Abstract:
A new class of high modulus polypropylene multifilament fiber and/or yarn is provided. Such a multifilament fiber and/or yarn exhibits an exceptional combination of high strength and toughness with low weight and density. The inventive fibers thus permit replacement of expensive polymeric fibers within certain applications with lower cost alternatives, or replacement of high density components with such low density fibers, without sacrificing strength or durability. Such multifilament fibers are produced through melt-spinning processes and exhibit highly unique microstructures therein, including significant void volumes, interspersed and crossed voids, and nanofilament bridges within such voids. Such microstructural characteristics appear to impart the exceptional properties noted above.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of co-pending U.S. patent application Ser. No. 12/610,007, filed Oct. 30, 2009, which is a continuation-in-part of U.S. patent application Ser. No. 11/438,530, filed May 22, 2006, which is a divisional of U.S. patent application Ser. No. 10/983,153, filed Nov. 5, 2004, which issued as U.S. Pat. No. 7,074,483 on Jul. 11, 2006. 
    
    
     FIELD OF THE INVENTION 
     A new class of high modulus polypropylene multifilament fiber and/or yarn is provided. Such a multifilament fiber and/or yarn exhibits an exceptional combination of high strength and toughness with low weight and density. The inventive fibers thus permit replacement of expensive polymeric fibers within certain applications with lower cost alternatives, or replacement of high density components with such low density fibers, without sacrificing strength or durability. Such multifilament fibers are produced through melt-spinning processes and exhibit highly unique microstructures therein, including significant void volumes, interspersed and crossed voids, and nanofilament bridges within such voids. Such microstructural characteristics appear to impart the exceptional properties noted above. 
     BACKGROUND OF THE INVENTION 
     Yarns and fibers formed from polyolefins can offer many desirable characteristics. For example, they can possess good tactile qualities such as hand feel, they can be resistant to degradation and erosion, and the raw materials can be easy to obtain as well as fairly inexpensive. As such, monofilament fibers as well as multifilament yarns have been formed from various polyolefins such as polypropylene. While the development of monofilament polyolefin fibers that have high modulus and high tenacity has been achieved, the ability to produce high modulus, high tenacity multifilament yarns of similar materials has not been as successful. As such, there remains room for improvement and variation within the art. 
     Previous polyolefin fibers have been produced through typical spinning procedures, primarily solution-spun methods, that result in polyolefin fibers having relatively large amounts of solvents present therein that dilute the overall polyolefin constituency. These typical spinning procedures also take into account monofilament-type polymers wherein the target fibers are produced from a sole spinneret. Multifilament fibers are produced from a plurality of spinnerets, to the contrary, and require a capability of interaction between the individual components to form a strong, effective fiber of multiple filaments. Additionally, such typical polyolefin fibers are produced with drawing subsequent to spinning production, albeit at draw ratios that permit the filaments to extend to very long lengths in order to provide very thin fibers thereof; there have been no disclosures or teachings of past polyolefin fiber producing methods wherein the draw ratio exceeds a limited number, for instance from 1 to about 4. 
     SUMMARY OF THE INVENTION 
     In one embodiment, the present invention is directed to a method of forming a polypropylene multifilament yarn. For example, the method can include forming a melted polymeric composition including a polypropylene, extruding the composition to form multiple filaments, quenching the filaments in a liquid bath, collecting the filaments to form a fiber bundle, and drawing the fiber bundle in a heated drawing step with a draw ratio greater than about 6, and in one embodiment, greater than about 10. 
     The polypropylene can be any such type suitable for forming yarn. For example, the polypropylene can be a copolymer of a mixture of a polypropylene and another such polymer or a different polyolefin. In one embodiment, the polypropylene can have a melt flow index between about 0.2 and about 50. 
     In one embodiment, the polypropylene can contain a nucleating agent. For example, the nucleating agent can be a dibenzylidene sorbitol nucleating agent as is generally known in the art. Generally, the nucleating agent can be present in the melt in an amount less than about 1% by weight of the extruded composition, though this is not a requirement of the invention. 
     The extruder can generally be any standard multi-orifice extruder. For example, the extruder can define multiple orifices, and each orifice can have a maximum cross-sectional dimension of between about 0.001 and about 0.050 inches. 
     The melt can be extruded fairly slowly, for example between about 1 m/min and about 25 m/min into the liquid quench bath. Optionally, the bath can be heated, such as to a temperature of between about 50° C. and about 130° C. In one embodiment, the surface of the quench bath can be quite close to the extruder orifices, for example within the distance of the die swell of the filaments. In another embodiment, the area immediately downstream of the orifice can be protected by a heated or an unheated gaseous shroud. 
     The heated drawing step can be carried out in an oven, utilizing heated drawing rolls, or according to any other suitable heating method. Generally, the heated drawing step can be carried out at a temperature of between about 80° C. and about 170° C. For example, the oven or the drawing rolls can be heated to the desired temperature. The heated drawing step can also be carried out at an even higher temperature if, for example, the yarn is exposed to the heat for a very short period of time. 
     Other processes can also be carried out in forming the disclosed multifilament yarn such as one or more of the following: application of a lubricant, a second draw, or heat setting of the yarn. 
     In another embodiment, the invention is directed to yarn that can be formed according to the disclosed processes. For instance, the yarn can include multiple filaments that can each describe a denier of less than about 300, in one embodiment each filament can have a denier of between about 0.5 and about 100. The yarn can have a high modulus, for instance greater than 40 g/d. In another embodiment, the yarn can have a modulus greater than 100 g/d, or greater than 150 g/d in some embodiments. The yarn can also have a high tenacity, for example greater than about 5 g/d in some embodiments, and greater than about 7 g/d in other embodiments. The disclosed yarns can also be fairly resistant to stretching, for example, the yarn can exhibit an elongation of less than about 10%. 
     The disclosed yarn is also believed to possess a crystalline structure that is unique for multifilament polypropylene yarn. For instance, at least one of the filaments in the yarn can possess greater than 80% crystallinity, according to known wide-angle x-ray scattering (WAXS) measuring techniques. In one embodiment, at least one of the filaments in the yarn can have a ratio of equatorial intensity to meridonal intensity greater than about 1.0, which can be obtained from known small angle x-ray scattering (SAXS) measuring techniques. In another embodiment, the ratio of equatorial intensity to meridonal intensity can be greater than about 3.0. 
     In another embodiment, the inventive polypropylene multifilament fibers and yarns exhibit a significant amount of voids therein leading to a rather low fiber density property while simultaneously exhibiting an extremely high modulus strength, a result that is seemingly counterintuitive in nature. The actual high void volume creates an extremely high surface area for the typically made inventive polypropylene fiber (about, for instance, 1.5 m.sup.2/g), particularly as compared with void-free polypropylene fibers. In actuality, as an example, inventive polypropylene fibers that are measured at a 52 micron mean diameter will exhibit a specific surface area equivalent to fibers of a mean diameter of only 3 microns. This increased surface area helps to increase the capability of adhesion promoters to increase the strength of composites made from such fibers. In addition, the high modulus strength appears to be provided through the existence and alignment of such voids and cracks throughout the fibers themselves. For example, the inventive polypropylene fibers and yarns exhibit, under SEM imaging, such voids and cracks aligned in the fiber axis direction, thus permitting intersection primarily (if not solely) across the subject fiber&#39;s diameter. The void presence thus reduces the density measurements (and overall weight), yet increases the surface area, and, at the same time, accords high strength to the overall fiber by their presence within low intensity regions while high intensity regions prevent further crack propagation. In effect, and as described to a greater degree below, it appears that the voids and cracks present within the inventive polypropylene fibers provide the low density, while also increasing the strength and toughness of the same fiber through their aligned placement within the fiber as well. As such, the specific manufacturing method described herein imparts a resultant high strength with very low density, providing the industry with the first low-weight, high modulus polypropylene fiber. 
     The inventive fibers may thus be defined (and thus encompass) as follows: 
     a) a polyolefin multifilament fiber exhibiting repeated multiple striations therein aligned substantially perpendicularly along the longitudinal axis of said fiber, wherein said striations extend from the surface of said fiber and wherein at least a portion of said striations extend within the internal regions of said fiber; 
     b) a polyolefin multifilament fiber exhibiting a modulus strength of at least 8 GPa with a fiber diameter of at most 100 microns, said fiber internally comprising a plurality of microfibrils therein, wherein said fiber further exhibits a plurality of voids interspersed within said microfibrils, wherein both said microfibrils and said voids are aligned substantially parallel to the longitudinal axis of said fiber; 
     c) a polyolefin multifilament fiber exhibiting a modulus strength of at least 8 GPa with a fiber diameter of at most 100 microns, said fiber further exhibiting voids therein, wherein said voids exhibit include a plurality of nanofilament bridges; 
     d) a polyolefin multifilament fiber exhibiting a shear stress tensile failure mechanism at a level less than a ductile fracture tensile failure mechanism; and/or 
     e) a polyolefin multifilament fiber exhibiting a modulus strength of at least 8 GPa with a fiber diameter of at most 100 microns, where said fiber exhibits a hot air shrinkage of less than 5% at 150° C. 
     In one embodiment, the invention is directed to secondary products that can be formed and can include the disclosed yarns. For example, the disclosed yarn can be beneficially utilized in forming ropes, woven materials, and nonwoven materials. 
     In one embodiment, the disclosed yarn can be utilized in reinforcement materials, for instance reinforcement materials for use in reinforcing a hydratable cementitious composition. For example, a yarn formed according to the disclosed processes can be chopped into smaller pieces, generally less than about 5 inches, to form a reinforcement material. In one embodiment, the yarn can be chopped into pieces of less than about 3 inches in length. In another embodiment, it can be chopped into pieces of less than about 1 inch in length. Optionally, the reinforcement materials can be degraded and/or deformed in addition to being cut into smaller pieces. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       A full and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying Figures in which: 
         FIG. 1  illustrates one embodiment of a process according to the present invention; 
         FIG. 2  illustrates the die swell of a single filament formed according to one embodiment of the present invention; 
         FIG. 3  is the WAXS scattering pattern of a polypropylene filament pulled from a multifilament yarn formed according to one embodiment of the presently disclosed processes; 
         FIG. 4  is the SAXS scattering pattern of the polypropylene filament of  FIG. 3 ; 
         FIG. 5  shows a Scanning Electron Microscope (SEM) view of the surface of the inventive polypropylene fibers; 
         FIG. 6  provides two separate cross-sections (one at 90° and the other at 45°) under SEM of inventive polypropylene fibers; 
         FIG. 7  shows a cross-sectional SEM view at 1,000× magnification of an inventive polypropylene fiber; 
         FIG. 8  shows a cross-sectional SEM view at 2,000× magnification of an inventive polypropylene fiber; 
         FIG. 9  shows a cross-sectional SEM view at 4,000× magnification of an inventive fiber, particularly showing nanofilament bridges spanning voids (or cracks); 
         FIG. 10  shows a cross-sectional SEM view at 30,000× magnification of an inventive fiber, showing in greater detail the nanofilament bridges of  FIG. 10 ; 
         FIG. 11  shows two aerial SEM views at 800× and 2,500× magnification, respectively, of the fracture morphology of inventive polypropylene fibers; 
         FIG. 12  is a graphical representation of the shrinkage rate of an inventive polypropylene fiber; and 
         FIG. 13  is a graphical representation of the coefficient of thermal expansions exhibited by a typical inventive polypropylene fiber. 
     
