Ultra-fine denier UHMW PE fiber

Abstract

Provided are polyethylene compositions and finish-free ultra-fine denier ultra-high molecular weight polyethylene (UHMW PE) fibers and tapes made therefrom that can be used in medical internal body applications.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of co-pending U.S. Provisional Patent Application No. 63 / 291,308, filed December 17, 2021, the disclosure of which is incorporated by reference herein in its entirety.

[0002] Field of the Invention The present disclosure relates to improved polyethylene compositions and finish-free, ultra-fine denier, ultra-high molecular weight polyethylene (UHMW PE) fibers and tapes made therefrom that can be used in medical internal body applications, and processes for making the same. [Background technology]

[0003] Multifilament polyolefin fibers have been produced that have high tensile properties such as toughness and tensile modulus. Such fibers have been known in the past to be useful in applications requiring impact absorption and ballistic resistance, such as bulletproof vests and sports equipment, such as kayaks, boats, fishing lines, and ropes. Such high strength polyolefin fibers can also be used in medical internal applications such as sutures in cardiovascular and orthopedic surgery. In cardiovascular applications, it is desirable for the fibers to be as thin as practical, and gel-spun ultra-high molecular weight polyethylene fibers can provide the desired high strength in combination with very fine diameters (low denier). High strength UHMW PE fibers have been commercially available for decades, but ultra-fine denier fibers have only recently become available, and the commercial processes used to make heavier denier UHMW PE fibers are not practical for making ultra-fine denier fibers.

[0004] Ultra-high molecular weight polyolefins include polyethylenes having a molecular weight of at least about 500,000 g / mol. However, it should be understood that all references herein to the term "ultra-high" with respect to the molecular weight of the polyolefins or polyethylenes of the present disclosure are also not intended to be limiting at the maximum end of the polymer viscosity and / or polymer molecular weight. The term "ultra-high" is only intended to limit the useful polymers within the scope of the present disclosure at the minimum end of the polymer viscosity and / or polymer molecular weight to the extent that they can be processed into fibers. It should also be understood that while the processes described herein are most preferably applied to the processing of UHMW polyethylene, they are equally applicable to all other poly(alpha-olefins), i.e., UHMW PO polymers, including polypropylene and other types of polyethylene, such as low, medium, and high density polyethylenes.

[0005] Many different techniques are known for fabricating high tenacity filaments and fibers formed from such ultra-high molecular weight polyethylene polymers. For example, high tenacity polyethylene fibers can be made by spinning a solution containing ultra-high molecular weight polyethylene. Ultra-high molecular weight polyethylene particles are mixed with a suitable solvent, whereby the particles are swollen and dissolved by the solvent to form a solution. The solution is then extruded through a spinneret to form solution filaments, which are subsequently cooled to a gel state to form gel filaments, and the spinning solvent is then removed to form solvent-free (or substantially solvent-free) filaments. One or more of the solution filaments, gel filaments, and solvent-free filaments are stretched or drawn in one or more stages to a highly oriented state to improve their tensile properties. Generally, such filaments are known as "gel-spun" polyethylene filaments. Multifilament gel-spun ultra-high molecular weight polyethylene fibers are manufactured, for example, by Honeywell International Inc. of Charlotte, North Carolina.

[0006] Various methods for forming gel spun polyethylene filaments are described, for example, in U.S. Pat. Nos. 4,413,110; 4,536,536; 4,551,296; 4,663,101; 5,006,390; 5,032,338; 5,578,374; 5,736,244; 5,741,451; 5,958,582; 5,972,498; 6,448,359; 6,746,971; and Nos. 5, 6,969,553, 7,078,099, 7,344,668, 7,846,363, 8,361,366, 8,444,898, 8,506,864, 8,747,715, 8,889,049, 9,169,581, 9,365,953, and 9,556,537, all of which are incorporated by reference herein to the extent consistent therewith. For example, U.S. Patent Nos. 4,413,110, 4,663,101 and 5,736,244 describe stretching a formed polyethylene gel precursor and a low porosity xerogel obtained from the polyethylene gel precursor to form a high tenacity, high modulus fiber. U.S. Patent Nos. 5,578,374 and 5,741,451 describe post-stretching of polyethylene fibers that have already been oriented by stretching at a specific temperature and stretching rate. U.S. Patent No. 6,746,975 describes a high tenacity, high modulus multifilament yarn formed from a polyethylene solution via extrusion through a multi-orifice spinneret to form a fluid product. The fluid product is gelled, stretched and formed into a xerogel. The xerogel is then subjected to a two-stage stretching to form the desired multifilament yarn. No. 7,078,099 describes drawn gel-spun multifilament yarns with increased molecular structure extension. The yarns are produced by an improved manufacturing process and drawn under special conditions to obtain multifilament yarns with high molecular weight and crystalline order. No. 7,344,668 describes a process for drawing essentially diluent-free gel-spun polyethylene multifilament yarns in a forced convection air orb and the drawn yarns produced thereby.The process conditions of draw ratio, elongation rate, residence time, oven length and feed rate are selected in specific relationships to each other to achieve improved efficiency and productivity.Finally, U.S. Patent No. 8,444,898 describes a process for the continuous preparation of solutions of ultra-high molecular weight polyethylene with improved homogeneity that produces strong materials at high throughputs.

[0007] While each of the above fiber manufacturing processes is suitable for the fabrication of multifilament UHMW PE fibers, each process utilizes a manufacturing process that is not ideal for producing fibers intended for use in human medical applications. In such medical internal body applications, biocompatibility is an important factor for the use of fibers. However, the gel spinning solvents used in typical fiber gel spinning processes such as those described above are often toxic to humans and are not suitable for in vivo use. In such processes, it is known to remove the spinning solvent from the fiber as part of the complete spinning process. However, since the solvent typically depletes ozone and is therefore harmful to the environment, great care must be taken when extracting or evaporating the solvent from the fiber and also when subsequently recycling or disposing of the solvent. Thus, there is a need in the art for an improved gel spinning process that utilizes solvents that are more environmentally acceptable and non-toxic to humans and animals.

[0008] In addition, as described in the above-referenced patents, spin finishes, which are surface finishes typically applied to fibers during manufacturing, are conventionally known to generally not be biocompatible or to be toxic to mammals. As a result, spin finishes must be removed from the fibers, such as by washing or extraction, before they can be used in medical applications. This adds additional complexity and cost to the fiber manufacturing process. Thus, there is a need in the art for a fiber manufacturing process that does not require the use of spin finishes. The present disclosure provides a solution to both of these needs in the art. Summary of the Invention

[0009] The present disclosure provides compositions and articles comprising a mixture of polyethylene and trimethylbenzene ("trimethylbenzene, TMB"), which is a very effective solvent for polyethylene, especially at high mixture temperatures. Trimethylbenzene poses lower health hazards to both mammals and the environment compared to other solvents, and its effectiveness and volatility as a solvent for polyethylene allows for improvements in fiber manufacturing processes to achieve high purity fibers, i.e., fibers that have ultra-low residual solvent content and do not require the use of spin finishes to be effectively processed. Polyethylene gels formed using trimethylbenzene solvent have been found to be of such high quality that spin finishes can be avoided, thereby allowing gel spinning of filaments with very high tensile strengths at extremely small filament deniers without requiring substantial in-line drawing of the filaments during the fabrication process to achieve such high tensile strengths, as is conventionally done in the art. Instead, most or all of the filament drawing is performed in an offline post-drawing operation. Eliminating most or all of the in-line drawing allows for the production of fibers at lower line speeds and the application of uniformly high fiber tensions maintained along the entire length of the fiber line. This effectively avoids static build-up during production, so that no spin finish is needed to combat static build-up. This is important because spin finishes can be toxic to mammals, and fibers with finishes cannot be used in vivo. The potential for static build-up and entanglement is minimal in off-line post-drawing operations. The volatility of trimethylbenzene also allows it to be evaporated from the filaments without the need for extraction with a second solvent, and the ultra-fine filament denier achievable with this process allows for more rapid and efficient solvent evaporation due to the higher surface area to volume ratio of the filaments. As a result, the fiber is suitable for use in mammals in vivo and is produced with greater commercial efficiency and environmental safety.

