Method for producing yarn with special solvent extraction techniques and yarns obtained by the method.

Abstract

The present invention relates to methods of producing polymer yarns utilising environmentally friendly techniques of solvent extraction. More particularly, certain methods relate to a method of producing Ultra High Molecular Weight Polyethylene (UHMWPE) yarn by gel-spinning processes in which the solvent used to dissolve the polymer is extracted using supercritical or subcritical fluids (e.g., CO2). This enables the production of polymer yarn without the use of environmentally harmful and toxic washing solvents, and the reuse of the processing solvents of gel spinning.

Description

[0001] METHOD FOR PRODUCING YARN WITH SPECIAL SOLVENT EXTRACTION TECHNIQUES AND YARNS OBTAINED BY THE METHOD.

[0002] Field of the Invention

[0003] The present invention relates to methods of producing polymer yarns utilising environmentally friendly techniques of solvent extraction. In some aspects, the present invention relates to methods of producing Ultra High Molecular Weight Polyethylene (UHMWPE) yarn by gelspinning processes using supercritical or subcritical fluids (e.g., CO2) as extractants.

[0004] Background of the invention

[0005] Gel spinning is applied in the processing of high molecular weight or ultra-high molecular weight polymers such as UHMWPE. Such polymers possess properties which render them useful in several applications, including high tenacity, tensile modulus, high impact strength, energy to break, resistance to corrosive chemicals and extreme hydrophobicity. For example, UHMWPE yarn is commonly used in body armour, tear resistant clothing, vehicle armour, composite sports equipment, and automotive winching.

[0006] Gel spinning typically involves contacting polymer particles with a first solvent to form a solution which is extruded through a spinneret and cooled to form gel fibres. An important step of the process is the removal of the first solvent from the gel fibres, which is traditionally achieved by syneresis and gel washing with an extraction solvent. The resulting fibres are then drawn to a highly oriented state. Gel-spinning techniques are described, for example, in Advanced Fiber Spinning Technology edited by T. Nakajima, K. Kajiwara, J. E. McIntyre Woodhead Publ. Ltd (1994), Fibres to Smart Textiles: Advances in Manufacturing, Technologies, and Applications edited by Asis Patnaik, Sweta Patnaik, ORC Press (2020), EP0205960A1 , EP0213208A1 , US4413110, GB2042414A, EP0200547B1 , EP0472114 B1 , WO01 / 73173A1 and references cited therein.

[0007] In such techniques, the extraction solvent used to remove the first solvent from the gel solution is typically fossil fuel-based, such as hexane or dichloromethane. Such alkanes are largely produced by the fractional distillation of crude oil, which is an energy intensive process that contributes significantly to the production of greenhouse gases and thus global warming. For example, making 3,000kg of UHMWPE yarn may require 2,000 tonnes of hexane washing. Further, the commonly used solvent hexane is highly toxic due to its neurotoxic metabolite 2,5-hexanedione which causes axonal swelling and degeneration in the human central and peripheral nervous system and reacts with amino acid side chains in axonal cytoskeletal proteins causing neurofilament cross-linking and loss of function. Hexane is also highly volatile and a high explosion risk. Dichloromethane also poses serious health risks, is highly volatile, and is metabolised by the human body to form carbon monoxide, which can ultimately result in carbon monoxide poisoning.

[0008] Thermoplastic polymers, such as UHMWPE, are desirable as stable non-resorbable materials in various applications due to their strength and hydrophobic properties. Such polymers may be utilised in joint replacements and other biomedical applications as they are non-degradable and bioinert. However, often due to solvents and additives used in the polymer production process, toxicity can occur.

[0009] It is an aim of some of the embodiments of the present invention to mitigate some of the problems identified in the prior art.

[0010] Summary of certain embodiments of the invention

[0011] The present invention relates to improved gel-spinning techniques for producing polymer yarns.

[0012] In certain embodiments, the invention relates to the development of environmentally friendly techniques to extract a first solvent which is used to dissolve the polymer. Advantageously, the development of extraction techniques using supercritical or subcritical fluids (such as supercritical or liquid CO2) avoids the use of large amounts of fossil fuel-based secondary solvents (e.g., hexane or dichloromethane). Advantageously, polymer yarns, as produced by methods described herein, may not contain any toxic and / or hazardous solvents (e.g., are hexane or dichloromethane free). Moreover, the use of supercritical or subcritical fluids (such as supercritical or liquid CO2) may provide a sterilising effect to the resulting yarn. As such, the polymer yarn, as produced by the methods described herein, is particularly suitable for medical implants such as sutures, cables, implantable valves, vascular grafts, meshes, prosthetics or the like.

[0013] Accordingly, the invention provides a method of producing a polymer yarn characterized in that the solvent used to dissolve the polymer (e.g., UHMWPE or the like) is extracted using a supercritical or subcritical fluid (e.g., supercritical or liquid CO2). In certain embodiments, the invention comprises at least one or more of the following steps:

[0014] (i) dissolving one or more polymers in one or more first solvents to form a solution;

[0015] (ii) extrusion of the solution to form intermediate gel fibres comprising the polymer and the first solvent(s);

[0016] (iii) optionally cooling and / or solidifying the gel fibres;

[0017] (iv) extraction of the first solvent(s) from the gel fibres, using one or more supercritical or subcritical fluids, and wherein the extracted first solvent is captured for re-use; and

[0018] (v) drawing the fibres one or more times to form the polymer yarn following extraction of the first solvent.

[0019] Advantageously, the extraction of the first solvent from the gel fibre using the supercritical or subcritical fluids takes place prior to the drawing of the fibres. The timing of the extraction step results in a greater amount of the first solvent being extracted and recovered from the gel fibre, as compared to the removal of residual oil from a gel spun polymer filament after the final drawing step, and therefore a greater proportion of the first solvent can be recycled and reused in future processes.

[0020] In certain embodiments, the first solvent(s) is extracted using supercritical or liquid CO2.

[0021] The first solvent may be extracted using only a supercritical or subcritical fluid (e.g., only supercritical or liquid CO2). As such, no co-solvent is required in addition to the subcritical or supercritical fluid. Alternatively, the solvent may be extracted using a supercritical or subcritical fluid (e.g., supercritical or liquid CO2) and one or more co-solvents. For example, the one or more co-solvents may be selected from methanol, acetonitrile, ethanol, acetone or the like.

