Patent Application
20150247262
Shape memory is the ability of a material to recover its original shape after temporary deformation upon application of an external stimulus. Materials exhibiting shape memory also are referred to as self-repairing, stimuli-responsive, smart, and intelligent (Lendlein and Kelch, 2002). Various external stimuli, including, but not limited to, heat, solvation, light, and other electromagnetic fields, can induce a change in material shape.
Polymeric materials capable of shape memory possess significant advantages over inorganic shape-memory alloys (SMAs). Shape-memory polymers (SMPs) can be manufactured at a lower cost and under scalable temperature and pressure conditions, while remaining applicable to a wide range of end uses (Behl and Lendlein, 2007). The fabrication of shape-memory devices from polymeric materials known in the art, however, often involves multistep processing mechanisms that could limit the applicability and the scalability of the technology.
In some aspects, the presently disclosed subject matter provides a multicomponent fiber or film comprising at least one component capable of forming a physically-crosslinked network and at least a second component capable of transitioning in response to a thermal stimulus, wherein the two components have strong interfacial adhesion; and wherein a temperature associated with the second component capable of transitioning in response to a thermal stimulus is lower than a temperature required to disrupt the molecular network of the component capable of forming a physically-crosslinked network.
In particular aspects, the fiber or film comprises at least two co-spun or co-extruded components configured in a core component-sheath component cross-sectional geometry, wherein one core component comprises a thermoplastic elastomer capable of forming a physically-crosslinked network and the sheath component comprises a polyolefin capable of transitioning in response to a thermal stimulus, and wherein the fiber or film can be deformed from an original shape, retain a temporary shape, and subsequently return to its original shape in response to a thermal stimulus.
In certain aspects, the core component comprises a styrenic block copolymer, for example, poly(styrene-b-butadiene-b-styrene) (SBS), poly(styrene-b-isoprene-b-styrene) (SIS), poly[styrene-b-(ethylene-co-propylene)-b-styrene] (SEPS), or poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS). In certain aspects, the sheath component comprises a linear low density polyethylene (LLDPE). In particular aspects, the core component comprises SEBS and the sheath component comprises LLDPE. In yet more particular aspects, the sheath component has a melting point lower than the upper glass transition temperature of the network-forming core component.
In some aspects, the presently disclosed fibers can be used as a thermal actuator in a deployable device. In other aspects, the presently disclosed subject matter provides an article comprising one or more of the presently disclosed shape-memory multicomponent fibers. Such articles can be used in or can include diapers, waist bands, stretch panels, disposable garments, medical or personal hygiene articles, and filters; or, in yet other aspects, a hinge, a truss, an antenna, a solar panel, or an optical reflector; or in still yet other aspects, a form fitting material, self-sealing packaging, a smart textile, and an intelligent fiber; or in yet other aspects, a wound closure suture, a vascular stent, a bone-setting sleeve, or a drug delivery device.
Certain aspects of the presently disclosed subject matter having been stated hereinabove, which are addressed in whole or in part by the presently disclosed subject matter, other aspects will become evident as the description proceeds when taken in connection with the accompanying Examples and Figures as best described herein below.
Having thus described the presently disclosed subject matter in general terms, reference will now be made to the accompanying Figures, which are not necessarily drawn to scale, and wherein:
The presently disclosed subject matter now will be described more fully hereinafter with reference to the accompanying Figures, in which some, but not all embodiments of the presently disclosed subject matter are shown. Like numbers refer to like elements throughout. The presently disclosed subject matter may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Indeed, many modifications and other embodiments of the presently disclosed subject matter set forth herein will come to mind to one skilled in the art to which the presently disclosed subject matter pertains having the benefit of the teachings presented in the foregoing descriptions and the associated Figures. Therefore, it is to be understood that the presently disclosed subject matter is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims.
The presently disclosed subject matter provides multicomponent fibers or films capable of thermally induced shape recovery after two types of strain fixing under conditions of (1) ambient temperature programming or (2) conventional heated programming Without wishing to be bound to any one particular theory, such properties are imparted on the presently disclosed fibers or films by separating the two features responsible for shape memory in a polymeric material: (1) a network-forming species and (2) a species exhibiting a switching mechanism when heated. It has been found that the incorporated components (not necessarily two) possess strong interfacial adhesion with at least one other component, which allows them to function as a single mechanical structure.
When subjected to a mechanical load, the components undergo deformation in a different fashion. The network-forming component, e.g., a core component, which in some embodiments is a thermoplastic elastomer (TPE), maintains a physically crosslinked network and is capable of recovering to its undeformed state when the load is removed. The switching component, e.g., a sheath component, reorders due to plastic deformation and retains the deformed shape. The interface between the two components remains largely intact, which results in a temporary deformed shape of the fibers or film. When the deformed fibers or film are heated in such a way that the sheath component (capable of switching) melts and softens, the core component (e.g., TPE) pulls it back to the original shape as a result of its own elasticity and at least partially preserved interfacial integrity.
A schematic illustrating shape-memory behavior is provided in
Polymeric materials exhibiting shape recovery require a molecular or supramolecular network that consists of long chains that define the initial shape (Lendlein and Kelch, 2002). The networks are stabilized by “binding” or “net” points, which remain intact upon exposure to the stimulus and thus enable memory of the initial shape (Liu et al., 2007). Therefore, the net points in a SMP network define the original shape and the chains connected by the net points impart the elasticity required for the deformed network to reacquire its initial shape after stimulation.
Shape-memory polymers also require recovery elements, or switching segments, in the network that are capable of forming temporary interactions (Liu et al., 2007; Lee et al., 2000). The interactions between these switching segments are affected by the external stimulus ((Lendlein and Kelch, 2002; Behl and Lendlein, 2007). The retention of temporary shape and the transition back to the original shape from the temporary shape are determined by the stimuli-responsive switching segments (Wei et al., 1998). Accordingly, the switching segments determine the transition/stimulation conditions of SMPs.
Recent advances in shape-memory materials have led to the development of multiple shape recoveries in an SMP network (Behl et al., 2010). The networks are capable of recovering partially to a secondary temporary shape (Bellin et al., 2006; Xie et al., 2009). Latest developments are capable of multiple-shape memory, wherein several temporary states of the material can be captured en route to the final recovery of the SMP network (
Shape-memory polymers can be broadly classified on the basis of composition into the following four different types (Liu et al., 2007): (I) covalently cross-linked glassy thermoset networks; (II) covalently cross-linked semi-crystalline networks; (III) physically cross-linked glassy copolymers; and (IV) physically cross-linked semi-crystalline block copolymers.