[0010] In particular, the present disclosure provides a composition comprising a mixture of polyethylene and trimethylbenzene.

[0011] The present disclosure also provides a process for preparing a polyethylene fibrous product, comprising: a) forming a solution of polyethylene having a weight average molecular weight of at least 500,000 g / mol in a trimethylbenzene solvent; b) spinning the solution through a spinneret to form one or more solution filaments; c) cooling the solution filaments, whereby one or more of the solution filaments are converted into gel filaments, the gel filaments comprising greater than 1% solvent by weight of the solvent-added polyethylene; d) evaporating the solvent from the gel filaments to form dry filaments, wherein the evaporation continues until the solvent concentration in the dry filaments is less than 1% by weight of the solvent plus polyethylene. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a side perspective schematic diagram of a process for forming and drawing a fiber without the application of a spin finish. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The polyethylene-trimethylbenzene compositions provided herein are particularly intended for the fabrication of high strength medical grade fibers that can be used in vivo in the human and animal body, although the intended end use is not intended to be narrowly limiting and the compositions may be used in the fabrication of fibers for any other end use including composites and composite armor, as well as any other non-textile, non-armor applications that may be desired.

[0014] As used herein, a "fiber" is a long strand of material, such as a strand of polymeric material, whose length dimension is much greater than the transverse dimensions of width and thickness. Fibers are preferably long, continuous (but of clearly defined length) strands, as distinguished from short sections of strands referred to in the art as "staple" or "staple fibers". A "strand" by conventional definition is an elongated body, such as a thread or fiber. The cross-section of a fiber for use herein may vary widely and may be circular, flat, or oval in cross-section. A strand may also be of irregular or regular multi-lobed cross-section, with one or more regular or irregular lobes protruding from the linear or longitudinal axis of the filament. Thus, the term "fiber" includes filaments, ribbons, strips, etc., with regular or irregular cross-sections. Fibers with a substantially circular cross-section are preferred.

[0015] A single fiber may be formed from only one filament or from multiple filaments. A fiber formed from only one filament is referred to herein as either a "single filament" fiber or a "monofilament" fiber, and a fiber formed from multiple filaments is referred to herein as a "multifilament" fiber. A multifilament fiber, as defined herein, preferably contains 2 to about 3000 filaments, more preferably 2 to 500 filaments, even more preferably 4 to 500 filaments, even more preferably 6 to 500 filaments, even more preferably about 6 filaments to about 250 filaments, and most preferably about 6 to about 125 filaments. Multifilament fibers are also often referred to in the art as fiber bundles or bundles of filaments. As used herein, the term "yarn" is defined as a single strand of multiple filaments and is used interchangeably with "multifilament fiber." The filaments forming the yarn are typically twisted together.

[0016] It is generally known that a process known as "gel spinning", also referred to as "solution spinning", involving gel / solution spinning of ultra-high molecular weight polyolefins (UHMW PO), particularly ultra-high molecular weight polyethylene (UHMW PE), produces very high strength filaments and fibers with excellent tensile properties. This method is used to produce high strength polyolefins because the high molecular weight and corresponding high polymer intrinsic viscosity make traditional polymer extrusion techniques difficult for producing very thin filaments / fibers. In a conventional gel spinning process, a solution of polyethylene and spinning solvent is formed, the solution is subsequently extruded through a multi-orifice spinneret to form solution filaments, the solution filaments are cooled into gel filaments, and the solvent is then evaporated or extracted to form solid dry (or substantially dry) filaments. These dry filaments are gathered into bundles, referred to in the art as either fibers or yarns. The fibers / yarns are then typically stretched (drawn) to their maximum draw capacity to increase their toughness, and at least one of the solution filaments, gel filaments, and dry filaments are stretched. In this process for forming polyethylene fibers, the polyethylene-solvent solution is generally drawn through the following series of steps: 1) forming a slurry, i.e., a dispersion (or suspension) of solid polyethylene polymer particles (such as UHMW PE particles) in a solvent capable of dissolving the polymer; 2) heating the slurry to melt the polymer and form a liquid mixture under conditions of vigorous distributive and dispersive mixing, thereby reducing the domain sizes of the molten polymer and solvent in the mixture to microscopic dimensions; 3) allowing sufficient time for diffusion of the solvent into the polymer and diffusion of the polymer into the solvent to occur, thereby forming a solution.

[0017] The particle size and particle size distribution of the particulate polyethylene polymer can affect the degree to which the polyethylene polymer dissolves in the spinning solvent during the formation of the gel spun solution. It is also desirable that the polyethylene polymer is completely dissolved in the solution and thoroughly mixed so that the solution is most preferably homogeneous. Thus, in one preferred example, polyethylene particles are provided having an average particle size of about 100 microns (μm) to about 200 μm. In such an example, it is preferred that up to about 90%, or at least about 90%, of the polyethylene particles have a particle size that is within 40 μm of the average polyethylene particle size. In other words, up to about 90%, or at least about 90% of the polyethylene particles have a particle size equal to plus or minus 40 μm of the average particle size. In another example, about 75% to about 100% by weight of the polyethylene particles utilized can have a particle size of about 100 μm to about 400 μm, and preferably about 85% to about 100% by weight of the polyethylene particles have a particle size of about 120 μm to 350 μm. In addition, the particle size can be distributed in a substantially Gaussian curve with particle size centered at about 125-200 μm. It is also preferred that about 75% to about 100% by weight of the polyethylene particles utilized are UHMW PE particles having a weight average molecular weight of about 500,000 to about 7,000,000, more preferably about 700,000 to about 5,000,000. Preferably, the UHMW PE starting material has a ratio of weight average molecular weight to number average molecular weight (M w / M n ) is 6 or less, more preferably 5 or less, even more preferably 4 or less, even more preferably 3 or less, even more preferably 2 or less, and even more preferably M w / M n The ratio is approximately 1.

[0018] Preferably, the polyethylene is a UHMW PE polymer starting material having less than about 5 side groups per 1000 carbon atoms, more preferably less than about 2 side groups per 1000 carbon atoms, even more preferably less than about 1 side group per 1000 carbon atoms, and most preferably less than about 0.5 side groups per 1000 carbon atoms. 10These may include, but are not limited to, alkyl groups, vinyl terminated alkyl groups, norbornene, halogen atoms, carbonyl, hydroxyl, epoxide, and carboxyl.

