Bicomponent fiber

Abstract

The present disclosure provides an article. In an embodiment, the article is a bicomponent fiber and the bicomponent fiber comprises a fiber centroid; from 60 wt% to 80 wt% of a first region having a first centroid; and from from 40 wt% to 20 wt% of a second region having a second centroid, with weight percent based on the total weight of the bicomponent fiber. The first region comprises an ethylene elastomer having (i) a density from 0.860 g / cc to 0.890 g / cc, and (ii) a melt index from 20 g / 10 min to 60 g / 10 min. The second region comprises an ethylene / alpha-olefin interpolymer having (i) a density from 0.910 g / cc to 0.945 g / cc, (ii) a melt index from 20 g / 10 min to 60 g / 10 min, (iii) a crystallization temperature, Tc, from 100°Cto 115°C, and (iv) an Mw / Mn from 1.8 to 3.6. The first region and the second region are arranged such that at least one of the first centroid and the second centroid is not the same as the fiber centroid. The bicomponent fiber has a curvature from 1.5 mm-1 to 6.0 mm-1.

Description

BICOMPONENT FIBERBACKGROUND

[0001] Bicomponent fibers are fibers made from at least two different polymer compositions that are extruded from the same spinneret with the compositions contained within the same filament or fiber. When the fiber leaves the spinneret, it consists of non-mixed components that are fused at the interface. The two polymer compositions can differ in their chemical properties and / or physical properties.

[0002] Bicomponent fibers can be formed by conventional spinning techniques known in the art and can be used for forming a nonwoven fabric. Nonwoven fabrics have numerous applications, such as filters, disposable materials in medical applications, and diaperstock. To assist in reducing nonwoven weight or obtaining other advantageous nonwoven properties, such as loft, bicomponent fibers having curvature are desirable. However, problems exist with obtaining bicomponent fibers with curvature.

[0003] Consequently, the art recognizes the need for nonwoven fabrics with loft and bicomponent fibers having enhanced curvature.SUMMARY

[0004] The present disclosure provides an article. In an embodiment, the article is a bicomponent fiber and the bicomponent fiber comprises a fiber centroid; from 60 wt% to 80 wt% of a first region having a first centroid; and from from 40 wt% to 20 wt% of a second region having a second centroid, with weight percent based on the total weight of the bicomponent fiber. The first region comprises an ethylene elastomer having (i) a density from 0.860 g / cc to 0.890 g / cc, and (ii) a melt index from 20 g / 10 min to 60 g / 10 min. The second region comprises an ethylene / alpha-olefin interpolymer having (i) a density from 0.910 g / cc to 0.945 g / cc, (ii) a melt index from 20 g / 10 min to 60 g / 10 min, (iii) a crystallization temperature, Tc, from 100°Cto 115°C, and (iv) an Mw / Mn from 1.8 to 3.6. The first region and the second region are arranged such that at least one of the first centroid and the second centroid is not the same as the fiber centroid. The bicomponent fiber has a curvature from 1.5 mm1to 6.0 mm1.BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Fig. 1 is a scanning electron micrograph (SEM) cross-section image of a bicomponent fiber having an eccentric core sheath configuration and centroid off-set.

[0006] Fig. 2 is a schematic representation of a polymerization process in accordance with an embodiment of the present disclosure.DEFINITIONS

[0007] Any reference to the Periodic Table of Elements is that as published by CRC Press, Inc., 1990- 1991. Reference to a group of elements in this table is by the new notation for numbering groups.

[0008] For purposes of United States patent practice, the contents of any referenced patent, patent application or publication are incorporated by reference in their entirety (or its equivalent US version is so incorporated by reference) especially with respect to the disclosure of definitions (to the extent not inconsistent with any definitions specifically provided in this disclosure) and general knowledge in the art.

[0009] The numerical ranges disclosed herein include all values from, and including, the lower and upper value. For ranges containing explicit values (e.g., a range from 1, or 2, or 3 to 5, or 6, or 7), any subrange between any two explicit values is included (e.g., the range 1-7 above includes subranges 1 to 2; 2 to 6; 5 to 7; 3 to 7; 5 to 6; etc.).

[0010] Unless stated to the contrary, implicit from the context, or customary in the art, all parts and percents are based on weight and all test methods are current as of the filing date of this disclosure.

[0011] The terms "comprising", "including", "having" and their derivatives do not exclude the presence of any additional component or procedure. The term, "consisting essentially of" excludes any other component or procedure, except those essential to operability. The term "consisting of" excludes any component or procedure not specifically stated.

[0012] "Elastomer" and like terms refer to a rubber-like polymer that can be stretched to at least twice its original length and which retracts very rapidly to approximately its original length when the force exerting the stretching is released. An elastomer has an elastic modulus of 10,000psi (68.95 MPa) or less and an elongation usually greater than 200% in the uncrosslinked state at room temperature using the method of ASTM D638 - 72.

[0013] An "ethylene elastomer" and like terms refer to an elastomer composed of an ethylene-based polymer.

[0014] An "ethylene-based polymer" is a polymer that contains more than 50 mole percent (mol%) polymerized ethylene monomer (based on the total amount of polymerizable monomers) and, optionally, may contain at least one comonomer. Ethylene-based polymer includes ethylene homopolymer, and ethylene copolymer (meaning units derived from ethylene and one or more comonomers). The terms "ethylene-based polymer" and "polyethylene" may be used interchangeably. Nonlimiting examples of ethylene-based polymer (polyethylene) include low density polyethylene (LDPE) and linear polyethylene. Nonlimiting examples of linear polyethylene include linear low density polyethylene (LLDPE), ultra low density polyethylene (ULDPE), very low density polyethylene (VLDPE), multi-component ethylene-based copolymer (EPE), ethylene / a-olefin multi-block copolymers (also known as olefin block copolymer (OBC)), substantially linear, or linear, plastomers / elastomers, and high density polyethylene (HDPE). Generally, polyethylene may be produced in gas-phase, fluidized bed reactors, liquid phase slurry process reactors, or liquid phase solution process reactors, using a heterogeneous catalyst system, such as Ziegler-Natta catalyst, a homogeneous catalyst system, comprising Group 4 transition metals and ligand structures such as metallocene, non-metallocene metal-centered, heteroaryl, heterovalent aryloxyether, phosphinimine, and others. Combinations of heterogeneous and / or homogeneous catalysts also may be used in either single reactor or dual reactor configurations.