[0022] In certain embodiments, the polymer is an Ultra High Molecular Weight Polyolefin. For example, the polymer may be UHMWPE, polypropylene (PP), polymethylpentene (PMP), polyisobutylene (PI B) and / or other grades of PE (LDPE, MDPE, HDPE). Additional polymers which may be used in the methods of invention are further described herein.

[0023] In certain embodiments, the polymer yarn is medical grade, colourless and / or alkane-free. For example, the polymer yarn may be non-toxic and / or solvent free. As used herein, the term “alkane-free”, “hexane-free” and / or “non-toxic” refers to solvent amounts which are below the lowest detection limit, e.g., lower than about 100ppb, lower than about 10ppb, lower than about 1 ppb or less.

[0024] In certain embodiments, the first solvent is non-polar. Typically, the first solvent is decalin, tetralin, naphthalene, dodecane, mineral oil, paraffin oil, benzene, toluene, xylene, dichlorobenzene and / or trichlorobenzene. Additional first solvents which may be used in the methods of the invention are further described herein.

[0025] In preferred embodiments, the first solvent is mineral oil.

[0026] In certain embodiments, the first solvent (e.g., mineral oil) is extracted using a supercritical fluid (e.g., supercritical CO2) at a temperature of greater than about 31 °C, at a pressure greater than about 74 bar and / or using a CO2flow rate of about 20g I min or more. Typically, the first solvent (e.g., mineral oil) is extracted at a temperature of about 40°C, about 50°C, about 60°C, about 80°, about 100°, about 150°, about 200°C or more, at a pressure of about 75 bar, about 100 bar, about 150 bar, about 200 bar, about 300 bar, about 400 bar, about 500 bar, about 600 bar, about 700 bar or more and / or a flow rate of about 5g / min, about 20g / min, about 50g / min, about 100g / min, about 200g / min, about 300g / min, about 400g / min, about 500g / min, about 600g / min, about 800g / min, about 1000g / min or more.

[0027] In certain embodiments, more than about 90%, more than about 95%, more than about 99% or more than about 99.7% or more of the first solvent is extracted from the gel fibre.

[0028] In certain embodiments, the gel fibres are exposed to the supercritical or subcritical fluid, thereby separating the first solvent from the fibres.

[0029] In certain embodiments, the method comprises: inserting the gel fibres, comprising the polymer and the first solvent, into one or more extraction vessels;

[0030] - flowing one or more supercritical fluids (e.g., supercritical CO2), optionally at a pressure range of about 100 bar to about 700 bar, a temperature of about 50°C to about 200°C or at a flow rate of about 100 g / min to about 1000g / min, through the gel fibres; and

[0031] - separating the gel fibres from the supercritical fluid (e.g. , supercritical CO2), thereby recovering the extracted gel fibres.

[0032] In certain embodiments, the first solvent and / or supercritical or subcritical fluid are recycled, as further described herein. In certain embodiments, a mixture of polymer powder and the first solvent is heated prior to and / or during extrusion to form the solution, as further described herein.

[0033] In certain embodiments, the solution is extruded through a spinneret to form continuous gel fibres, as further described herein.

[0034] In certain embodiments, the extracted first solvent is recovered separately and / or inline.

[0035] In certain embodiments, the polymer fibres undergo hot and / or cold drawing across multiple stages to form the polymer yarn.

[0036] In certain embodiments, the polymer yarn is collected on a rotating spool.

[0037] In certain embodiments, the polymer yarn is wound, knit, packaged, coiled and / or further processed into a semi-finished and / or end-use article.

[0038] In certain embodiments, the polymer yarn is sterile and / or non-toxic. The polymer yarn may further comprise an antimicrobial coating or the like.

[0039] In certain embodiments, the polymer yarn is medical grade, and / or alkane-free as further described herein. The polymer yarn may be coloured or colourless.

[0040] The invention further provides a polymer yarn obtainable by any method as described herein.

[0041] The invention further provides a medical implant comprising any polymer yarn as described herein. Typically, the implant is a suture, cable, implantable valve, vascular graft, mesh or prosthetic.

[0042] In certain embodiments, the invention provides use of any polymer yarn as described herein in medicine.

[0043] The invention further provides an aerospace and / or anti-ballistic article comprising the polymer yarn as described herein.

[0044] The polymer yarn is also useful, for example, in ropes and cables, traffic barriers, energy storage, sports equipment, hospital equipment, sailcloth or the like.

[0045] Detailed description

[0046] Embodiments of the present invention will now be described hereinafter, by way of example only, with reference to the accompanying drawings in which:

[0047] Figure 1 is a flowchart of a method of producing a polymer yarn using a supercritical fluid according to some embodiments described herein;

[0048] Figure 2 is an illustration of an extraction system according to some embodiments described herein.

[0049] Figure 3 is a mass spectra of Mineral Oil prior to use and after recovery with scCO2.

[0050] Figure 4 is an UHMWPE yarn before and after oil extraction by scCO2.

[0051] Figure 5 is a table showing the residual oil content of yarn after oil was removed using the novel process.

[0052] Figure 6 is a tensile test report illustrating the Tensile properties of UHMWPE yarn made after full processing using conventional solvents for oil removal.

[0053] Figure 7 is a tensile test report illustrating the example tensile properties of UHMWPE yarn after full processing using scCO2for oil removal.

[0054] The practice of embodiments of the present invention employs, unless otherwise indicated, conventional techniques of chemistry, materials science, engineering, and medicine, which are within the skill of those working in the art.

[0055] Most general chemistry techniques can be found in Comprehensive Heterocyclic Chemistry IF (Katritzky et al., 1996, published by Pergamon Press); Comprehensive Organic Functional Group Transformations (Katritzky et al., 1995, published by Pergamon Press); Comprehensive Organic Synthesis (Trost et al, 1991 , published by Pergamon); Heterocyclic Chemistry (Joule et al. published by Chapman & Hall); Protective Groups in Organic Synthesis (Greene et al., 1999, published by Wiley Interscience); and Protecting Groups (Kocienski et al., 1994).