[0019] The polyethylene polymer, or mixture of polyethylene and solvent (slurry or liquid mixture or solution), may contain small amounts, generally less than about 5% by weight, preferably about 1% by weight or less, of additives such as antioxidants, heat stabilizers, colorants, flow promoters, solvents, etc. Small amounts of other additives may also be optionally added to the polymer and solvent mixture. For example, processing aids such as mineral oil may be added in small amounts (about 1,000 PPM to about 9,000 PPM) if desired.

[0020] Generally, higher fiber tensile properties are obtained from polymers having higher intrinsic viscosity. The intrinsic viscosity of a polymer is a measure of the molecular weight of the polymer. In this regard, the UHMW PE polymers selected for use in the gel spinning process of the present invention preferably have an intrinsic viscosity of at least about 15 dl / g, preferably greater than about 21 dl / g in decalin at 135°C. The UHME PE polymers preferably have an intrinsic viscosity of about 21 dl / g to about 100 dl / g, more preferably about 21 dl / g to about 45 dl / g. As used herein, all reference intrinsic viscosities (IV) are measured in decalin at 135°C according to the technique of ASTM D1601. Generally, higher molecular weight polymers have higher intrinsic viscosity and can form higher fiber toughness than lower molecular weight polymers. Suitable UHMW PE polymers for use herein that satisfy all of the above properties are commercially available.

[0021] The spinning solvent selected for use in the gel spinning process of the present disclosure comprises, consists of, or consists essentially of trimethylbenzene, such that the compositions of the present disclosure comprise, consist of, or consist essentially of polyethylene and trimethylbenzene, which may be a combination, such as a mixture or solution, of polyethylene and trimethylbenzene, which combination may be homogeneous or heterogeneous. Trimethylbenzene is available in three isomers: 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, and 1,3,5-trimethylbenzene. Each of these three forms is an acceptable solvent for polyethylene. Of these, 1,2,4-trimethylbenzene is the most desirable due to its optimal biocompatibility, and in preferred embodiments of the present disclosure, the spinning solvent comprises either a mixture of 1,2,4-trimethylbenzene with one or both of the other isomers, but most preferably the spinning solvent consists essentially of 1,2,4-trimethylbenzene. Each of these forms of trimethylbenzene is commercially available. Most preferably, 100% of the spin solvent consists of one or more of the isomeric forms of trimethylbenzene, although other non-trimethylbenzene solvent types may be present in minor amounts, which, if present, are less than 1% by weight of the total solvent weight.

[0022] An exemplary process for forming the fibers of the present disclosure is shown in FIG. 1. The components of the slurry can be provided in any suitable manner. For example, the slurry can be formed by combining a polyethylene polymer (e.g., UHME PE) and a spinning solvent in an agitated mixing tank 10, followed by providing the combined polymer and spinning solvent to a feed hopper 12, which then feeds the mixture to an extruder 14. The extruder 14 can be heated or unheated. The polyethylene particles and solvent can be continuously fed to the mixing tank 10 with the slurry formed (or slurry formation initiated) in the tank 10, which is then discharged to the hopper 12. The mixing tank 10 can be optionally heated, and the slurry can be formed at a temperature below the temperature at which the polyethylene polymer melts and thus below the temperature at which the polyethylene completely dissolves in the spinning solvent. For example, the slurry can be formed at room temperature or can be heated in the tank 10 to a temperature of up to about 110° C. The temperature and residence time of the slurry in the mixing tank are optionally such that the polyethylene particles absorb at least 5% by weight of the solvent at a temperature below the temperature at which the polyethylene polymer would dissolve, as determined by one of ordinary skill in the art. Preferably, the slurry is at room temperature (20°C to 22°C) upon exiting the mixing tank. Alternatively, it may be heated to a temperature of about 40°C to about 140°C.

[0023] Several alternative modes of feeding the extruder 14 are contemplated. For example, the polyethylene-TMB slurry formed in the mixing tank 10 may be fed to the feed hopper 12 under no pressure, or the feed hopper 12 may be sealed and pressurized such that the slurry enters the sealed hopper 12 of the extruder 14 under a positive pressure of at least about 20 kPa. The feed pressure enhances the conveying capacity of the extruder 14. However, most preferably, no pressure is applied as the slurry is fed to the feed hopper 12. In an alternative embodiment, the slurry may be formed in the extruder 14. In this case, the polyethylene particles may be fed to an open feed hopper 12 and the solvent is not added at the hopper 12 but is pumped directly into the extruder 14, for example, one or two barrel sections downstream of the extruder 14. In yet another alternative feed mode, a concentrated slurry is formed in mixing tank 10, the concentrated slurry is then transferred to hopper 12, and then a pure solvent stream preheated to a temperature above the polymer melt temperature is dosed to extruder 14, for example at one or more zones downstream of extruder 14.

[0024] The extruder 14 to which the slurry is provided can be any suitable extruder, including, for example, a single screw extruder or a twin screw extruder, such as a non-intermeshing twin screw extruder or an intermeshing co-rotating twin screw extruder. Conventional equipment, including but not limited to a Banbury mixer, are also suitable alternatives to conventional extruders. Preferably, the extruder is an intermeshing co-rotating twin screw extruder, and the screw elements of the intermeshing co-rotating twin screw extruder are preferably forward conveying elements and preferably do not include backmixing or kneading segments.

[0025] Preferably, the slurry upon entering the extruder 14 is at a temperature below the melting point of the particular polyethylene polymer and is then preferably heated in the extruder 14 to a temperature above the melting point of the polyethylene polymer. Thus, a preferred gel spinning process of the present disclosure includes extruding the slurry in the extruder 14 to form a mixture of molten polyethylene polymer (e.g., UHMW PE) and spinning solvent inside the extruder 14, where the molten polyethylene at least partially mixes with the solvent in the extruder 14. Thus, the mixture of polyethylene polymer and spinning solvent formed in the extruder can be referred to as a liquid mixture of molten polyethylene polymer and spinning solvent. The temperature at which the liquid mixture of molten polyethylene polymer and spinning solvent is formed in the extruder can be about 120°C to about 165°C, preferably about 125°C to about 155°C, more preferably about 130°C to about 145°C. The lower temperature minimizes polymer degradation.

[0026] One example of a method for processing a polyethylene slurry through an extruder is described in commonly owned U.S. Patent No. 8,444,898, which describes processing the slurry through an extruder to form a liquid mixture of molten UHMW PE polymer and spinning solvent in the extruder, but the liquid mixture is rapidly discharged from the extruder before the solution is completely formed. This patent specifically describes first forming the UHMW PE powder and solvent into a slurry in the extruder, and then pumping the slurry at a rate of at least 2.0 D / min. 2 They teach that polymer degradation can be minimized by processing the polymer through an extruder at a throughput rate of 100 g / min (g / min, where D is the extruder screw diameter in cm) to form a liquid mixture, which is then converted to a solution in a heated vessel rather than in the extruder, such that the heated vessel exerts very little, if any, shear stress on the mixture.

