Bicomponent fibers with improved curvature

Abstract

A bicomponent fiber having improved curvature is provided. The bicomponent fiber includes a first region and a second region. The first region includes a first polyethylene composition and the second region includes a second polyethylene composition, the first polyethylene composition having a crystallization temperature (Tc) higher than the crystallization temperature (Tc) of the second polyethylene composition. The bicomponent fiber can be used to form a nonwoven fabric.

Description

[Technical Field]

[0001] SUMMARY OF THE DISCLOSURE Embodiments of the present disclosure generally relate to bicomponent fibers with improved curvature comprising polyethylene, and nonwoven fabrics comprising the fibers.

[0002] Introduction Bicomponent fibers are fibers composed of two different polymer compositions extruded from the same spinneret, with both compositions contained within the same filament or fiber. When the fiber leaves the spinneret, it consists of unmixed components that fuse at the interface. The two polymer compositions may differ in their chemical and / or physical properties. Bicomponent fibers can be formed by conventional spinning techniques known in the art and used to form nonwoven fabrics. Nonwoven fabrics have a variety of uses, including filters, disposable materials for medical applications, and diaper stock. Bicomponent fibers with curvature can be used to reduce the weight of nonwoven fabrics or to obtain other advantageous nonwoven properties, such as loft. However, challenges exist regarding obtaining bicomponent fibers with improved curvature that maintain or improve other advantageous properties, such as spinnability, flexibility, recyclability, and extensibility. Summary of the Invention

[0003]

[0006] Embodiments of the present disclosure provide bicomponent fibers that can be used to form nonwovens and that, in aspects, provide a unique and surprisingly high curvature while maintaining or improving other properties, such as spinnability, tactile softness, recyclability, and extensibility. Bicomponent fibers according to embodiments of the present disclosure include first and second regions comprising a first and second polyethylene composition, respectively, that contribute to the fiber having improved curvature and advantageous spinnability, softness, recyclability, and extensibility. Specifically, bicomponent fibers according to embodiments of the present disclosure include a first and second polyethylene composition that can improve spinnability, softness, recyclability, and extensibility, and can be tailored to improve the inherent curvature of the fiber (e.g., fiber curvature that is not the result of mechanical crimping or post-extrusion processes, such as damping by the application of hot air or tension).

[0004] Disclosed herein are bicomponent fibers. In one embodiment, the bicomponent fiber includes a fiber center of gravity and a first region having a first center of gravity and a second region having a second center of gravity, the first region having a ratio of weight average molecular weight to number average molecular weight (M w(GPC) / M n(GPC) ), the second region comprising a second polyethylene composition having a density less than the density of the first polyethylene composition, at least one of the first centroid and the second centroid is not the same as the fiber centroid, and the first polyethylene composition has a crystallization temperature (Tc) that is at least 2°C higher than the crystallization temperature (Tc) of the second polyethylene composition.

[0005] In a different embodiment, the bicomponent fiber includes a fiber center of gravity, a first region having a first center of gravity, and a second region having a second center of gravity, the first region having a ratio of weight average molecular weight to number average molecular weight (M w(GPC) / M n(GPC)), greater than 3.0, the second region comprising a second polyethylene composition having a density less than the density of the first polyethylene composition, at least one of the first centroid and the second centroid is not the same as the fiber centroid, and the first polyethylene composition has a crystallization temperature (Tc) that is at least 3.5°C higher than the crystallization temperature (Tc) of the second polyethylene composition.

[0006] Also disclosed herein are nonwoven fabrics formed from the bicomponent fibers disclosed herein. For example, spunbond nonwoven fabrics can be formed from the bicomponent fibers disclosed herein. In one embodiment, the spunbond nonwoven fabric comprises bicomponent fibers having a fiber centroid and a first region having a first centroid and a second region having a second centroid, the first region having a ratio of weight average molecular weight to number average molecular weight (M w(GPC) / M n(GPC) ) less than 3.0, and the second region comprises a second polyethylene composition having a density less than the density of the first polyethylene composition, at least one of the first and second centroids is not the same as the fiber centroid, and the first polyethylene composition has a crystallization temperature (Tc) at least 2°C higher than the crystallization temperature (Tc) of the second polyethylene composition. In a different embodiment, the spunbond nonwoven fabric comprises bicomponent fibers comprising a fiber centroid, a first region having the first centroid and a second region having the second centroid, and the first region has a ratio of weight average molecular weight to number average molecular weight (M w(GPC) / M n(GPC) ), greater than 3.0, the second region comprising a second polyethylene composition having a density less than the density of the first polyethylene composition, at least one of the first centroid and the second centroid is not the same as the fiber centroid, and the first polyethylene composition has a crystallization temperature (Tc) that is at least 3.5°C higher than the crystallization temperature (Tc) of the second polyethylene composition.

[0007] Additional features and advantages of the embodiments will be set forth in the detailed description that follows, and in part will be readily apparent to those skilled in the art from that description, or will be learned by practicing the embodiments described herein, including the following detailed description, claims, and accompanying drawings.

[0008] It is to be understood that both the foregoing and the following descriptions are intended to describe various embodiments and provide an overview or framework for understanding the nature and features of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments described herein and, together with the description, serve to explain the principles and operation of the claimed subject matter. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a scanning electron micrograph (SEM) cross-sectional image of a bicomponent fiber having an eccentric core-sheath configuration and a center of gravity offset. [Figure 2] FIG. 1 is a diagram of a single reactor stream feed data flow used to produce the polyethylene compositions disclosed herein. [Figure 3] FIG. 1 is a diagram of the dual reactor stream feed data flow used to produce the polyethylene compositions disclosed herein. DETAILED DESCRIPTION OF THE INVENTION

[0010] Aspects of the disclosed bicomponent fibers are described in more detail below. Bicomponent fibers with increased curvature can be used to form nonwoven fabrics, which may have a wide variety of uses, including, for example, wipes, face masks, tissues, bandages, and other medical and hygiene products. However, it should be noted that this is merely an exemplary implementation of the embodiments disclosed herein. The embodiments are also applicable to other technologies prone to problems similar to those described above.

[0011] As used herein, the terms "comprising," "including," "having," and their derivatives are not intended to exclude the presence of any additional component, step, or procedure, whether specifically disclosed or not. For the avoidance of doubt, all compositions claimed through the use of the term "comprising" may include any additional additive, adjuvant, or compound, whether polymeric or otherwise, unless otherwise stated to the contrary. In contrast, the term "consisting essentially of" excludes from the scope of any subsequent description any other component, step, or procedure, except those that are not essential to operability. The term "consisting of" excludes any component, step, or procedure not specifically delineated or listed.

[0012] As used herein, the term "interpolymer" refers to a polymer prepared by the polymerization of at least two different types of monomers. Thus, the term interpolymer includes copolymers (used to refer to polymers prepared from two different types of monomers) and polymers prepared from three or more different types of monomers.

[0013] As used herein, the term "polymer" refers to a polymeric compound prepared by polymerizing monomers, whether of the same or different types. Thus, the generic term polymer encompasses the terms homopolymer (used to refer to a polymer prepared from only one type of monomer, with the understanding that trace amounts of impurities may be incorporated into the polymer structure) and interpolymer. Trace amounts of impurities (e.g., catalyst residues) may be incorporated into and / or within the polymer. The polymer may be a single polymer or a polymer blend.

[0014] As used herein, the term "polyethylene composition" refers to a polymer containing greater than 50% by weight of units derived from ethylene monomers and, optionally, one or more comonomers. Polyethylene compositions include polyethylene homopolymers, copolymers, and interpolymers. Common forms of polyethylene compositions known in the art include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), ultra-low-density polyethylene (ULDPE), very low-density polyethylene (VLDPE), single-site catalyzed linear low-density polyethylene (m-LLDPE) containing both linear and substantially linear low-density resins, medium-density polyethylene (MDPE), and high-density polyethylene (HDPE).

[0015] As used herein, the terms "nonwoven," "nonwoven web," and "nonwoven fabric" are used interchangeably herein. "Nonwoven" refers to a web or fabric having a structure of individual fibers or threads interleaved randomly, rather than in a discernible manner as in knitted fabrics.