[0015] High density polyethylene (or "HDPE") is an ethylene homopolymer or an ethylene / a-olefin copolymer with at least one C3-C10 a-olefin comonomer, or C4-C8 a-olefin comonomer and a density from 0.940 g / cc, or 0.945 g / cc, or 0.950 g / cc, 0.953 g / cc to 0.955 g / cc, or 0.960 g / cc, or 0.965 g / cc, or 0.970 g / cc, or 0.975 g / cc, or 0.980 g / cc. The HDPE can be a monomodal copolymer or a multimodal copolymer. A "monomodal ethylene copolymer" is an ethylene / Ca-Cio a-olefin copolymer that has one distinct peak in a gel permeation chromatography (GPC) showing the molecular weight distribution. A "multimodal ethylenecopolymer" is an ethylene / C4-Cioa-olefin copolymer that has at least two distinct peaks in a GPC showing the molecular weight distribution. Multimodal includes copolymer having two peaks (bimodal) as well as copolymer having more than two peaks. Nonlimiting examples of HDPE include DOW™ High Density Polyethylene (HDPE) Resins (available from The Dow Chemical Company), CONTINUUM™ Bimodal Polyethylene Resins (available from The Dow Chemical Company), LUPOLEN™ (available from LyondellBasell), as well as HDPE products from Borealis, Ineos, and ExxonMobil.

[0016] "Low density polyethylene" (or "LDPE") may also be referred to as "high pressure ethylene polymer" or "highly branched polyethylene" and consists of ethylene homopolymer, or ethylene / a-olefin copolymer comprising at least one C3-C10 a-olefin that has a density from 0.915 g / cc to less than 0.940 g / cc and contains long chain branching with broad MWD. LDPE is typically produced by way of high pressure free radical polymerization (tubular reactor or autoclave with free radical initiator). LDPE resins typically have a density in the range of 0.915 to 0.935 g / cc. Nonlimiting examples of LDPE include MarFlex™ (Chevron Phillips), LUPOLEN™ (LyondellBasell), as well as LDPE products from Dow, Borealis, Ineos, ExxonMobil, and others.

[0017] "Linear low density polyethylene" (or "LLDPE") is a linear ethylene / a-olefin copolymer containing heterogeneous short-chain branching distribution comprising units derived from ethylene and units derived from at least one C3-C10 a-olefin comonomer. LLDPE is characterized by little, if any, long chain branching, in contrast to conventional LDPE. LLDPE has a density from 0.910 g / cc to less than 0.940 g / cc. Nonlimiting examples of LLDPE include TUFLIN™ linear low density polyethylene resins (available from The Dow Chemical Company), DOWLEX™ polyethylene resins (available from the Dow Chemical Company), FINGERPRINT™ polyethylene resins (available from the Dow Chemical Company), and MARLEX™ polyethylene (available from Chevron Phillips).

[0018] A "fiber," as used herein, is an elongated strand of polymeric material in which the length to diameter ratio is greater than 10. A fiber typically has a round, or substantially round, cross section. Other cross-sectional shapes for the fiber include a trilobal shape, or a flat ( / .e., "ribbon" like) shape. A fiber excludes a film which has opposing parallel, or substantially parallel, sides.

[0019] The term "meltblown fibers" refers to fibers formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into converging high velocity, usually hot, gas (e.g., air) streams which attenuate the filaments of molten thermoplastic material to reduce their diameter, which may be to microfiber diameter. Thereafter, the meltblown fibers are carried by the high velocity gas stream and are deposited on a collecting surface to form a web of randomly dispersed meltblown fibers. Meltblown fibers, which may be continuous or discontinuous, typically have an average fiber diameter less than or equal to 25 microns, or from 1.5 micron to 25 microns. Meltblown webs can be bonded by a variety of means including, but not limited to, autogeneous bonding, i.e., self bonding without further treatment, thermo-calendaring process, adhesive bonding process, hot air bonding process, needle punch process, hydroentangling process, and combinations thereof.

[0020] The terms "nonwoven," and "nonwoven web," are used herein interchangeably. "Nonwoven" refers to a web having a structure of individual fibers or threads which are randomly interlaid, but not in an identifiable manner as is the case for a knitted fabric.

[0021] An "olefin-based polymer" is a polymer that contains a majority mole percent polymerized olefin monomer (based on total amount of polymerizable monomers), and optionally, may contain at least one comonomer. Nonlimiting examples of olefin-based polymers include ethylene-based polymer and propylene-based polymer.

[0022] The term "polymer" is a macromolecular compound prepared by polymerizing monomers of the same or different type. "Polymer" includes homopolymers, copolymers, terpolymers, interpolymers, and so on. The term "interpolymer" means a polymer prepared by the polymerization of at least two types of monomers or comonomers. It includes, but is not limited to, copolymers (which usually refers to polymers prepared from two different types of monomers or comonomers, terpolymers (which usually refers to polymers prepared from three different types of monomers or comonomers), tetrapolymers (which usually refers to polymers prepared from four different types of monomers or comonomers), and the like.

[0023] A "propylene-based polymer" is a polymer that contains a majority mole percent of polymerized propylene based on the weight of the polymer and, optionally, may comprise atleast one comonomer. Propylene-based polymers typically comprise at least 50 mole percent (mol%) units derived from propylene (based on the total amount of polymerizable monomers.

[0024] The term "spunbond" refers to the fabrication of nonwoven fabric including the following steps: (a) extruding molten thermoplastic strands from a plurality of fine capillaries called a spinneret; (b) quenching the strands with a flow of air which is generally cooled in order to hasten the solidification of the molten strands; (c) attenuating the strands by advancing them through the quench zone with a draw tension that can be applied by either pneumatically entraining the strands in an air stream or by winding them around mechanical draw rolls of the type commonly used in the textile fibers industry; (d) collecting the drawn strands into a web on a foraminous surface (e.g., moving screen or porous belt); and (e) bonding the web of loose strands into a nonwoven fabric. Bonding can be achieved by a variety of means including, but not limited to, thermo-calendaring process, adhesive bonding process, hot air bonding process, needle punch process, hydroentangling process, and combinations thereof. The average fiber diameter for fibers made from a spunbond fabrication process is typically greater than 15 microns.TEST METHODS

[0025] Average fiber diameter. The average fiber diameter was measured by Optical Microscope. A minimum of 10 different fibers were measured. The average fiber diameter is reported according to average fiber diameter = d t / n, where d_n is the diameter of the nthfiber.

[0026] Cross-Section Images for Measuring the Centroid Off-Set. SEM or Atomic Force Microscope (AFM) analysis can be used to gather cross-section images of fibers. In the SEM analysis, approximately ten stained fibers were mounted in epoxy, cured overnight in the same oven, and cryogenically polished to expose the fiber in cross section. For polishing, a Leica UC7 ultramicrotome was operated at -120°C and fitted with diamond knives. The polished fibers were mounted to a SEM sample stub, coated with 25 seconds of sputtered Iridium, and examined in the scanning electron microscope (SEM). FEI Nova SEM operated at 5kV ofaccelerating voltage, spot size of 4.5, the #5 objective aperture, and a working distance ~12 mm has been used and all images are captured from secondary electron emissions using SEM.