[0027] This is also a preferred process of the present disclosure. Although the formation of the solution may begin in the extruder such that the polyethylene is at least partially dissolved in the trimethylbenzene solvent / solvent mixture while in the extruder, the complete formation of the liquid mixture into a solution in which the polyethylene is completely dissolved in the trimethylbenzene solvent / solvent mixture, preferably forming a homogeneous solution, is performed in a heated vessel located downstream from the extruder, which exerts less stress on the mixture than the extruder. This reduces thermal and shear degradation of the polymer, preserves the molecular weight of the polymer, and allows for the fabrication of stronger fibers (or other articles). In this regard, "partially" dissolved means that at least some, but not all, of the polyethylene is dissolved in the solvent / solvent mixture, including from greater than 0% to less than 100% by weight of the polyethylene, and "completely" dissolved means that 100% of the polyethylene is dissolved in the solvent / solvent mixture. Preferably, 0.1% to about 50% by weight of the polyethylene is dissolved while the mixture of polyethylene and solvent is in the extruder, more preferably 0.1% to about 33% by weight of the polyethylene is dissolved in the extruder, even more preferably about 0.1% to about 25% by weight of the polyethylene is dissolved in the extruder, and even more preferably 0.1% to about 10% by weight of the polyethylene is dissolved in the extruder. Thus, in an exemplary composition of the present disclosure in which the polyethylene is partially but not completely dissolved in a liquid solvent such as trimethylbenzene (e.g., 1,2,4-trimethylbenzene liquid solvent), the composition includes some dissolved polyethylene and some undissolved solid polyethylene. In this regard, such exemplary compositions having only partially dissolved polyethylene include from 50% to about 99.9% by weight solid polyethylene, more preferably from 67% to about 99.9% by weight solid polyethylene, even more preferably from about 75% to about 99.9% by weight polyethylene, and even more preferably from 90% to about 99.9% by weight polyethylene, with the remainder of the composition including the dissolved polyethylene and optionally some solvent not yet mixed with the polyethylene.

[0028] Referring again to Figure 1, once the liquid mixture is formed in the extruder 14, the liquid mixture (and / or the partially formed solution) is then rapidly transferred to a heated vessel 16 where the remaining time necessary for the solvent and polymer to completely diffuse into one another to form a uniform, homogenous solution is provided. Preferably, the average residence time of the mixture in the extruder is less than the residence time in the heated vessel, and most preferably, the average residence time of the mixture in the extruder is less than half the residence time of the mixture in the heated vessel. For example, the residence time of the liquid mixture in the extruder can be from about 1 minute to about 60 minutes, preferably from about 3 minutes to about 30 minutes.

[0029] The liquid mixture of polyethylene and spinning solvent leaving the extruder can be passed to a heated vessel via a pump, such as a positive displacement pump. The vessel is preferably a heated pipe, which may be a straight length of pipe, or it may have bends, or it may be a helical coil. It may include sections of different lengths and diameters selected such that the pressure drop through the pipe is not excessive. The polymer / solvent mixture entering the pipe is typically highly pseudoplastic and viscous, and therefore the heated pipe preferably contains one or more static mixers to redistribute the flow at intervals across the pipe cross section and / or to provide additional dispersion. The heated vessel is preferably maintained at a temperature of at least about 130°C, preferably from about 130°C to about 165°C, and most preferably from about 135°C to about 155°C. The heated vessel can have a volume sufficient to provide an average residence time of the liquid mixture in the heated vessel to form a solution of the polyethylene polymer with the solvent. For example, the residence time of the liquid mixture in the heated vessel can be from about 2 minutes to about 120 minutes, preferably from about 6 minutes to about 60 minutes. In alternative examples, the arrangement and utilization of the heated vessel and extruder in forming the solution of polyethylene and spinning solvent can be reversed. In such examples, a liquid mixture of polyethylene and spinning solvent can be formed in the heated vessel and then passed through the extruder to form a solution comprising polyethylene and spinning solvent, or the polyethylene-solvent mixture can be transferred from the extruder to a second heated vessel to complete the formation of the homogenous solution.

[0030] Each of the slurry, liquid mixture, and solution may contain polyethylene in an amount (concentration) of about 1% to about 50% by weight of the solution, preferably about 1% to about 30% by weight of the solution, more preferably about 2% to about 20% by weight of the solution, and even more preferably about 3% to about 10% by weight of the solution. In the most preferred embodiment where the solution is spun into filaments, the solution contains polyethylene (preferably UHMW PE) in an amount of 6.5% or less by weight of the solution (i.e., weight of dissolved polymer plus weight of solvent), more specifically 5.0% or less by weight of the solution, or even more preferably 4.0% or less by weight of the solution. Most preferably, the solution contains polyethylene in an amount of greater than 3% to less than 6.5% by weight of the solution, more specifically greater than 3% to less than 5% by weight, based on the weight of polyethylene polymer plus weight of solvent.

[0031] After the solution is formed, processing the solution into filaments conventionally involves the following steps: 4) passing the solution thus formed through a spinneret to form solution filaments; 5) passing the solution filament through a short gas space and through a liquid quench bath, whereby the solution filament is rapidly cooled to form a gel filament; 6) removing the solvent from the gel filaments to form solid filaments; 7) stretching at least one of the solution filaments, the gel filaments, and the solid filaments in one or more stages.

[0032] As shown in FIG. 1, a removable spinneret 21 is attached to the spinneret 20. The spinneret 20 distributes the polyethylene-TMB solution evenly to the spinneret 21. The process of providing the solution of polyethylene polymer and spinning solvent from the heated vessel 16 to the spinneret 21 can include passing the solution through a metering pump 18, which can be a gear pump. As the solution passes through the spinneret, it is extruded into a plurality of solution filaments 100, which can also be referred to as multifilament solution fibers, as conventionally known in the art. The spinneret can form a solution fiber having any suitable number of filaments, depending on the number of spinnerets it contains. In one example, the spinneret can have about 2 spinnerets to about 3000 spinnerets, and thus the solution fiber contains about 2 filaments to about 3000 filaments. Preferably, the spinneret can have about 6 spinnerets to about 500 spinnerets, and the solution fiber contains about 6 filaments to about 500 filaments. The spinhole may have a conical entrance, the cone having an included angle of about 15 degrees to about 75 degrees. Preferably, the included angle is about 30 degrees to about 60 degrees. In addition, following the conical entrance, the spinhole may have a straight bore capillary that extends to the exit of the spinhole. The capillary may have a length to diameter ratio of about 10 to about 100, more preferably about 15 to about 40.

[0033] As the solution filaments 100 flow out of the spinneret 21, they are passed through a liquid quench bath held in a quench tank 22, where they are rapidly cooled to form gel filaments 102. The liquid in the quench bath is preferably selected from the group consisting of water, ethylene glycol, ethanol, isopropanol, water-soluble antifreeze, and mixtures thereof. Preferably, the liquid quench bath temperature is about -35°C to about 35°C. A small gas space (i.e., gap) exists between the end of the spinneret and the quench bath, and as the solution filaments pass through this gas space, the solution filaments are susceptible to oxidation if the space contains oxygen, such as when the space is filled with air. Because oxidation of the solution filaments can reduce the molecular weight of the polymer and thereby reduce the fiber tensile properties, it is known to fill the gas space with another inert gas, such as nitrogen or argon, to minimize degradation of the polymer. Also, limiting the length of the gas space also minimizes the likelihood of oxidation, especially when filling the gap with an inert gas is not practical. The length of the gas space between the spinneret and the surface of the liquid quench bath is preferably about 1.0 mm to about 100 mm, more preferably about 3.0 mm to about 30 mm. If the residence time of the solution thread in the gas space is less than about 1 second, the gas space may be filled with air, otherwise it is most preferred to fill the space with an inert gas.