[0016] As used herein, the term "meltblown" refers to the production of nonwoven fabrics via a process that includes the following steps: (a) extruding molten thermoplastic strands through a spinneret, (b) simultaneously quenching and attenuating the polymer stream immediately below the spinneret using a high-velocity, heated air stream, and (c) collecting the drawn strands into a web on a collecting surface. Meltblown nonwoven webs can be bonded by a variety of means, including, but not limited to, autogenous bonding (i.e., self-bonding without further processing), thermal calendering processes, adhesive bonding processes, hot air bonding processes, needlepunching processes, hydroentangling processes, and combinations thereof.

[0017] As used herein, the term "spunbond" refers to the production of nonwoven fabrics that includes the steps of: (a) extruding molten thermoplastic strands through a plurality of minute capillaries called spinnerets; (b) quenching the strands of thermoplastic resin, including, for example, a polyethylene composition, to hasten the solidification of the molten strands of thermoplastic; (c) attenuating the filaments by advancing them through a quench zone under a drawing tension, which can be applied by entraining the filaments with an air stream or by winding them around mechanical drawing rolls of the type commonly used in the textile industry; (d) collecting the drawn strands into a web on a foraminous surface (e.g., a moving screen or perforated 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, thermal calendering, adhesive bonding, hot air bonding, needlepunching, hydroentangling, and combinations thereof.

[0018] As used herein, the term "curvature" refers to the curve or crimp of an individual fiber that is the result of its composition and not the result of any post-extrusion processes that may affect the curve or crimp of the fiber (e.g., mechanical crimping or damping due to heat). The amount of curvature of the bicomponent fibers disclosed herein can be measured by the test method described below.

[0019] fiber The fibers taught herein can be formed by any conventional spinning technique. For example, the first and second regions of a bicomponent fiber can be formed into a fiber via melt spinning. In melt spinning, a first region comprising a first polyethylene composition and a second region comprising a second polyethylene composition can be melted, coextruded, and forced into air or other gas through fine orifices in a metal plate called a spinneret, where they cool and solidify to form a bicomponent fiber. The solidified fibers can be drawn through an air jet, rotating roll, or godet and laid on a conveyor belt as a web to form a nonwoven fabric. Meltblown nonwoven fabrics can be formed comprising bicomponent fibers according to embodiments of the present disclosure. In other embodiments, spunbond nonwoven fabrics can be formed comprising bicomponent fibers according to embodiments of the present disclosure.

[0020] The fibers disclosed herein have improved curvature and other advantageous properties, such as recyclability, tactile softness, and extensibility, as a result of being composed of polyethylene. The improved curvature of the fibers disclosed herein is not the result of mechanical crimping or post-extrusion processes, such as hot air damping or application of tension. The fibers of embodiments comprise all or a majority of a polyethylene composition. Nonwovens comprising a polyethylene composition are known for their tactile softness, and materials comprising a polyethylene composition are candidates for compatibility with polyethylene recycle streams.

[0021] In an embodiment, the bicomponent fiber has a thickness of at least 0.50 mm -1 The curvature of a bicomponent fiber can be measured by the test method described below. -1 All individual values ​​and subranges are disclosed and included herein. For example, in some embodiments, the bicomponent fiber has a fiber tensile strength of at least 0.50, 0.60, 0.70, or 0.80 mm, as measured by the test methods described below. -1In other embodiments, the bicomponent fiber can have a curvature of 0.50 to 3.00, 0.50 to 2.50, 0.50 to 2.00, 0.50 to 1.50, 0.50 to 1.00, 1.00 to 3.00, 1.00 to 2.50, 1.00 to 2.00, 1.00 to 1.50, 1.50 to 3.00, 1.50 to 2.50, 1.50 to 2.00, 2.00 to 3.00, or 2.00 to 2.50 mm, as measured by the test methods described below. -1 The curvature can be in the range of

[0022] In embodiments, the bicomponent fiber includes a first region and a second region, and the weight ratio of the first region to the second region is from 90:10 to 10:90. All individual values ​​and subranges between the ratios of 90:10 to 10:90 are disclosed and included herein. For example, in embodiments, the weight ratio of the first region to the second region can be from 80:20 to 20:80, from 70:30 to 30:70, from 60:40 to 40:60, or from 55:45 to 45:55.

[0023] While the fibers taught herein are bicomponent fibers, those skilled in the art will understand that because the two regions of the fiber both contain polyethylene compositions, the fiber may not be readily distinguishable from the fiber itself as comprising two distinct regions. Those skilled in the art will understand that Raman microscopy and multivariate calibration, as described in the Test Methods section below, can be used to measure the percent crystallinity (%) of individual polyethylene regions of a bicomponent fiber. The difference in the Raman-measured % crystallinity of the two regions of a bicomponent fiber according to embodiments of the present disclosure corresponds to improved fiber curvature. In embodiments, a first polyethylene composition of a first region of a bicomponent fiber has a Raman-measured % crystallinity that is at least 5.0% higher than the Raman-measured % crystallinity of a second polyethylene composition of a second region of the bicomponent fiber, where the Raman-measured % crystallinity is measured by the test method described below. All individual values ​​and subranges of at least 5.0% higher are disclosed and included herein, for example, a first polyethylene composition of a first region of a bicomponent fiber may have a Raman-measured % crystallinity that is at least 5.0% higher, at least 7.5% higher, at least 10.0% higher, or from 5.0% to 20.0% higher, from 5.0% to 15.0% higher, from 7.5% to 15.0% higher, from 10.0% to 15.0% higher, from 3.5% to 12.0% higher, from 5.0% to 12.0% higher, from 7.5% to 12.0% higher, or from 10.0% to 12.0% higher than the Raman-measured % crystallinity of the second polyethylene composition of a second region of the bicomponent fiber, where the Raman-measured % crystallinity is measured according to the test methods described below.

[0024] center of gravity In an embodiment, the bicomponent fiber includes a fiber centroid and a first region having the first centroid and a second region having a second centroid, wherein at least one of the first centroid and the second centroid is not the same as the fiber centroid.

[0025] As used herein, the term "center of gravity" refers to the arithmetic mean of all points in the area of ​​the cross section of a bicomponent fiber. For example, a bicomponent fiber according to an embodiment of the present disclosure may have a C fand a region of the bicomponent fiber (e.g., the first or second region) has a fiber centroid that can be designated as C rx where x is the region designation (e.g., the first region is C r1 and the second region can be specified as C r2 ), where "r" is the C of the bicomponent fiber. f The average distance from the center of gravity of the fiber to the outer surface is calculated as √(A / π), where A is the area of ​​the bicomponent fiber cross section. Figure 1 shows a bicomponent fiber and its center of gravity, as well as the center of gravity of the second region of the bicomponent fiber. The distance from the region center of gravity to the fiber center of gravity is called "P rx " and the centroid offset of the first centroid or the second centroid can be defined as "P rx / r".

[0026] In some embodiments, at least one of the first and second centroids is not the same as the fiber centroid. If the first or second centroid is different from the fiber centroid, the bicomponent fiber can have a different configuration, such as an eccentric core-sheath, side-by-side, or compartmentalized pie configuration, but cannot have a concentric configuration in which the fiber centroid, the first centroid, and the second centroid are the same (e.g., a core-sheath concentric configuration). In some embodiments, the first centroid of the first region and the second centroid of the second region are arranged such that the first and second regions 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 and second regions are in a compartmentalized pie configuration. In a further embodiment, the first center of gravity of the first region and the second center of gravity of the second region are such that the first region and the second region are in an eccentric core-sheath configuration, the first region being the sheath of the bicomponent fiber, the second region being the core region of the bicomponent fiber, and the sheath region is arranged to surround the core region.

[0027] In embodiments, 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 less than 1 or less than 0.9, where the offset is measured by the test method described below.