[0027] Curvature. The amount of curvature is measured via optical microscopy. The amount of curvature is calculated based on the inverse of the radius of the helix formed by the fiber. This is equal to the radius of the circle formed by projection of the helix formed by the fiber on a surface perpendicular to it. Average value of at least 5 measurements is reported. Measurements are reported in units of 1 / millimeter ( mm1).

[0028] Density. Samples for density measurements were prepared according to ASTM D 4703-10. Samples were pressed at 374°F (190°C), for five minutes, at 10,000 psi (68 MPa). The temperature was maintained at 374°F (190°C) for the above five minutes, and then the pressure was increased to 30,000 psi (207 MPa) for three minutes. This was followed by a one minute hold at 70°F (21°C) and 30,000 psi (207 MPa). Measurements were made within one hour of sample pressing using ASTM D792-08, Method B.

[0029] Melt Index. Melt index (Ml) or 12 was measured in accordance with ASTM D 1238- 10, Condition 190°C / 2.16 kg, Method B, and was reported in grams eluted per 10 minutes.

[0030] Molecular Weight Distribution. Gel Permeation Chromatography (GPC) is used to determine polymer molecular weight. GPC is obtained by high temperature gel permeation chromatography (GPC) equipment (PolymerChar, Spain). The IR5 detector ("measurement channel") is used as a concentration detector. GPCOne software (PolymerChar, Spain) is used to calculate weight-average (Mw), and number-average (Mn) molecular weight of the polymer and to determine molecular weight distribution (Mw / Mn). The method uses three 10 micron PL gel mixed B columns (Agilent Technologies, column dimension 100 X 7.6 mm) or four 20 micron PL gel mixed A columns (Agilent Technologies, column dimension 100 X 7.6 mm) operating at a system temperature of 150 °C. Samples are prepared at a 2 mg / mL concentration in 1,2,4-trichlorobenzene solvent containing 200 part per million of antioxidant butylated hydroxytoluene (BHT) for 3 hours at 160 °C with a gentle shaking by autosampler (PolymerChar, Spain). The flow rate is 1.0 mL / min, the injection size is 200 microliters. GPCOne software is used to calculate the plate count. The chromatographic system must have a minimum of 22,000 plates.

[0031] The GPC column set is calibrated by running at least 20 narrow molecular weight distribution polystyrene standards. The calibration uses a third order fit for the system with threelO micron PL gel mixed B columns or a fifth order fit for the system with four 20 micron PL gel mixed A columns. The molecular weight (MW) of the standards range from 580 g / mol to 8,400,000 g / mol, and the standards are contained in 6 "cocktail" mixtures. Each standard mixture has approximately a decade of separation between individual molecular weights. The standard mixtures are purchased from Agilent Technologies. The polystyrene standards are prepared at "0.025 g in 50 mL of solvent" for molecular weights equal to, or greater than, 1,000,000 g / mol, and at "0.05 g in 50 mL of solvent" for molecular weights less than 1,000,000 g / moL The polystyrene standards are dissolved at 80°C, with gentle agitation, for 30 minutes. The narrow standards mixtures are run first, and in order of decreasing highest molecular weight component, to minimize degradation. The polystyrene standard peak molecular weights are converted to polyethylene molecular weights using Equation (1) (as described in Williams and Ward, J. Polym. Sci ., Polym. Letters, 6, 621 (1968)):MWPE= A x MWps)B(Eq. 1) where MW is the molecular weight of polyethylene (PE) or polystyrene (PS) as marked, and B is equal to 1.0. It is known to those of ordinary skill in the art that A may be in a range of about 0.38 to about 0.44 such that the A value yields 52,000 MWPE for Standard Reference Materials (SRM) 1475a. Use of this polyethylene calibration method to obtain molecular weight values, such as the molecular weight distribution (MWD or Mw / Mn), and related statistics, is defined here as the modified method of Williams and Ward. The numberaverage molecular weight, the weight-average molecular weight, and the z-average molecular weight are calculated from the following equations.where Mn,cc, Mw,cc, and Mz,Cc (in g / mole) are the number-, weight-, and z-average molecular weight obtained from the conventional calibration, respectively, w, is the weight fraction of the polyethylene molecules eluted at retention volume Vi. Mcc,i is the molecular weight (in g / mole)of the polyethylene molecules eluted at retention volume Vi obtained using the conventional calibration (see Equation (1)).

[0032] The chromatographic peaks should be set to include area marking a significant visible departure from baseline when the chromatogram is viewed at 20 percent peak height. The baseline should not be integrated to less than 100 polyethylene-equivalent molecular weight and care must be used to account for anti-oxidant mismatch from the prepared sample and the chromatographic mobile phase.

[0033] Use of a decane flow rate marker is shown in the IR5 chromatogram. At no point should the baseline (response) Y-value difference between the start and the end of the baseline be greater than 3 percent of the integrated peak height of the chromatogram. In such a case, the chromatographic sample must be handled through proper matching of the sample and mobile phase antioxidant.

[0034] (wt. fraction greater than 105g / mole) is calculated according the MWD curve ( w, versus log Mcc, i) obtained from GPCOne software according to Equation (5)

[0035] Permanent set. A bundle of 288 fibers is stretched to 100% of its original length at a deformation rate of 250 mm / min in an INSTRON testing machine. Grip distance is 10 cm. At 100% extension, the sample is allowed to relax for 30 seconds before returning to 0% strain at the same rate of 250 mm / min. The sample is held for another 60 seconds at 0% strain before stretching to 100% of its original length at a deformation rate of 250 mm / min. The strain at 0.1 N upon second stretching is taken as the permanent set and is reported in percent (%).DETAILED DESCRIPTION

[0036] The present disclosure provides an article. In an embodiment, the article is a bicomponent fiber. The bicomponent fiber has a fiber centroid. The bicomponent fiber includes from 60 wt% to 80 wt% of a first region with a first centroid and from 40 wt% to 20 wt% of a second region with a second centroid (weight percent based on the total weight of the bicomponent fiber). The first region includes an ethylene-based elastomer having (i) a densityfrom 0.860 g / cc to 0.890 g / cc, and (ii) a melt index from 20 g / 10 min to 60 g / 10 min. The second region includes an ethylene / alpha-olefin interpolymer having (i) a density from 0.910 g / cc to 0.945 g / cc, (ii) a melt index from 20 g / 10 min to 60 g / 10 min, (iii) a crystallization temperature, Tc, from 100°C to 115°C, and (iv) an Mw / Mn from 1.8 to 3.6. The first region and the second region are arranged such that at least one of the first centroid and the second centroid is not the same as the fiber centroid. The bicomponent fiber has a curvature from 1.5 mm1to 6.0 mm1.