1. Covalently Cross-Linked Glassy Thermoset Networks (Type I).
These materials are composed of a cross-linked polymer network that exhibits a sharp glass transition temperature (Tg). They behave as elastomers beyond Tg, which can be tuned by varying the cross-link density and, in the case of bi/multicomponent systems, the composition. For example, chemically cross-linked vinylidene random copolymers of poly(methyl methacrylate) and poly(butyl methacrylate) have Tg's of 110° C. and 20° C., respectively. By varying the composition of these two species in the material, a sharp and tunable Tg can be achieved for the resulting SMP network (Liu and Mather, 2002).
Ultra-high molecular weight glassy polymer networks can also be considered as this type of SMP because they do not flow above their Tg. These types of materials also show good shape fixity due to vitrification. Examples of such materials include high-molecular-weight poly(methyl methacrylate) (Irie, 1998). Polystyrene copolymers, epoxy networks and amorphous polyurethanes constitute other examples of chemically cross-linked glassy SMPs (Tong, 2002; Beloshenko et al., 2003); Chen et al., 2002).
2. Covalently Cross-Linked Semi-Crystalline Networks (Type II).
Polymers in this category use their inherent crystallinity to establish the conditions associated with shape fixing and memory (Liu et al., 2007). In this case, the melting temperature (Tm) of the polymer effectively becomes the transition temperature for the SMP network. The permanent shape of these networks is established similarly to that of the first category by chemical cross-links (Behl and Lendlein, 2007; Liu et al., 2007). Since melting is a first-order transition (unlike a glass transition, which is second order), the shape recovery is much faster as compared to the first case. The transition temperatures also are much narrower in range (Liu et al., 2007).
These SMPs include bulk polymers that form crystalline domains (Otsuka et al., 1998). Examples of materials in this category of SMPs include chemically cross-linked semi-crystalline rubber (Otsuka et al., 1998; Zhu et al., 2003) and polycaprolactone (Chowdhury and Das, 2003). A schematic of this type of material is provided in
Once initially shaped, Type I and II SMPs cannot be processed again into another shape or form. They also present significant challenges to recycling and reuse (Otsuka and Wayman; 1998). Chemical cross-linking is introduced by site-specific reactions that form covalent bonds between neighboring chains and is therefore a stochastic phenomenon that can continue beyond the time of the primary reaction. The result is additional cross-linking and eventual embrittlement (Liu et al., 2007; Otsuka and Wayman, 1998). Physically cross-linked networks developed on the basis of microphase separation or site-specific interactions (e.g., hydrogen bonding or electrostatic interactions) possess significant advantages over the previous materials for long-term end-use applications (Lendlein and Kelch, 2002; Behl and Lendlein, 2007).
3. Physically Cross-Linked Glassy Copolymers (Type III).
These SMPs have unique advantages due to their rheological properties that facilitate melt processing using conventional thermoplastic technology (Liu et al., 2007; Otsuka and Wayman, 1998). This class of materials is characterized by the presence of rigid, amorphous microdomains that serve as physical cross-links. One example of such materials includes microphase-separated block copolymers (Lee et al., 2001; Ahir et al., 2006). These materials exhibit excellent recovery beyond the transition temperature for rapid shape recovery (Otsuka and Wayman, 1998; Lee et al., 2001). Another species is, however, required to introduce temporary shape fixation in the network through either crystallization or vitrification (Liu et al., 2007; Lee et al., 2001).
Examples of Type III materials include, but are not limited to, polylactide copolymers (Min et al., 2005), aromatic amide/polycaprolactone blends (Kraft and Rabani, 2004), polyamide/polycaprolactone blends (Lee et al., 2000), and polyethylene terephthalate/polyethylene oxide blends (Luo et al., 1997). Polyurethane block copolymers exhibiting a sharp glass transition also belong to this category. Another example is the miscible blend of a segmented polyurethane with phenoxy resin and polycaprolactone (Jeong et al., 2001). In addition to block copolymer systems, homopolymer blends, such as those composed of poly(methyl methacrylate) and poly(vinylidene fluoride), can yield a melt-miscible system over all compositions (Campo and Mather, 2005). In this case, the poly(methyl methacrylate) is amorphous, while the poly(vinylidene fluoride) crystallizes to serve as the source of physical cross-linking and likewise contributes to the modulus of the blend. The SMP transitions at the glass transition of the acrylic (Campo and Mather, 2005).
Other physical associations, such as hydrogen bonding and ionic clusters, also can serve as physical cross-links (Li et al., 1998; Kim et al., 1998). These cross-links exist in the hard segments of the networks and can be dissociated when melt- or solution-processing the polymer network. Such a material is reusable and can be reshaped multiple times.
4. Physically Cross-Linked Semi-Crystalline Block Copolymers (Type IV).
In this case, the block copolymers contain a soft segment that is capable of crystallizing so that the melting point of this species establishes the transition of the SMP network (Liu et al., 2007). A classic example of this type of material is a poly[styrene-b-(trans-butadiene)-b-styrene) triblock copolymer (Ikematsu et al., 1990). The styrenic endblocks constitute 10-30 wt % of the molecule, and the system develops into a strongly-segregated network composed of a semi-crystalline polybutadiene matrix. Endblock-rich micelles exhibit a glass transition at 92° C. (depending on block length), above which the copolymer can be melt-processed. The midblock, on the other hand, melts at 68° C., thereby providing about a 30° window for the shape-memory functioning of the copolymer.
An entire class of thermoplastic polyurethanes (TPUs) with semi-crystalline segments has evolved as excellent shape-memory candidates (Li et al., 1997; Komiya et al., 1989). These TPUs can be envisaged as multiblock copolymers with alternating hard and soft segments. The hard segments interact via hydrogen bonding, whereas crystallization of the soft segments is responsible for the transitioning phase. Crystallization of the soft segments introduces a secondary shape in the SMP network. These materials are of considerable interest due to their tunable stiffness and transition temperature and they are readily foamed (Liu et al., 2007).
Shape-memory behavior in polymers can be characterized by analyzing the mechanical response of the material on a stress-strain curve, as depicted in
Two ratios are often used to describe shape memory in polymers: strain fixity and strain recovery. The Strain Fixity ratio (Rf) relates to the strain fixed in the temporary shape under a set of loading conditions (Behl and Lendlein, 2007) and is given by
where N is the cycle number, and εm denotes the maximum strain applied.