[0056] Most general materials science and general engineering techniques can be found in Foundations of Materials Science and Engineering (Smith et al., 2009, published by McGraw Hill), Materials Science and Engineering (Callister et al., 2020, published by Wiley) and The Science and Engineering of Materials (Askeland et al., 2010, published by Cl-Engineering).

[0057] Most general medicine techniques can be found in Oxford Textbook of Medicine (Firth et al., 2020, published by Oxford University Press). Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. For example, Foundations of Materials Science and Engineering (Smith et al., 2009, published by McGraw Hill), Materials Science and Engineering (Callister et al., 2020, published by Wiley) and The Science and Engineering of Materials (Askeland et al., 2010, published by Cl-Engineering), provide a person skilled in the art with a general dictionary of many of the terms used in this disclosure. For chemical terms, the skilled person may refer to the International Union of Pure and Applied Chemistry (IUPAC).

[0058] Units, prefixes and symbols are denoted in their Systeme International d’Unites (SI) accepted form. Numeric ranges are inclusive of the numbers defining the range.

[0059] Method of producing yarn

[0060] The invention provides a method of producing a polymer yarn. Reference is made to Figure 1 , which is a flowchart of a method of producing a polymer yarn according to some embodiments of the invention.

[0061] In some embodiments, the method comprises dissolving one or more polymers (e.g., UHMWPE) in a first solvent (e.g., mineral oil) to form a solution. The solution may be processed for extraction immediately, within about 1 hour, within about 2 hours, within about 5 hours, within about 10 hours, within about 20 hours, or within less than about 24 hours. Alternatively, the solution may be stored and / or incubated, e.g., for at least 24 hours, 48 hours, 72 hours or more. Typically, the solution is stored and / or incubated around room temperature.

[0062] In some embodiments, the first solvent may at least be partially removed by syneresis, e.g., wherein the first solvent at least partially drains out of the gel fibre, leading to at least partial solidification of the solution.

[0063] In step 110, the solution is extruded e.g., to form gel fibres comprising the polymer and the first solvent, as further described herein.

[0064] In step 120, the first solvent is extracted using a supercritical fluid (e.g., scCO2) or subcritical fluid (e.g., liquid CO2) as further described herein. For example, the supercritical or subcritical fluid may be obtained by pressurizing and heating the fluid into supercritical or subcritical conditions, as further described herein. The supercritical (e.g., scCO2) or subcritical fluid (e.g., liquid CO2) may then be passed through the gel fibres, and the gel fibres separately recovered from the supercritical or subcritical fluid.

[0065] In some embodiments, the mineral oil and / or supercritical or subcritical fluid may also be separately recovered and / or recycled, as further described herein.

[0066] In step 130, the fibres are drawn (e.g., stretched) to form the polymer yarn, as further described herein.

[0067] As used herein, the term ‘polymer yarn’ refers to one or more fibres made from polymers (e.g., multifilament yarns produced by gel-spinning techniques. For example, the yarn may comprise about 1 , about 5, about 10, about 20, about 30, about 100, about 200, about 300, about 400, about 500 or about 1000 or more fibres. Typically, the fibres comprise an elongated body in which length is greater than width or thickness. In certain embodiments, the fibres may comprise a circular, rectangular, oval, square, or flat cross-section. The term “fibre” includes filaments, ribbons, strips, tape, and bands which may have a regular or irregular cross section. In certain embodiments, the fibres may have continuous lengths and may be referred to as continuous filaments or filaments. In certain embodiments, the fibres may have discontinuous lengths and may be referred to as staple fibres.

[0068] Starting polymer material

[0069] Any suitable polymers may be used in the methods described herein. Typically, the polymer yarn is produced using a starting material of one or more polymers in particulate, powder, or resin form. For example, a starting polymer powder may be produced through various known methods, including polymerization, grinding, and milling. The manufacturing process can influence the size, shape, and properties of the particles. Polymer powders, such as UHMWPE, are commercially available and typically have a particle size diameter from about 100 to about 200 microns. Typically, the polymer that is selected requires dissolving in a solvent prior to a gel spinning process as further described herein.

[0070] In certain embodiments, a starting polymer powder is a synthetic polymer or a natural polymer. Typically, synthetic polymers are derived from crude oil. Typically, natural polymers are plantbased polymers. For example, the natural polymer may be selected from polyethylene, polypropylene, or polylactic acid. The natural polymers may be produced from corn waste. In certain embodiments, the natural polymer may be produced from corn waste. The manufacturing process of a natural polymer produced from corn waste comprises growing the corn, fermenting the corn to ethanol which is then reduced to ethylene gas. The ethylene gas is then polymerised to UHMWPE.

[0071] In certain embodiments, the polymer is synthetic. For example, the polymer may be a thermoplastic polymer. As used herein, the term ‘thermoplastic polymer’ refers to a polymer that is plastic or deformable and melts when heated. Typically, the polymer is substantially linear.

[0072] In certain embodiments, the polymer is a high or ultra-high weight polymer. For example, the polymer may have an average molecule weight of at least about 200,000 g / mol, about 400,000 g / mol, about 600,000 g / mol, about 800,000 g / mol, about 1 x 106g / mol, about 2 x 106g / mol, about 3 x 106g / mol, about 4 x 106g / mol, about 5 x 106g / mol, about 6 x 106g / mol, about 7 x 106g / mol, about 8 x 106g / mol, about 9 x 106g / mol, about 10 x 106g / mol or more. Typically, the polymer has a molecular weight ranging between about 3.5 x 106g / mol to about 6 x106g / mol.

[0073] In certain embodiments, the polymer is a polyolefin. For example, the polymer may be selected from polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polybutene (PB), polyisobutylene (PIB) or the like.

[0074] In certain embodiments, the polymer is polyvinyl alcohol (PVA).

[0075] In certain embodiments, the polymer is polyacrylonitrile (PAN).

[0076] In certain embodiments, the polymer is a plant-based polymer such as polylactic acid (PLA).