    
    
     Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present invention. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to various embodiments of the invention, one or more examples of which are set forth below. Each embodiment is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, can be used in another embodiment to yield a still further embodiment. Thus, it is intended that the present invention cover such modifications and variations as come within the scope of the appended claims and their equivalents. 
     In general, the present invention is directed to multifilament polyolefin yarns and methods suitable for forming the disclosed multifilament polyolefin yarns. Beneficially, the disclosed methods can be utilized to form multifilament polyolefin yarns that can exhibit at least one of higher modulus or higher tenacity as compared to previously known multifilament polyolefin yarns. 
     The methods of the disclosed invention are generally directed to a melt-spinning yarn formation process. More particularly, the process utilized in forming the disclosed yarns can include forming a molten composition including a polyolefin, extruding multiple (i.e., at least three) individual filaments of the composition at a relatively low spinning rate, quenching the filaments in a liquid, forming a yarn structure of the multiple individual filaments, and mechanically drawing the yarn structure while the structure is heated. 
     In one particular embodiment, the polyolefin utilized in forming the disclosed yarns can be a polypropylene. This is not a requirement of the present invention, however, and though the ensuing discussion is generally directed toward polypropylene, it should be understood that other polyolefins can optionally be utilized in the invention. For example, in one embodiment, the disclosed invention can be directed to the formation of polyethylene or polybutylene multifilament yarn. 
     In addition, and for purposes of this disclosure, the term polypropylene is intended to include any polymeric composition comprising propylene monomers, either alone (i.e., homopolymer) or in mixture or copolymer with other polyolefins, dienes, or other monomers (such as ethylene, butylene, and the like). The term is also intended to encompass any different configuration and arrangement of the constituent monomers (such as syndiotactic, isotactic, and the like). Thus, the term as applied to fibers is intended to encompass actual long strands, tapes, threads, and the like, of drawn polymer. 
     For purposes of this disclosure, the terms fiber and yarn are intended to encompass structures that exhibit a length that far exceeds their largest cross-sectional dimension (such as, for example, the diameter for round fibers). Thus, the term fiber as utilized herein differs from structures such as plaques, containers, sheets, and the like that are blow-molded or injection molded. Moreover, the term multifilament yarn is intended to encompass a structure that includes at least three filaments that have been individually formed such as, for example, via extrusion through a spinneret, prior to being brought in proximity to one another to form a single yarn structure. 
     One embodiment of the presently disclosed process generally  10  is schematically illustrated in  FIG. 1 . According to the illustrated embodiment, a polymeric composition can be provided to an extruder apparatus  12 . For example, in one embodiment, the polymeric composition can include polypropylene. 
     Generally, any polypropylene suitable for forming drawn yarn can be utilized in the disclosed process. For instance, polypropylene suitable for the present invention can generally be of any standard melt flow. For example, in one embodiment, standard extrusion grade polypropylene resin possessing ranges of melt flow indices (MFI) between about 0.2 and about 50 can be utilized in forming the disclosed multifilament yarns. In one embodiment, polypropylene possessing an MFI between about 0.5 and about 25 can be utilized. In one embodiment, the polypropylene utilized in forming the multifilament yarn can have an MFI between about 1 and about 15. 
     In one embodiment, the polymeric composition provided to the extruder apparatus  12  can include polypropylene and a nucleating agent. According to this embodiment, the nucleating agent can generally be any material that can provide nucleation sites for the polypropylene crystals that can form during the transition of the polypropylene from the molten state to the solid structure. In one embodiment, the nucleating agent can exhibit high solubility in the polypropylene, though this is not a requirement of the invention. A non-limiting list of exemplary nucleating agents can include, for example, dibenzylidene sorbitol nucleating agents, as are generally known in the art, such as dibenzylidene sorbitol (DBS), monomethyldibenzylidene sorbitols such as 1,3:2,4-bis(p-methylbenzylidene) sorbitol (p-MDBS), dimethyl dibenzylidene sorbitols such as 1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol (3,4-DMDBS), and the like. Other suitable nucleating agents can include sodium benzoate, phosphate ester salts, such as NA-11 and NA-21, developed by Asahi Denka of Japan, or the hyper nucleating agents developed by Milliken Chemical of South Carolina such as, for example, HYPERFORM® HPN-68L. 
     According to the disclosed process, the polymeric composition, which can, in one embodiment include polypropylene combined with a nucleating agent, can be provided to an extruder apparatus  12 . In this particular embodiment, the polypropylene component and the nucleating agent can be provided to the extruder apparatus  12  either separately or together, as at an inlet  13 . For example, polypropylene and a nucleating agent can be provided to the extruder  12  either separately or together in liquid, powder, or pellet form. For instance, in one embodiment, both the polypropylene and the nucleating agent can be provided to the extruder  12  in pellet form at inlet  13 . In another embodiment, the nucleating agent can be provided to the extruder apparatus  12  in a liquid form. For example, nucleating agents in a liquid form such as those disclosed in U.S. Pat. No. 6,102,999 to Cobb, Ill., et al., which is incorporated herein by reference, can be utilized in the process. 
     When included, the nucleating agent can generally be present in the mixture to be extruded in an amount less than about 1% by weight of the composition. For example, the nucleating agent can be present in the mixture in an amount less than about 0.5% by weight. In one embodiment, the nucleating agent can be present in the mixture in an amount between about 0.01% by weight and about 0.3% by weight. In another embodiment, the nucleating can be present in the mixture in an amount between about 0.05% by weight and about 0.25% by weight. 
     The mixture including the polypropylene and, optionally, the nucleating agent can also include various other additives as are generally known in the art. For example, in one embodiment, the disclosed multifilament yarn can be colored yarn, and the mixture can include suitable coloring agents, such as dyes or other pigments. According to this embodiment, it may be preferable to utilize a nucleating agent that will not affect the final color of the multi-component yarn, but this is not a requirement of the invention, and in other embodiments, nucleating agents can be utilized that enhance or otherwise affect the color of the formed yarn. Other additives that can be combined with the mixture can include, for example, one or more of anti-static agents, antioxidant agents, antimicrobial agents, adhesion agents, stabilizers, plasticizers, brightening compounds, clarifying agents, ultraviolet light stabilizing agents, surface active agents, odor enhancing or preventative agents, light scattering agents, halogen scavengers, and the like. In addition, additives can be included in the melt, or in some embodiments, can be applied as a surface treatment to either the undrawn fiber bundle or optionally to the drawn yarn, as generally known in the art. 
     In one embodiment, the extruder apparatus  12  can be a melt spinning apparatus as is generally known in the art. For example, the extruder apparatus  12  can include a mixing manifold  11  in which a composition including one or more polyolefins and any other desired additives can be mixed and heated to form a molten composition. The formation of the molten mixture can generally be carried out at a temperature so as to ensure melting of essentially all of the polypropylene. For example, in one embodiment, the mixture can be mixed and melted in a manifold  11  heated to a temperature of between about 175° C. and about 325° C. 
     Optionally, to help ensure the fluid state of the molten mixture, in one embodiment, the molten mixture can be filtered prior to extrusion. For example, the molten mixture can be filtered to remove any fine particles from the mixture with a filter of between about 180 and about 360 gauge. 