The Strain Recovery ratio (Rr) relates to the strain introduced in the recovered SMP after returning to its original shape (Behl and Lendlein, 2007) and is expressed as
Thermoplastic elastomers are capable of excellent strain fixity, as well as strain recovery. Physically cross-linked networks, as described hereinabove as Type III and IV, also are capable of moderately to very high tensile deformation (Liu et al., 2007; Otsuka and Wayman, 1998; Kraft and Rabani, 2004; Li et al., 1997).
Thermodynamics, expressed in terms of repeat unit interactions and chain elasticity/packing, govern the self-organization of block copolymers and their blends with homopolymers or solvents. Some of the seminal theoretical developments aimed at elucidating general polymer (and, more specifically, block copolymer) phase behavior include: (1) quasichemical description of the free energy of mixing (Huggins, 1941); (2) the random phase approximation (de Gennes, 1979); and (3) the development of mean-field theory (Leibler, 1980) and self-consistent field theory (Helfand, 1975).
Thermodynamic incompatibility in polymeric blends and copolymer systems can be expressed by the Flory-Huggins interaction parameter (X), which is incorporated into the free energy function to describe the interaction of two chemically distinct repeat units. Although the original definition of X is over-simplistic, it provides a valuable parameter that can be determined experimentally from several different analytical techniques (Huggins, 1941) or estimated using a variety of theoretical approaches.
The random phase approximation employs X to predict the phase behavior (e.g., the spinodal decomposition condition) of complex multicomponent systems primarily from small-angle scattering data (de Gennes, 1979). It also can be used to measure X
Self-consistent field theory generally can be used to predict the equilibrium properties of a microphase-separated (or -ordered) block copolymer or a physical mixture containing a block copolymer if X and the copolymer architecture and characteristics (block lengths and incompatibilities) are known. The premise behind this theoretical approach is that the repeat units comprising the blocks of the copolymer are spatially arranged in such fashion that the field they introduce must be uniform and consistent with the copolymer characteristics so that the free energy is minimized. In the case of block copolymer/homopolymer blends, microphase-separated morphologies can be predicted in this fashion, but macrophase separation cannot. Another use of this framework is to predict the equilibrium distribution of block copolymer molecules at an interface.
Triblock copolymers (for example, thermoplastic elastomers available from Kraton) blended with polyolefins are of prime consideration for practical and fundamental purposes. The rubbery midblock of each copolymer shows affinity toward polyolefins, such as polyethylene or polypropylene, whereas the styrenic endblocks microphase-separate and form well-defined microdomains. In the case of fibers as one of the targeted shape-memory outcomes, the size of the glassy endblocks is limited by viscosity constraints. In some of the formulations designed herein, the copolymer endblocks either self-assemble into spheroidal micelles or, in rare cases, cylindrical (worm-like) micelles (Mark, 1996). It should be noted that the high-molecular-weight polyolefins used herein and some styrenic copolymers, e.g., Kraton® copolymers, macrophase-separate when melt-blended (Li et al., 2002).
Shape-memory behavior in polymer fibers or films is principally dictated by the relaxation of polymer molecules, as well as the phase-separated morphology present (if one exists). In a representative, non-limiting example, thermoplastic elastomers (TPEs) and their blends with various polymers, including, for example, polyolefins, can, under favorable conditions, self-assemble into supramolecular networks that exhibit excellent memory of shape and form. The presently disclosed subject matter provides, in some embodiments, multicomponent polyolefin/TPE fibers or films produced at different compositions and concentric geometries that impart shape memory upon cyclic loading.
More particularly, in some embodiments, the presently disclosed subject matter introduces shape-memory properties into devices using commercially available polymers that are already produced on an industrial scale. The compositions and methods of the presently disclosed subject matter are cost effective and, because no complex processing is involved, the materials are easily recyclable. Another significant advantage of the presently disclosed compositions is that the recovery of the permanent shape in the fibers or films is brought about in a very short time (in some embodiments, under 2 sec) under the external stimulus.
In some embodiments, the presently disclosed subject matter relates to multicomponent, for example, bicomponent, melt-spun fibers or melt-extruded/pressed films that exhibit shape recovery properties when heat is applied as an external stimulus. Accordingly, in some embodiments, the presently disclosed methods include mixing or blending two or more polymer components to form a bicomponent fiber or film.
As used herein, the term “component” refers to a separate part of a fiber or film that has a spatial relationship to another part of the fiber or film. By way of illustration, a bicomponent fiber comprises two components that can be configured in, for example, a sheath-core or islands-in-the-sea configuration, wherein the sheath comprises one component and the core comprises another component that can be the same or different than that of the sheath. Further, the term “component” can refer to a part of a fiber that imparts some structural characteristic to the fiber, e.g., a core, sheath, or other cross-sectional segment of the fiber, or a part of a fiber that can be selectively removed from the fiber to impart some other characteristic to the fiber, for example, porosity.
As used herein, the term “multicomponent fiber” refers to a fiber formed from two or more components, e.g., two or more polymeric materials, that have been extruded from separate extruders and are then spun together to form a contiguous interface that extends along the length of the fiber. Multicomponent fibers also can be referred to art as “conjugate fibers.” The two or more components comprising a multicomponent fiber typically are different from each other, although multicomponent fibers also can use the same material, e.g., the same polymeric material, for each component. Further, a multicomponent fiber also can be formed by extruding a blend or mixture of two or more components from the same extruder and then spinning the extrudate to form a continuous fiber comprising the two or more components.
In particular embodiments, two components are used to form a multicomponent fiber and the product is referred to as a “bicomponent fiber.” A “bicomponent fiber” can be formed by combining, in heterogeneous fashion two components, e.g., two polymeric materials, having, for example, different or, in some embodiments, the same chemical and/or physical properties, and extruding the combined materials together from the same spinneret. The two components comprising a bicomponent fiber can be present in any desired ratio, for example, 99:1, 95:5, 90:10, 85:15, 80:20, 75:25, 70:30, 65:35, 60:40, 55:45, 50:50, 45:55, 40:60, 30:70, 25/75, 20:80, 15:85, 10:90, 5:95, 1:99 and the like at intermediate compositions. In particular embodiments, the fiber or film has a core or island component and a sheath component in a w/w ratio of about 40/60 (sheath/core). It should be understood, however, that the scope of the presently disclosed subject matter includes fibers with more than two components and possessing various other possible cross-sectional geometries including, but not limited to, trilobal core, sheath/interlayer/core, islands-in-sea, segmented pie, and side-by-side geometries. For example, when three components, e.g., three polymeric materials, at least two of which can be the same, are used to form the multicomponent fiber, the product is referred to as a “tricomponent fiber.”