[0034] Once the solution filaments 100 have cooled and converted to gel filaments 102, the trimethylbenzene spinning solvent (or solvent mixture) must be removed from the gel filaments 102. At this stage, the gel filaments contain at least 1% solvent by weight of the fiber and up to about 96% solvent by weight of the fiber. Thus, a gel composition is a polymer composition that still contains at least 1% solvent by weight, based on the weight of the solvent plus the weight of the polymer. Removal of trimethylbenzene is accomplished by drying, i.e., evaporation, according to techniques well known in the art. Because it is a volatile solvent, there is no need to extract it with a second solvent as is required with non-volatile solvents. Each of the three trimethylbenzene isomers has an atmospheric boiling point of about 165°C to 176°C (1,2,3-TMB: 176°C, 1,2,4-TMB: 169°C, 1,3,5-TMB: 165°C), which is higher than the melting point of ultra-high molecular weight polyethylene, which is approximately 130°C to 136°C, so it is preferable to evaporate the solvent at a temperature below 130°C, preferably below 100°C, or even at ambient room temperature (i.e., about 20°C to 22°C). Drying of the gel filaments 102 may be achieved by passing them through a chamber 26 (e.g., an oven) heated to a desired temperature that is high enough to evaporate the solvent in a reasonable time (as determined by one of skill in the art) but not so high that the filaments fuse together during drying, with the optimum drying temperature being the highest temperature that does not cause filament fusion during drying. This temperature depends on the solvent concentration in the gel fiber as well as the fiber speed and tension during drying. Alternatively, chamber 26 may contain hot plates 28 and 30 over which the gel filaments pass to induce evaporation of the solvent. Hot plates 28 and 30 may be heated to any desired temperature, and this method of drying the fibers is conventionally known in the art. Whether drying is performed in an oven or with a hot plate, the drying temperature is typically from about 50° C. to about 100° C. Most preferably, the drying temperature increases from about 60° C. to about 90° C. along the length of the drying path.

[0035] Removal of all or nearly all of the solvent forms dry fibers 104. The partially dried fibers may contain an amount of residual solvent less than about 5 weight percent based on the weight of the fiber plus any residual solvent, and preferably less than about 2 weight percent based on the weight of the fiber plus any residual solvent, while the dry fibers after the solvent evaporation process is completed contain less than about 1 weight percent solvent based on the weight of the fiber plus any residual solvent.

[0036] As shown in FIG. 1, the gel spinning process can include drawing (stretching) the solution filaments 100 (solution fibers) flowing out of the spinneret 21, the gel filaments 102 (gel fibers) formed in the quench bath, and the solid dry fibers 104 resulting from the evaporation of the spinning solvent. Drawing of the fibers is conventionally known in the art and is accomplished, for example, by passing the fibers over rolls at various stages of their life. In the embodiment shown in FIG. 1, the process includes unheated, non-driven guide rolls 32, 34, 36, 38, and 40, unheated driven stretching rolls 42 and 44, and a final driven winding roll 46, although this setup is merely exemplary and may be adjusted or customized by one skilled in the art to include more or fewer rolls. For example, the fibers can be wound onto a beam or one or more core tubes rather than onto rolls. Winding of the fibers can also be accomplished without or without imparting twist to the fibers. It should also be noted that the rolls shown in FIG. 1 are not necessarily drawn to scale.

[0037] 1 , solution filaments 100 flowing from spinneret 21 and quenched into gel filaments 102 are optionally drawn as gel filaments 102. These gel filaments 102 pass over a first guide roll 32 located within quench tank 22, and then from guide roll 32, the gel filaments 102 pass over a second guide roll 34 located outside quench tank 22. From there, the gel filaments 102 are transferred to drawing bench 24, which contains additional guide rolls 36 and 40 as well as first and second drawing rolls 42 and 44. In the embodiment of FIG. 1, the gel filaments 102 pass once around the first draw roll 42, then around the guide roll 36, then back around the first draw roll 42, then up and around the guide roll 38, then once around the second draw roll 44, then around the guide roll 40, then around the second draw roll 44 again, and finally wound up on the drive take-up roll 46. In this process, between the draw rolls 42 and 44, as shown in FIG. 1, the fibers pass through a contact drying zone 26, which may be a heated oven or may contain hot plates 28 and 30, over which the gel filaments pass to induce evaporation of the solvent as described above. Whether the drying zone 26 includes hot plates 28 and 30, or is an oven heated by other means, the gel fibers 102 are heated to any desired temperature below the melting temperature of the polyethylene polymer. These methods of drying the fibers (oven or hot plate drying techniques) are conventionally known in the art. The drying process may also include a means for venting the evaporated solvent (not shown in FIG. 1 ) from the atmosphere for disposal (e.g., in a thermal oxidizer) or recycling (e.g., by condensing the evaporated solvent back into a liquid for reuse). The means for venting the evaporated solvent from the atmosphere may include an exhaust fan with ducting between the fiber drying enclosure and the fan, and additional ducting after the fan for solvent vapor delivery to a disposal or recycling device.Upon completion of the drying process, the solvent is preferably completely removed to obtain dry, completely solvent-free filaments, i.e., dry, completely solvent-free fibers. In other embodiments, some residual solvent may remain in the fibers, but such residual solvent is still very low, i.e., less than 1% by weight of the fibers, more preferably less than 0.5% by weight of the fibers, or less than 0.25% by weight of the fibers, or less than 0.1% by weight of the fibers, whereas gel fibers that are not completely dried contain more than 1% solvent by weight of the polyethylene plus the weight of the solvent.

[0038] In a typical gel spinning process, polyethylene fibers are drawn in each of the solution fiber, gel fiber, and dry fiber states. The solution fibers 100 are drawn due to tension exerted on the spun filaments as they are continuously produced and wound as a continuous strand on the draw roll 42 toward the driven take-up roll 46. In a preferred embodiment of the present disclosure, the solution fibers 100 flowing out of the spinneret are drawn at a draw ratio of about 1.1:1 to about 30:1 to form drawn solution fibers. The elongation of the solution fibers in the gas space between the spinneret and the liquid quench bath is affected by the length of the gas space. A longer space may result in greater elongation of the solution filaments inside the space, so this variable may be controlled as desired if more or less elongation of the solution filaments is desired.

[0039] In a preferred embodiment, the gel fiber 102 is drawn in one or more stages at a first draw ratio DR1 of about 1.1:1 to about 30:1. Drawing the gel fiber 102 in one or more stages at the first draw ratio DR1 can be accomplished by passing the gel fiber through a set of rolls (rollers), such as guide rolls 36 and draw rolls 42, as shown in FIG. 1. Preferably, drawing the gel fiber 102 at the first draw ratio DR1 can be performed without applying heat to the fiber, and can be performed at a temperature of about 25° C. or less. Drawing the gel fiber 102 can also include drawing the gel fiber 102 at a second draw ratio DR2. Drawing the gel fiber 102 at the second draw ratio DR2 can also include simultaneously removing at least a portion of the spinning solvent from the gel fiber 102, such as in chamber 26 or by passing the fiber along hot plates 28 and / or 30, to form a dry fiber 104. Thus, the second drawing step DR2 may be performed in the chamber 26, the drawing bench 24, or both the chamber 26 and the drawing bench 24. Preferably, the gel fiber 102 is drawn at a second draw ratio DR2 of from about 1.5:1 to about 10:1, more preferably from about 2:1 to about 8:1, and most preferably from about 3:1 to about 6:1.