[0077] In certain embodiments, the polymer is Ultra High Molecular Weight Polyethylene (UHMWPE). Typically, UHMWPE polymers are produced from ultra-high molar mass polyethylene. The UHMWPE may be a linear polyethylene with less than one branch per 100 carbon atoms, and typically less than one side chain per 300 carbon atoms, a branch typically containing at least 10 carbon atoms. In certain embodiments, filaments of two or more polymers are produced. For example, the polymer yarn may comprise a mixture of different polymers (e.g., polyethylene and polypropylene or any other combination of two or more suitable polymers).

[0078] In some embodiments, a modified polyethylene is obtained by copolymerizing ethylene and at least one other monomer. For example, a linear polyethylene may further contain up to about 5 mol% of one or more co-monomers, including alkenes such as propylene, butene, pentene, 4-methylpentene, hexene, octene or the like.

[0079] First solvent

[0080] In certain embodiments, the method of producing the polymer yarn comprises dissolving the polymer in a first solvent to form a solution. Typically, the starting polymer material is provided in particulate, resin, or powder form, prior to dissolution in the first solvent.

[0081] Any suitable concentration of polymer may be used, depending, for example, on the type of first solvent and / or the desired properties of the polymer yarn that is being produced. In some embodiments, the concentration of polymer (e.g., UHMWPE) may be no more than about 8 wt. % for a suitable viscosity and to prevent entanglement of polymer (e.g., polyethylene) molecular chains.

[0082] Typically, the polymer concentration is at least about 1 wt. % or more. For example, the concentration of the polymer (e.g., UHMWPE) may be about 2 wt. % to about 15 wt. %, typically about 4 wt. % to 10 wt. % or 5 % to 8 wt. %. In some embodiments, the solution comprises about 10% to about 20% of the polymer by weight.

[0083] Any suitable solvent may be used to dissolve the starting polymer material. The one or more solvents selected may depend on the type of polymer being used. Typically, the solvent is selected to have a good solubility with the polymer, to be readily extracted using a supercritical or subcritical liquid (e.g., CO2), and to have a boiling point higher than a dissolving or spinning temperature.

[0084] In certain embodiments, the first solvent is non-polar. Typically, the first solvent has a boiling point over 100°C.

[0085] In certain embodiments, the first solvent is a hydrocarbon. For example, the first solvent may be selected from aliphatic compounds, aromatic compounds, alicyclic compounds, and halogenated hydrocarbons. The first solvent may be selected from the group consisting of decalin, mineral oil, paraffin oil, benzene, toluene, xylene, dihydrolevoglucosenone, acetophenone, anisole, terpenoids, dichlorobenzene, trichlorobenzene, hexane, heptane, pentane, octane, cyclohexane, tetralin, naphthalene, dodecane, undecane, decane, kerosene, and mixtures thereof. Typically, the first solvent is selected from decalin, mineral oil, dichlorobenzene, trichlorobenzene and their mixtures. For example, the first solvent may be mineral oil.

[0086] In certain embodiments, the solution comprises UHMWPE powder dissolved in the first solvent (e.g., mineral oil, decalin, dichlorobenzene or trichlorobenzene).

[0087] In certain embodiments, the solution comprising the polymer and the first solvent has a volume of between about 1 L and about 100 L. In other embodiments, the solution is formed continuously during processing. For example, powder may be added to oil during extrusion, typically at a concentration of about 5% to 10% w / v in oil (e.g., 7% w / v in oil).

[0088] In certain embodiments, the solution is heated prior to and / or during extrusion. For example, the polymer and first solvent may be heated to any suitable temperature to achieve complete dissolution of the polymer in the first solvent. Typically, the temperature may vary depending on the specific extrusion process and / or the desired properties of the polymer yarn being produced.

[0089] In certain embodiments, the solution is heated to a temperature of about 150°C to about 220°C prior to extrusion. For example, the solution may be heated to about 170°C when a polyethylene concentration of about 7% of a weight average molar mass of about 2 x 106g / mol is spun. Typically, the dissolution and spinning temperature of the polymer are the same.

[0090] The solution comprising the polymer (e.g., UHMWPE) and the first solvent (e.g., mineral oil, decalin, dichlorobenzene or trichlorobenzene) may be provided in any suitable manner. Typically, the particulate form of the polymer and the first solvent are continuously fed into the mixing tank. Typically, the mixing tank is heated prior to extrusion of the solution as further described herein.

[0091] Extrusion

[0092] In certain embodiments, the method of producing the polymer yarn comprises extrusion of the solution to form gel fibres comprising the polymer and the first solvent.

[0093] As used herein, the term ‘extrusion’ refers to a process of producing elongated gel fibres with a constant (or substantially constant) cross-section. Typically, the gel fibres that are produced are highly aligned in the direction of extrusion. Methods of polymer extrusion are known in the art.

[0094] Typically, the gel fibres are produced continuously. Any desired amount of gel fibre may be produced. In certain embodiments, between about 2 g to about 200 g per minute of gel fibre may be produced. Typically, about 20 g per minute of gel fibre is produced.

[0095] In certain embodiments, the solution is continuously fed to the extruder. The solution may be fed to the extruder under any suitable temperature, flow rate and / or pressure. In some embodiments, the solution is fed to the extruder at a temperature of about 50°C. In some embodiments, the solution is fed to the extruder at a flow rate of between about 10ml / min to about 100ml / min, typically about 25ml / min. In some embodiments, the solution is fed to the extruder at a pressure of about 15 bar.

[0096] In certain embodiments, the extruder is a single screw extruder, a twin extruder, a multiple screw extruder or a ram extruder. Twin screw extruders may be co-rotating or counter-rotating. The screw diameter and length may be tailored to achieve specific properties of the final polymer yarn that is being produced. For example, the screw diameter may be between about 10mm and about 30mm, typically about 19mm. In some embodiments, the screw length is about 120cm. In some embodiments, the length to diameter ratio is about 60.

[0097] As referred to herein, the average residence time in the extruder is the ratio of free volume in the extruder to the volumetric throughput rate. Typically, the volumetric throughput rate is between about 10ml / min and about 25ml / min.

[0098] In certain embodiments, the solution is extruded through a spinneret. The spinneret may comprise apertures that shape the solution into continuous filaments. The shape and / or size of the extruder orifices may be tailored to achieve specific properties of the final polymer yarn that is being produced.