Bicomponent fibers can be configured in various spatial arrangements wherein each component is arranged in substantially the same position in distinct segments across the cross-section and extends continuously along the length of the fiber. Representative spatial arrangements of bicomponent fibers include, but are not limited to, concentric sheath-core, eccentric sheath-core, tipped tri-lobal, and “islands in the sea”.
As used herein, the term “sheath-core” or “sheath/core” refers to a multicomponent fiber having a core component surrounded, or enclosed, by at least one outer layer, or sheath, of a second component, and in some embodiments, e.g., in a tricomponent fiber, a third component. In such configurations, the sheath can be continuous or non-continuous around the core. The ratio, measured by weight or by volume, of the sheath to the core can be from about 95/5 to about 5/95, that is, about 95/5, 90/10, 85/15, 80/20, 75/25, 70/30, 65/35, 60/40, 55/45, 50/50, 45/55, 40/60, 35/65, 30/70, 25/75, 20/80, 15/85, 10/90, 5/95, and the like at intermediate compositions.
Sheath-core fibers can be concentric, wherein the core component is centered relative to the sheath component, or eccentric, wherein the core is shifted off-center. Further, sheath-core fibers can have various outer geometries, i.e., a geometry defined by that of the sheath, including, but not limited to, substantially round or circular, oval, elliptical, star-shaped, rectangular, and other eccentricities. The core filament also can have various geometries, including circular or multi-lobal, for example tri-lobal. Further, the core in sheath-core fibers can be hollow or non-hollow, e.g., solid, or have a porous, solid core. Multiple cores can be simultaneously generated in the “islands in the sea” geometry.
Representative materials for use in elastomeric bicomponent fibers are disclosed in U.S. Patent Application Publication No. 2007/0055015 A1 to Flood et al., entitled “Elastomeric Fibers Comprising Controlled Distribution Block Copolymers,” published Mar. 8, 2007; U.S. Pat. No. 7,662,323 B1 to Flood et al., entitled “Elastomeric Bicomponent Fibers Comprising Block Copolymers Having High Flow,” issued Feb. 16, 2010; U.S. Pat. No. 7,910,208 B2 to Flood et al., entitled “Elastomeric Bicomponent Fibers Comprising Block Copolymers Having High Flow,” issued Mar. 22, 2011; and U.S. Pat. No. 8,003,209 B2 to Flood et al., entitled “Elastomeric Bicomponent Fibers Comprising Block Copolymers Having High Flow,” issued Aug. 23, 2011, each of which is incorporated herein by reference in its entirety.
More particularly, in some embodiments, the presently disclosed subject matter provides a multicomponent melt-spun fiber that exhibits deformation at room temperature, as well as at temperatures beyond the softening temperature of the switching component (but below the disruption of the molecular network), and shape recovery properties when heat is applied. In some embodiments, the fiber is a bicomponent fiber that comprises two co-spun or co-extruded components in a core-sheath cross-sectional geometry, wherein the core component is a multiblock copolymer and the sheath component comprises a second component that is different from the core component, and the fiber can be deformed at room temperature conditions and recover its shape when heated. In other embodiments, islands-in-the-sea filaments comprised of a multiblock copolymer in the islands and the homopolymer as the sea component exhibit shape recovery when a temporary deformation is induced by ambient-temperature or heated programming.
As used herein, the term “multiblock copolymer” refers to any block copolymer possessing more than two chemically dissimilar contiguous sequences (“blocks”) arranged in either linear or non-linear fashion. Multiblock copolymers possessing glassy/crystalline and rubbery blocks that microphase-separate to form a physically crosslinked rubbery network are commonly referred to as thermoplastic elastomers (TPEs).
The presently disclosed filaments can be deformed by loading at room temperature conditions. Recovery to the original shape is nearly spontaneous (for example, within 2 sec of heating or within about 5 sec after being exposed to a thermal stimulus) and is almost complete. The presently disclosed multicomponent fibers exhibit repeatable shape recovery and are capable of deformations above 400% strain (e.g., at least about four times the original length). Similar strain fixity and recovery behavior are observable under heated programming conditions.
The presently disclosed fibers can be multicomponent fibers and, in some embodiments, are bicomponent fibers or tricomponent fibers. In particular embodiments, the fibers are bicomponent fibers. Generally, the presently disclosed multicomponent fibers, e.g., in some embodiments, a bicomponent fiber, comprise at least one component, e.g., a core component, capable of forming a physically crosslinked network and another component, e.g., a sheath component, capable of transitioning with thermal stimulus, wherein the two components have strong interfacial adhesion; and wherein the temperature associated with the transitioning component is lower than the temperature required to disrupt the molecular network of the other component.
In some embodiments, the core can be an elastic material, such as a thermoplastic elastomer as described herein below. In certain embodiments, the core has an upper Tg between about 95° C. and about 100° C., although this Tg can be tuned through the inclusion of additives in the material comprising the core. Accordingly, in some embodiments, the transition point of the core material is higher than 100° C. and, in some embodiments, can be as high as 140° C. (Martins et al., 2003). Therefore, in some embodiments, the core component further comprises one or more additives and has an upper glass transition temperature in the range from about 90° C. to about 140° C. In some embodiments, the additive comprises a long-chain alkyl compound. In some embodiments, the upper glass transition temperature can be increased even more through modification.
The sheath functions as the switching point in the presently disclosed shape-memory fibers and, in some embodiments, the sheath comprises a polyolefin as described herein below. Generally, the material comprising the sheath has a melting point lower than the upper Tg of the material comprising the core. For example, in representative, non-limiting embodiments, the material comprising the sheath has a melting point lower than about 95° C.
More particularly, in some embodiments, the core comprises a thermoplastic elastomer (TPE). Thermoplastic elastomers generally are a class of copolymers that have both thermoplastic and elastomeric properties and exhibit the advantages typical of elastomers and plastics. Physical crosslinking contributes to the highly elastic properties exhibited by thermoplastic elastomers. Elastomers can be physically cross-linked (thermoplastic elastomers) or chemically cross-linked (permanent elastomers). Thermoplastic elastomers typically have the following characteristics: the ability to be stretched to moderate elongations and, upon removal of the stress, return to approximately its original shape; processable as a melt at elevated temperatures; and absence of significant creep.