[0037] A "bicomponent fiber," as used herein, is a fiber made of at least two different polymer compositions that are extruded from the same spinneret with the polymer compositions contained within the same filament or the same fiber. When the fiber leaves the spinneret, it consists of non-mixed components that are fused at the interface. The two polymer compositions can differ in their chemical and / or in their physical properties.

[0038] The bicomponent fiber has a fiber centroid. As used herein, the term "fiber centroid" refers to the arithmetic mean of all the points of a region of a cross-section of a bicomponent fiber. For example, the bicomponent fiber according to embodiments of the present disclosure has a fiber centroid, which can be designated as Cf, and a region of the bicomponent fiber (e.g., the first or second region) has an independent centroid, which can be designated as Crx, where x is a designation of the region (e.g., the first region can be designated as Cri and the second region can be designated as Crz). Fig. 1 illustrates a bicomponent fiber and its centroid as well as the centroids of the first region and second regions of the bicomponent fiber. The distance from a region centroid to the fiber centroid can be defined as "Prx", and the centroid offset of the first centroid or second centroid to the fiber centroid can be defined as "Prx / rx.", where "r" is average radius of the fiber cross-section (average distance from Cf to the outer surface of the bicomponent fiber) and is calculated aswhere A is the area of the bicomponent fiber cross-section.

[0039] In an embodiment, at least one of the first centroid and the second centroid is not the same as the fiber centroid. Where the first centroid or the second centroid are different than the fiber centroid, the bicomponent fiber can have different configurations, such as eccentric core sheath, side by side, or segmented pie, but cannot have a concentric configuration (e.g., a core sheath concentric configuration) where the fiber centroid, first centroid, and the secondcentroid are the same. In embodiments, the first centroid of the first region and the second centroid of the second region are arranged such that the first region and the second region are in a side by side configuration. In other embodiments, the first centroid of the first region and the second centroid of the second region are arranged such that the first region and the second region are in a segmented pie configuration. In further embodiments, the first centroid of the first region and the second centroid of the second region are arranged such that the first region and the second region are in an eccentric core-sheath configuration, where the first region is the core region, and the second region is the sheath region of the bicomponent fiber and the sheath region surrounds the core region. In embodiments, the first and second regions are arranged in core sheath, side by side, segmented pie, or islands-in-the sea structures.

[0040] In an embodiment, the first centroid or the second centroid is offset from the fiber centroid by at least 0.1, or at least 0.2, or at least 0.4, and is less than 1 or less than 0.9, where offset is measured in accordance with the test method described below.

[0041] First region

[0042] The bicomponent fiber has a first region. The first region is from 60 wt% to 80 wt%, or from 65 wt% to 80 wt% of the total weight of the bicomponent fiber. The first region can be the core region in a core-sheath configured bicomponent fiber. The first region has a first centroid. The first region comprises an ethylene elastomer. The first region includes at least 75%, or at least 80%, or at least 85%, or at least 90%, or at least 95%, or at least 97%, or at least 98%, or at least 99%, or 100% (all percents being by weight based on total weight of the first region) of the first region of the bicomponent fiber. The remainder of the first region may be additional components such as one or more other polymers and / or one or more additives. Other polymers could be another propylene-based polymer or another ethylene-based polymer (different than the ethylene elastomer). The amount of the other polymer may be up to 25%. Nonlimiting examples of suitable additives include antistatic agents, color enhancers, dyes, lubricants, fillers such as TiOz or CaCOs, opacifiers, nucleators, processing aids, pigments, primary antioxidants, secondary antioxidants, processing aids, UV stabilizers, anti-blocks, slip agents, tackifiers, fire retardants, anti-microbial agents, odor reducer agents, anti-fungal agents, and combinations thereof. The ethylene elastomer may contain from 0.01 wt% to 25 wt%, or from 0.1 wt% to 20wt%, or from 1 wt% to 15 wt%, or from 1 wt% to 10 wt%, or from 1 wt% to 5 wt% additive based on the total weight of the ethylene elastomer and additive.

[0043] In an embodiment, the ethylene elastomer is an ethylene / C^Cs a-olefin copolymer.

[0044] In an embodiment, the ethylene elastomer is an ethylene / C4-C8 a-olefin multi-block copolymer. The term "ethylene / a-olefin multi-block copolymer" refers to an ethylene / C4-C8 a- olefin multi-block copolymer consisting of ethylene and one copolymerizable C4-C8 a-olefin comonomer in polymerized form (and optional additives), the polymer characterized by multiple blocks or segments of two polymerized monomer units differing in chemical or physical properties, the blocks joined (or covalently bonded) in a linear manner, that is, a polymer comprising chemically differentiated units which are joined end-to-end with respect to polymerized ethylenic functionality. Ethylene / a-olefin multi-block copolymer includes block copolymer with two blocks (di-block) and more than two blocks (multi-block). The C4-C8 a-olefin is selected from butene, hexene, and octene. The ethylene / a-olefin multi-block copolymer is void of, or otherwise excludes, styrene ( / .e., is styrene-free), and / or vinyl aromatic monomer, and / or conjugated diene. When referring to amounts of "ethylene" or "comonomer" in the copolymer, it is understood that this refers to polymerized units thereof. In some embodiments, the ethylene / a-olefin multi-block copolymer can be represented by the following formula: (AB)n; where n is at least 1, preferably an integer greater than 1, such as 2, 3, 4, 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, or higher, "A" represents a hard block or segment, and "B" represents a soft block or segment. The As and Bs are linked, or covalently bonded, in a substantially linear fashion, or in a linear manner, as opposed to a substantially branched or substantially star-shaped fashion. In other embodiments, A blocks and B blocks are randomly distributed along the polymer chain. In other words, the block copolymers usually do not have a structure as follows: AAA-AA-BBB- BB. In an embodiment, the ethylene / a-olefin multi-block copolymer does not have a third type of block, which comprises different comonomer(s). In another embodiment, each of block A and block B has monomers or comonomers substantially randomly distributed within the block. In other words, neither block A nor block B comprises two or more sub-segments (or sub-blocks) of distinct composition, such as a tip segment, which has a substantially different composition than the rest of the block.