[0028] First and Second Region - Metallocene or Single-Site Catalyst Embodiments In certain embodiments, the bicomponent fiber comprises a first region and a second region, the first region having a ratio of weight average molecular weight to number average molecular weight (M w(GPC) / M n(GPC) ) less than 3.0, and the second region comprises a second polyethylene composition having a density less than the density of the first polyethylene composition, the first polyethylene composition having a crystallization temperature (Tc) at least 2°C higher than the crystallization temperature (Tc) of the second polyethylene composition. In such embodiments, the first polyethylene composition may be formed in the presence of a metallocene or single-site catalyst.

[0029] Further, in such embodiments, the first polyethylene composition has a ratio of weight average molecular weight to number average molecular weight (M w(GPC) / M n(GPC) ) of less than 3.0. w(GPC) / M n(GPC) All individual values ​​and subranges of the molecular weight distribution (M) are disclosed and included herein; for example, in embodiments, the first polyethylene composition has a molecular weight distribution (M) of less than 3.0, less than 2.8, less than 2.6, less than 2.4, or less than 2.2, or in ranges of 1.8 to 3.0, 1.8 to 2.6, 1.8 to 2.4, 1.8 to 2.2, 2.0 to 3.0, 2.0 to 2.6, 2.0 to 2.4, 2.0 to 2.2, 2.2 to 2.6, or 2.2 to 2.4. w(GPC) / M n(GPC) ), and the molecular weight distribution is the ratio of the weight average molecular weight to the number average molecular weight (M w(GPC) / M n(GPC) ) and can be measured by the test methods described below.

[0030] Further, in such embodiments, the first polyethylene composition has a crystallization temperature (Tc) that is at least 2° C. higher than the crystallization temperature (Tc) of the second polyethylene composition. All individual values ​​and subranges of the crystallization temperature (Tc) of the first polyethylene composition that are at least 2° C. higher than the crystallization temperature (Tc) of the second polyethylene composition are disclosed and included herein. For example, the first polyethylene composition may have a crystallization temperature (Tc) that is at least 2°C higher, at least 4°C higher, at least 6°C higher, at least 8°C higher, at least 10°C higher, at least 12°C higher, at least 14°C higher, at least 16°C higher, or at least 18°C ​​higher than the crystallization temperature (Tc) of the second polyethylene composition; alternatively, the difference between the crystallization temperature (Tc) of the first polyethylene composition and the crystallization temperature (Tc) of the second polyethylene composition is 2°C to 30°C, 2°C to 25°C, 2°C to 20°C, 2°C to 15°C, 2°C to 10°C, 2°C to 5°C, 5°C to 30°C, 5°C to 25°C, or 5°C to 20°C. The crystallization temperature (Tc) can be in the range of 5°C to 15°C, 5°C to 10°C, 10°C to 30°C, 10°C to 25°C, 10°C to 20°C, 10°C to 15°C, 15°C to 30°C, 15°C to 25°C, or 15°C to 20°C, and the crystallization temperature (Tc) can be measured by differential scanning calorimetry (DSC) as described below.

[0031] Further, in such embodiments, the first polyethylene composition may have a melting temperature (Tm) that is at least 2° C. higher than the melting temperature (Tm) of the second polyethylene composition. All individual values ​​and subranges of the melting temperature (Tm) of the first polyethylene composition that are at least 2° C. higher than the melting temperature (Tm) of the second polyethylene composition are disclosed and included herein. For example, the first polyethylene composition may have a melting temperature (Tm) that is at least 2°C higher, at least 4°C higher, at least 6°C higher, at least 8°C higher, at least 10°C higher, at least 14°C higher, at least 18°C ​​higher, at least 22°C higher, at least 26°C higher, or at least 30°C higher than the melting temperature (Tm) of the second polyethylene composition; alternatively, the difference between the melting temperature (Tm) of the first polyethylene composition and the melting temperature (Tm) of the second polyethylene composition is 2°C to 50°C, 2°C to 45°C, 2°C to 40°C, 2°C to 35°C, 2°C to 30°C, 2°C to 25°C, 2°C to 20°C, 2°C to 15°C, 2°C to 10°C, 2°C to 5°C, 5°C to 50°C, 5°C to 45°C, 5°C to 40°C, 5°C to 35°C, 5°C to 30°C, 5°C to 25°C, or 5°C to 20°C. The melting temperature may be in the range of 5°C to 15°C, 5°C to 10°C, 10°C to 50°C, 10°C to 40°C, 10°C to 30°C, 10°C to 20°C, 20°C to 50°C, 20°C to 40°C, 20°C to 30°C, 25°C to 50°C, 25°C to 40°C, 25°C to 35°C, 30°C to 50°C, 30°C to 40°C, 30°C to 35°C, or 30°C to 32°C, and the melting temperature can be measured by DSC as described below.

[0032] Further, in such embodiments, the melting temperature (Tm) of the first polyethylene composition may be less than 130°C. All individual values ​​and subranges less than 130°C are disclosed and included herein, for example, the melting temperature (Tm) of the first polyethylene composition may be less than 130°C, less than 129.8°C, less than 129.6°C, less than 129.4°C, less than 129.2°C, less than 129°C, or less than 128.9°C, where the melting temperature (Tm) may be measured by DSC as described below. In an embodiment, the melting temperature (Tm) of the second polyethylene composition may be less than 127°C. All individual values ​​and subranges less than 127°C are disclosed and included herein, for example, the melting temperature (Tm) of the second polyethylene composition can be less than 127°C, less than 126.5°C, less than 125°C, less than 120°C, less than 115°C, less than 110°C, less than 105°C, less than 100°C, less than 99°C, 98.5°C, or less than 98°C, where the melting temperature (Tm) can be measured by DSC as described below.

[0033] In embodiments, the difference between the melting temperature (Tm) of the first polyethylene composition and the melting temperature (Tm) of the second polyethylene composition may be at least 1.5° C. All individual values ​​and subranges of at least 1.5° C. are included and disclosed herein, for example, the difference between the melting temperature (Tm) of the first polyethylene composition and the melting temperature (Tm) of the second polyethylene composition may be at least 1.5° C., at least 2.0° C., at least 2.5° C., at least 3° C., at least 5° C., at least 10° C., at least 15° C., at least 20° C., at least 25° C., or at least 30° C., or from 1.5° C. to 40° C., from 2.0° C. to 40° C., from 2.5° C. to 40° C., from 1.5° C. to 40° C., or from 1.5° C. to 40° C. The melting temperature (Tm) may be in the range of 30°C, 2.0°C to 30°C, 2.5°C to 30°C, 1.5°C to 20°C, 2.0°C to 20°C, 2.5°C to 20°C, 1.5°C to 10°C, 2.0°C to 10°C, 2.5°C to 10°C, 1.5°C to 5°C, 2.0°C to 5°C, 2.5°C to 5°C, 10°C to 40°C, 10°C to 35°C, 10°C to 30°C, 10°C to 20°C, 20°C to 40°C, 20°C to 35°C, 20°C to 30°C, 25°C to 40°C, 25°C to 35°C, 28°C to 32°C, or 29°C to 31°C, and the melting temperature (Tm) can be measured by DSC as described below.

[0034] First and Second Zones—Ziegler-Natta Catalyst Embodiments In other embodiments, the bicomponent fiber includes a first region and a second region, the first region having a ratio of weight average molecular weight to number average molecular weight (M w(GPC) / M n(GPC) The first polyethylene composition may have a molecular weight distribution, expressed as a ratio of weight average molecular weight to number average molecular weight (M), greater than 3.0, and the second region may comprise a second polyethylene composition having a density less than the density of the first polyethylene composition, the first polyethylene composition having a crystallization temperature (Tc) at least 3.5°C higher than the crystallization temperature (Tc) of the second polyethylene composition. In such embodiments, the first polyethylene composition may be formed in the presence of a Ziegler-Natta catalyst. In such embodiments, the first polyethylene composition may have a ratio of weight average molecular weight to number average molecular weight (M w(GPC) / M n(GPC)) greater than 3.0. w(GPC) / M n(GPC) All individual values ​​and subranges of the molecular weight distribution (M) are disclosed and included herein; for example, in embodiments, the first polyethylene composition has a molecular weight distribution (M) of greater than 3.0, greater than 3.02, greater than 3.04, greater than 3.06, greater than 3.08, greater than 3.10, greater than 3.12, or greater than 3.14, or in the ranges of 3.0 to 5.0, 3.0 to 4.5, 3.0 to 4.0, 3.0 to 3.5, 3.0 to 3.2, 3.1 to 5.0, 3.1 to 4.5, 3.1 to 4.0, 3.1 to 3.5, or 3.1 to 3.2. w(GPC) / M n(GPC) ), and the molecular weight distribution is the ratio of the weight average molecular weight to the number average molecular weight (M w(GPC) / M n(GPC) In such embodiments, the first polyethylene composition may be formed in the presence of a Ziegler-Natta catalyst.