[0099] In certain embodiments, the diameter of apertures is about 0.02mm to about 1 .0mm. In some embodiments, larger apertures (e.g., about 1 .0 mm, 2.0 mm, 5.0 mm or more) may be used.

[0100] In certain embodiments, the extruded solution is rapidly cooled to form gel fibres. For example, the extruded solution may be cooled by immediately passing through a liquid quench bath. This acts to solidify the gel as it is extruded or pulled to form fibres. This rapid cooling helps preserve the orientation and alignment of the polymer chains, which may be important in achieving the desired properties in the final fibre.

[0101] The quench bath typically comprises a cold, non-solvent liquid. The temperature and / or composition of the quench bath can vary depending on the polymer being used and the desired properties of the polymer yarn being produced.

[0102] In certain embodiments, the extruded solution is cooled from the first temperature to the second temperature at a rate of about 200°C or more per minute. Typically, the liquid is maintained at a temperature of about 5°C. Typically, the liquid is water. Typically, the liquid in the quench bath flows substantially perpendicular to the gel fibres being formed.

[0103] In certain embodiments, the gel fibres go through one or more additional baths, to remove any impurities or the like.

[0104] Solvent extraction

[0105] In certain embodiments, the method of producing the polymer yarn comprises extraction of the first solvent from the gel fibres using one or more supercritical or subcritical fluids. Advantageously, such methods do not require the use of hazardous secondary solvents such as hexane or the like.

[0106] In certain embodiments, the method of producing the polymer yarn comprises extraction of the first solvent from the gel fibres using one or more supercritical or subcritical fluids and one or more co-solvents. Typically, the co-solvent may be one or methanol, acetonitrile, ethanol or acetone. Alternatively, solvent extraction may be performed in the absence of any cosolvent.

[0107] As used herein, the term ‘extraction’ refers to the removal of the first solvent from the gel fibres. Advantageously, the use of supercritical or subcritical fluids may allow the formation of dry fibres by replacing the first solvent without (or with only a limited) impact on the structure of the gel fibre.

[0108] In certain embodiments, the extraction of the solvent does not cause changes to the structure of UHMWPE fibres. As used herein, the term ‘supercritical fluid’ refers to a substance which is at a temperature and pressure that is above its critical point, but below the pressure required to compress it into a solid.

[0109] In certain embodiments, the supercritical fluid is supercritical CO2. For example, carbon dioxide becomes supercritical when it is exposed to a specific combination of temperature and pressure, known as its critical point. In this state, CO2exhibits properties of both a gas and a liquid allowing it to extract one or more solvents. In certain embodiments, supercritical CO2and one or more co-solvents are used to extract the first solvent from the gel fibres. Typically, the co-solvent may be one or methanol, acetonitrile, ethanol or acetone. Alternatively, only supercritical CO2may be used to extract the first solvent from the gel fibres.

[0110] In certain embodiments, supercritical CO2extraction is used to extract any first solvent as described herein. Advantageously, supercritical CO2is more environmentally friendly and less toxic than traditional solvent extraction methods used in gel-spinning processes (e.g., hexane or the like).

[0111] In certain embodiments, the gel fibres comprising the polymer and the first solvent are loaded into an extraction vessel or chamber specifically designed for supercritical CO2extraction. Carbon dioxide may then be pumped into the extraction vessel at controlled pressures and temperatures, usually above its critical point. As a supercritical fluid, CO2may penetrate the gel fibres like a gas, whilst dissolving and carrying away the first solvent like a liquid.

[0112] The first solvent may be extracted using a supercritical fluid under any suitable conditions. Such parameters may be selected depending on the specific properties of the polymer yarn being produced. For example, different polymers may have varying solubilities in supercritical CO2, so the conditions (e.g., temperature, pressure and / or CO2flow rate) may be adjusted to optimize the extraction of first solvents depending on the polymer(s) being used.

[0113] In certain embodiments, the first solvent is extracted using a supercritical fluid (e.g., supercritical CO2) at a temperature of greater than about 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 100°C, 200°C or more. In certain embodiments, the supercritical fluid (e.g., supercritical CO2) has a temperature range of about 50°C to about 200°C. Typically, the first solvent is extracted using a supercritical fluid (e.g., supercritical CO2) at a temperature of above about 50°C.

[0114] In certain embodiments, the first solvent is extracted using a supercritical fluid at a pressure greater than about 75 bar, 100 bar, 125 bar, 150 bar, 175 bar, 200 bar, 225 bar, 250 bar, 275 bar, 300 bar, 325 bar, 350 bar, 375 bar, 400 bar, 500 bar, 600 bar, 700 bar or more. In certain embodiments, the first solvent is extracted using a supercritical at a pressure range of about 100 bar to about 700 bar. Typically, the first solvent is extracted using a supercritical fluid (e.g., supercritical CO2) at a pressure of above about 100 bar.

[0115] In certain embodiments, the first solvent is extracted using a supercritical CO2flow rate of about 5 g / min, about 10 g / min, about 50 g / min, about 100 g / min, about 200 g / min, about 300 g / min, about 400 g / min, about 500 g / min, about 600 g / min, about 700 g / min, about 800 g / min, about 900 g / min, about 1000 g / min or more. Typically, the first solvent is extracted using a CO2 flow rate of between about 100 g / min and about 1000 g / min.

[0116] In certain embodiments, the gel fibres are exposed to the supercritical fluid for a duration of about 5 minutes, about 10 minutes, about 20 minutes, about 30 minutes, about 1 hour, about 2 hours, about 10 hours or more. Typically, the gel fibres are exposed to the supercritical fluid for a duration of about 30 minutes.

[0117] In certain embodiments, the step of extracting the solvent comprises: inserting the gel fibres, comprising the polymer and the first solvent, into one or more extraction vessels;

[0118] - flowing supercritical fluid (e.g., supercritical CO2), optionally at a pressure range of about 100 bar or more, a temperature of about 50 °C or more and / or flow rate of about 100 g / min or more, through the gel fibres; and

[0119] - separating the gel fibres from the supercritical fluid (e.g., supercritical CO2).

[0120] Typically, the supercritical fluid (e.g., supercritical CO2) is the only secondary solvent used.