[0045] In an embodiment, ethylene comprises the majority mole fraction of the whole ethylene / a-olefin multi-block copolymer, i.e., ethylene comprises at least 50 wt% of the whole ethylene / a-olefin multi-block copolymer. More preferably, ethylene comprises at least 60 wt%, at least 70 wt%, or at least 80 wt%, with the substantial remainder of the whole ethylene / a-olefin multi-block copolymer comprising the C4-C8 a-olefin comonomer. In an embodiment, the ethylene / a-olefin multi-block copolymer contains from 50 wt% to 90 wt% ethylene, or from 60 wt% to 85 wt% ethylene, or from 65 wt% to 80 wt% ethylene. For many ethylene / octene multiblock copolymers, the composition comprises an ethylene content greater than 80 wt% of the whole ethylene / octene multi-block copolymer and an octene content from 10 wt% to 15 wt%, or from 15 wt% to 20 wt% of the whole multi-block copolymer.

[0046] The ethylene / a-olefin multi-block copolymer includes various amounts of "hard" segments and "soft" segments. "Hard" segments are blocks of polymerized units in which ethylene is present in an amount greater than 90 wt%, or 95 wt%, or greater than 95 wt%, or greater than 98 wt%, based on the weight of the polymer, up to 100 wt%. In other words, the comonomer content (content of monomers other than ethylene) in the hard segments is less than 10 wt%, or 5 wt%, or less than 5 wt%, or less than 2 wt%, based on the weight of the polymer, and can be as low as zero. In some embodiments, the hard segments include all, or substantially all, units derived from ethylene. "Soft" segments are blocks of polymerized units in which the comonomer content (content of monomers other than ethylene) is greater than 5 wt%, or greater than 8 wt%, greater than 10 wt%, or greater than 15 wt%, based on the weight of the polymer. In an embodiment, the comonomer content in the soft segments is greater than 20 wt%, greater than 25 wt%, greater than 30 wt%, greater than 35 wt%, greater than 40 wt%, greater than 45 wt%, greater than 50 wt%, or greater than 60 wt% and can be up to 100 wt%.

[0047] The soft segments can be present in an ethylene / a-olefin multi-block copolymer from 1 wt% to 99 wt% of the total weight of the ethylene / a-olefin multi-block copolymer, or from 5 wt% to 95 wt%, from 10 wt% to 90 wt%, from 15 wt% to 85 wt%, from 20 wt% to 80 wt%, from 25 wt% to 75 wt%, from 30 wt% to 70 wt%, from 35 wt% to 65 wt%, from 40 wt% to 60 wt%, or from 45 wt% to 55 wt% of the total weight of the ethylene / a-olefin multi-block copolymer. Conversely, the hard segments can be present in similar ranges. The soft segment weightpercentage and the hard segment weight percentage can be calculated based on data obtained from DSC or NMR. Such methods and calculations are disclosed in, for example, USP 7,608,668, entitled "Ethylene / a-Olefin Block Inter-Polymers," filed on March 15, 2006, in the name of Colin L. P. Shan, Lonnie Hazlitt, et. al. and assigned to Dow Global Technologies Inc., the disclosure of which is incorporated by reference herein in its entirety. In particular, hard and soft segment weight percentages and comonomer content may be determined as described in column 57 to column 63 of USP 7,608,668.

[0048] The ethylene / a-olefin multi-block copolymer comprises two or more chemically distinct regions or segments (referred to as "blocks") joined (or covalently bonded) in a linear manner, that is, it contains chemically differentiated units which are joined end-to-end with respect to polymerized ethylenic functionality, rather than in pendent or grafted fashion. In an embodiment, the blocks differ in the amount or type of incorporated comonomer, density, amount of crystallinity, crystallite size attributable to a polymer of such composition, type or degree of tacticity (isotactic or syndiotactic), regio-regularity or regio-irregularity, amount of branching (including long chain branching or hyper-branching), homogeneity or any other chemical or physical property. Compared to block interpolymers of the prior art, including interpolymers produced by sequential monomer addition, fluxional catalysts, or anionic polymerization techniques, the present ethylene / a-olefin multi-block copolymer is characterized by unique distributions of both polymer polydispersity (PDI or Mw / Mn or MWD), polydisperse block length distribution, and / or polydisperse block number distribution, due, in an embodiment, to the effect of the shuttling agent(s) in combination with multiple catalysts used in their preparation.

[0049] In an embodiment, the ethylene / a-olefin multi-block copolymer is produced in a continuous process and possesses a polydispersity index (Mw / Mn) from 1.7 to 3.5, or from 1.8 to 3, or from 1.8 to 2.5, or from 1.8 to 2.2. When produced in a batch or semi-batch process, the ethylene / a-olefin multi-block copolymer possesses Mw / Mn from 1.0 to 3.5, or from 1.3 to 3, or from 1.4 to 2.5, or from 1.4 to 2.

[0050] In addition, the ethylene / a-olefin multi-block copolymer possesses a PDI (or Mw / Mn) fitting a Schultz-Flory distribution rather than a Poisson distribution. The present ethylene / a-olefin multi-block copolymer has both a polydisperse block distribution as well as a polydisperse distribution of block sizes. This results in the formation of polymer products having improved and distinguishable physical properties. The theoretical benefits of a polydisperse block distribution have been previously modeled and discussed in Potemkin, Physical Review E (1998) 57 (6), pp. 6902-6912, and Dobrynin, J. Chem. Phvs. (1997) 107 (21), pp 9234-9238.

[0051] In an embodiment, the present ethylene / a-olefin multi-block copolymer possesses a most probable distribution of block lengths.

[0052] In a further embodiment, the ethylene / a-olefin multi-block copolymer of the present disclosure, especially those made in a continuous, solution polymerization reactor, possess a most probable distribution of block lengths. In one embodiment of this disclosure, ethylene / a- olefin multi-block copolymers are defined as having:(A) Mw / Mn from about 1.7 to about 3.5, at least one melting point, Tm, in degrees Celsius, and a density, d, in grams / cubic centimeter, where in the numerical values of Tm and d correspond to the relationship:Tm > -2002.9 + 4538.5(d) - 2422.2(d)2, and / or(B) Mw / Mn from about 1.7 to about 3.5, and is characterized by a heat of fusion, AH in J / g, and a delta quantity, AT, in degrees Celsius defined as the temperature difference between the tallest DSC peak and the tallest Crystallization Analysis Fractionation ("CRYSTAF") peak, wherein the numerical values of AT and AH have the following relationships:AT > -0.1299 AH + 62.81 for AH greater than zero and up to 130 J / g AT > 48°C for AH greater than 130 J / g wherein the CRYSTAF peak is determined using at least 5 percent of the cumulative polymer, and if less than 5 percent of the polymer has an identifiable CRYSTAF peak, then the CRYSTAF temperature is 30°C; and / or(C) elastic recovery, Re, in percent at 300 percent strain and 1 cycle measured with a compression-molded film of the ethylene / a-olefin interpolymer, and has a density, d, in grams / cubic centimeter, wherein the numerical values of Re and d satisfy the following relationship when ethylene / a-olefin interpolymer is substantially free of crosslinked phase:Re > 1481 - 1629(d); and / or(D) has a molecular fraction which elutes between 40°C and 130°C when fractionated using TREF, characterized in that the fraction has a molar comonomer content of at least 5 percent higher than that of a comparable random ethylene interpolymer fraction eluting between the same temperatures, wherein said comparable random ethylene interpolymer has the same comonomer(s) and has a melt index, density and molar comonomer content (based on the whole polymer) within 10 percent of that of the ethylene / a-olefin interpolymer; and / or(E) has a storage modulus at 25°C, G'(25°C), and a storage modulus at 100°C, G'(100°C), wherein the ratio of G'(25°C) to G'(100°C) is in the range of 1:1 to 9:1.