     Following formation of the molten mixture, the mixture can be conveyed under pressure to the spinneret  14  of the extruder apparatus  12 , where it can be extruded through multiple spinneret orifices to form multiple filaments  9 . For instance, the spinneret can define at least three spinneret orifices. In one embodiment, the spinneret can define between 4 and about 100,000 individual spinneret orifices. For purposes of this disclosure, the terms extrusion die and spinneret are used herein interchangeably and intended to mean the same thing; the same is true for the terms spinneret orifice, spinneret aperture, extruder orifice and extruder aperture. The spinneret  14  can generally be heated to a temperature that can allow for the extrusion of the molten polymer while preventing breakage of the filaments  9  during formation. For example, in one embodiment, the spinneret  14  can be heated to a temperature of between about 175° C. and about 325° C. In one embodiment, the spinneret  14  can be heated to the same temperature as the mixing manifold  11 . This is not a requirement of the process, however, and in other embodiments, the spinneret  14  can be at a different temperature than the mixing manifold  11 . 
     The spinneret orifices through which the polymer can be extruded can generally be less than about 0.1 inches in maximum cross-sectional distance (e.g., diameter in the particular case of a circular orifice). For example, in one embodiment, the spinneret orifices can be between about 0.002 inches and about 0.050 inches in maximum cross-sectional distance. 
     According to the present invention, the polymer can be extruded through the spinneret at a relatively high throughput. For example, the polymer can be extruded through the spinneret at a throughput of not less than about 50% of that required to give melt fracture. In other words, the throughput can be at least 50% of the throughput at which the molten exudate can become excessively distorted. The specific melt fracture throughput can generally vary depending upon one or more of the exudate material, the total number of apertures in the spinneret, the spinneret aperture size, as well as the exudate temperature. For example, when considering the extrusion of molten polypropylene through a spinneret of 8 round apertures of 0.012-inch diameter each, melt fracture can occur at a pump speed of between about 22 and about 24 revolutions/minute of a 0.160 cm.sup.3/rev melt pump, or a throughput of about 5.5-6.0 g/min, when extruding a 4 melt flow homopolymer polypropylene at a spinneret temperature of about 230° C. Specific melt fracture throughput values for any particular system and materials as well as methods of obtaining such are generally known to those of skill in the art, and thus a detailed discussion of this phenomenon is not included herein. 
     In addition to a relatively high throughput, the filaments can also be formed at a relatively low spinline tension. The combination of high throughput with low spinline tension can allow the filaments to be formed with a relatively low ratio of orifice size to final drawn filament size as compared to other previously known multifilament formation processes. For instance, the ratio of the maximum cross-sectional width of an orifice to the maximum cross-sectional distance of a single fully drawn filament extruded through the orifice can, in one embodiment, be between about 2 and about 10. In one embodiment, this ratio can be between about 3 and about 8. Accordingly, the material forming each filament can be in a fairly relaxed, disorganized state as it begins to cool and crystallize. 
     Referring again to  FIG. 1 , following extrusion of the polymer, the undrawn filaments  9  can be quenched in a liquid bath  16  and collected by a take-up roll  18  to form a multifilament fiber structure or fiber bundle  28 . While not wishing to be bound by any particular theory, it is believed that by extruding the filaments at a relatively low spinline tension and high throughput combined with quenching the polymeric filaments in a liquid bath, the presently disclosed process encourages the formation of folded chain crystals in a highly disordered state in the polymer, which in turn enables a high draw ratio to be utilized in the process and thereby enables the formation of a multifilament yarn having high tenacity and modulus. 
     As is generally known in the art, polymers that are crystallized from a melt under dynamic temperature and stress conditions crystallize with the rate of crystallization dependent upon both the number of nucleation sites as well as on the growth rate of the polymer. Moreover, both of these factors are in turn related to the conditions that the polymer is subject to as it is quenched. In addition, polymers that crystallize when in a highly oriented state tend to have limited tenacity and modulus as evidenced by the limited draw ratios possible for such highly oriented polymers. Thus, in order to obtain a multifilament yarn with high tenacity and modulus, i.e., formed with a high draw ratio, crystallization of the polymer while in a highly disordered state is suggested. Accordingly, the present invention discloses a multifilament yarn formation process in which crystallization of the polymer in a highly disordered state is promoted by encouraging the filament to maximize its relaxation into the desired disoriented state during crystallization by forming the polymer at a relatively high throughput and low spinline tension. Optionally, a higher rate of crystallization can also be encouraged in certain embodiments through addition of a nucleating agent to the melt. In addition, quenching the formed polymer filaments in a liquid bath can promote the formation of folded chain crystals, which is also associated with the high draw ratios of high tenacity, high modulus materials. 
     As described, the individual filaments  9  can be extruded according to the disclosed process at relatively low spinline tension. As such, the take-up roll  18  can operate at a relatively low speed. For example, the take-up roll  18  can generally be set at a speed of less than about 25 meters per minute (m/min). In one embodiment, the take-up roll  18  can be set at a speed of between about 1 m/min and about 20 m/min. 
     The liquid bath  16  in which the filaments  9  can be quenched can be a liquid in which the polymer is insoluble. For example, the liquid can be water, ethylene glycol, or any other suitable liquid as is generally known in the art. In one embodiment, in order to further encourage the formation of folded chain crystals in the filaments  9 , the bath  16  can be heated. For example, the bath can be heated to a temperature near the maximum crystallization temperature (T c ) of the polymer. For example, the bath can be heated to a temperature of between about 50° C. and about 130° C. 
     Generally, in order to encourage formation of filaments with substantially constant cross-sectional dimensions along the filament length, excessive agitation of the bath  16  can be avoided during the process. 
     In one embodiment, quenching of the polymer can begin as soon as possible following exit from the spinneret, in order to encourage crystallization of the polymer while in the highly disoriented, relaxed state immediately following extrusion. For example, in one embodiment, the surface of the bath  16  can be located at a minimum distance from the spinneret  14 . For instance, in the embodiment illustrated in  FIG. 2 , the surface of the bath  16  can be at a distance from the spinneret  14  such that an extruded filament  9  can enter the bath  16  within the distance of the die swell  31  of the filament  9 . Optionally, the individual filaments  9  can pass through a heated or a non-heated shroud prior to entering the bath  16 . For example, a heated shroud may be utilized in those embodiments where the distance between the orifice and the bath surface is greater than the die swell. In one embodiment, the distance between the spinneret and the bath can be less than 2 inches. In another embodiment, this distance can be less than 1 inch. 
     Take-up roll  18  and roll  20  can be within bath  16  and convey individual filaments  9  and fiber bundle  28  through the bath  16 . Dwell time of the material in the bath  16  can vary, depending upon particular materials included in the polymeric material, particular line speed, etc. In general, filaments  9  and subsequently formed fiber bundle  28  can be conveyed through bath  16  with a dwell time long enough so as to ensure complete quench, i.e., crystallization, of the polymeric material. For example, in one embodiment, the dwell time of the material in the bath  16  can be between about 6 seconds and about 1 minute. 
     At or near the location where the fiber bundle  28  exits the bath  16 , excess liquid can be removed from the fiber bundle  28 . This step can generally be accomplished according to any process known in the art. For example, in the embodiment illustrated in  FIG. 1 , the fiber bundle  28  can pass through a series of nip rolls  23 ,  24 ,  25 ,  26  to remove excess liquid from the fiber bundle. Other methods can be alternatively utilized, however. For example, in other embodiments, excess liquid can be removed from the fiber bundle  28  through utilization of a vacuum, a press process utilizing a squeegee, one or more air knives, and the like. 