Commercially available TPEs include at least seven general classes: styrenic block copolymers; acrylic block copolymers; polyolefin blends, such as ethylene propylene diene (EPDM)/polypropylene (PP) and nitrile-butadiene rubber (NBR)/PP; elastomeric alloys, such as a thermoplastic vulcanate, e.g., TPE-v or TPV;
thermoplastic polyurethanes (TPU), including polyether and polyester urethanes; thermoplastic copolyesters; and thermoplastic polyamides. Representative commercially available block copolymer TPEs include, but are not limited to, ARNITEL® (DSM Engineering Plastics, Birmingham, Mich., United States of America), a copolyester; ENGAGE™ (Dow Chemical, Midland, Mich., United States of America), a polyolefin; HYTREL® (DuPont, Wilmington, Del., United States of America), a polyester; DRYFLEX® and MEDIPRENE® (Elasto, Sweden), SEBS-based materials; and KRATON® styrenic block copolymers (Kraton Performance Polymers, Houston, Tex., United States of America); and SEPTON® styrenic block copolymers (Kuraray America, Houston, Tex., United States of America).
In particular embodiments, the core comprises a styrenic block copolymer, including, but not limited to poly(styrene-b-butadiene-b-styrene) (SBS), poly(styrene-b-isoprene-b-styrene) (SIS), poly[styrene-b-(ethylene-co-propylene)-b-styrene] (SEPS), or poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS). In particular embodiments, the core comprises SEBS. In particular embodiments, the core component comprises SEBS.
In some embodiments, the sheath comprises a polyolefin. Polyolefins generally are polymers produced from a simple olefin, i.e., an alkene, having the general formula CnH2n as a monomer. For example, polyethylene is produced by polymerizing ethylene, polypropylene is produced by polymerizing propylene, and the like. Representative polyolefins suitable for use with the presently disclosed subject matter include thermoplastic polyolefins including, but not limited to, polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), and polybutene-1 (PB-1). In particular embodiments, the sheath comprises linear low density polyethylene (LLDPE). LLDPE is a substantially linear polymer commonly made by copolymerization of ethylene with longer-chain olefins. LLDPEs differ structurally from conventional low-density polyethylene (LDPE) because of the absence of long chain branching. LLDPE has a higher tensile strength than LDPE and is very flexible and elongates under stress.
In further embodiments, the presently disclosed subject matter provides tricomponent fibers. In some embodiments, the presently disclosed tricomponent fiber comprises three co-spun or co-extruded components configured in an inner core component-outer core component-sheath component cross-sectional geometry, wherein at least one of the core components comprises a thermoplastic elastomer and the sheath component comprises a polyolefin, and wherein the fiber can be deformed from an original shape and return to the original shape in response to a thermal stimulus, e.g., when heated. In particular embodiments, the inner core component/outer core component/sheath component comprise LLDPE/SEBS/LLDPE.
Extrusion processes for making multicomponent continuous fibers and films are known in the art and are not described in detail herein. Generally, to form a multicomponent fiber, two or more components, for example, two or more polymeric materials which can be the same or different, are extruded separately and fed into a polymer distribution system, wherein the components are introduced into a spinneret having one or more capillaries. In such embodiments, the two components are combined in a common capillary. Alternatively, a single extrudate comprising a blend or mixture of two or more components can be extruded and introduced into the spinneret. The spinneret can be configured such that the extruded fiber has the desired cross section, for example, sheath-core or tipped tri-lobal. Such a process is described, for example, in U.S. Pat. No. 5,162,074 to Hills, which is incorporated herein by reference in its entirety.
In particular embodiments, the presently disclosed multicomponent fibers can be produced by co-extruding two components in a core-sheath, islands-in-sea, side by side, or other bicomponent cross-sectional geometry through a melt-spinning process. Although a variety of ways to produce multicomponent fibers exist, including wet spinning and dry spinning, producing a multicomponent fiber through melt spinning can offer several advantages. Melt-spun multicomponent fibers generally are resistant to higher temperatures and chemicals and can be several times stronger than multicomponent fibers produced by other methods. Melt-spun fibers also can be advantageous for use in structures, such as those used in blood treatment procedures, because the surface roughness of the fiber walls can be smaller than that of wet spun fibers. See de Rovere, A. and Shambaugh, R. L., “Melt-spun hollow fibers for use in nonwoven structures.” Ind. Eng. Chem. Res., 40:176-187 (2001).
The individual components of the multicomponent fiber can be selected to have melting temperatures such that the components can be extruded and spun through a common capillary at about the same temperature without degrading one component or the other. The processing temperature is determined by the chemical nature, molecular weights and concentration of each component. The extrusion and spinning process typically occurs at a melt temperature between about 90° C. to about 350° C., for example, in some embodiments about 175° C., depending on the melt properties of the two components.
The presently disclosed subject matter pertains not only to fibers, but also to films comprising at least two co-spun or co-extruded components configured in a core component-sheath component cross-sectional geometry. The film can be a hollow tube, relatively flat, or other suitable structure. As such, the presently disclosed subject matter provides a multicomponent film comprising at least two co-spun or co-extruded components configured in a core component-sheath component cross-sectional geometry, wherein the core component comprises a thermoplastic elastomer and the sheath component comprises a polyolefin, and wherein the film can be deformed from an original shape and return to the original shape when heated. In particular embodiments, the core component comprises SEBS and the sheath comprises LLDPE. In a representative, non-limiting example, the film includes a bilayer film comprising LLDPE/SEBS (sheath layer/core layer). As another example, the film is a trilayer film comprising LLDPE/SEBS/LLDPE (sheath layer/outer core layer/inner core layer).
As used herein the term “blend” and derivatives thereof refers to a macroscopic mixture of two or more different polymers, whereas the term “mixture” and derivatives thereof can refer to either a homogeneous or heterogeneous combination of two or more different polymers. The term “admixing” and derivatives thereof is intended to encompass both “blending” and “mixing” of a combination of components. Such blends can be extruded and subsequently spun into fibers. The spinning can be followed by hot drawing at a constant draw ratio to form bicomponent fibers. The resulting fibers can be washed in a shaker bath, sonicated in an ultrasonicator for a period of time, and then vacuum dried.