[0121] In certain embodiments, flowing supercritical CO2comprises the following steps:

[0122] - obtaining liquidized CO2; increasing the pressure of the liquidized CO2to reach a required supercritical pressure; heating the pressurized liquid CO2to reach a required supercritical temperature; and inserting the supercritical CO2fluid to the one or more extraction chambers.

[0123] In certain embodiments, the extracted gel fibres are recovered from the extraction chambers following the supercritical extraction. Alternatively, the gel fibres may be introduced into a separation vessel having one or more separation stages. In certain embodiments, the extracted gel fibres are collected for further processing into polymer yarn, e.g., drawing stages as further described herein.

[0124] In certain embodiments, the first solvent is also separately recovered during (or immediately after) the supercritical carbon dioxide extraction step. For example, following extraction, the supercritical CO2(comprising the first solvent) may be introduced to a separation vessel having one or more separation stages. In this vessel, the pressure and / or temperature may be reduced, causing the supercritical CO2to revert to a gas and release the first solvent. In this way, the first solvent can be separated from the CO2. Advantageously, the extraction process may not alter the chemical properties of the first solvent. For example, this may minimize loss of the first solvent, reduce waste, and allow the first solvent to be recycled and re-used in future processes, rather than being disposed of as waste. The remaining CO2is typically also recycled, for additional extraction cycles.

[0125] In certain embodiments, the amount of first solvent extracted from the gel fibre is 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% of the total amount of solvent added to the polymer starting material. Preferably, at least 98% of the first solvent is extracted from the gel fibre.

[0126] In certain embodiments, at least 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% of the extracted first solvent is recycled. Preferably, at least 66% of the extracted first solvent is recycled.

[0127] Advantageously, the use of supercritical CO2as an extractant in gel-spinning techniques as described herein is safe and environmentally friendly, as it does not use toxic or flammable solvents. It allows for precise control over temperature and pressure, enabling selective extraction of the first compound. It also results in higher-quality yarn polymer being produced which is alkane-free, medical-grade and sterilized. As such, the yarn which is produced using the methods of the invention is distinct from polymer yarns produced using conventional techniques (e.g., hexane washing).

[0128] While supercritical CO2extraction operates above CO2's critical point, subcritical CO2extraction works at lower pressures and temperatures, below the critical point. Like supercritical extraction, the process may be performed in an extraction vessel or chamber designed for subcritical CO2extraction. The gel fibres, comprising the polymer and the first solvent, may be loaded into this vessel. Carbon dioxide may then be introduced into the extraction vessel but is not pressurized to supercritical levels. Instead, it is pressurized to subcritical pressures, and the temperature is maintained below the critical point. This allows the CO2 to exist as a gas.

[0129] As used herein, the term ‘subcritical fluid’ refers to a substance which is at a temperature and pressure above its boiling point but below its critical point. Typically, the subcritical fluid is liquid CO2.

[0130] In certain embodiments, the step of extracting the solvent comprises: inserting the gel fibres, comprising the polymer and the first solvent, into one or more extraction vessels;

[0131] - flowing subcritical fluid (e.g., liquid CO2), through the gel fibres; and

[0132] - separating the gel fibres from the subcritical fluid (e.g., liquid CO2).

[0133] Typically, the subcritical fluid (e.g., liquid CO2) is the only secondary solvent used.

[0134] In certain embodiments, the subcritical CO2 interacts with the gel fibres, dissolving and carrying away the first solvent. Although it operates at lower pressures and temperatures, subcritical CO2can still penetrate the gel fibres and extract the first compound. Again, the first solvent may be extracted using a subcritical fluid under any suitable conditions. Such parameters may be selected depending on the specific properties of the polymer yarn being produced. For example, different polymers may also have varying solubilities in subcritical CO2 SO the conditions (e.g., temperature, pressure and / or CO2flow rate) may be adjusted to optimize the extraction of first solvents depending on the polymer which is being used.

[0135] In certain embodiments, the first solvent is extracted using a subcritical fluid at a temperature of below about 30°C. Typically, the first solvent is extracted using subcritical CO2 at a temperature of below about 30°C.

[0136] In certain embodiments, the first solvent is extracted using a subcritical fluid at a pressure of below about 74 bar. Typically, the first solvent is extracted using subcritical CO2at a pressure of below about 74 bar.

[0137] In certain embodiments, the first solvent is extracted using a subcritical CO2flow rate of about 5 g / min, 10 g / min, 15 g / min, 20 g / min, 25 g / min, 30 g / min, 35 g / min, 40 g / min, 45 g / min, 50 g / min, 55 g / min, 60 g / min, 65 g / min, 70 g / min, 75 g / min, 80 g / min, 85 g / min, 90 g / min, 95 g / min, 100 g / min, 200 g / min, 300 g / min, 400 g / min, 500 g / min, 600 g / min, 700 g / min, 800 g / min, 900 g / min, 1000 g / min or more. Typically, the first solvent is extracted using a CO2flow rate of about 20 g / min. In certain embodiments, the gel fibres are exposed to the subcritical fluid for a duration of about 5 minutes, about 10 minutes, about 20 minutes, about 30 minutes, about 1 hour, about 2 hours, about 10 hours or more. Typically, the gel fibres are exposed to the subcritical fluid for a duration of about 30 minutes.

[0138] After extraction, the mixture of CO2and first solvent may be transported to a separation vessel. The pressure may be reduced, allowing the CO2to revert to its gaseous state and release the first solvent. The first solvent may then readily be separated from the CO2, and typically collected for re-use, as described above.

[0139] In certain embodiments, the extracted gel fibres are collected for further processing into polymer yarn, e.g., for additional drawing stages as further described herein. The remaining CO2is typically released, vented, and / or liquefied for reuse.

[0140] Subcritical CO2extraction may be used for certain solvents and / or polymers which may be sensitive to the higher pressures and temperatures used in supercritical CO2extraction.

[0141] In certain embodiments, the undrawn fibres obtained after extraction of the first solvent have a linear mass density of about 1 ,00 denier to about 100,000 denier.

