lamellar microstructure.

2. comprising an array of connected hollow fibers, each having the morphology of an individual hollow fiber; Adjacent hollow fibers are connected at a bond region; The porous hollow fiber web of claim 1 , wherein the web is a continuous web.

3. comprising an array of connected hollow fibers, each having the morphology of an individual hollow fiber; a plurality of spacer segments between at least a plurality of adjacent hollow fibers; the hollow fibers lie in one or more planes; The porous hollow fiber web of claim 1 , wherein the web is a continuous web.

4. The porous hollow fiber web of claim 3 , wherein at least a portion of the spacer segments have an open porous structure.

5. a net comprising an array of polymer strands; the polymer strands are periodically bonded throughout the entire bond region of the array with spaces between adjacent strands; at least some of the strands are connected hollow fibers each having the form of an individual hollow polymeric strand; 10. The porous hollow fiber web of claim 1, wherein at least 50% of the strands do not cross each other.

6. at least some of the polymeric strands are solid strands; The porous hollow fiber web of claim 5 , wherein at least a portion of said solid strands have an open porous structure.

7. the solid strands comprise a first polymeric material; The porous hollow fiber web of claim 6 , wherein the hollow polymeric strands comprise a second polymeric material different from the first polymeric material.

8. The porous hollow fiber web of any one of claims 1 to 7, wherein the hollow fibers comprise one or more semi-crystalline polymers.

9. 9. The porous hollow fiber web according to claim 1, wherein the hollow fibers comprise at least one of polypropylene (PP), polyethylene (PE), polymethylpentene (PMP), polybutene-1, polyoxymethylene (POM), or copolymers thereof.

10. The porous hollow fiber web of any one of claims 1 to 9, wherein the hollow fibers comprise PP.

11. The porous hollow fiber web of any one of claims 1 to 10, wherein the hollow fibers comprise a blend of at least two semi-crystalline polymers.

12. 12. The porous hollow fiber web of claim 1, wherein the hollow fibers exhibit a porosity of from 5% to 80% by volume.

13. obtaining a hollow fiber web comprising a plurality of connected hollow fibers; stretching the hollow fiber web in the machine direction to break at least a portion of the hollow fibers and produce an open porous structure containing microfibrils connecting lamellar microstructures within the broken hollow fibers; A method for producing a porous hollow fiber web, comprising:

14. 14. The method of producing a porous hollow fiber web of claim 13, further comprising the step of annealing the porous hollow fiber web before stretching the hollow fiber web.

15. obtaining the hollow fiber web, providing an extrusion die defining a first cavity and a second cavity and a dispensing surface, the dispensing surface having an array of alternating dispensing orifices, the extrusion die providing first passageways extending from the first cavity to a first plurality of orifices, and the extrusion die providing second passageways extending from the second cavity to a second plurality of orifices; dispensing a first hollow fiber from the first dispensing orifice and providing an open air passage to the second cavity and the second dispensing orifice; 15. A method for producing the porous hollow fiber web of claim 13 or 14, comprising:

16. obtaining the hollow fiber web, providing an extrusion die defining a first cavity, a second cavity, and a third cavity and a dispensing surface, the dispensing surface having an array of alternating dispensing orifices, the extrusion die providing second passageways extending from the second cavity to a second plurality of orifices, and the extrusion die providing third passageways extending from the third cavity to a third plurality of orifices; dispensing a first polymer strand from the first dispensing orifice at a first strand velocity while simultaneously dispensing a second polymer strand from the second dispensing orifice at a second strand velocity, and providing an open air passageway to the third cavity and the third dispensing orifice, wherein the first strand velocity is at least twice the second strand velocity to provide a net; 15. The method for producing a porous hollow fiber web according to claim 13 or 14, comprising:

17. obtaining the hollow fiber web, providing an extrusion die defining a first cavity, a second cavity, and a third cavity and a distribution surface, the distribution surface having an array of alternating distribution orifices, the extrusion die providing a fluid passageway between the second cavity and a second plurality of orifices, the extrusion die providing a fluid passageway between the first cavity and the first plurality of orifices, and the extrusion die providing a third passageway extending from the third cavity to a third plurality of orifices; dispensing a first hollow fiber from the first distribution orifice while simultaneously dispensing a spacer segment from the second distribution orifice to provide an open air passageway to the third cavity and the third distribution orifice; 15. A method for producing the porous hollow fiber web of claim 13 or 14, comprising:

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