Unless otherwise indicated, the term “fiber” as used herein refers to fibers having a substantially continuous structure, such as continuous filaments, and fibers of finite length, such as conventional staple fibers. The term “staple fiber” refers to a non-continuous fiber, which can be produced with a conventional fiber spinning process and then cut to a staple length, from about one inch to about eight inches.
Further, as used herein, a “substantially continuous filament of fibers” refers to filaments or fibers prepared by extrusion from a spinneret, which are not cut from their original length. Substantially continuous filaments or fibers can have average lengths ranging from greater than about 15 cm to more than one meter. Spunbond fibers typically have diameters larger than about 5 microns, frequently, between about 10 and 20 microns. Spunbonding methods are described, for example, in U.S. Pat. No. 4,340,563 to Appel et al., U.S. Pat. No. 3,692,618 to Dorschner et al., U.S. Pat. No. 3,802,817 to Matsuki et al., U.S. Pat. No. 3,338,992 and U.S. Pat. No. 3,341,394 to Kinney, U.S. Pat. No. 3,502,763 to Hartman, U.S. Pat. No. 3,502,538 to Petersen, and U.S. Pat. No. 3,542,615 to Dobo et al., each of which is incorporated herein by reference in its entirety.
In general, the presently disclosed multicomponent fibers can be used to form a variety of articles. These articles include elastic mono filaments, woven fabrics, spun bond non-woven fabrics or filters, melt-blown fabrics, staple fibers, yarns, bonded, carded webs, and the like. Any of the processes typically used to make these articles can be employed when they are equipped, for example, to extrude two materials into a bicomponent fiber.
In particular, non-woven fabrics or webs can be formed by any of the processes known in the art. One process, typically referred to as spunbond, is well known in the art. U.S. Pat. No. 4,405,297, which is incorporated herein by reference in its entirety, describes a typical spunbond process. The spunbond process commonly comprises extruding the fibers from the melt through a spinneret, quenching and/or drawing the fibers using an air flow, and collecting and bonding the non-woven web. The bonding of the non-woven web is typically accomplished by any thermal, chemical or mechanical methods, including water entanglement and needle punch processes, effective in creating a multiplicity of intermediate bonds among the fibers of the web. Non-woven webs also can be formed using melt-blown process such as described in U.S. Pat. No. 5,290,626, which is incorporated herein by reference in its entirety. Carded webs may be formed from non-woven webs by folding and bonding the non-woven web upon itself in the cross machine direction.
Non-woven fabrics comprising the presently disclosed multicomponent fibers can be used for a variety of elastic fabrics including, but not limited to, diapers, waist bands, stretch panels, disposable garments, medical and personal hygiene articles, filters, and the like.
Elastic mono-filaments of the presently disclosed multicomponent fibers can be continuous, single, bicomponent fibers used for a variety of purposes and can be formed by any of the known methods of the art comprising spinning, drawing, quenching and winding. As used herein, staple fiber means cut or chopped segments of the continuously coextruded bicomponent fiber.
Yarns of the presently disclosed multicomponent fibers can be formed by processes known in the art. U.S. Pat. No. 6,113,825, which is incorporated herein by reference in its entirety, teaches the general process of yarn formation. In general, the process comprises melt extrusion of multiple fibers from a spinneret, drawing and winding the filaments together to form a multi-filament yarn, extending or stretching the yarn optionally through one or more thermal treatment zones, and cooling and winding the yarn.
The articles comprising the presently disclosed multicomponent fibers can be used alone or in combination with other articles made with the bicomponent fibers or with other classes of materials. As an example, non-woven webs can be combined with elastic mono-filaments to provide elastic stretch panels. As another example, non-woven webs can be bonded to other non-elastomeric non-woven webs or polymeric films of many types.
More particularly, an emerging class of materials, SMPs can be used in a wide variety of applications ranging from in vivo implants to outer space applications. Their low densities and large allowable deformations make them suitable for deployable components in aerospace (Metcalfe et al., 2003). These applications include hinges, trusses, antennas, optical reflectors, and morphing skins.
One type of application for SMPs is in the biomedical field. Since the discovery of SMPs in the 1980s, biocompatible polymers and their blends were consistently developed to enhance stimuli responsive behavior (Hampikian et al., 2006). One pioneering application for SMP smart materials is controlled drug release (Feninat et al., 2002). In addition, polymer vascular stents have been developed that also serve as drug delivery devices (Wache et al., 2003).
Another type of application for SMPs is in deployable structures. Devices fabricated using SMPs and their variants have overcome some inherent disadvantages over conventional devices. These disadvantages include complex assembling process, massive mechanisms, large volumes, undesired deployment defects, and high densities. One application is to replace hinges in deployable devices. A carbon-fiber-reinforced SMP composite was investigated (Lan et al., 2009) with flexural deformation as the main mode of deformation.
Actuation of solar arrays using the SMP component also has been demonstrated by Leng and coworkers (Lan et al., 2009;
In particular embodiment, the presently disclosed fibers can be used in thermal actuation applications, including, but not limited to, form fitting materials, packaging with self-sealing capability, deployable devices, smart textiles, intelligent fibers, and the like.
Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this presently described subject matter belongs.
By “programming”, it is meant mechanical deformation and subsequent fixation of the deformation.
By ‘recovery’, it is meant an external stimulus causing a polymer to switch from a temporary shape back to its initial shape.
The term “returning to the original shape” or “return to the original shape” refers to the fiber or film reforming to its original shape after heating. In some embodiments, the fiber or film returns to at least approximately 70% of its original shape. In other embodiments, the fiber or film returns to approximately 90% or more of its original shape, such as 95%, 96%, or 97% of its original shape.
The term “room temperature” in non-limiting embodiments refers to temperatures from about 18° C. to about 30° C., e.g., 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30° C. In some embodiments, the term room temperature refers to a temperature of about 20° C. In other embodiments, the term room temperature refers to a temperature of about 25° C.
As used herein the term “monomer” refers to a molecule that can undergo polymerization, thereby contributing constitutional units to the essential structure of a macromolecule or polymer.
A “polymer” is a molecule of high relative molecule mass, the structure of which essentially comprises the multiple repetition of a unit derived from molecules of low relative molecular mass, i.e., a monomer.
Following long-standing patent law convention, the terms “a,” “an,” and “the” refer to “one or more” when used in this application, including the claims. Thus, for example, reference to “a subject” includes a plurality of subjects, unless the context clearly is to the contrary (e.g., a plurality of subjects), and so forth.