[0040] The gel spinning process can also include drawing the dry fibers 104 at a third draw ratio DR3 in at least one stage. Drawing the dry fibers 104 at the third draw ratio can be accomplished, for example, by passing the dry fibers 104 through a drawing bench 24. The third draw ratio can be from about 1.1:1 to about 3.0:1, more preferably less than about 1.5:1, and even more preferably from about 1.1:1 to about 1.5:1.

[0041] As shown in FIG. 1, drawing the gel fiber 102 and the dry fiber 104 with draw ratios DR1, DR2, and DR3 can be done in-line. In one example, the composite draw ratio of the gel fiber 102 and the dry fiber 104, DR1xDR2xDR3:1, which can be determined by multiplying DR1, DR2, and DR3 (DR1xDR2xDR3:1 or (DR1)(DR2)(DR3):1), can be at least about 5:1, preferably at least about 10:1, more preferably at least about 15:1, and most preferably at least about 20:1. Preferably, the dry fiber 104 is maximally drawn in-line until the final stage of drawing is at a draw ratio of less than about 1.2:1. Optionally, following the final stage of in-line drawing of the dry fiber 104, the fiber can be relaxed between about 0.5 percent of its length and about 5 percent of its length.

[0042] Preferably, stretching is performed on all three of the solution fibers 100 (solution filaments), gel fibers 102 (gel filaments), and solid dry fibers 104 (solid dry filaments). During fiber processing, stretching is performed on at least one of the solution fibers 100, gel fibers 102, and solid fibers 104 in one or more stages to a composite stretch ratio (draw ratio) of at least about 10:1, with preferably an in-line stretch of less than 1.5:1 being applied to the solid fibers 104 to form high strength multifilament polyethylene fibers. Additional post-drawing operations, including further drawing of the dry fibers 104, may be performed as described in commonly owned U.S. Patent Nos. 6,969,553, 7,370,395, 7,344,668, 8,361,366, 8,444,898, or 8,747,715, each of which is incorporated by reference herein to the extent compatible therewith.

[0043] As used herein, the terms "drawn" filaments / fibers or "drawn" filaments / fibers are known in the art and are also known in the art as "oriented" or "oriented" filaments / fibers or "stretched" or "elongated" filaments / fibers. These terms are used interchangeably herein. Also, as used herein, the term "draw ratio" refers to the ratio of the speeds of the drawing rolls used during the orientation process. Stretching solid filaments / fibers most commonly involves a post-drawing operation to increase the final yarn tenacity. See, for example, the co-owned U.S. patent referenced in the previous paragraph, which describes a post-drawing operation performed on partially oriented yarns / fibers to form highly oriented yarns / fibers of higher tenacity. Such post-drawing is performed offline as a separate process using a separate drawing device.

[0044] In an exemplary post-draw process, the dry fiber wound onto the driven take-up roll 46 may be unwound from the driven take-up roll 46 and drawn again, i.e., post-drawn, to a fourth draw ratio DR4 (off-line and not shown in FIG. 1) of about 1.1:1 to about 15:1 according to the process disclosed in U.S. Patent No. 9,365,953, which is incorporated herein by reference. In preferred embodiments, the post-draw draw ratio DR4 is from about 1.1:1 to about 9:1, or from about 1.5:1 to about 6.0:1, or from about 2.5:1 to about 5.5:1. Alternatively, the second post-draw may be conducted at a draw ratio of about 1.1:1 to 1.7:1, or about 1.1:1 to 1.6:1, or 1.1:1 to 1.5:1, or about 1.1:1 to about 1.4:1, or 1.1:1 to 1.3:1, or 1.1:1 to 1.2:1, preferably resulting in a highly oriented fiber product having a tenacity of at least about 30 g / denier, or about 35 g / denier or more, or about 40 g / denier or more, or about 45 g / denier or more.

[0045] The main purpose of drawing fibers, including the post-drawing process described above, is to increase their tensile strength, thereby forming high tensile strength fibers. As used herein, a "high tensile strength" fiber is one that has a tenacity of at least 10 g / denier, an initial tensile modulus of at least about 150 g / denier or more, and an energy to break of at least about 8 J / g or more, each measured by ASTM D2256. In this regard, the term "toughness" refers to the tensile stress of an unstressed sample, expressed as force (grams) per unit of linear density (denier). The term "initial tensile modulus" refers to the ratio of the change in tenacity, expressed in grams of gravity per denier (g / d), to the change in tension, expressed as a fraction of the original fiber / tape length (inches / inches).

[0046] The high tensile strength dry fibers of the present disclosure preferably have a tenacity of greater than 10 g / denier, more preferably at least about 15 g / denier, even more preferably at least about 20 g / denier, even more preferably at least about 27 g / denier, more preferably from about 28 g / denier to about 60 g / denier, even more preferably from about 33 g / denier to about 60 g / denier, even more preferably 39 g / denier or greater, even more preferably at least 39 g / denier to about 60 g / denier, even more preferably 40 g / denier or greater, even more preferably 43 g / denier or greater, or at least 43.5 g / denier, even more preferably from about 45 g / denier to about 60 g / denier, even more preferably at least 45 g / denier, at least about 48 g / denier, at least about 50 g / denier, at least about 55 g / denier, or at least about 60 g / denier.

[0047] As is conventionally known, drawing / stretching a fiber also affects the denier of the resulting drawn fiber. As used herein, the term "denier" refers to a unit of linear density, equal to the mass in grams per 9000 meters of a filament / fiber. Fiber denier is determined by both the linear density of each filament forming the fiber, i.e., denier per filament (dpf), and the number of filaments forming the fiber. Generally, once all drawing steps are complete, the fibers of the present disclosure have a denier per filament of about 0.1 to about 10.0 dpf, more preferably about 0.5 to about 2.5 dpf, and even more preferably about 0.75 to about 1.5 dpf. These low dpf ranges are preferred for medical applications, although wider ranges may be useful for other applications. For example, the fiber denier per filament may range from about 1.4 dpf to about 15 dpf, or from about 2.2 dpf to about 15 dpf, or from about 2.5 dpf to about 15 dpf, however, other filament deniers are also useful, including from about 3 dpf to about 15 dpf, from about 4 dpf to about 15 dpf, or from about 5 dpf to about 15 dpf.

[0048] The total denier of the multifilament fibers of the present disclosure will depend on the total number of filaments forming the fiber. In a preferred embodiment, the multifilament fibers of the present disclosure preferably contain from 2 to about 1000 filaments, more preferably from 2 to 500 filaments, even more preferably from 4 to 500 filaments, more preferably from about 6 to 500 filaments, and most preferably from about 6 filaments to about 250 filaments. The resulting multifilament fibers having the above dpf ranges for the component filaments will preferably have a total fiber denier in the range of from about 2 to about 1000 denier, more preferably from about 2 to about 500 denier, even more preferably from about 3 to about 500 denier, even more preferably from about 4 to about 500 denier, and most preferably from about 5 to about 250 denier.