[0035] Further, in such embodiments, the first polyethylene composition has a crystallization temperature (Tc) that is at least 3.5°C higher than the crystallization temperature (Tc) of the second polyethylene composition. All individual values ​​and subranges of the crystallization temperature (Tc) of the first polyethylene composition that are at least 3.5°C higher than the crystallization temperature (Tc) of the second polyethylene composition are disclosed and included herein. For example, the first polyethylene composition may have a crystallization temperature (Tc) that is at least 3.5°C higher, at least 4°C higher, at least 4.5°C higher, at least 5°C higher, at least 5.5°C higher, at least 6°C higher, at least 6.2°C higher, or at least 6.4°C higher than the crystallization temperature (Tc) of the second polyethylene composition; alternatively, the difference between the crystallization temperature (Tc) of the first polyethylene composition and the crystallization temperature (Tc) of the second polyethylene composition may be in the range of 3.5°C to 15°C, 3.5°C to 10°C, 3.5°C to 7.5°C, 3.5°C to 6°C, 5°C to 15°C, 5°C to 10°C, 5°C to 7.5°C, 5°C to 6°C, 6°C to 15°C, 6°C to 10°C, 6°C to 8°C, or 6°C to 7°C, where (Tc) can be measured by DSC as described below.

[0036] Further, in such embodiments, the first polyethylene composition may have a melting temperature (Tm) that is at least 5°C higher than the melting temperature (Tm) of the second polyethylene composition. All individual values ​​and subranges of the melting temperature (Tm) of the first polyethylene composition that are at least 5°C higher than the melting temperature (Tm) of the second polyethylene composition are disclosed and included herein. For example, the first polyethylene composition may have a melting temperature (Tm) that is at least 5°C higher, at least 5.2°C higher, at least 5.4°C higher, at least 5.6°C higher, at least 5.8°C higher, at least 6.0°C higher, at least 6.2°C higher, at least 6.4°C higher, at least 6.6°C higher, at least 6.8°C higher, or at least 6.9°C higher than the melting temperature (Tm) of the second polyethylene composition; The melting temperature (Tm) of the composition minus the melting temperature (Tm) of the second polyethylene composition may be in the range of 5°C to 10°C, 5°C to 7.5°C, 5°C to 7°C, 5°C to 6.5°C, 5°C to 6°C, 5.5°C to 10°C, 5.5°C to 7.5°C, 5.5°C to 7°C, 5.5°C to 6°C, 6°C to 10°C, 6°C to 7.5°C, 6°C to 7°C, 6.5°C to 10°C, 6.5°C to 7.5°C, or 6.5°C to 7°C, and the melting temperature (Tm) may be measured by DSC as described below.

[0037] First and second areas - general In embodiments described herein, the second polyethylene composition has a density less than the density of the first polyethylene composition, where the density can be measured by ASTM D792. In some embodiments, the density of the first polyethylene composition is at least 0.015 g / cm greater than the density of the second polyethylene composition. 3 High. At least 0.015g / cm 3 All individual values ​​and subranges of greater than or equal to 0.015 g / cm are included and disclosed herein, for example, in some embodiments, the density of the first polyethylene composition is at least 0.015 g / cm greater than the density of the second polyethylene composition. 3 , at least 0.030 g / cm 3 , or at least 0.040 g / cm3 or the difference between the density of the first polyethylene composition and the density of the second polyethylene composition is 0.015 g / cm 3 ~0.100g / cm 3 , 0.015g / cm 3 ~0.080g / cm 3 , 0.015g / cm 3 ~0.060g / cm 3 , 0.015g / cm 3 ~0.040g / cm 3 , 0.015g / cm 3 ~0.020g / cm 3 , 0.020g / cm 3 ~0.100g / cm 3 , 0.020g / cm 3 ~0.080g / cm 3 , 0.020g / cm 3 ~0.060g / cm 3 , 0.020g / cm 3 ~0.040g / cm 3 , 0.020g / cm 3 ~0.030g / cm 3 , 0.030g / cm 3 ~0.100g / cm 3 , 0.030g / cm 3 ~0.080g / cm 3 , 0.030g / cm 3 ~0.060g / cm 3 , 0.030g / cm 3 ~0.050g / cm 3 , 0.030g / cm 3 ~0.040g / cm 3 , or 0.040 g / cm 3 ~0.050g / cm 3 and the density can be measured by ASTM D792.

[0038] In embodiments described herein, the first polyethylene composition has a viscosity of at least 0.925 g / cm 3 and the density may be measured by ASTM D792. 3All individual values ​​and subranges of density in the range are disclosed and included herein. For example, in some embodiments, the first polyethylene composition has a density of at least 0.935, at least 0.940, at least 0.945, at least 0.950, at least 0.955, at least 0.960, or at least 0.965 g / cm. 3 and the density can be measured by ASTM D792, or the first polyethylene composition can have a density of 0.925 to 0.980, 0.930 to 0.980, 0.940 to 0.980, 0.950 to 0.980, 0.930 to 0.980, 0.930 to 0.970, 0.930 to 0.960, 0.930 to 0.950, 0.940 to 0.980, 0.950 to 0.980, 0.940~0.970, 0.940~0.960, 0.940~0.950, 0.945~0.980, 0.945~0.970, 0.945~0.960, 0.945~0.955, 0.950~0.980, 0.950~0.970, 0.950~0.960, 0.960~0.980, or 0.960~0.980g / cm 3 The density can be measured by ASTM D792.

[0039] In embodiments described above and herein, the first region of the bicomponent fiber comprises at least 75 wt% of the first polyethylene composition. All individual values ​​and subranges of at least 75 wt% are included and disclosed herein, for example, the first region can comprise at least 75 wt%, at least 80 wt%, at least 85 wt%, at least 90 wt%, at least 95 wt%, or 75 wt% to 100 wt%, 75 wt% to 90 wt%, 75 wt% to 80 wt%, 80 wt% to 100 wt%, or 90 wt% to 100 wt% of the first polyethylene composition, where the weight percentages are based on the total weight of the first region.

[0040] In embodiments described above and herein, the second region of the bicomponent fiber comprises at least 75 wt% of the second polyethylene composition. All individual values ​​and subranges of at least 75 wt% are included and disclosed herein, for example, the second region can comprise at least 75 wt%, at least 80 wt%, at least 85 wt%, at least 90 wt%, at least 95 wt%, or 75 wt% to 100 wt%, 75 wt% to 90 wt%, 75 wt% to 80 wt%, 80 wt% to 100 wt%, or 90 wt% to 100 wt% of the second polyethylene composition, where the weight percentages are based on the total weight of the second region.

[0041] In the embodiments described above and herein, the first region and / or second region can include additional components, such as one or more other polymers and / or one or more additives. The other polymers can include polyester, another polyethylene composition, a propylene-based polymer (e.g., a polypropylene homopolymer, a propylene-ethylene copolymer, or a propylene / alpha-olefin interpolymer), or a propylene-based plastomer or elastomer. The amount of the other polymer can be up to 25% by weight, based on the total weight of the first region or second region including such other polymer. For example, in one embodiment, the first region and / or second region can include up to 25% by weight of a propylene-based plastomer or propylene-based elastomer (such as VERSIFY™ polymers available from Dow Chemical Company and VISTAMAXX™ polymers available from ExxonMobil Chemical Co.), a low modulus and / or low molecular weight polypropylene (such as Idemitsu's L-MODU™ polymers), a random copolypropylene, or a propylene-based olefin block copolymer (Intune). Possible additives may include, but are not limited to, antistatic agents, color enhancers, dyes, lubricants, fillers, pigments, primary antioxidants, secondary antioxidants, processing aids, UV stabilizers, antiblocking agents, slip agents, tackifiers, flame retardants, antimicrobial agents, odor reducers, antifungal agents, and combinations thereof. The first and / or second regions may contain from about 0.01, 0.1, or 1 to about 25, 20, 15, or 10 weight percent total weight of such additives, based on the weight of the first or second region containing such additives.