     In one embodiment, a lubricant can be applied to the fiber bundle  28 . For example, a spin finish can be applied at a spin finish applicator chest  22 , as is generally known in the art. In general, a lubricant can be applied to the fiber bundle  28  at a low water content. For example, a lubricant can be applied to the fiber bundle  28  when the fiber bundle is at a water content of less than about 75% by weight. Any suitable lubricant can be applied to the fiber bundle  28 . For example, a suitable oil-based finish can be applied to the fiber bundle  28 , such as Lurol PP-912, available from Goulston Technologies, Inc. Addition of a finishing or lubricant coat on the yarn can, in some embodiments of the invention, improve handling of the fiber bundle during subsequent processing and can also reduce friction and static electricity build-up on the yarn. In addition, a finish coat on the yarn can improve slip between individual filaments of the yarn during a subsequent drawing process and can increase the attainable draw ratio, and thus increase the modulus and tenacity of the drawn multifilament yarn formed according to the disclosed process. 
     After quenching of the fiber bundle  28  and any optional process steps, such as addition of a lubricant for example, the fiber bundle can be drawn while applying heat. For example, in the embodiment illustrated in  FIG. 1 , the fiber bundle  28  can be drawn in an oven  43  heated to a temperature of between about 80° C. and about 170° C. Additionally, in this embodiment, the draw rolls  32 ,  34  can be either interior or exterior to the oven  43 , as is generally known in the art. In another embodiment, rather than utilizing an oven as the heat source, the draw rolls  32 ,  34  can be heated so as to draw the yarn while it is heated. For example, the draw rolls can be heated to a temperature of between about 80° C. and about 170° C. In another embodiment, the yarn can be drawn over a hotplate heated to a similar temperature (i.e., between about 80° C. and about 170° C.). In one embodiment, the oven, draw rolls, hotplate, or any other suitable source of heat can be heated to a temperature of between about 120° C. and about 150° C. 
     According to the disclosed process, the multifilament fiber bundle can be drawn in a first (or only) draw at a high draw ratio, higher than those attainable in previously known polyolefin melt-spun multifilament yarn formation processes. For example, the fiber bundle  28  can be drawn with a draw ratio (defined as the ratio of the speed of the second or final draw roll  34  to the first draw roll  32 ) of greater than about 6. For instance, in one embodiment, the draw ratio of the first (or only) draw can be between about 6 and about 25. In another embodiment, the draw ratio can be greater than about 10, for instance, greater than about 15. Additionally, the yarn can be wrapped on the rolls  32 ,  34  as is generally known in the art. For example, in one embodiment, between about 5 and about 15 wraps of the yarn can be wrapped on the draw rolls. 
     While the illustrated embodiment utilizes a series of draw rolls for purposes of drawing the yarn, it should be understood that any suitable process that can place a force on the yarn so as to elongate the yarn following the quenching step can optionally be utilized. For example, any mechanical apparatus including nip rolls, godet rolls, steam cans, air, steam, or other gaseous jets can optionally be utilized to draw the yarn. 
     According to the embodiment illustrated in  FIG. 1 , following the yarn drawing step, the multifilament yarn  30  can be cooled and wound on a take-up roll  40 . In other embodiments, however, additional processing of the yarn  30  may be carried out. For example, in one embodiment, the multifilament yarn can be subjected to a second draw. In general, a second drawing step can be carried out at a higher temperature than the first draw. For instance, the heating element of the second drawing step can be heated to a temperature between about 10° C. and about 50° C. higher than the heating element of the first drawing step. In addition, a second draw can generally be at a lower drawing ratio that the first draw. For example, a second draw can be carried out at a draw ratio of less than 5. In one embodiment, a second draw can be carried out at a draw ratio of less than 3. In the case of multiple draws, the total draw ratio will be the product of each of the individual draws, thus a yarn first drawn at a draw ratio of 3, and then subsequently drawn at a draw ratio of 2 will have been subjected to a total draw ratio of 6. 
     Optionally, the drawn multifilament yarn can be heat set. For example, the multifilament yarn can be relaxed or subjected to a very low draw ratio (e.g., a draw ratio of between about 0.7 and about 1.3) and subjected to a temperature of between about 130° C. and about 150° C. for a short period of time, generally less than 3 minutes. In some embodiment, a heat setting step can be less than one minute, for example, about 0.5 seconds. This temperature can generally be higher than the drawing temperature(s). This optional heat set step can serve to “lock” in the crystalline structure of the yarn following drawing. In addition, it can reduce heat shrinkage, which may be desired in some embodiments. 
     In another embodiment, the finished yarn can be surface treated to improve certain characteristics of the yarn, such as wettability or adhesion, for example. For instance, the yarn can be fibrillated, subjected to plasma or corona treatments, or can include an added surface yarn sizing, all of which are generally known in the art, to improve physical characteristics of the yarns. Beneficially, the multifilament yarns of the invention can have a high surface area available for surface treatments, and thus can exhibit greatly improved characteristics, such as adhesion, as compared to, for instance, monofilament fibers formed of similar materials. 
     In general, the finished multifilament yarn  30  can be wound on a spool or take-up reel  40 , as shown, and transported to a second location for formation of a secondary product. In an alternative embodiment, however, the multifilament yarn can be fed to a second processing line, where the yarn can be further processed to form a secondary product, such as a woven fabric, for example. 
     The polyolefin multifilament yarn of the present invention can generally have a drawn size of between about 0.5 denier per filament and about 100 denier per filament. Beneficially, the disclosed multifilament yarn can have a high tenacity and modulus, as measured in ASTM D2256-02, which is incorporated herein by reference, and as compared to other, previously known multifilament polyolefin yarn. For example, the disclosed multifilament yarn can have a tenacity greater than about 5 grams/denier. 
     In one embodiment, the multifilament yarn can have a tenacity greater than about 7 grams/denier. In addition, the multifilament yarn of the present invention can have a high modulus, for example, greater than about 100 grams/denier. In one embodiment, the disclosed yarn can have a modulus greater than about 125 grams/denier, for example, greater than about 150 grams/denier, or greater than about 200 grams/denier. 
     In addition, the disclosed yarn can exhibit relatively low elongation characteristics. For example, the multifilament yarn of the present invention can exhibit an elongation percentage of less than about 15%, as measured in ASTM D2256-02. In another embodiment, the yarn can exhibit less than about 10% elongation, for example, less than about 8% elongation. 
     The inventive multifilament yarns are also believed to possess a unique crystalline structure as compared to other, previously known polyolefin multifilament yarns. There are several widely accepted means by which to measure molecular orientation in oriented polymer systems, among them scattering of light or X-rays, absorbance measurements, mechanical property analysis, and the like. Quantitative methods include wide angle X-ray scattering (WAXS), and small angle X-ray scattering (SAXS). 
     Through the utilization of WAXS and SAXS techniques, the disclosed multifilament yarns can be shown to be highly crystalline, highly oriented, with little or no lamellar structure. In particular, the filaments of the yarns can possess greater than about 80% crystallinity according to WAXS measuring techniques described below. For example,  FIG. 3  illustrates the WAXS scattering pattern of a single filament pulled from a multifilament yarn formed according to the presently disclosed process. In particular, the yarn (listed as sample Q in the Example section, below) was extruded through a spinneret with eight orifices of 0.012 inches diameter each, quenched in a water bath at 73° C., and drawn at a draw ratio of 16.2. The drawn yarn had a final denier of 406 grams/9000 m. As can be seen with reference to the Figure, where 0φ (phi) is parallel to the yarn, the amorphous region of the disclosed yarns can be 2φ from 10 to 30 and φ from 60 to 90 (the dark region near bottom of  FIG. 3 ), and the crystalline region can be 2φ from 10 to 30 and φ from −15 to 15 (including bright spots on the sides of  FIG. 3 ). Thus by integrating the x-ray scattering intensity in the crystalline and amorphous regions, the crystallinity of the filament can be obtained as: 
               (       l   x     -     l   A       )       (     l   x     )           
where l x  is the intensity in the crystalline region and l A  is the intensity in the amorphous region.
 