[0053] The ethylene / a-olefin multi-block copolymer may also have:(F) a molecular fraction which elutes between 40°C and 130°C when fractionated using TREF, characterized in that the fraction has a block index of at least 0.5 and up to 1 and a molecular weight distribution, Mw / Mn, greater than 1.3; and / or(G) average block index greater than zero and up to 1.0 and a molecular weight distribution, Mw / Mn greater than 1.3.

[0054] It is understood that the ethylene / a-olefin multi-block copolymer may have one, some, all, or any combination of properties (A)-(G). Block Index can be determined as described in detail in USP 7,608,668 herein incorporated by reference for that purpose. Analytical methods for determining properties (A) through (G) are disclosed in, for example, USP 7,608,668, col. 31 line 26 through col. 35 line 44, which is herein incorporated by reference for that purpose.

[0055] In an embodiment, the ethylene / a-olefin multi-block copolymer has hard segments and soft segments, is styrene-free, consists of only (i) ethylene and (ii) a C4-C8 a-olefin or Cs a- olefin (and optional additives), and is defined as having a Mw / Mn from 1.7 to 3.5, at least one melting point, Tm, in degrees Celsius, and a density, d, in grams / cubic centimeter, wherein the numerical values of Tm and d correspond to the relationship:Tm > -2002.9 + 4538.5(d) - 2422.2(d)2, where the density, d, is from 0.850 g / cc, or 0.860 g / cc, or 0.870 g / cc to 0.875 g / cc, or 0.877 g / cc, or 0.880 g / cc, or 0.890 g / cc; and the melting point, Tm, is from 110°C, or 115°C, or 120°C to 125°C, or 130°C, or 135°C.

[0056] In an embodiment, the ethylene / C4-Cs a-olefin multi-block copolymer is an ethylene / l-octene multi-block copolymer (consisting only of ethylene, octene comonomer, and optional additives) and has one, some, or all of the following properties:(i) a Mw / Mn from 1.7 to 3.5, or from 1.8 to 2.2; and / or(ii) a density from 0.860 g / cc to 0.890 g / cc, or from 0.865 g / cc to 0.890 g / cc, or from 0.865 g / cc to 0.885 g / cc; and / or(iii) a melting point, Tm, from 115°C to 125°C, or from 116°C to 124°C, or from 118°C, or 123°C; and / or(iv) a melt index (Ml) from 1.0 g / 10 min to 60.0 g / 10 min, or from 10.0 g / 10 min to 60.0 g / 10 min, or from 20 g / 10 min to 60 g / 10 min, or from 25 g / 10 min to 55 g / 10 min, or from 30 g / 10 min to 50 g / 10 min; and / or(v) from 50 to 85 wt% soft segment and from 40 to 15 wt% hard segment (based on total weight of the ethylene / octene multi-block copolymer); and / or(vi) from 10 mol%, or 13 mol%, or 14 mol%, or 15 mol% to 16 mol%, or 17 mol%, or 18 mol%, or 19 mol%, or 20 mol% octene in the soft segment; and / or(vii) from 0.5 mol%, or 1.0 mol%, or 2.0 mol%, or 3.0 mol% to 4.0 mol%, or 5 mol%, or 6 mol%, or 7 mol%, or 9 mol% octene in the hard segment; and / or(viii) an elastic recovery (Re) from 50%, or 60% to 70%, or 80%, or 90%, at 300% min1deformation rate at 21°C as measured in accordance with ASTM D 1708; and / or(ix) a polydisperse distribution of blocks and a polydisperse distribution of block sizes (hereafter referred to as multi-block copolymer properties (i)-(ix)).

[0057] In an embodiment, the ethylene / a-olefin multi-block copolymer is an ethylene / octene multi-block copolymer. The ethylene / octene multi-block copolymer is sold under the tradename INFUSE™, available from The Dow Chemical Company, Midland, Michigan, USA.

[0058] The ethylene / a-olefin multi-block copolymer can be produced via a chain shuttling process such as described in USP 7,858,706, which is herein incorporated by reference. In particular, suitable chain shuttling agents and related information are listed in col. 16 line 39 through col. 19 line 44. Suitable catalysts are described in col. 19 line 45 through col. 46 line 19and suitable co-catalysts in col. 46 line 20 through col. 51 line 28. The process is described throughout the document, but particularly in col. 51 line 29 through col. 54 line 56. The process is also described, for example, in the following: USP 7,608,668; USP 7,893,166; and USP 7,947,793.

[0059] Second Region

[0060] The bicomponent fiber includes a second region. The second region has a second centroid. The second region is from 40 wt% to 20 wt% or from 35 wt% to 20 wt% of the total weight of the bicomponent fiber. The second region can be the sheath region in a core sheath configured bicomponent fiber. The second region has a second centroid. The second region includes an ethylene / alpha-olefin interpolymer. As used herein, the term "ethylene / alpha-olefin interpolymer" refers to an interpolymer that comprises, in polymerized form, a majority amount of ethylene monomer (based on the mole percent of the interpolymer), and at least one alphaolefin monomer and is different than the ethylene elastomer. The ethylene / alpha-olefin interpolymer has (a) less than 100 percent, for example, at least 80 percent, or at least 90 percent, of the units derived from ethylene; and (b) less than 20 percent, for example, less than 15 percent, or less than 10 percent, by weight of units derived from one or more alpha-olefin comonomers. The alpha-olefin comonomers typically have no more than 20 carbon atoms. For example, the alpha-olefin comonomers have from 3 to 10 carbon atoms, or from 3 to 8 carbon atoms, or from 4 to 8 carbon atoms. Exemplary alpha-olefin comonomers include, but are not limited to, propylene, 1 -butene, 1 -pentene, 1- hexene, 1 -heptene, 1 -octene, 1- nonene, 1 - decene, and 4-methyl- 1 -pentene. The remainder of the second region may be additional components such as one or more other polymers and / or one or more additives. Other polymers could be another propylene-based polymer or another ethylene-based polymer (different than the ethylene-based elastomer). The amount of the other polymer may be up to 25%. Nonlimiting examples of suitable additives include antistatic agents, color enhancers, dyes, lubricants, fillers such as TiOz or CaCOs, opacifiers, nucleators, processing aids, pigments, primary antioxidants, secondary antioxidants, processing aids, UV stabilizers, anti-blocks, slip agents, tackifiers, fire retardants, anti-microbial agents, odor reducer agents, anti-fungal agents, and combinations thereof. The ethylene / alpha-olefin interpolymer may contain from 0.01 wt%to 25 wt%, or from 0.1 wt% to 20 wt%, or from 1 wt% to 15 wt%, or from 1 wt% to 10 wt%, or from 1 wt% to 5 wt% additive based on the total weight of the ethylene / alpha-olefin interpolymer and additive.