[0042] polymerization Any conventional polymerization process can be used to produce the first or second polyethylene composition. Such conventional polymerization processes include, but are not limited to, solution polymerization processes using one or more conventional reactors, such as loop reactors, isothermal reactors, stirred tank reactors, parallel or series batch reactors, and / or any combination thereof. Such conventional polymerization processes also include gas phase, solution, or slurry polymerization, or any combination thereof, using any type of reactor or reactor configuration known in the art.

[0043] In an embodiment, the solution phase polymerization process occurs in one or more well-stirred reactors, such as one or more loop reactors, at a temperature ranging from 115 to 250°C, e.g., 155 to 225°C, and a pressure ranging from 300 to 1000 psi, e.g., 400 to 750 psi. In one dual reactor embodiment, the temperature in the first reactor is 115 to 190°C, e.g., 115 to 150°C, and the temperature in the second reactor is 150 to 200°C, e.g., 170 to 195°C. In another single reactor embodiment, the temperature in the reactor is 115 to 250°C, e.g., 155 to 225°C. The residence time in a solution phase polymerization process is typically in the range of 2 to 30 minutes, e.g., 10 to 20 minutes. Ethylene, solvent, one or more catalyst systems, optionally one or more cocatalysts, optionally one or more impurity removers, and optionally one or more comonomers are continuously fed into one or more reactors. Exemplary solvents include, but are not limited to, isoparaffin. For example, such a solvent is commercially available from ExxonMobil Chemical Co. (Houston, Texas) under the name ISOPAR E. The resulting mixture of the first or second polyethylene composition and solvent is then removed from the reactor, and the first or second polyethylene composition is isolated. The solvent is typically recovered via a solvent recovery unit, i.e., a heat exchanger and a gas-liquid separator drum, and then recycled to the polymerization system.

[0044] In one embodiment, the first or second polyethylene composition may be produced via solution polymerization in a dual reactor system, e.g., a dual loop reactor system, in which ethylene and, optionally, one or more a-olefins are polymerized in the presence of one or more catalyst systems. In another embodiment, the first or second polyethylene composition may be produced by a solution polymerization process in a single reactor system, e.g., a single loop reactor system, in which ethylene and, optionally, one or more a-olefins are polymerized in the presence of one or more catalyst systems. As noted above, in certain embodiments, the first polyethylene composition is formed in the presence of a metallocene or single-site catalyst system. In other embodiments, the first polyethylene composition is formed in the presence of a Ziegler-Natta catalyst system.

[0045] An example of a catalyst system suitable for producing the second polyethylene composition can be a catalyst system comprising a procatalyst component comprising a metal-ligand complex of formula (I). [ka]

[0046] In formula (I), M is a metal selected from titanium, zirconium, or hafnium, the metal being in a +2, +3, or +4 formal oxidation state; n is 0, 1, or 2; when n is 1, X is a monodentate or bidentate ligand; when n is 2, each X is a monodentate ligand and is the same or different; the metal-ligand complex is overall charge neutral; and each Z is independently —O—, —S—, —N(R N )-, or -P(R P )-, and each R N and R P is (C1-C30)hydrocarbyl or (C1-C30)heterohydrocarbyl, and L is (C1-C 40 ) hydrocarbylene or (C1-C 40 ) heterohydrocarbylene, (C1-C 40) Hydrocarbylene has a moiety that includes a linker skeleton of 1 carbon atom to 10 carbon atoms that connects the two Z groups in formula (I) (to which L is attached), or (C1-C 40 ) Heterohydrocarbylene has a moiety containing a linker skeleton of 1 atom to 10 atoms connecting the two Z groups in formula (I), (C1-C 40 Each of the 1 to 10 atoms of the 1 to 10 atom linker backbone of the heterohydrocarbylene is independently a carbon atom or a heteroatom, and each heteroatom is independently O, S, S(O), S(O), Si(R C )2, Ge(R C )2, P(R C ), or N(R C ) and each R C are independently (C1-C 30 ) hydrocarbyl or (C-C 30 ) heterohydrocarbyl, and R 1 and R 8 are independently -H, (C1~C 40 ) hydrocarbyl, (C1-C 40 ) heterohydrocarbyl, -Si(R C )3, -Ge(R C )3, -P(R P )2, -N(R N )2, -OR C , -SR C , -NO2, -CN, -CF3, R C S(O)-, R C S(O)2-, (R C )2C=N-, R C C(O)O-, R C OC(O)-, R C C(O)N(R N )-, (R N )2NC(O)-, halogen, and a radical having formula (II), formula (III), or formula (IV). [ka]

[0047] In formulas (II), (III), and (IV), R31-35 , R 41-48 , or R 51-59 Each of (C1-C 40 ) hydrocarbyl, (C1-C 40 ) heterohydrocarbyl, -Si(R C )3, -Ge(R C )3, -P(R P )2, -N(R N )2, -N=CHR C , -OR C , -SR C , -NO2, -CN, -CF3, R C S(O)-, R C S(O)2-, (R C )2C=N-, R C C(O)O-, R C OC(O)-, R C C(O)N(R N )-, (R N )2NC(O)—, halogen, or —H, with the proviso that R 1 or R 8 is a radical having formula (II), formula (III), or formula (IV), wherein R C、 R N , and R P is as defined above.

[0048] In formula (I), R 2-4 , R 5-7 , or R 9-16 Each of (C1-C 40 ) hydrocarbyl, (C1-C 40 ) heterohydrocarbyl, -Si(R C )3, -Ge(R C )3, -P(R P )2, -N(R N )2, -N=CHR C , -OR C , -SR C , -NO2, -CN, -CF3, R C S(O)-, R C S(O)2-, (R C )2C=N-, R C C(O)O-, R C OC(O)-, RC C(O)N(R N )-, (R C )2NC(O)—, halogen, or —H, wherein R C、 R N , and R P is as defined above.

[0049] Catalyst systems containing the metal-ligand complexes of formula (I) can be catalytically activated by any technique known in the art for activating metal-based catalysts for olefin polymerization reactions. For example, metal-ligand complexes of formula (I) can be made catalytically active by contacting or combining the complex with an activating cocatalyst. Activating cocatalysts suitable for use herein include alkylaluminums, polymeric or oligomeric alumoxanes (also known as aluminoxanes), neutral Lewis acids, and non-polymeric, non-coordinating, ion-forming compounds (including the use of such compounds under oxidizing conditions). A suitable activation technique is bulk electrolysis. Combinations of one or more of the foregoing activating cocatalysts and techniques are also contemplated. The term "alkylaluminum" refers to monoalkylaluminum dihydrides or dihalides, dialkylaluminum hydrides or halides, or trialkylaluminums. Examples of polymeric or oligomeric alumoxanes include methylalumoxane, triisobutylaluminum modified methylalumoxane, and isobutylalumoxane.