     In addition, the polyolefin yarns of the invention can be highly oriented, as shown by the narrow width of the WAXS peaks in  FIG. 3 . 
       FIG. 4  is the SAXS pattern of the filament shown in  FIG. 3 . Surprisingly, none of the expected structures relating to the crystalline form, orientation, and amorphous regions appear in the Figure, and the yarn appears to have no true amorphous regions at all, but appears to be composed entirely of crystalline regions and highly oriented amorphous regions. 
     SAXS patterns of multifilament yarns formed according to previously known methods generally include alternating crystalline and amorphous regions as illustrated by bright spots of scattering intensity in the yarn axis. (See, for example,  Polypropylene Fibers - Science and Technology , M. Ahmed, Elsevier Scientific Publishing Company, 1982, pp. 192-203, which is incorporated herein by reference.) The positions of these spots can be utilized to obtain the long period spacing between repeating crystalline regions. The absence of these spots in  FIG. 4  indicates that any amorphous regions in the inventive yarn of  FIG. 4  have nearly identical electron density to the crystalline regions, and are thus composed of dense, highly oriented amorphous chains, or are absent altogether. When combined with the WAXS pattern of  FIG. 3 , which indicates that the amorphous intensity is at least 15%, it may be assumed that amorphous regions of the illustrated filament most likely consists of the highly oriented chains. 
     In addition, the equatorial scattering in SAXS patterns in general arises from the center normal to the fiber axis and projects in a long, thin streak away from the center in each direction. In the inventive yarns, and in further reference to  FIG. 4 , these equatorial scattering streaks have amplified greatly, to the point that they are more aptly described as “wings.” This equatorial scattering arises from fibrillation of the crystalline segments into more clearly defined needle-like assemblies. A long equatorial streak arises from a high concentration of cylindrical, shish-type structures in the yarn with the lamellae organized among or around the shishes, as “kabobs.” These streaks generally appear in higher draw situations such as those of the present invention. As can also be seen in  FIG. 4 , the filaments forming the yarns of the present invention under high draw conditions can describe a nearly absent meridonal reflection and an equatorial scattering that is strong such that the scattering ratio of equatorial to meridional scattering intensity is high, but there remains strong density contrast as indicated by the overall intensity. 
     In general, the filaments forming the multifilament yarns of the present invention can have SAXS characteristics including a ratio of equatorial intensity to meridonal intensity of greater than about 1.0. In one embodiment, this ratio can be greater than about 3. The filaments forming the disclosed yarns can generally exhibit an equatorial intensity integrated from 2θof between about 0.4 to about 1.0 and φ from about 60 to about 120 and from about 240 to about 300 (zero φ being parallel to the yarn, or vertical in reference to  FIG. 4 ). In addition, the yarns can exhibit a meridonal intensity integrated from 20 of between about 0.4 and about 1.0 and φ from about −60 to about 60 and from about 120 to about 240. 
     The disclosed multifilament polyolefin yarns can be beneficially utilized in many applications. For example, the high strength and high tenacity of the disclosed yarns can provide them with excellent qualities for utilization in any application suitable for previously known multifilament polyolefin yarns. For example, in certain embodiments, the disclosed yarns can be beneficially utilized as reinforcement material in a matrix. For example, in one embodiment, following formation of the multifilament drawn yarn according to the disclosed processes, the yarn can be further processed so as to be suitable for use as a reinforcement material in a matrix. For instance, the multifilament yarns of the present invention can be chopped, fibrillated, flattened or otherwise deformed as is generally known in the art. As the multifilament yarns are processed in order to form the disclosed reinforcement materials, the multifilament yarns can not only be shortened, deformed, abraded, and the like, but in addition, the multifilament yarns can become shredded. That is, during processing, individual filaments of the yarns can become separated from one another in forming the disclosed reinforcement materials. 
     Accordingly, in one embodiment, the present invention is directed to reinforcement materials formed of the disclosed yarns. In particular, the reinforcement materials of the present invention can include chopped, shredded, and/or degraded yarns as herein described. In general, the reinforcement materials can include relatively short lengths of the multifilament yarns and/or individual filaments that have been shredded off of the formed multifilament yarns. For example, the reinforcement materials of the present invention can generally be less than about 5 inches in length. In one embodiment, the reinforcement materials can be less than about 3 inches in length, for instance, less than about 1 inch in length. 
     During use, the reinforcement materials of the disclosed invention can be combined with a matrix material such as adhesives, asphalt, plastics, rubber, or hydratable cementitious compositions including ready-mix or pre-cast concrete, masonry concrete, shotcrete, bituminous concrete, gypsum compositions, cement-based fireproofing compositions, and the like. 
     In one embodiment of the present invention, the disclosed yarns can be further processed if necessary and utilized in forming secondary products including those products that in the past have been formed with previously known multifilament polyolefin yarns. For example, the disclosed yarns can be utilized in forming ropes, and woven or nonwoven fabrics such as may be found in machinery belts or hoses, roofing fabrics, geotextiles, and the like. In particular, the disclosed multifilament yarns can be suitable for use in forming a secondary product according to any known technique that has been used in the past with previously known polyolefin multifilament yarns. Due to the improved physical properties of the disclosed yarns, however, and particularly, the higher modulus and tenacity of the disclosed yarns, secondary products formed utilizing the inventive yarns can provide improved characteristics, such as strength and tenacity, as compared to similar products formed of previously known multifilament polyolefin yarns. The invention may be better understood with reference to the following Example. 
     EXAMPLE 
     Yarn samples were formed on system similar to that illustrated in  FIG. 1 . In particular, the system included a ¾ inch, 24:1 single screw extruder with three temperature zones, a head with a melt pump and spinneret, a liquid quench tank (40 inch length), with two rollers in the tank, a vacuum water removal system, a spin finish applicator, three heated godet rolls, a forced air oven (120 inch length) and a LEESONA® winder. 
     Materials utilized in forming the yarns included ATOFINA® 3462, a polypropylene homopolymer with a melt flow index of 3.7, and ATOFINA® 3281, a polypropylene homopolymer with a melt flow index of 1.3 (both available from ATOFINA Petrochemicals, Inc. of Houston, Tex.); a 10% concentrate of a nucleating agent composition, specifically MILLAD® 3988 (3,4-dimethyl dibenzylidiene sorbitol) in a 12 MFI polypropylene homopolymer (available from Standridge Color Corporation, Social Circle, Ga., USA); and a polyethylene homopolymer with a melt flow index of 12 (available from TDL Plastics, of Houston, Tex.). 
     Table 1, below, tabulates the formation conditions of 37 different samples including the material make-up (including the polymer used and the total weight percent of the nucleating agent in the melt), the spinneret hole size in inches, the total number of filaments extruded, the temperature of the quench water bath, the roll speeds of the drawing rolls, the total draw ratio (Roll 3/Roll 1), and the temperature of the drawing oven. In addition, as the nucleating agent is provided in a 10% concentrate composition of the nucleating agent in a 12 MFI polypropylene homopolymer, the material make-up of those samples that include an amount of a nucleating agent will also include an amount of the 12 MFI polypropylene homopolymer from the concentrate. For example, a sample that is listed as containing FINA 3462/0.2% Millad will contain 0.2 wt % of the nucleating agent, 1.8 wt % of the 12 MFI polypropylene homopolymer used in forming the 10% nucleating agent composition, and 98 wt % of the FINA 3462 3.7 MFI polypropylene homopolymer. 
     