Throughout this specification and the claims, the terms “comprise,” “comprises,” and “comprising” are used in a non-exclusive sense, except where the context requires otherwise. Likewise, the term “include” and its grammatical variants are intended to be non-limiting, such that recitation of items in a list is not to the exclusion of other like items that can be substituted or added to the listed items.
For the purposes of this specification and appended claims, unless otherwise indicated, all numbers expressing amounts, sizes, dimensions, proportions, shapes, formulations, parameters, percentages, parameters, quantities, characteristics, and other numerical values used in the specification and claims, are to be understood as being modified in all instances by the term “about” even though the term “about” may not expressly appear with the value, amount or range. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are not and need not be exact, but may be approximate and/or larger or smaller as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art depending on the desired properties sought to be obtained by the presently disclosed subject matter. For example, the term “about,” when referring to a value can be meant to encompass variations of, in some embodiments, ±100% in some embodiments ±50%, in some embodiments ±20%, in some embodiments ±10%, in some embodiments ±5%, in some embodiments ±1%, in some embodiments ±0.5%, and in some embodiments ±0.1% from the specified amount, as such variations are appropriate to perform the disclosed methods or employ the disclosed compositions.
Further, the term “about” when used in connection with one or more numbers or numerical ranges, should be understood to refer to all such numbers, including all numbers in a range and modifies that range by extending the boundaries above and below the numerical values set forth. The recitation of numerical ranges by endpoints includes all numbers, e.g., whole integers, including fractions thereof, subsumed within that range (for example, the recitation of 1 to 5 includes 1, 2, 3, 4, and 5, as well as fractions thereof, e.g., 1.5, 2.25, 3.75, 4.1, and the like) and any range within that range.
The following Examples have been included to provide guidance to one of ordinary skill in the art for practicing representative embodiments of the presently disclosed subject matter. In light of the present disclosure and the general level of skill in the art, those of skill can appreciate that the following Examples are intended to be exemplary only and that numerous changes, modifications, and alterations can be employed without departing from the scope of the presently disclosed subject matter. The synthetic descriptions and specific examples that follow are only intended for the purposes of illustration, and are not to be construed as limiting in any manner to make compounds of the disclosure by other methods.
Morphological development in copolymer/homopolymer blends has been previously characterized by electron microscopy and small-angle scattering.
Tensile testing of bi/tricomponent fibers composed of a TPE/polyolefin will yield a signature of their mechanical response to deformation. Tensile testing under cyclic loading is required to discern the level of hysteresis of the network. Whereas the recovery can be analyzed by performing tensile tests under different temperature conditions (Ji et al., 2006; Meng and Hu, 2008).
Fibers comprising poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) and LLDPE were spun using the co-extruder melt-spinning facility (Hills Inc.) in a concentric core-sheath geometry. Kraton G1643 was used as the triblock copolymer and EXACT 0230 were used as the sheath material. Various ratios of the two components were spun ranging from 25/75 w/w SEBS/LLDPE to 75/25 SEBS/LLDPE.
Cross-sectional optical micrographs obtained from six different composition ratios (see labels) are provided in
The fibers shown in
The fiber samples from the preliminary spinning experiments provided immediately hereinabove were tested for shape-memory behavior under thermally-induced recovery. In these experiments, a single fiber was clamped to a simple Vernier caliper with a gauge length of 25 mm. The fiber was strained up to 400% at ambient temperature, the strain was maintained for a predetermined time, the fiber was released at a constant rate to the initial length, the fiber was immersed in a water bath at 72° C. for two seconds, and the fiber recovery was measured. This procedure was repeated several times to evaluate fiber recovery.
The strain introduced to the fibers was gradually increased from 100% to 400%. An irrecoverable strain at ambient temperature was observed at 100% strain. The fibers exhibited excellent shape recovery within a second of immersion in a water bath held at 72° C.
These fibers were shown to exhibit excellent strain recovery with a very quick response to a thermal stimulus. The fibers also exhibited remarkable deformation tolerance and near perfect recovery. This recovery was observed even after 10 strain cycles. The fixity of the fiber was likewise being evaluated. In addition,
Bicomponent fibers were melt-spun in a coaxial geometry for different homopolymer sheaths and a thermoplastic elastomer (KRATON® G1643). In addition to LLDPE (EXACT® 0230), PP (BRASKEM CP360H) and PBT (Crastin S600F40NC010) also were spun as the sheath component to vary the core-sheath interfacial adhesion. A range of fibers from 25/75 sheath/core to 75/25 sheath core compositions were spun with each sheath component.
Without wishing to be bound to any one particular theory, it can be assumed that the ethylene-co-butylene block of the core was the component interacting with the sheath. The X values for each homopolymer/ethylene butylene were estimated from theoretical thermodynamic compatibility calculations (Huggins, 1941). Details of the solubility parameters and the X value are provided in Table 1.
From the above estimate, PP is expected to have the greatest interfacial adhesion and PBT is expected to have the least adhesion. The single fiber extension and shape-memory characteristics reveal, however, that LLDPE has the best interfacial adhesion among the three homopolymers.
To estimate the shape-memory behavior, all fiber samples from the spinning runs were tested for shape-memory behavior under thermally-induced recovery. A single fiber was clamped to a simple Vernier caliper with a gauge length of 25 mm. The fiber was strained up to 400% at ambient temperature, the strain was maintained for a predetermined time, the fiber was released at a constant rate to the initial length, the fiber was immersed in a water bath at 72° C. for 2 seconds, and the fiber recovery was measured. This procedure was repeated several times to evaluate fiber recovery.
The strain introduced to the fibers was gradually increased from 100% to 400%. An irrecoverable strain at ambient temperature was observed at 100% strain. The fibers exhibited excellent shape recovery within a second of immersion in a water bath held at an elevated temperature below 100° C.
The LLDPE/SEBS fibers exhibit excellent strain recovery with a very quick response to a thermal stimulus at all tested compositions. The fibers also exhibit remarkable deformation tolerance and near perfect recovery. This recovery was observed even after 10 strain cycles.
The PP/SEBS fibers were observed to ‘slip’ at the interface when a strain was introduced. Above 65% SEBS content, however, the PP/SEBS fibers exhibited very good strain recovery. When tested for repetitive straining, the PP/SEBS fibers did not recover the strain completely after 10 cycles.