[0050] The Lewis acid activator (cocatalyst) may be, as described herein, a compound having one to three (C1-C 20 Examples of Group 13 metal compounds include tri((C-C) hydrocarbyl substituents. 20 )hydrocarbyl)-substituted aluminum, or tri((C-C 20 )hydrocarbyl)-boron compounds, tri(hydrocarbyl)-substituted aluminum, tri((C-C 20 )hydrocarbyl)-boron compounds, tri((C-C 10) alkyl) aluminum, tri((C6-C 18 )aryl)boron compounds and their halogenated (including perhalogenated) derivatives. In a further embodiment, the Group 13 metal compound is tris(fluoro-substituted phenyl)borane, tris(pentafluorophenyl)borane. The activating cocatalyst is tris((C-C 20 )hydrocarbyl)borate (e.g., trityl tetrafluoroborate) or tri((C-C 20 )hydrocarbyl)ammonium tetra((C1-C 20 As used herein, the term "ammonium" refers to a ((C1-C2) ammonium tetrakis(pentafluorophenyl)borane, such as bis(octadecyl)methylammonium tetrakis(pentafluorophenyl)borane. 20 ) Hydrocarbyl) 4N + , ((C1~C 20 )hydrocarbyl)3N(H) + , ((C1~C 20 )hydrocarbyl)2N(H)2 + , (C1~C 20 ) Hydrocarbyl N(H)3 + , or N(H)4 + Each of the nitrogen cations (C1 to C 20 When two or more hydrocarbyls are present, they may be the same or different.

[0051] As a combination of neutral Lewis acid activators (cocatalysts), tri((C1-C4) alkyl)aluminum and tri((C6-C 18(aryl)boron compounds, particularly tris(pentafluorophenyl)borane, or a mixture of such neutral Lewis acids with a polymeric or oligomeric alumoxane, or a single neutral Lewis acid, particularly tris(pentafluorophenyl)borane, with a polymeric or oligomeric alumoxane. The molar ratio of (metal-ligand complex):(tris(pentafluorophenyl)borane):(alumoxane) [e.g., Group 4 metal-ligand complex):(tris(pentafluorophenyl)borane):(alumoxane)] is 1:1:1 to 1:10:30, or 1:1:1.5 to 1:5:10.

[0052] Catalyst systems comprising the metal-ligand complexes of formula (I) may be activated to form active catalyst compositions by combination with one or more cocatalysts, such as cation-forming cocatalysts, strong Lewis acids, or combinations thereof. Suitable activating cocatalysts include polymeric or oligomeric aluminoxanes, particularly methylaluminoxane, as well as inert, compatible, non-coordinating, ion-forming compounds. Examples of suitable cocatalysts include modified methyl aluminoxane (MMAO), bis(hydrogenated tallow alkyl)methyl, tetrakis(pentafluorophenyl)borate (1 - ) amines, and combinations thereof.

[0053] One or more of the aforementioned activating cocatalysts may be used in combination with one another. One preferred combination is a mixture of tri((C1-C4)hydrocarbyl)aluminum, tri((C1-C4)hydrocarbyl)borane, or ammonium borate with an oligomeric or polymeric alumoxane compound. The ratio of the total number of moles of the one or more metal-ligand complexes of formula (I) to the total number of moles of the one or more activating cocatalysts is 1:10,000 to 100:1. This ratio may be at least 1:5000, or at least 1:1000, and may be 10:1 or less, or 1:1 or less. When alumoxane is used alone as the activating cocatalyst, preferably the number of moles of alumoxane used is at least 100 times the number of moles of the metal-ligand complex of formula (I). When tris(pentafluorophenyl)borane is used alone as the activating cocatalyst, the ratio of the number of moles of tris(pentafluorophenyl)borane used to the total number of moles of the one or more metal-ligand complexes of Formula (I) can be from 0.5:1 to 10:1, from 1:1 to 6:1, or from 1:1 to 5:1. The remaining activating cocatalyst is generally used in a molar amount approximately equal to the total molar amount of the one or more metal-ligand complexes of Formula (I).

[0054] Test Method density Density is measured by ASTM D792 and is in grams / cm 3 (g / cm 3 )

[0055] Melt Index (I2) Melt index (I2) is measured according to ASTM D1238 at 190° C. and 2.16 kg and is expressed in grams dissolved / 10 minutes (g / 10 minutes).

[0056] 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, which is equal to the radius of the circle formed by projecting the helix formed by the fiber onto a surface perpendicular to it. The average of at least five measurements is reported. Measurements are reported in 1 / millimeter (mm-1 ) units.

[0057] Center of Gravity Offset Fibers were embedded in epoxy and cryogenically polished for AFM analysis using a Leica UCT / FCS microtome operated at -140 °C. Topography and phase images were captured at ambient temperature using a Bruker Icon AFM system equipped with a MikroMasch probe. The probe has a spring constant of 40 N / m and a resonant frequency of approximately 170 kHz. An imaging frequency of 0.5-2 Hz was used with a setpoint ratio of approximately 0.8. The cross-sectional diameter of the fiber was measured using a single cord, and this measurement was divided in half to mark the midpoint as the fiber centroid (Cf). The core region of the bicomponent fiber was divided by two cords at 90° to visually create four quadrants of equal area, and the intersection of the two cords defines the centroid of the core region (Cr2). The distance between the fiber centroid (Cf) and the centroid of the core region (Cr2) is measured and then divided by the radius of the fiber to calculate the fiber centroid offset (Pr2 / r).

[0058] Conventional GPC (Mw / Mn) Conventional GPC analysis was performed using a high-temperature gel permeation chromatography (GPC) instrument (PolymerChar, Spain). The IR5 detector ("measurement channel") was used as a concentration detector. The weight-average (MW) and number-average (Mn) molecular weights of the polymers were calculated using GPCOne software (PolymerChar, Spain) to determine the molecular weight distribution (MW / Mn). The method uses three 10-micron PL gel mixed B columns (Agilent Technologies, column dimensions 100 x 7.6 mm) or four 20-micron PL gel mixed A columns (Agilent Technologies, column dimensions 100 x 7.6 mm), operated at a system temperature of 150 °C. Samples were prepared at a concentration of 2 mg / mL in 1,2,4-trichlorobenzene solvent containing 200 parts per million of the antioxidant butylated hydroxytoluene (BHT) at 160 °C for 3 hours with gentle shaking using an autosampler (PolymerChar, Spain). The flow rate is 1.0 mL / min and the injection size is 200 microliters. The GPCOne software is used to calculate the number of plates. The chromatography system requires a minimum of 22,000 plates.

[0059] The GPC column set is calibrated by running at least 20 narrow molecular weight distribution polystyrene standards. Calibration uses a third-order fit on a system with three 10-micron PL gel mixed B columns or a fifth-order fit on a system with four 20-micron PL gel mixed A columns. The molecular weights (MW) of the standards range from 580 g / mol to 8,400,000 g / mol. The standards are contained in six "cocktail" mixtures. Each standard mixture has approximately one order of magnitude of separation between the 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 ≥ 1,000,000 g / mol and 0.05 g in 50 mL of solvent for molecular weights < 1,000,000 g / mol. The polystyrene standards are dissolved at 80°C with gentle agitation for 30 minutes. Narrow standards mixtures are run first and in order of decreasing highest molecular weight component to minimize degradation. 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)).

number

number

number

number

[0060] Chromatographic peaks should be set to contain areas that show significant visible deviations from the baseline when the chromatogram is displayed at 20% peak height. The baseline should not be integrated to less than 100 polyethylene-equivalent molecular weights, and care should be taken to account for discrepancies in antioxidants from prepared samples and chromatographic mobile phases.

[0061] The use of a decane flow rate marker is shown in the IR5 chromatogram. The difference in the baseline (response) Y value between the start and end of the baseline should not exceed 3% of the integrated peak height of the chromatogram. In such cases, chromatographic samples should be processed by properly matching the antioxidants in the sample and mobile phase.

[0062] w(10 5 The weight fraction (w g / mol) of the hydroxyl group is calculated from the MWD curve (w i versus log M cc,i ) is calculated by

number

[0063] Differential scanning calorimetry (DSC) DSC is used to measure the melting temperature (Tm) and crystallization temperature (Tc) behavior of polymers over a wide temperature range. For example, a TA Instruments Q1000 DSC equipped with a refrigerated cooling system (RCS) and autosampler is used to perform this analysis. A nitrogen purge gas flow rate of 50 ml / min is used during testing. Each sample is melt-pressed into a thin film at approximately 175°C, and then the molten sample is air-cooled to room temperature (approximately 25°C). Film samples are formed by pressing 0.1-0.2 gram samples at 175°C, 1,500 psi, and 30 seconds to form a 0.1-0.2 mil thick film. A 3-10 mg, 6 mm diameter specimen is extracted from the cooled polymer, weighed, placed in a light (approximately 50 mg) aluminum pan, and crimped shut. Analysis is then performed to determine its thermal properties.