       
         
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 Spinneret 
                   
                 Water 
                   
                   
                   
                   
                   
               
               
                   
                   
                 Hole Size 
                   
                 Temp 
                 Roll 1 
                 Roll 2 
                 Roll 3 
                   
                 Oven T 
               
               
                 Sample 
                 Material 
                 (inches) 
                 # Fils. 
                 (° C.) 
                 m/min 
                 m/min 
                 m/min 
                 DR 
                 (° C.) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 A 
                 Fina 3462 
                 0.04 
                 1 
                 25 
                 11.3 
                 100 
                 110 
                 9.7 
                 120 
               
               
                 B 
                 Fina 3462/0.2% Millad 
                 0.04 
                 1 
                 25 
                 8 
                 123 
                 123 
                 15.4 
                 140 
               
               
                 C 
                 Fina 3462/0.2% Millad 
                 0.027 
                 17 
                 25 
                 5 
                 30 
                 30 
                 6.0 
                 120 
               
               
                 D 
                 Fina 3462/0.2% Millad 
                 0.027 
                 17 
                 25 
                 5 
                 37.5 
                 37.5 
                 37.5 
                 150 
               
               
                 E 
                 Fina 3462/0.25% Millad 
                 0.018 
                 1 
                 25 
                 10.5 
                 135 
                 135 
                 12.9 
                 130 
               
               
                 F 
                 Fina 3462/0.25% Millad 
                 0.018 
                 8 
                 25 
                 9 
                 85 
                 85 
                 9.4 
                 130 
               
               
                 G 
                 Fina 3462/0.25% Millad 
                 0.018 
                 8 
                 25 
                 6 
                 85 
                 85 
                 14.2 
                 130 
               
               
                 H 
                 Fina 3462/0.25% Millad 
                 0.012 
                 8 
                 25 
                 8.75 
                 85 
                 85 
                 9.7 
                 130 
               
               
                 I 
                 Fina 3462/0.25% Millad 
                 0.012 
                 8 
                 25 
                 9.5 
                 85 
                 85 
                 8.9 
                 130 
               
               
                 J 
                 Fina 3462/0.20% Millad 
                 0.012 
                 8 
                 25 
                 8 
                 85 
                 85 
                 10.6 
                 130 
               
               
                 K 
                 Fina 3462/0.20% Millad 
                 0.012 
                 8 
                 25 
                 6.25 
                 85 
                 85 
                 13.6 
                 130 
               
               
                 L 
                 Fina 3462/0.20% Millad 
                 0.012 
                 8 
                 25 
                 5.5 
                 85 
                 85 
                 15.5 
                 130 
               
               
                 M 
                 Fina 3462/0.20% Millad 
                 0.012 
                 8 
                 25 
                 5.5 
                 85 
                 85 
                 15.5 
                 130 
               
               
                 N 
                 Fina 3462/0.20% Millad 
                 0.012 
                 5 
                 25 
                 5 
                 85 
                 85 
                 17.0 
                 130 
               
               
                 O 
                 Fina 3462/0.20% Millad 
                 0.012 
                 5 
                 55 
                 6 
                 85 
                 85 
                 14.2 
                 130 
               
               
                 P 
                 Fina 3462/0.20% Millad 
                 0.012 
                 5 
                 55 
                 6 
                 85 
                 85 
                 14.2 
                 130 
               
               
                 Q 
                 Fina 3462/0.20% Millad 
                 0.012 
                 8 
                 73 
                 5.25 
                 84 
                 85 
                 16.2 
                 130 
               
               
                 R 
                 Fina 3462/0.20% Millad 
                 0.012 
                 8 
                 85 
                 5.5 
                 84 
                 85 
                 15.5 
                 130 
               
               
                 S 
                 Fina 3462/0.20% Millad 
                 0.012 
                 8 
                 85 
                 5.25 
                 84 
                 85 
                 16.2 
                 130 
               
               
                 T 
                 Fina 3462/0.20% Millad 
                 0.012 
                 8 
                 82 
                 4.75 
                 84 
                 85 
                 17.9 
                 145 
               
               
                 U 
                 Fina 3462/0.20% Millad 
                 0.012 
                 8 
                 82 
                 4.6 
                 84 
                 85 
                 18.5 
                 150 
               
               
                 V 
                 Fina 3281/0.2% Millad 
                 0.012 
                 8 
                 75 
                 4.5 
                 84 
                 85 
                 18.9 
                 140 
               
               
                 W 
                 Fina 3281/0.2% Millad 
                 0.012 
                 8 
                 75 
                 4.5 
                 84 
                 85 
                 18.9 
                 140 
               
               
                 X 
                 Fina 3281 
                 0.012 
                 8 
                 75 
                 6 
                 84 
                 85 
                 14.2 
                 130 
               
               
                 Y 
                 Fina 3281 
                 0.012 
                 8 
                 75 
                 4.5 
                 84 
                 85 
                 18.9 
                 140 
               
               
                 Z 
                 Fina 3281 
                 0.012 
                 8 
                 75 
                 4.25 
                 84 
                 85 
                 20.0 
                 140 
               
               
                 AA 
                 Fina 3281 w/ 5% 12MFI 
                 0.012 
                 8 
                 75 
                 5 
                 84 
                 85 
                 17.0 
                 130 
               
               
                   
                 PE 
               
               
                 BB 
                 Fina 3281/0.2% Millad 
                 0.012 
                 8 
                 75 
                 4.75 
                 84 
                 85 
                 17.9 
                 150 
               
               
                 CC 
                 Fina 3281/0.2% Millad 
                 0.012 
                 8 
                 75 
                 4.25 
                 84 
                 85 
                 20.0 
                 140 
               
               
                 DD 
                 Fina 3281/0.2% Millad 
                 0.012 
                 8 
                 75 
                 4 
                 84 
                 85 
                 21.3 
                 140 
               
               
                 EE 
                 Fina 3281/0.2% Millad 
                 0.012 
                 8 
                 75 
                 4 
                 84 
                 85 
                 21.3 
                 140 
               
               
                 FF 
                 Fina 3281/0.2% Millad 
                 0.012 
                 8 
                 75 
                 4 
                 84 
                 85 
                 21.3 
                 140 
               
               
                 GG 
                 Fina 3281/0.2% Millad 
                 0.012 
                 8 
                 75 
                 5 
                 84 
                 85 
                 17.0 
                 140 
               
               
                 HH 
                 Fina 3281/0.2% Millad 
                 0.012 
                 8 
                 75 
                 4.75 
                 84 
                 85 
                 17.9 
                 140 
               
               
                 II 
                 Fina 3281/0.2% Millad 
                 0.012 
                 20 
                 75 
                 4.25 
                 84 
                 85 
                 20.0 
                 140 
               
               
                 JJ 
                 Fina 3281/0.2% Millad 
                 0.012 
                 20 
                 75 
                 5.5 
                 84 
                 85 
                 15.5 
                 150 
               
               
                 KK 
                 Fina 3281/0.2% Millad 
                 0.012 
                 20 
                 75 
                 4.25 
                 84 
                 85 
                 20.0 
                 140 
               
               
                   
               
             
          
         
       
     
     Following formation, the samples were tested for a number of physical properties including denier, denier per filament, elongation, tenacity, modulus, and toughness, all according to ASTM D2256-02, previously incorporated by reference. Results are shown below in Table 2. 
                                                                                   TABLE 2                       Denier   Denier/fil       Ten   Mod   Toughness       Sample   Material   g/9000 m   g/9000 m   Elong %   g/d   g/d   g/d                                A   Fina 3462   302   302   24   5.2   60           B   Fina 3462/0.2% Millad   292   292   8   5.9   107       C   Fina 3462/0.2% Millad   1300   76   21   5.5   50       D   Fina 3462/0.2% Millad   1414   83   16   4.2   43       E   Fina 3462/0.25% Millad   63   63   10   7.9   125       F   Fina 3462/0.25% Millad   293   37   22   8.5       G   Fina 3462/0.25% Millad   532   67   11.7   10.4   173       H   Fina 3462/0.25% Millad   210   26   16.9   8.1   100       I   Fina 3462/0.25% Millad   161   20   14.8   7.2   100       J   Fina 3462/0.20% Millad   222   28   15.0   9.0   108       K   Fina 3462/0.20% Millad   316   40   9.1   8.4   154       L   Fina 3462/0.20% Millad   362   45   8.9   8.8   159       M   Fina 3462/0.20% Millad   420   53   11.2   9.6   146       N   Fina 3462/0.20% Millad   297   59   10.4   10.5   171       O   Fina 3462/0.20% Millad   287   57   11.3   9.4   144       P   Fina 3462/0.20% Millad   276   55   9.2   7.7   132       Q   Fina 3462/0.20% Millad   406   51   9.3   11.6   207       R   Fina 3462/0.20% Millad   369   46   14.0   8.2       S   Fina 3462/0.20% Millad   390   49   14.0   8.4       T   Fina 3462/0.20% Millad   345   43   9.3   10.4   189       U   Fina 3462/0.20% Millad   324   41   8.8   10.9   201       V   Fina 3281/0.2% Millad   353   44   7.3   9.3   185       W   Fina 3281/0.2% Millad   358   45   6.9   9.7   203       X   Fina 3281   329   41   12.5   9.3   131   0.75       Y   Fina 3281   301   38   10.7   10.3   160   0.73       Z   Fina 3281   316   40   9.7   9.8   165   0.66       AA   Fina 3281 w/ 5% 12MFI PE   328   41   14.0   8.9       BB   Fina 3281/0.2% Millad   270   34   9.1   8.5   159   0.62       CC   Fina 3281/0.2% Millad   287   36   8.6   8.9   181   0.58       DD   Fina 3281/0.2% Millad   265   33   8.9   10.4   203   0.68       EE   Fina 3281/0.2% Millad   364   46   8.1   9.1   178   0.61       FF   Fina 3281/0.2% Millad   403   50   6.5   8.5   181   0.41       GG   Fina 3281/0.2% Millad   356   45   8.4   10.3   200   0.60       HH   Fina 3281/0.2% Millad   375   47   5.3   8.8   203   0.39       II   Fina 3281/0.2% Millad   396   20   6.4   8.3   178   0.46       JJ   Fina 3281/0.2% Millad   589   29   9.6   9.2   166   0.65       KK   Fina 3281/0.2% Millad   423   21   6.1   7.8   178   0.47                    
X-Ray Scattering Analysis
 