[0049] The fibers described herein are particularly useful for the fabrication of sutures for use inside the human and animal body, i.e. in vivo. Exemplary applications are cardiovascular and orthopedic sutures, as well as stents and catheters, or even dental floss. It is known that in medical applications, colorants may be added to polyethylene fibers to make the fibers visually identifiable during surgery. The compositions of the present disclosure, which are made from a solvent or solvent mixture that is removed only by evaporation and does not require solvent extraction with a second solvent, are also ideal for the use of colorants to form colored fibers.

[0050] Furthermore, to ensure their suitability for in vivo use, it is important that the fibers are not coated with any lubricants or spin finishes during the manufacturing process. Application of spin finishes during gel spinning is typical to avoid static build-up and entanglement of the fibers during their manufacture, which are issues that would normally be expected if no finishes were applied, and therefore adjustments to the processing steps are necessary. In a preferred embodiment of the present disclosure, the fibers can be manufactured without application of any lubricants or spin finishes by minimizing in-line stretching of the dry fibers during the spinning process, limiting fiber speed by maintaining a relatively high tension on the dry fibers during the spinning process, at least up to about 1 g / denier to 10 g / denier, and avoiding low humidity conditions during spinning by controlling the humidity in the room or equipment where stretching is being performed, such as by applying a water mist or steam around the dry fibers after the solvent is removed. The application of cold water mist or water vapor to the fibers is carried out according to conventional methods in the art, such as by spraying with a spray nozzle using water pressure only, or by a spray nozzle using pressurized air (or another gas, e.g., an inert gas such as helium or argon) to produce the water mist, or by injecting water vapor into an enclosure through which the fibers pass during processing. Methods for generating such steam are well known. Twisting the fibers before post-drawing also limits static-related problems as discussed above when the fibers are post-drawn. Various methods of twisting fibers are known in the art, and any method may be utilized. Useful twisting methods are described, for example, in U.S. Pat. Nos. 2,961,010, 3,434,275, 4,123,893, 4,819,458, and 7,127,879, the disclosures of which are incorporated herein by reference to the extent consistent herewith. In a preferred embodiment, the fibers are twisted to have an angle of from 5° to about 40° relative to the twisted bundle axis, more preferably from about 5° to about 30°, and most preferably from about 15° to about 30°. A standard method for determining twist in twisted fibers is ASTM D1423.

[0051] In an alternative embodiment of the present disclosure, it may be desirable to convert the gel spun multifilament fibers into the form of a fiber tape, for example as described in commonly owned U.S. Patent Nos. 8,263,119, 8,697,220, 8,685,519, 8,852,714, 8,906,485, 9,138,961, and 9,291,440, each of which is incorporated herein by reference to the extent consistent herewith and which teach a process in which the multifilament fibers are compressed and flattened. In this regard, the term "tape" refers to a flat, narrow, monolithic strip of material having a length greater than its width and an average cross-sectional aspect ratio, i.e., the ratio of the largest dimension to the smallest dimension of the average cross-section throughout the length of the tape, of at least about 3:1. Such tapes preferably have a substantially rectangular cross-section with a thickness of about 0.5 mm or less, more preferably about 0.25 mm or less, even more preferably about 0.1 mm or less, and even more preferably about 0.05 mm or less. In the most preferred embodiment, the tape has a thickness of up to about 3 mils (76.2 μm), more preferably about 0.35 mils (8.89 μm) to about 3 mils (76.2 μm), and most preferably about 0.35 mils to about 1.5 mils (38.1 μm). The thickness is measured at the thickest area of ​​the cross-section. Tapes formed according to the present disclosure have a preferred width of about 2.5 mm to about 50 mm, more preferably about 5 mm to about 25.4 mm, even more preferably about 5 mm to about 20 mm, and most preferably about 5 mm to about 10 mm. While these dimensions may vary, the tapes are most preferably fabricated to have dimensions which achieve an average cross-sectional aspect ratio of greater than about 3:1, more preferably at least about 5:1, even more preferably at least about 10:1, even more preferably at least about 20:1, even more preferably at least about 50:1, even more preferably at least about 100:1, even more preferably at least about 250:1, and most preferably at least about 400:1, or an aspect ratio of from about 3:1 to about 400:1.

[0052] The fiber tape includes one or more filaments. Like the fibers, the fiber tape may be of any suitable denier, preferably having a denier of about 5 to about 5000 denier, more preferably about 10 to 2000 denier, even more preferably about 15 to about 500 denier, and most preferably about 20 to about 200 denier. In addition, the tape formed from the composition of the present disclosure is preferably a "high tensile strength" tape having a tenacity of at least 10 g / denier, an initial tensile modulus of at least 150 g / denier or more, and an energy to break of at least about 8 J / g or more, each measured by ASTM D882-09 at a 10 inch (25.4 cm) gauge length and an elongation rate of 100% / min. The high tensile strength tape is preferably a "high tensile strength" tape having a tenacity of at least 10 g / denier, an initial tensile modulus of at least 150 g / denier or more, and an energy to break of at least about 8 J / g or more, each measured by ASTM D882-09 at a 10 inch (25.4 cm) gauge length and an elongation rate of 100% / min. Preferably, the tenacity is greater than 10 g / denier, more preferably at least about 15 g / denier, even more preferably at least about 20 g / denier, even more preferably at least about 27 g / denier, more preferably from about 28 g / denier to about 60 g / denier, even more preferably from about 33 g / denier to about 60 g / denier, even more preferably 39 g / denier or more, even more preferably at least 39 g / denier to about 60 g / denier, even more preferably 40 g / denier or more, even more preferably 43 g / denier or more, or at least 43.5 g / denier, even more preferably from about 45 g / denier to about 60 g / denier, even more preferably at least 45 g / denier, at least about 48 g / denier, at least about 50 g / denier, at least about 55 g / denier, or at least about 60 g / denier, each measured by D882-09.

[0053] It has also been unexpectedly discovered that the polyethylene-trimethylbenzene compositions produced according to the present disclosure may be utilized in other non-medical end uses, such as hollow braids, woven fabrics, robotic cables, composites, and other uses, such as those of the co-owned references incorporated herein by reference. In one alternative use, the composition comprising a mixture of polyethylene and trimethylbenzene may be applied onto a surface or substrate using conventional methods to form a film or coating having high strength and toughness, or the composition may be extruded or otherwise formed into other (non-fibrous) shapes or articles by conventional methods such as extrusion or molding. In such an embodiment, the composition may be formed from a polyethylene-trimethylbenzene slurry, converted to a liquid mixture and solution as described above for the gel spinning process, and the solution may then be formed into other shapes or articles, such polyethylene-trimethylbenzene solutions may similarly comprise polyethylene in an amount of about 1% to about 50% by weight of the solution, preferably about 1% to about 30% by weight of the solution, more preferably about 2% to about 20% by weight of the solution, and even more preferably about 3% to about 10% by weight of the solution. The polyethylene-trimethylbenzene composition may be further heated to evaporate most or all of the trimethylbenzene solvent to form a dry solid, or the solvent / solvent mixture may simply be allowed to dry under ambient conditions. In these non-fibrous embodiments, the polyethylene-TMB composition may retain a higher amount of residual solvent in the final product, e.g., about 1.0% to about 5.0%, based on the total weight of the composition, and may contain other additives that may be desired, e.g., one or more colorants, such as pigments or dyes.