[0064] The thermal behavior of a sample is determined by raising and lowering the sample temperature to generate a heat flow versus temperature profile. First, the sample is rapidly heated to 180°C and held isothermal for 5 minutes to remove thermal history. Next, the sample is cooled to -40°C at a cooling rate of 10°C / min and held isothermal at -40°C for 5 minutes. The sample is then heated to 150°C at a heating rate of 10°C / min (this is the "second heat" ramp). A cooling curve and a second heating curve are recorded. The cooling curve is analyzed by setting a baseline endpoint from the onset of crystallization to -20°C. The heating curve is analyzed by setting a baseline endpoint from -20°C to the end of melting. Values ​​determined include the maximum peak melting temperature (referred to herein as "melting temperature (Tm)"), the maximum peak crystallization temperature (referred to herein as "crystallization temperature (Tc)"), and the heat of fusion (H f ) (Joules / gram), and crystallinity % = ((H f The heat of fusion (H) is the calculated % crystallinity for a polyethylene sample using (292 J / g) / (292 J / g) × 100. fThe melting temperature (Tm) is reported from the second heat curve. The crystallization temperature (Tc) is determined from the cooling curve.

[0065] Raman microscopy Raman microscopy and multivariate calibration are used to measure the percent crystallinity of individual polyethylene regions of bicomponent fibers in situ. Raman microscopy, a type of vibrational spectroscopy technique, is sensitive to polymer backbone vibrations and can provide information about both the amorphous and crystalline phases of the polymer and polyethylene composition. Raman can use visible or near-infrared radiation and, when coupled with an optical microscope, provides a lateral spatial resolution of approximately 0.8 to 1.2 micrometers (depending on the excitation laser and microscope objective used).

[0066] A Partial Least Squares (PLS) model was constructed to correlate the Raman data with the annealed base resin density and percent crystallinity (%) calculated from the annealed polyethylene composition density. Annealed density is measured according to ASTM D792. Percent crystallinity (%) is calculated from the measured annealed density using the following equation (Equation 6):

number

[0067] Polarized Raman spectra are acquired using an equivalent Thermo Scientific DXR2 micro-Raman instrument. Raman spectra are acquired using a 900 groove / mm grating. The spectral range is 0.964 cm with a data spacing of 0.964 cm. -1 So, 50~3500cm -1The Raman shifts were covered. Other data acquisition parameters were as follows: acquisition time: 3-10 seconds, number of acquisitions: 3-6, dark current subtraction, cosmic ray filter, and white light correction: on. Calibration data were recorded using an Olympus M PlanN 20x (0.40 NA) objective with a 25-micrometer slit and an Olympus M PlanN 100x (0.90 NA) objective with a 50-micrometer pinhole.

[0068] 0.859~0.964g / cm 3 Twenty-eight polyethylene composition resins ranging in density are used to calibrate and cross-validate the PLS model. The PLS model is validated using an independent set of density plaques, which are then used to measure resin crystallinity for resins used in the bicomponent fiber region. The PLS model is based on the following parameters: Spectral region: 1571 cm 1 ~971cm -1 , Normalization: integral area 1356~1227cm -1 -Same reference point, total number of samples: 28, number of calibration standards: 26, number of independent cross-validation samples: 2, number of independent validation samples: 6, data preprocessing: annealed base resin density model and calculated value % crystallinity model % - mean centering, two 次 Derivatives, SG smoothing (15 points, three 次 Polynomial), the number of factors used to calibrate both models: annealed base resin density and calculations were constructed in TQ Analyst™ software using: % Crystallinity = 4.

[0069] After validation of the PLS model, longitudinal (parallel to the draw direction) cross sections of each bicomponent fiber example are prepared. The cross sections are oriented on the sample stage so that the fiber draw direction is oriented in the east-west direction on the sample stage. Polarized Raman spectra are acquired at three different locations in each region of the bicomponent fiber example using a 100x (0.9 NA) objective lens and a 25 micrometer pinhole. The resulting Raman spectra from each region are averaged, and the average spectra are used to measure the % regional crystallinity using the PLS model. [Example]

[0070] Synthesis of polyethylene compositions The generated resins ("Resin 1," "Resin 2," "Resin 3," and "Resin 4") are prepared according to the following process and table.

[0071] All raw materials (monomers and comonomers) and process solvents (high-purity narrow-boiling range isoparaffinic solvent, Isopar-E) are purified with molecular sieves before being introduced into the reaction environment. Hydrogen is supplied under pressure as a high-purity grade and is not further purified. The reactor monomer feed stream is pressurized to a pressure above the reaction pressure by a mechanical compressor. Solvent and comonomer (if present) feeds are pressurized above the reaction pressure via pumps. Individual catalyst components are manually batch diluted with purified solvent and pressurized above the reaction pressure. All reaction feed streams are metered using mass flow meters and independently controlled by computer-automated valve control systems.

[0072] The reactor configuration is either a single reactor operation or a dual reactor in series operation as specified in Table 2.

[0073] Either a single reactor system or a two-reactor system in a series configuration is used. Each reactor is a continuous solution polymerization reactor consisting of a liquid-filled, non-adiabatic, isothermal circulating loop reactor, replicating a heat-removing continuous stirred tank reactor (CSTR). Independent control of all fresh solvent, monomer, comonomer (if present), hydrogen, and catalyst component feeds is possible. The total fresh feed stream to each reactor (solvent, monomer, comonomer (if present), and hydrogen) is temperature-controlled, typically between 15 and 50°C, 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 volume between each injection location. The fresh feed is controlled so that each injector receives half of the total fresh feed mass flow rate. Catalyst components are injected into the polymerization reactor through injection nozzles, introducing the components into the center of the reactor flow. The primary catalyst component feed is computer-controlled to maintain reactor monomer conversion at a specific value. The cocatalyst component(s) are fed to the main catalyst component based on a calculated specific molar ratio. Immediately after the injection point of each reactor feed, the feed stream is mixed with the contents of a circulating polymerization reactor with static mixing elements. The contents of each reactor are continuously circulated through a heat exchanger that serves to remove the majority of the heat of reaction, with the coolant side temperature serving to maintain an isothermal reaction environment at a specific temperature. Circulation around each reactor loop is provided by a pump.

[0074] In a dual reactor in series configuration, the effluent from the first polymerization reactor (containing solvent, monomer, comonomer [if present], hydrogen, catalyst components, and polymer) exits the first reactor loop and is added to the second reactor loop.

[0075] In all reactor configurations, the final reactor effluent (the second reactor effluent in the case of a dual reactor in series, or the single reactor effluent) enters a zone where it is deactivated by adding and reacting with a suitable reagent (water). At this same reactor exit location, other additives are added for polymer stabilization.

[0076] Following catalyst deactivation and additive addition, the reactor effluent enters a devolatilization system where polymer is removed from the non-polymer stream. The isolated polymer melt is pelletized and collected. The non-polymer stream passes through various equipment that separates most of the ethylene removed from the system. Most of the solvent and unreacted comonomer (if present) are recycled to the reactor after passing through a purification system. Small amounts of solvent and comonomer (if present) are purged from the process.

[0077] The reactor stream feed data flows used to produce the outgassed resin, corresponding to the values ​​in Table 2, are illustrated graphically in Figures 2 and 3. The data are presented in a way that takes into account the complexity of the solvent recycle system and allows the reaction system to be more easily treated as a once-through flow diagram. [Table 1] [Table 2]

[0078] The following materials are used in the examples:

[0079] Polymer 1 (Poly. 1) is Resin 1 described above.

[0080] Polymer 2 (Poly. 2) is ASPUN™ 6835, a polyethylene composition and linear low density polyethylene fiber resin commercially available from The Dow Chemical Company (Midland, MI).

[0081] Polymer 3 (Poly.3) is Resin 2 described above.

[0082] Polymer 4 (Poly.4) is Resin 3 described above.