     The samples were studied by small angle x-ray scattering (SAXS). The SAXS data were collected on a Bruker AXS (Madison, Wis.) Hi-Star multi-wire detector placed at a distance of 105.45 cm from the sample in an Anton-Paar vacuum. X-rays (λ=0.154178 nm) were generated with a MacScience rotating anode (40 kV, 40 mA) and focused through three pinholes to a size of 0.2 mm. The entire system (generator, detector, beampath, sample holder, and software) is commercially available as a single unit from Bruker AXS. The detector was calibrated per manufacturer recommendation using a sample of silver behenate. 
     A typical SAXS data collection was conducted as follows: a polypropylene filament bundle was wrapped around a holder, which was placed in the x-ray beam inside an Anton-Paar vacuum sample chamber on the x-ray equipment. The sample chamber and beam path was evacuated to less than 100 mTorr and the sample was exposed to the X-ray beam for between about 45 minutes and one hour. Two-dimensional data frames were collected by the detector and unwarped automatically by the system software. 
     An analysis of the scattered intensity distribution) (2θ=0.2° 2.5° into the equatorial or meridonal directions was calculated from the raw data frames by dividing the scattering into 2 regions: an equatorial scattering region, integrated from 2θ of between about 0.4 to about 1.0 and φ from about 60 to about 120 and from about 240 to about 300 (zero φ being parallel to the yarn, or vertical in  FIG. 4 ), and the meridonal scattering region, integrated from 28 of between about 0.4 and about 1.0 and b from about −60 to about 60 and from about 120 to about 240. Total counts were summed for each of the two regions and the ratio calculated and tabulated for each sample in Table 3, below. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
                   
                   
                   
                 Equa- 
               
               
                   
                   
                 Meriodional 
                 Equatorial 
                 torial/ 
               
               
                   
                   
                 Scattering  
                 Scattering  
                 Merid- 
               
               
                 Sample 
                 Material 
                 counts 
                 counts 
                 ional 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 A 
                 Fina 3462 
                 150499 
                 18174 
                 0.12 
               
               
                 B 
                 Fina 3462/0.2% Millad 
                 83716 
                 293818 
                 3.51 
               
               
                 C 
                 Fina 3462/0.2% Millad 
                 125348 
                 20722 
                 017 
               
               
                 D 
                 Fina 3462/0.2% Millad 
                 169657 
                 37642 
                 0.22 
               
               
                 E 
                 Fina 3462/0.25% Millad 
                 57067 
                 265606 
                 4.65 
               
               
                 F 
                 Fina 3462/0.25% Millad 
                 28192 
                 23494 
                 0.83 
               
               
                 G 
                 Fina 3462/0.25% Millad 
                 34164 
                 182207 
                 5.33 
               
               
                 H 
                 Fina 3462/0.25% Millad 
                 14203 
                 11505 
                 0.81 
               
               
                 I 
                 Fina 3462/0.25% Millad 
                 21722 
                 17758 
                 082 
               
               
                 J 
                 Fina 3462/0.20% Millad 
                 36264 
                 74971 
                 2.07 
               
               
                 K 
                 Fina 3462/0.20% Millad 
                 82734 
                 662846 
                 8.01 
               
               
                 L 
                 Fina 3462/0.20% Millad 
                 47815 
                 175599 
                 3.67 
               
               
                 M 
                 Fina 3462/0.20% Millad 
                 53247 
                 323136 
                 6.07 
               
               
                 N 
                 Fina 3462/0.20% Millad 
                 89254 
                 561719 
                 6.29 
               
               
                 O 
                 Fina 3462/0.20% Millad 
                 52212 
                 313477 
                 6.00 
               
               
                 P 
                 Fina 3462/0.20% Millad 
                 57344 
                 365467 
                 6.37 
               
               
                 Q 
                 Fina 3462/0.20% Millad 
                 107220 
                 401479 
                 3.74 
               
               
                 R 
                 Fina 3462/0.20% Millad 
                 40419 
                 59163 
                 1.46 
               
               
                 S 
                 Fina 3462/0.20% Millad 
                 48712 
                 106876 
                 2.19 
               
               
                 T 
                 Fina 3462/0.20% Millad 
                 49098 
                 153474 
                 3.13 
               
               
                 U 
                 Fina 3462/0.20% Millad 
                 65459 
                 210907 
                 3.22 
               
               
                 V 
                 Fina 3281/0.2% Millad 
                 54222 
                 220056 
                 4.06 
               
               
                 W 
                 Fina 3281/0.2% Millad 
                 43058 
                 257097 
                 5.97 
               
               
                 X 
                 Fina 3281 
                 53060 
                 159811 
                 3.01 
               
               
                 Y 
                 Fina 3281 
                 57218 
                 210415 
                 3.68 
               
               
                 Z 
                 Fina 3281 
                 45224 
                 186045 
                 4.11 
               
               
                 AA 
                 Fina 3281 w/5% 12MFI PE 
                 35826 
                 87938 
                 2.45 
               
               
                 BB 
                 Fina 3281/0.2% Millad 
                 37907 
                 98972 
                 2.61 
               
               
                 CC 
                 Fina 3281/0.2% Millad 
                 54109 
                 164494 
                 3.04 
               
               
                 DD 
                 Fina 3281/0.2% Millad 
                 47656 
                 202256 
                 4.24 
               
               
                 EE 
                 Fina 3281/0.2% Millad 
                 51026 
                 171581 
                 3.36 
               
               
                 FF 
                 Fina 3281/0.2% Millad 
                 48872 
                 181346 
                 3.71 
               
               
                 GG 
                 Fina 3281/0.2% Millad 
                 49382 
                 282525 
                 5.72 
               
               
                 HH 
                 Fina 3281/0.2% Millad 
                 54467 
                 348671 
                 6.40 
               
               
                 II 
                 Fina 3281/0.2% Millad 
                 57703 
                 260487 
                 4.51 
               
               
                 JJ 
                 Fina 3281/0.2% Millad 
                 52353 
                 178923 
                 3.42 
               
               
                 KK 
                 Fina 3281/0.2% Millad 
                 46881 
                 203281 
                 4.34 
               
               
                   
               
             
          
         
       
     