[0054] In yet another alternative embodiment, the polyethylene-trimethylbenzene composition may be extruded into a non-fibrous tape, which may be formed, for example, from a strip of polymer formed by slicing a polymer film, or from any other method such as those described in U.S. Patents 9,138,961 and 9,291,440. Such a tape has the same dimensions and denier as the aforementioned fibrous tapes, but is not formed by compressing spun fibers / filaments, does not contain gel-spun filaments, and may or may not contain residual solvent. EXAMPLES

[0055] The following non-limiting examples serve to illustrate preferred embodiments of the present disclosure.

[0056] Example 1 A slurry consisting of 6 wt. % UHMW PE and 94 wt. % TMB was prepared in an agitated mixing tank at room temperature (22° C.). The UHMW PE was a linear polyethylene having an intrinsic viscosity of 20 dl / g in decalin at 135° C. The linear polyethylene had less than about 0.5 substitutions per 1000 carbon atoms and a melting point of 138° C. The TMB was 1,2,4-trimethylbenzene, 98% grade.

[0057] The slurry was fed into the feed hopper of a conically intermeshing twin screw extruder with screw diameters ranging from 25.6 mm at the inlet to 9.2 mm at the discharge end. All screw flights were progressive. The free volume in the extruder (barrel volume minus screw volume) was 15 cm 3 The extruder barrel was heated in three equal length successive zones at temperatures of 130° C., 150° C., and 160° C. The screw rotation speed was 150 revolutions per minute (RPM). The UHMW PE / TMB slurry was converted to a liquid mixture at 150° C. as it passed through the extruder at an average throughput rate of 0.67 g / min.

[0058] The liquid mixture leaving the extruder is then passed through an external heating pipe heated to a temperature of 150° C., which is 25.8 cm 3 The liquid mixture was converted to a solution as it passed through this vessel with an average residence time of 27.9 minutes.

[0059] The UHMW PE solution leaving the pipe vessel passed through a gear pump and from there through a spin block fitted with a multi-hole spinneret having six holes of 1 mm diameter, thereby forming a six filament solution fiber. The solution fiber was then stretched at a draw ratio of 5.86:1 (DR0) as it passed through a 0.5 inch air gap into a water bath where it was quenched to form a gel fiber. The gel fiber was then stretched at a draw ratio of 3.25:1 (DR1) at room temperature (22°C) without heating.

[0060] The TMB was then evaporated from the gel fiber by passing it over a heated plate. Some stretching of the fiber occurred during drying, and the fiber was stretched with a draw ratio (DR2) of 4.57:1 during drying at an average temperature of 75° C., but there was no measurable in-line stretch of the dried fiber (i.e., there was no measurable DR3). The dried fiber was then wound onto an unheated take-up roll. The dried UHMW PE fiber had a denier of 25.9.

[0061] The dried fiber was then stretched in an off-line post-drawing operation at a draw ratio of 2.88:1 (DR4) on a heated plate at an average temperature of 131° C. The final post-drawn 6 filament UHMW PE fiber had a denier of 9 (1.50 denier per filament (dpf)) and a tenacity of 33.5 g / d. The data for this example are summarized in Tables I and II below.

[0062] Example 2 A solution of UHMW PE and 1,2,4-TMB was formed as in Example 1, and this solution was also formed into a six filament solution fiber as in Example 1. The solution fiber was then stretched at a draw ratio of 8.88:1 (DR0) as it was passed through a 0.38 inch air gap and into a water bath where it was quenched to form a gel fiber. The gel fiber was then stretched at a draw ratio of 4.29:1 (DR1) at room temperature (22° C.) without heating.

[0063] The TMB was then evaporated from the gel fiber by passing it over a heated plate. Some stretching of the fiber occurred during drying, and the fiber was stretched with a draw ratio (DR2) of 4.14:1 during drying at an average temperature of 75° C., but there was no measurable in-line stretch of the dried fiber (i.e., there was no measurable DR3). The dried fiber was then wound onto an unheated take-up roll. The dried UHMW PE fiber had a denier of 14.5.

[0064] The dried fiber was then stretched in an off-line post-drawing operation at a draw ratio of 3.09:1 (DR4) on a heated plate at an average temperature of 131° C. The final post-drawn 6 filament UHMW PE fiber had a denier of 4.7 (0.78 dpf) and a tenacity of 40.2 g / d. The data for this example are summarized in Tables I and II below.

[0065] Example 3 A solution of UHMW PE and 1,2,4-TMB was formed as in Example 1, and this solution was also formed into a 6 filament solution fiber as in Example 1. The solution fiber was then stretched at a draw ratio of 8.88:1 (DR0) as it passed through a 0.38 inch air gap through a water bath where it was quenched to form a gel fiber, as in Example 2. The gel fiber was then stretched at a draw ratio of 4.29:1 (DR1) at room temperature (22°C) without heating, also as in Example 2. The TMB was then evaporated from the gel fiber by passing it over a heated plate, and the fiber was stretched somewhat during drying. Also as in Example 2, the fiber was stretched at a draw ratio of 4.14:1 (DR2) during drying at an average temperature of 75°C, but there was no measurable in-line stretch of the dried fiber (i.e., there was no measurable DR3). The dried fiber was then wound onto an unheated take-up roll, with the dried UHMW PE fiber having a 14.5 denier, similar to Example 2. The dried fiber was then stretched in an off-line post-drawing operation at a draw ratio of 4.14:1 (DR4) on a heated plate at an average temperature of 131° C. The final post-drawn 6 filament UHMW PE fiber had a 3.5 denier (0.58 dpf) and a tenacity of 42.6 g / d. The data for this example are summarized in Tables I and II below.

[0066] [Table 1]

[0067] [Table 2]

[0068] While the present disclosure has been particularly shown and described with reference to preferred embodiments, it will be readily understood by those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the present disclosure. It is intended that the claims be construed to cover the disclosed embodiments, their alternatives as described above, and all equivalents thereof.

Claims

1. A composition comprising a mixture of polyethylene and trimethylbenzene.

2. 2. The composition of claim 1, wherein said trimethylbenzene is a liquid solvent and said polyethylene is at least partially dissolved in said trimethylbenzene.

3. 3. The composition of claim 2, wherein the composition is a solution and the polyethylene is completely dissolved in a trimethylbenzene solvent.

4. The composition of claim 2 , wherein the composition comprises at least one additional liquid solvent.

5. The composition of claim 2, wherein the trimethylbenzene comprises 1,2,4-trimethylbenzene.

6. 2. The composition of claim 1, wherein the polyethylene comprises ultra high molecular weight polyethylene and the trimethylbenzene comprises 1,2,4-trimethylbenzene.

7. A fiber formed from the composition of claim 1.

8. 12. The fiber of claim 11, wherein the fiber does not include any spin finish.

9. 1. A process for preparing a polyethylene fiber product, comprising: a) forming a solution of polyethylene having a weight average molecular weight of at least 500,000 g / mol in a trimethylbenzene solvent; b) spinning the solution through a spinneret to form one or more solution filaments; c) cooling the solution filaments, wherein the one or more solution filaments are converted to gel filaments, the gel filaments comprising greater than 1% solvent by weight of the polyethylene plus the solvent; and d) evaporating the solvent from the gel filaments to form dry filaments, the evaporation continuing until the solvent concentration in the dry filaments is less than 1% by weight of the polyethylene plus the solvent.

10. 10. The process of claim 9, wherein the solution is spun into a plurality of solution filaments in step b) and the polyethylene textile product is a multifilament fiber.

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