[0083] Polymer 5 (Poly.5) is Resin 4 described above.

[0084] Polymer 6 (Poly. 6) is ELITE™ 5860, a polyethylene composition and reinforced polyethylene resin commercially available from The Dow Chemical Company (Midland, MI).

[0085] Poly.1 through Poly.6 have the densities, melt indexes (I2), molecular weight distributions (Mw / Mn), crystallization temperatures (Tc), and melting temperatures (Tm) as reported in Table 3 below.

[0086] [Table 3]

[0087] Fiber formation

[0088] Fibers are spun on a Hills Bicomponent Continuous Filament Fiber Spinning Line. Bicomponent fibers with an eccentric core-sheath configuration are produced. Fibers are spun on the Hills line according to the following conditions: The extruder profile is adjusted to achieve a melt temperature of 240°C. The throughput rate of each hole is 0.5 ghm (grams per minute per hour). A Hills Bicomponent die is used, operating at a core / sheath ratio of 40 / 60 (by weight), with a first zone containing examples in one extruder and a second zone containing other examples in the other extruder, according to Table 4 below, to form Inventive Examples 1, 2, 3, and 4, and Comparative Examples 1, 2, 3, 4, 5, and 6. The Hills Line pressure is set at 40 psi. The die consists of 144 holes with a hole diameter of 0.6 mm and a length / diameter (L / D) ratio of 4 / 1. The quench air temperature and flow rate are set at 15-18°C and 520 cfm (cubic feet per minute), respectively. After the quench zone, the airflow applies drawing tension to the 144 filaments by pneumatically drawing the filaments into the slot unit. The airflow velocity is controlled by the pressure of the slot aspirator.

[0089] [Table 4]

[0090] Table 5 provides the melting temperature difference (ΔTm), crystallization temperature difference (ΔTc), and density difference (ΔDensity) for the first region minus the second region for Inventive Examples 1 and 2 and Comparative Examples 1 and 2, which have polyethylene compositions in the first region having a molecular weight distribution (Mw / Mn) of less than 3.

[0091] [Table 5]

[0092] Table 6 provides the melting temperature difference (ΔTm), crystallization temperature difference (ΔTc), and density difference (ΔDensity) for the first region minus the second region for Inventive Examples 3 and 4 and Comparative Examples 3, 4, and 5, which have polyethylene compositions in the first region having a molecular weight distribution (Mw / Mn) greater than 3.

[0093] [Table 6]

[0094] Certain inventive and comparative examples are tested for % crystallinity by the Raman microscopy test method described above. Table 7 shows the results.

[0095] [Table 7]

[0096] Table 8 shows the amount of curvature associated with the examples. Examples 1-4 of the present invention have significantly higher curvature than the comparative example, which has no curvature.

[0097] [Table 8]

[0098] Table 9 provides the centroid offset and radius of fiber data for specific examples.

[0099] [Table 9] The present invention can provide the following aspects. [1] A bicomponent fiber, The fiber center of gravity and a first region having a first center of gravity and a second region having a second center of gravity; The first region has a ratio of weight average molecular weight to number average molecular weight (M w(GPC) / M n(GPC) a first polyethylene composition having a molecular weight distribution, expressed as the second region comprises a second polyethylene composition having a density less than a density of the first polyethylene composition; At least one of the first centroid and the second centroid is not the same as the fiber centroid; A bicomponent fiber, wherein the first polyethylene composition has a crystallization temperature (Tc) that is at least 2°C higher than the crystallization temperature (Tc) of the second polyethylene composition. [2] The bicomponent fiber according to [1] above, wherein the first polyethylene composition has a melting temperature (Tm) that is at least 2°C higher than the melting temperature (Tm) of the second polyethylene composition. [3] The bicomponent fiber according to [1] or [2] above, wherein the melting temperature (Tm) of the first polyethylene composition is less than 130°C. [4] A bicomponent fiber, The fiber center of gravity and a first region having a first center of gravity and a second region having a second center of gravity; The first region has a ratio of weight average molecular weight to number average molecular weight (M w(GPC) / M n(GPC) a first polyethylene composition having a molecular weight distribution greater than 3.0, expressed as the second region comprises a second polyethylene composition having a density less than a density of the first polyethylene composition; At least one of the first centroid and the second centroid is not the same as the fiber centroid; A bicomponent fiber, wherein the first polyethylene composition has a crystallization temperature (Tc) that is at least 3.5°C higher than the crystallization temperature (Tc) of the second polyethylene composition. [5] [4] The bicomponent fiber according to the above [4], wherein the first polyethylene composition has a melting temperature (Tm) that is at least 5°C higher than the melting temperature (Tm) of the second polyethylene composition. [6] the density of the first polyethylene composition is at least 0.015 g / cm greater than the density of the second polyethylene composition. 3 The bicomponent fiber according to any one of [1] to [5] above, having high elasticity. [7] The fibers are 0.5 mm -1 The bicomponent fiber according to any one of the above [1] to [6], having a curvature of greater than 1000. [8] The bicomponent fiber according to any one of the above [1] to [7], wherein the first polyethylene composition has a % crystallinity measured by Raman that is at least 5.00% higher than the % crystallinity measured by Raman of the second polyethylene composition. [9] A spunbond nonwoven fabric comprising the bicomponent fiber according to any one of the above [1] to [8].

Claims

1. A bicomponent fiber, The fiber center of gravity and a first region defining a core of the bicomponent fiber and having a first center of gravity, and a second region defining a sheath of the bicomponent fiber and having a second center of gravity; The first region has a ratio of weight average molecular weight to number average molecular weight (M ｗ（ＧＰＣ） / M ｎ（ＧＰＣ） a first polyethylene composition having a molecular weight distribution, expressed as the second region comprises a second polyethylene composition having a density less than a density of the first polyethylene composition; at least one of the first centroid and the second centroid is not the same as the fiber centroid; A bicomponent fiber, wherein the first polyethylene composition has a crystallization temperature (Tc) that is at least 2°C higher than the crystallization temperature (Tc) of the second polyethylene composition.

2. 10. The bicomponent fiber of claim 1, wherein the first polyethylene composition has a melting temperature (Tm) that is at least 2°C higher than the melting temperature (Tm) of the second polyethylene composition.

3. 3. The bicomponent fiber of claim 2, wherein the melting temperature (Tm) of the first polyethylene composition is less than 130°C.

4. A bicomponent fiber, The fiber center of gravity and a first region defining a core of the bicomponent fiber and having a first center of gravity, and a second region defining a sheath of the bicomponent fiber and having a second center of gravity; The first region has a ratio of weight average molecular weight to number average molecular weight (M ｗ（ＧＰＣ） / M ｎ（ＧＰＣ） a first polyethylene composition having a molecular weight distribution, expressed as the second region comprises a second polyethylene composition having a density less than a density of the first polyethylene composition; at least one of the first centroid and the second centroid is not the same as the fiber centroid; A bicomponent fiber, wherein the first polyethylene composition has a crystallization temperature (Tc) that is at least 3.5°C higher than the crystallization temperature (Tc) of the second polyethylene composition.

5. 5. The bicomponent fiber of claim 4, wherein the first polyethylene composition has a melting temperature (Tm) that is at least 5°C higher than the melting temperature (Tm) of the second polyethylene composition.

6. the density of the first polyethylene composition is at least 0.015 g / cm greater than the density of the second polyethylene composition. ３ The bicomponent fiber according to any one of claims 1 to 5, wherein the fiber has a high viscosity.

7. The fibers are 0.5 mm －１ The bicomponent fiber of any one of claims 1 to 6, having a curvature of greater than 1 / 2.

8. 8. The bicomponent fiber of any one of claims 1 to 7, wherein the first polyethylene composition has a percent crystallinity, as measured by Raman, that is at least 5.00% higher than the percent crystallinity, as measured by Raman, of the second polyethylene composition.

9. A bicomponent fiber described in any one of claims 1 to 8, wherein the weight ratio of the first region to the second region is 70:30 to 30:

70.

10. A spunbond nonwoven fabric comprising the bicomponent fiber of any one of claims 1 to 9.

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