[0061] In an embodiment, the ethylene / alpha-olefin interpolymer is an ethylene / C4-C8 alpha-olefin copolymer and the alpha-olefin is selected from butene, hexene, octene, and combinations thereof.

[0062] In an embodiment, the ethylene / alpha-olefin interpolymer is an ethylene / C4-C8 alpha-olefin copolymer and has one, some, or all of the following properties:(i) a density from 0.910 g / cc to 0.945 g / cc, or from 0.910 g / cc to 0.940 g / cc, or from 0.915 g / cc to 0.935 g / cc; and / or(ii) a melt index from 20 g / 10 min to 60 g / 10 min, or from 20 g / 10 min to 50 g / 10 min, or from 20 g / 10 min to 40 g / 10 min, or from 20 g / 10 min to 30 g / 10 min to 20 g / 10 min to 25 g / 10 min, or from 21 g / 10 min to 25 g / 10 min; and / or(iii) a crystallization temperature, Tc, from 100°C to 115°C, or from 101°C to 114°C, or from 101.5°C to 113.5°C; and / or(iv) an Mw / Mn from 1.8 to 3.6, or from 2.2 to 3.6.

[0063] In an embodiment, the bicomponent fiber has a fiber centroid;(A) from 60 wt% to 80 wt%, or from 65 wt% to 80 wt% of the first region (having a first centroid) that is the core in a core-sheath configuration, the first region including an ethylene elastomer that is an ethylene / C4-Cs a-olefin multi-block copolymer having one, some, or all of the following properties:(i) a density from 0.860 g / cc to 0.890 g / cc, or from 0.865 g / cc to 0.890 g / cc, or from 0.865 g / cc to 0.885 g / cc; and / or(ii) a melt index from 20 g / 10 min to 60 g / 10 min, or from 25 g / 10 min to 55 g / 10 min, or from 30 g / 10 min to 50 g / 10 min; and / or(iii) a Mw / Mn from 1.7 to 3.5; or from 1.8 to 2.2;(B) from 40 wt% to 20 wt%, or from 35 wt% to 20 wt% of the second region (having a second centroid) that is the sheath in a core-sheath configuration with weight percent based on total weight of the bicomponent fiber, the second region including an ethylene / C4-C8 alpha-olefin copolymer having one, some, or all of the following properties:(i) a density from 0.910 g / cc to 0.945 g / cc, or from 0.910 g / cc to 0.940 g / cc, or from 0.915 g / cc to 0.935 g / cc; and / or(ii) a melt index from 20 g / 10 min to 60 g / 10 min, or from 20 g / 10 min to 50 g / 10 min, or from 20 g / 10 min to 40 g / 10 min, or from 20 g / 10 min to 30 g / 10 min to 20 g / 10 min to 25 g / 10 min, or from 21 g / 10 min to 25 g / 10 min; and / or(iii) a crystallization temperature, Tc, from 100°C to 115°C, or from 101°C to 114°C, or from 101.5°C to 113.5°C; and / or(iv) an Mw / Mn from 1.8 to 3.6, or from 2.2 to 3.6; and the first region and the second region are arranged such that at least one of the first centroid and the second centroid is not the same as the fiber centroid; and the bicomponent fiber has one, some, or all, of the following properties:(1) a fiber curvature from 1.5 mm1to 6.0 mm1; or from 1.6 mm1to 5.0 mm4, or from 1.7 mm1to 4.9 mm1; and / or(2) an average fiber diameter from 10 pm to 30 pm, or from 15 pm to 25 pm, or from16 pm to 24 pm, or from 17 pm to 23 pm; and / or(3) a permanent set from 15% to 45%, or from 16% to 44%, or from 17% to 43%; and / or(4) the bicomponent fiber is void of propylene or void of a polymer containing units derived from propylene monomer.

[0064] In an embodiment, the present bicomponent fiber is produced by melt spinning. In melt spinning, the first region and second region can be melted, coextruded, and forced through the fine orifices in a metallic plate, called a spinneret, into air or other gas, where they are cooled and solidified forming a bicomponent fiber. The solidified fiber may be drawn off via air jets, rotating rolls, or godets, and can be laid on a conveyer belt as a web for forming anonwoven. A meltblown nonwoven comprising a bicomponent fiber according to embodiments of the present disclosure can be formed. In a further embodiment, a spunbond nonwoven fabric comprising the present bicomponent fiber can be formed.Formed.

[0065] Applicant discovered the combination of ethylene elastomer and ethylene / alpha- olefin interpolymer unexpectedly produces the present bicomponent fiber with (i) high curliness (fiber curvature from 1.5 mm1to 6.0 mm'1) and (ii) elasticity (permanent set 15%- 45%) through melt spinning. The present bicomponent fiber (with curliness and elasticity) is advantageous in personal hygiene applications, such as diapers, adult incontinence products, and feminine hygiene products. The one-step melt-spinning process to produce the present bicomponent fiber is more economical than conventional procedures which require the fiber to be made via a staple fiber process followed by a carding / bonding process.

[0066] The present bicomponent fiber is an "all-polyethylene fiber" making the present bicomponent fiber readily recyclable. As an all-polyethylene fiber, the present bicomponent fiber has improved haptics and improved soft-touch, compared to propylene-containing fiber.

[0067] By way of example, and not limitation, examples of the present disclosure will now be described in detail in the following examples.EXAMPLES Materials

[0068] Catalysts and co-catalysts used to produce Resin 1 are provided in Table 1 below.