[0142] In certain embodiments, the undrawn fibres obtained after extraction of the first solvent have a tenacity of about 0.1 g / denier, 0.5 g / denier, 1.0 g / denier, 1.5 g / denier, 2.0 g / denier, 2.5 g / denier, 3.0 g / denier, 3.5 g / denier, 4.0 g / denier, 4.5 g / denier, 5.0 g / denier, 5.5 g / denier, 6.0 g / denier, 6.5 g / denier, 7.0 g / denier, 7.5 g / denier, 8.0 g / denier, 8.5 g / denier, 9.0 g / denier, 9.5 g / denier or 10.0 g / denier.

[0143] In certain embodiments, the undrawn fibres have a relaxation crossover point of less than about 10, less than about 5, or less than about 1 radian per second. Typically, the undrawn fibres have a relaxation crossover point of less than about 1 radian per second. As used herein, the ‘crossover point’ is when the tensile modulus of the undrawn fibre is equal to the viscous modulus of the undrawn fibre. The viscous modulus represents the energy stored in the elastic structure of the undrawn fibre.

[0144] Gel drawing

[0145] In certain embodiments, the method of producing the polymer yarn comprises drawing (e.g., stretching) the fibres to form the polymer yarn.

[0146] In certain embodiments, the gel-spinning process may include drawing of the extracted gel fibre in one or more stages. Varying methods of drawing are known in the art and can be used within the method of the present invention. For example, the extracted fibre can be drawn by passing through one or more rollers. The extracted fibre can also be drawn by passing through one or more draw stand. Drawing the dry yarn can be done in line.

[0147] As used herein, “drawing” techniques involve stretching of the extracted gel fibre and are employed to further align the polymer chains and improve the tensile strength of the resulting fibres.

[0148] The drawing of the fibre may be carried out by any suitable means known in the art. In certain embodiments, the drawing techniques comprise extrusion and / or tensile stretching on suitable drawing units. The exact parameters, temperatures, and draw ratios for drawing, along with annealing, can vary depending on the polymer yarn that is being produced.

[0149] In some embodiments, the fibre is drawn at a temperature within about 5°C to 10°C of the melting point of the polymer.

[0150] In some embodiments, the fibre is drawn at a rate of less than about 1 second-1. As used herein, the term “drawing rate” refers to the drawing velocity difference divided by the length of the drawing zone.

[0151] In some embodiments, the fibre is drawn at a ratio sufficient to have a single filament denier of about 3 d or less, a single filament tenacity of about 40 g / d or more and / or a single filament initial modulus of about 1 ,200 g / d and more.

[0152] In some embodiments, the fibre is drawn at a stretch ratio of at least about 5, 10, 20, 30 or 40 or more. As used herein, the “stretch ratio” refers to the ratio of the final length of the fibre to its initial length.

[0153] In some embodiments, the fibre is cooled under tension sufficient to retain a highly orientated state (e.g., about 2 grams per denier, about 1 grams per denier, or less).

[0154] In some embodiments, the drawing of the fibre is carried out in multiple steps. Advantageously, drawing over multiple steps may result in increased mechanical strength and stiffness. Typically, the drawing of the fibres is performed uniaxially and is carried out in multiple steps.

[0155] In certain embodiments, the extracted gel fibres, which may already be solidified and aligned to some extent, undergo an initial drawing stage (hot drawing). In this step, the fibres are heated to an elevated temperature while being stretched or drawn. The elevated temperature helps to make the polymer chains more mobile, allowing them to align along the length of the fibre. This process is often performed in multiple stages to gradually increase the level of alignment and tensile strength. Typically, hot drawing is conducted at a temperature of at least about 135°C, typically for about 1 to about 5 seconds.

[0156] In certain embodiments, the extracted and / or drawn gel fibres undergo secondary (or cold) drawing. This step may take place at or near room temperature, typically for about 1 to about 5 seconds. Advantageously, cold drawing further extends the fibres, enhances the alignment of polymer chains and provides high tensile strengths.

[0157] Polymer yarn

[0158] In certain embodiments, the polymer yarn, obtained after the drawing and / or annealing stages, is collected on one or more rotating spools.

[0159] In certain embodiments, the polymer yarn is wound, woven, knit, packed, coiled and / or further processed into a semi-finished and / or end-use article as further described herein.

[0160] In certain embodiments, the polymer yarn has a tenacity of at least about 0.1 g / Denier, 0.5 g / Denier, 1.0 g / Denier, 1.5 g / Denier, 2.0 g / Denier, 2.5 g / Denier, 3.0 g / Denier, 3.5 g / Denier, 4.0 g / Denier, 4.5 g / Denier, 5.0 g / Denier, 10 g / Denier, 20 g / Denier, 30 g / Denier, 40 g / Denier, 50 g / Denier or more. Tensile strength, specific strength or tenacity of fibres may be determined by known methods. For example, tenacity may be calculated by dividing the breaking load of the fibre by the fibre’s mass per unit length. The breaking load of the fibre is determined via a tensile testing machine which pulls the fibre from either end and measures the force required to break the fibre.

[0161] In certain embodiments, the polymer yarn has a high tensile modulus. For example, the polymer yarn may have a tensile modulus of about 1 ,000 g / d or more. The term tensile modulus is known in the art as a mechanical property that measures the stiffness of the fibre and its resistance to external forces. Tensile modulus may be determined by known methods such as by dividing tensile stress by tensile strain.

[0162] In certain embodiments, the polymer yarn is resistant to corrosive chemicals, hydrophobic, resistant to abrasion, has a low density and / or high impact strength.

[0163] In certain embodiments, the polymer yarn is medical grade. As used herein, the term “medical grade” refers to a polymer yarn which meets specific regulatory and quality standards such as those defined by the United States Food and Drug Administration (FDA) and the European Medicines Agency (EMA). Typically, such polymer yarns are biocompatible, capable of withstanding sterilizing methods, chemically inert, and / or have mechanical properties suitable for their intended medical use (e.g., flexibility, strength and / or resistance to wear and tear within the body). As such, medical grade yarn produced by the methods described herein may be distinguished from yarns used in textile (clothing) manufacture or the like.

[0164] In certain embodiments, the polymer yarn is non-resorbable. As used herein, the term ‘non- resorbable’ refers to a polymer which does not substantially break down or degrade within the human body to form non-toxic components.