In the case of PBT/SEBS fibers, no recovery was observed at any composition and an interfacial ‘slipping’ was observed when straining the fibers. Without wishing to be bound to any one particular theory, this effect indicates that the interface between the PBT/SEBS exhibits the least adhesion among the tested samples. A summary of the shape recovery observations is provided in Table 2.
In addition, bicomponent fibers were melt-spun in a coaxial geometry for different homopolymer sheaths and a core comprised of a thermoplastic elastomer (KRATON® G1643). In addition to LLDPE (EXACT® 0230), PP (BRASKEM CP360H) and PBT (Crastin S600F40NC010) also were spun as the sheath component to vary the core-sheath interfacial adhesion. The fibers were subjected to optical and electron microscopy analysis to discern their geometry and morphology. Shape-memory behavior of the bicomponent fibers was investigated as a function of the sheath/core composition for the three different homopolymer sheath components. The recovery behavior of these fibers was verified by successive heating and stretching. Elastic modulus and storage modulus of PE/SEBS fibers increased with an increase in the sheath (PE) content. Strain required to retain initial storage modulus decreased with increase in the sheath (PE) content. PE/SEBS fibers possessed excellent shape recovery in all compositions whereas PP/SEBS fibers exhibited recovery above 65% core composition. Although, shape memory under cold fixity was observed in the fibers with LLDPE and PP, PBT/SEBS fibers did not exhibit shape recovery in any composition. PE and LLDPE are used interchangeably herein and both refer to LLDPE.
The fiber samples comprised of 40/60 PE/SEBS filaments were tested for shape-memory behavior under thermally-induced recovery. As described above, a single fiber was clamped to a simple Vernier caliper with a gauge length of 25 mm. The fiber was strained up to 400% at ambient temperature, the strain was maintained for a predetermined time, the fiber was released at a constant rate to the initial length, the fiber was immersed in a water bath at 72° C. for 2 seconds, and the fiber recovery was measured. This procedure was repeated several times to evaluate fiber recovery.
Scanning electron microscopy (SEM) of the 40/60 PE/SEBS fibers was performed at an undeformed state, deformed state (400% strain), and recovered state (
Single filament tensile testing also was performed on the PE/SEBS fibers (
A summary of tensile testing with the PE sheath/SEBS fibers is shown in Table 3. As can be seen, the storage modulus and quasi-static modulus decreased with decreasing sheath content. In addition, the strain required to retain the initial storage modulus increased as sheath content decreased.
Cyclic loading studies were performed on LLDPE/SEBS sheath/core filament bundles. A 3 mm gage length was used under a constant rate of strain. The cyclic loading and unloading was performed at a constant temperature to determine the effect of the hysteresis of the filaments using stress-strain behavior. Cyclic loading also was followed by heating/cooling cycles to determine the temperatures required for recovery and the shape-memory of the filaments.
For cyclic loading at constant temperature, the loading was performed at room temperature (25° C.). The loading was initiated with a gage length of 3 mm, the load was increased at a constant strain rate of 0.02 s−1, and the loading was stopped at the prescribed strain (6 mm at 100% or 21 mm for 600% strain). The load was then reduced until the stress reached 0 MPa. The fibers were allowed to return to 0% strain or to the initial gage length (3 mm) The above steps were repeated for successive cycles.
For cyclic loading followed by heating/cooling cycles, the loading was initiated with a gage length of 3 mm, the load was increased at a constant strain rate of 0.02 s−1, and the loading was stopped at the prescribed strain. The load was then reduced until the stress reached 0 MPa. The fibers were allowed to return to 0% strain or to the initial gage length (3 mm) Then the sample was heated from 25 to 75° C. at 20° C./min and cooled from 75 to 25° C./min. The above steps were repeated for successive cycles.
Cyclic loading followed by heating/cooling cycles was performed with 30/70 LLDPE/SEBS filaments (
Cyclic loading followed by heating/cooling cycles also was performed with 50/50 LLDPE/SEBS filaments (
Table 4 shows the shape fixity (Sf; unrecovered temporary strain/maximum strain) and strain recovery (Sr; recovered strain (after heating)/maximum strain) for pure PE filaments and 50/50 and 30/70 LLDPE/SEBS sheath/core bicomponent filaments.
The interface between the core and the sheath of a filament was examined by varying the sheath component. In
Shape memory in a polymer network reflects the existence of netpoints and switching segments that can be immobilized. Thermoplastic elastomers are capable of shape memory and tend to exhibit better strain recovery as compared to chemically cross-linked networks. Bicomponent fibers produced from a triblock copolymer and polyolefin result in increased polyolefin orientation under high irrecoverable strain. Single fiber testing with superimposed semi-static and oscillatory modes gives insight on the load sharing between the constituents.
The presently disclosed subject matter can be used to develop novel melt-spun bi/tricomponent fibers capable of shape memory by exploiting the elasticity afforded by triblock copolymer supramolecular networks.
In contrast, a multicomponent fiber, such as a tricomponent fiber, exhibits enhanced shape memory. In this embodiment, the inner core and the outer core contribute equally to the load bearing, hence abating the crimping of filaments. The strain fixity (Sr) ratios for these fibers are enhanced. The sheath/interlayer/core filaments have equal stress in the inner most and outermost components because they are the same material. The strain fixity and strain recovery of the sheath/interlayer/core filaments are significantly enhanced due to the balancing of stresses on both interfaces of the TPE segment. This balancing of stresses eliminates the crimping of filaments when the load is released. As an example, the multicomponent fiber can be LLDPE/SEBS/LLDPE (sheath/outer core/inner core) as shown in
All publications, patent applications, patents, and other references mentioned in the specification are indicative of the level of those skilled in the art to which the presently disclosed subject matter pertains. All publications, patent applications, patents, and other references are herein incorporated by reference to the same extent as if each individual publication, patent application, patent, and other reference was specifically and individually indicated to be incorporated by reference. It will be understood that, although a number of patent applications, patents, and other references are referred to herein, such reference does not constitute an admission that any of these documents forms part of the common general knowledge in the art.
Although the foregoing subject matter has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be understood by those skilled in the art that certain changes and modifications can be practiced within the scope of the appended claims.
This application is a PCT International Application which claims the benefit of U.S. Provisional Application No. 61/709,787, filed Oct. 4, 2012, the content of which is herein incorporated by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2013/063575 | 10/4/2013 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61709787 | Oct 2012 | US |