     As can be seen with reference to Table 3, while the disclosed materials can in some cases give to rise to a SAXS scattering profile with both meridonal scattering and equatorial scattering, the meridonal scattering is low compared to the highly unique strong equatorial scattering giving rise to a high ratio of equatorial scattering to meridonal scattering. At the very least, then, the presence of intense scattering wings in the equatorial direction provides the desired crystal structures that impart the properties of high tenacity and high modulus found in the multifilament yarns. 
     Microstructural Analysis 
     Example JJ from above was further analyzed to make a determination as to further explanations for the significantly high modulus strength, high tenacity, and other results noted above. As well, high temperature shrinkage rates were studied in relation to such inventive fibers. 
     As noted above, the actual appearance of the inventive fibers, under Scanning Electron Microscopy (SEM), at least, is unique for synthetic fibers, let alone for polyolefin or polypropylene types. As presented in  FIG. 5 , the microphotograph image shows clear striations visible externally and in relatively uniform repetitive formation throughout the inventive fibers. Notable also in this photomicrograph are significant numbers of voids. With transparent fibers, such internally present voids (a/k/a cracks) can be clearly viewed from this perspective. As discussed previously, such voids apparently cause the low density measurements exhibited by such inventive fibers. As measured by the Brunauer, Eller and Teller method (BET), the presence of such a significant number of voids results in an unusually high surface area (roughly 1.5 m 2 /g) which is itself about eighteen times higher than would be expected from a void-free fiber of equal diameter and customary 0.93 g/cm 3  density. 
       FIG. 6  shows two different cross section SEM photomicrographs of an inventive fiber (Example JJ, again) and the presence of a network of interconnected channels throughout the entire fiber. A large number of such voids are clearly present (thus, again, causing the apparent reduction in overall fiber density with increased surface area) and it would be expected that that such cracks would not impart anything but a weakened fiber structure. Of great interest, then, was trying to understand how such internal and surface area-increasing voids would not lead to a weakening, rather than the resultant strengthening of the fiber, particularly to levels of modulus strength in excess of 100 g/d (˜8 GPa). 
       FIG. 7  provided a very surprising result in terms of the internal fiber structure from a cross-sectional view; clearly the striations present on the external surface of the fiber (such as seen in  FIG. 5 ) are also present internally and, again, in substantially uniform repetitive formation (in this instance, measured at roughly 1 micron apart throughout the length of the viewed portion of the fiber). Under analysis by Atomic Force Microscopy (AFM), it was noted that such striations do not simply exist and appear within the transparent fibers, but such phenomena actually extend outwardly from the fiber surface as well (from about 100 to 300 nm in distance therefrom). Additionally,  FIG. 7  intervals of roughly 1 micron distance between the striations (on average, apparently). 
     Within both  FIGS. 7 and 8 , the presence of the aforementioned voids is noticeable and distinct, both in number and direction (longitudinal to the fiber direction). These voids are within low intensity crystalline regions of the fiber, indicating, it is believed, without relying upon any specific scientific theory, that such void regions comprise extended-chain microfibrillar structures and the voids propagate between adjacent microfibrils throughout the entire fiber itself. Such microfibrils are clearly seen in  FIG. 7 , as well as such adjacent voids. It is further believed, again, without relying upon any specific scientific theory, that the high intensity regions of crystalline formation, notably the striations discussed previously, provide a mechanism for preventing further crack propagation within the fiber structure. In essence, the apparent disk-shaped (more pointedly, substantially disk-shaped) striations (the disk-like appearance is extrapolated from the cross-section view in  FIG. 7 , at least, as it appears that such striations are present throughout the entire fiber in the repeating formations as noted above. As this is a substantially round fiber, it is noted that the results would be expected in like fashion if the fiber were of different geometrical shape), being of high intensity crystalline regions, and spaced in a substantial uniform periodic formation, provide a resistance to crack propagation within such high intensity regions. As such, it is theorized that these unique striations, being present substantially (at least) throughout the inventive fiber in periodic form and in substantially disk-shaped configuration impart the necessary prevention of further void/crack formation within the inventive fiber, thereby allowing for the reduction in density, but with simultaneous increase in overall fiber strength. To date, such an appearance within a synthetic multifilament fiber, not to mention a result of a reduced density with very high modulus strength, has not been available. 
     Furthermore, the microfibrils ( FIG. 7 , at least) appear to be present throughout the high and low intensity crystalline regions of the inventive fibers as well. Such microfibrils have been measured to exhibit diameters within an approximate range of from 30 to 80 nm. Such a result is noted in  FIG. 8 , particularly with the clear distinction between the repeated striations (that extend throughout the fiber in some places, but clearly provide a crack prevention mechanism, at the very least, within the internal regions of the inventive fiber). The connections between adjacent microfibrils most likely lend themselves to the crack resistant properties of the inventive fibers as well as the presence of the striations noted above. It may be possible that the striations are actually the result of highly crystalline regions of crystalline bridges, possibly in the form of chain-folded lamellae, wherein the microfibrils are manipulated during the high drawing procedure with the subsequent cooling and heat-setting. In any event, it is evident that the cracks/voids within the inventive fiber are present within low intensity crystalline regions and the striations themselves are distinctly high intensity regions. In such a configuration, the lack of interfering amorphous regions within the inventive fiber lends itself to the resultant SAXS and WAXS measurements noted above in that the resultant values for each analysis comports with the theoretical arrangement of microfibrils, voids, and striations as put forth herein. 
     Further analysis in terms of other possible microstructures within the inventive fiber were undertaken as well.  FIG. 9  provides a 4,000× magnification of a cross-section of such a fiber (Example JJ, as above) and yields even more unexpected results. Most notably very small “cross-linking” constituents are clearly viewed within the void spaces of such a fiber. These constituents are referred to here as “nanofilament bridges” due to their noticeably microscopic size (nanoscopic, as it were) and the clear appearance that such constituents are present in substantially perpendicular relation to the voids and adjacent microfibrils (that run in the fiber&#39;s longitudinal direction, in essence).  FIG. 10  provides an even closer view of such nanofilament bridges as they appear in relatively high number throughout the voids of the inventive fiber. Such a resultant configuration has never been seen within synthetic fibers, much less polyolefin or, further, polypropylene, fibers. Although it is not possible to determine if such nanofilament bridges contribute to the overall high modulus strength of the inventive fibers, the appearance of such constituents is certainly unique to polyolefin fibers, at least. Without intending to be bound to any specific scientific theory, again, it is surmised that such nanofilament bridges would provide some degree of modulus strength impartation by reducing the propensity of the adjacent microfibrils from moving in a fashion that would permit notching of surface deformations and thus rupture of the microfibrils during tensioning. 
     Such a potential rationale for nanofilament bridge contribution is possible for a number of reasons. Importantly, however, the actual tensile failure potential for these inventive fibers (exhibiting modulus strengths of at least 40 g/d, preferably at least 100 g/d) appears to rely primarily on axial splitting, rather than, as noted above, fiber fracturing through notching, stress concentration and elongation thereafter leading to catastrophic failure. Typical polyolefin fibers exhibit a lack of dimensional stability once a surface deformation is present. Once such a flaw exists, as noted above, the continued stresses on the subject fiber invariably lead to a relatively clean break between distinct retained fiber portions (i.e., a cylindrical fiber is split into two separate cylindrical fibers). 
     To the contrary, with the highly oriented crystalline fibers of the invention, the capability of generating surface deformations that lead to ductile fracture are drastically reduced. In actuality, the failure of such fibers is more easily accomplished through axially applied shear stresses as opposed to notching.  FIG. 11  shows axially split inventive fibers after tensile loading has been applied to the breaking point in relation to such shear stresses. The typical breakage possibilities are difficult to create with such fibers. Such shear stresses apparently function to create fiber fracture due to the eventual excessive shear application that overcomes the cohesive forces between the polyolefin molecules within the fiber. At that point, which is well above a level of typical lower density polyolefin fibers, on par with polyaramid and/or ultra-high molecular weight polyethylene ethylene, for example, failure mechanism would be caused by the ability of cracks/voids to propagate and reach the fiber surface, thereby causing rupture. Again, as the level of shear stresses necessary to reach this result is extremely high, the capability of such inventive fibers to withstand typical fracture mechanisms and fail upon application of incredibly high shear stresses provides a highly unique low density polyolefin fiber, the likes of which there has been nothing heretofore provide the industry. 
     The utilization of such a unique synthetic fiber has been discussed above. In addition to the modulus strength (high), elongation measurements (very low), surface area (very high) and overall measured density (very low), high temperature dimensional stability was also analyzed. Thermal shrinkage was measured by placing a fiber of set length within a hot air oven and monitoring the potential length reduction as the temperature is gradually increased. Conventional spun-drawn polypropylene multifilament fibers typically exhibit a shrinkage rate of about 30% at a temperature of 150° C. As seen in  FIG. 12 , the inventive polypropylene melt-spun/drawn multifilament fiber (Example JJ) exhibits a shrinkage rate far below that level (less than 5%) for that temperature. In fact, at 70° C., the inventive fiber shows negligible, if any, shrinkage characteristics. In comparison, the literature regarding SPECTRA® ultra high molecular weight polyethylene fibers indicates shrinkage rates of 23% for the 900 series and 9% for the 1000 series, at 143° C. 
     The axial coefficient of thermal expansion for the inventive fiber (Example JJ, at least) is plotted in  FIG. 13 . An initially static plateau exists for an exceedingly large range of temperatures, with a relatively minor slope effect downward for another large range of temperatures, with a final rapid drop off once the temperature exceeds .about 120° C. Such a coefficient signature is, as with everything else described above, unique to the inventive polyolefin fiber produced through the specific melt spun-drawn method described herein. 
     It will be appreciated that the foregoing examples, given for purposes of illustration, are not to be construed as limiting the scope of this invention. Although only a few exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention that is defined in the following claims and all equivalents thereto. Further, it is recognized that many embodiments may be conceived that do not achieve all of the advantages of some embodiments, yet the absence of a particular advantage shall not be construed to necessarily mean that such an embodiment is outside the scope of the present invention.