[0069] Table 1

[0070] Production of Resin 1

[0071] All raw materials (ethylene monomer and 1-octene comonomer) and the process solvent (a narrow boiling range high-purity isoparaffinic solvent, product name Isopar-E commercially available from ExxonMobil Chemical) are purified with molecular sieves before introduction into the reaction environment. Hydrogen is supplied pressurized as a high puritygrade and is not further purified. The reactor ethylene feed stream is pressurized via a mechanical compressor to above reaction pressure. The solvent and comonomer feed is pressurized via a pump to above reaction pressure. The individual catalyst components are manually batch diluted to suitable component concentrations with purified solvent and pressured to above reaction pressure. All reaction feed flows are measured with mass flow meters and independently controlled with computer automated valve control systems.

[0072] A two-reactor system is used in a series configuration. Each continuous solution polymerization reactor consists of a liquid full, non-adiabatic, isothermal, circulating, loop reactor which mimics a continuously stirred tank reactor (CSTR) with heat removal. Independent control of all fresh solvent, ethylene, hydrogen, and catalyst component feeds is possible. The total fresh feed stream to each reactor (solvent, ethylene, comonomer, and hydrogen) is temperature controlled to maintain a single solution phase by passing the feed stream through a heat exchanger. The total fresh feed to each polymerization reactor is injected into the reactor at two locations with approximately equal reactor volumes between each injection location. The fresh feed is controlled with each injector receiving half of the total fresh feed mass flow. The catalyst components are injected into the polymerization reactor through a specially designed injection stingers. The primary catalyst component feed is computer controlled to maintain each reactor ethylene conversion at the specified targets. The cocatalyst components are fed based on calculated specified molar ratios to the primary catalyst component or alternatively a cocatalyst may be controlled to the specified component concentration in the reactor. Immediately following each reactor feed injection location, the feed streams are mixed with the circulating polymerization reactor contents with static mixing elements. The contents of each reactor are continuously circulated through heat exchangers responsible for removing much of the heat of reaction and with the temperature of the coolant side responsible for maintaining an isothermal reaction environment at the specified temperature. Circulation around each reactor loop is provided by a pump.

[0073] In dual series reactor configuration, the effluent from the first polymerization reactor (containing solvent, ethylene, comonomer, hydrogen, catalyst components, and polymer) exits the first reactor loop and is added to the second reactor loop.

[0074] The second reactor effluent enters a zone where it is deactivated with the addition of and reaction with water. At this same reactor exit location other additives are added for polymer stabilization such as phenol, 2-(l,l-dimethylethyl)-6-methyl-4-(3-((2,4,8,10- tetrakis(l,l-dimethyethyl)dibenzo(d,f)(l,3,2)dioxaphosphepin-6-yl)oxy)propyl) and tris(2,4-di- tert-butylphenyl)phosphite].

[0075] Following catalyst deactivation and additive addition, the reactor effluent enters a devolatization system where the polymer is removed from the non-polymer stream. The isolated polymer melt is pelletized and collected. The non-polymer stream passes through various pieces of equipment which separate most of the ethylene which is removed from the system. Most of the solvent and unreacted comonomer is recycled back to the reactor after passing through a purification system. A small amount of solvent and comonomer is purged from the process.

[0076] The reactor stream feed data flows that correspond to the values in Table 2 used to produce Resin 1 are graphically described in Fig. 2. The data are presented such that the complexity of the solvent recycle system is accounted for and the reaction system can be treated more simply as a once through flow diagram. The structure and compositions of the catalyst components used are provided in Table 1.

[0077] Table 2

[0078] Properties for Resin 1, and other polymers used in the inventive examples ("IE") and in the comparative samples ("CS") are listed in Table 3 below.Table 3

[0079] Formation of Fibers

[0080] Fibers are spun on a Hills Bicomponent Continuous Filament Fiber Spinning Line. Bicomponent fibers having an eccentric core sheath configuration are made. The fibers are spun on the Hills Line according to the following conditions. Extruder profiles are adjusted to achieve a melt temperature of 230°C. Throughput rate of each hole is 0.6 ghm (grams per hole per minute). A Hills Bicomponent die is used and operated at various core / sheath ratio (in weight) with the first region comprising one polymer in one extruder and second region comprising another polymer in the other extruder. The die consists of 144 holes, with a hole diameter of 0.6 mm and a length / diameter (L / D) of 4 / 1. Quench air temperature and flow rate are set at 20 °C and 520 cfm (cubic foot per minute), respectively. After the quenching zone, a draw tension is applied on the 144 filaments by pneumatically entraining the filaments in a slot unit with an air stream. Velocity of the air stream is controlled by the slot aspirator pressure. The slot aspirator pressure is set at 20, 30, 40, 50 psi, respectively.

[0081] Properties for inventive examples (IE) and comparative samples (CS) of bicomponent fibers are provided in Table 4 below.Table 4 - Bicomponent fiber properties

[0082] Compared to CS1-CS18, each of I El-5 exhibit high fiber curvature (1.5-6.0 mm ) and high elasticity (15% to 45%, the lower the better) at an average fiber diameter of 10-30 microns.

[0083] Using HDPE as core does not contribute to elasticity as the permanent set values are high and also do not change as a function of drawing. Applicant discovered that using ethylene elastomer in the core (INFUSE 9900) increases fiber curvature and lowers the permanent set.

[0084] It is specifically intended that the present disclosure not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims.

Claims

CLAIMS1. A bicomponent fiber comprising: a fiber centroid; from 60 wt% to 80 wt% of a first region having a first centroid, the first region comprising an ethylene elastomer having(i) a density from 0.860 g / cc to 0.890 g / cc, and(ii) a melt index from 20 g / 10 min to 60 g / 10 min; from 40 wt% to 20 wt% of a second region having a second centroid, with weight percent based on the total weight of the bicomponent fiber, the second region comprising an ethylene / alpha-olefin interpolymer having(i) a density from 0.910 g / cc to 0.945 g / cc,(ii) a melt index from 20 g / 10 min to 60 g / 10 min,(iii) a crystallization temperature, Tc, from 100°C to 115°C, and(iv) an Mw / Mn from 1.8 to 3.6; the first region and the second region are arranged such that at least one of the first centroid and the second centroid is not the same as the fiber centroid; and the bicomponent fiber has a curvature from 1.5 mm1to 6.0 mm4.

2. The bicomponent fiber of claim 1 wherein the ethylene-based elastomer is an ethylene / C4-Cs a-olefin multi-block copolymer.

3. The bicomponent fiber of any of claims 1-2 wherein the bicomponent fiber has an average fiber diameter from 10 microns to 30 microns.

4. The bicomponent fiber of any of claims 1-3 wherein the bicomponent fiber has a curvature from 1.5 mm1to 5.0 mm .

5. The bicomponent fiber of any of claims 1-4 wherein the bicomponent fiber has a permanent set from 15% to 45%.

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