[0165] In certain embodiments, the polymer yarn is colourless (e.g., is non-coloured with any dye and / or pigment).

[0166] In certain embodiments, the polymer yarn is alkane-free. In contrast to polymer yarn produced by traditional methods of gel-spinning (utilising toxic secondary solvents), the polymer may contain no detectable alkane (e.g., no hexane, heptane, dichloromethane and / or pentane). Advantageously, polymer yarn with no residual and / or detectable amounts of alkanes is particularly suitable for medical implants as further described herein.

[0167] Applications

[0168] Methods of further processing of polymer yarn are well known in the art. For example, polymer yarn may be woven using techniques that are well known in the art using any fabric weave such as basket weave, twill weave, plain weave and three-dimensional woven fabrics. Polymer yarn may be knitted according to conventional methods. In certain embodiments, the polymer yarn is knitted using a knitting machine. Tensioners can be used on the knitting machine to maintain constant tension of the fibres.

[0169] Medical Uses

[0170] In certain embodiments, the polymer yarn may be used to produce medical implants. For example, the polymer yarn may be used to produce sutures, cables, implantable valves, vascular grafts, mesh, or the like. For the purposes of the invention, medical implants may have excellent properties of biocompatibility and sterility. Typically, they are medical grade and preferably alkane-free.

[0171] In certain embodiments, the polymer yarn may be used to produce non-resorbable medical implants. For example, the polymer yarn may be used to produce non-resorbable sutures. The sutures may have braided or monofilament constructions. The sutures may have a surgical needle mounted to one or both ends of the suture. The sutures may be provided without surgical needles mounted. The sutures may be used in any suitable medical and / or surgical procedures. The size and type of suture may be dictated by the specific procedure being performed.

[0172] In certain embodiments, non-resorbable sutures are used in cardiovascular, vascular, orthopaedic, gastrointestinal applications. Non-resorbable sutures are typically used in applications where a permanent or extended period of fixation is required because a permanent or extended period of fixation is desirable during healing.

[0173] In certain embodiments, the polymer yarn may be used in soft tissue patches, thin film dressings, surgical felts, artificial blood vessels, artificial skins, sternum tapes, surgical mesh.

[0174] In certain embodiments, the polymer yarn is at least partially coated with an antimicrobial coating. For example, the polymer yarn may be immersed in an antimicrobial coating solution.

[0175] In certain embodiments, the polymer yarn is biocompatible.

[0176] In certain embodiments, the medical implant of the present invention comprises one or more additives. For example, the medical implant may further comprise antioxidants, processing aids, lubricants, anti-static agents, dyes. The additives may be present in typically effective amounts well known in the art, such as about 0.01 weight % to about 25 weight %.

[0177] In certain embodiments, the polymer is biologically inert and thus does not permit undesired growth of microorganisms and is not sensitive to attack by microorganisms. Typically, the medical implants comprise UHMWPE yarn as described herein.

[0178] Anti-ballistic articles

[0179] In certain embodiments, the polymer yarn, as produced in methods described herein, may be used to produce anti-ballistic articles. Typically, the anti-ballistic articles of the present invention may include bulletproof vests, body armour, helmets and / or the like.

[0180] In certain embodiments, the anti-ballistic article contains a stack of sheets. The sheets may comprise a layer of unidirectionally orientated fibres of the present invention.

[0181] In certain embodiments, the anti-ballistic article contains highly orientated polymer fibres.

[0182] In certain embodiments, the sheets may contain one or more monolayers of unidirectionally orientated fibres of the present invention. In certain embodiments, the sheet may be woven or non-woven. In certain embodiments, the use of the polymer yarn results in excellent anti-ballistic performance per unit weight. Typically, the anti-ballistic articles comprise UHMWPE yarn as produced by any method as described herein.

[0183] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to” and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0184] Features, integers, characteristics or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of the features and / or steps are mutually exclusive. The invention is not restricted to any details of any foregoing embodiments. The invention extends to any novel one, or novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0185] The reader’s attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0186] Examples

[0187] In the following, the invention will be explained in more detail by means of non-limiting examples of specific embodiments. In the example experiments, standard reagents and buffers free from contamination are used.

[0188] Example 1 - Extraction system

[0189] An extraction system 200 according to some embodiments of the invention is illustrated in Figure 2. System 200 may include a CO2storage tank (201), a pump (204) for increasing the extraction pressure of the CO2, and a heat exchanger (205) for heating the pressurised CO2to supercritical conditions.

[0190] The supercritical CO2fluid may be introduced into one or more extraction vessels (206). The extraction vessels may be pre-loaded with gel fibres comprising the polymer (e.g., UHMWPE) and the first solvent. The supercritical CO2fluid may be capable of flowing through the gel fibres in at least one or more of the extraction vessels (206).

[0191] The supercritical CO2solution, which includes the extracted first solvent, may be introduced into one or more separation vessels (207) to be separated. The separation vessels may further include one or more filters and / or containers (not shown) for collecting the separated first solvent.

[0192] Once the first solvent has been separated, the fraction containing the extracted gel fibres is typically re-collected from the extraction vessels (206). In other words, the gel fibres typically remain in the extraction vessels (206) where they may be physically removed after the supercritical CO2extraction step. The supercritical CO2which contains the first solvent can be released in one or more separation vessels (207) where the solvent can be deposited once the pressure and / or temperature have been reduced.

[0193] Typically, the separation vessels include a tank at which the supercritical CO2may be depressurized using a pressure release valve and maintained at a particular temperature (e.g., 30C to 60C) until the CO2is converted into gas. The evaporated CO2may be recycled and condensed back into liquid CO2.

[0194] Example 2 - UHMWPE gel production

[0195] UHMWPE gel was produced 24 hours prior to the extraction process, using mineral oil as the first solvent. This allowed a significant amount of oil to be removed via syneresis.

[0196] A number of samples were produced. Each of these samples was washed in varying amounts of hexane. The samples were assessed via a Soxhlet extraction to determine the quantity of oil in the yarn.

[0197] Sample A were samples which had not been washed in hexane. This was shown to have 80% oil content of the total mass.

[0198] Sample B were samples which had been washed in a small amount (i.e., through 4 metres of hexane). Specifically, the spool of yarn was passed through a 2 x 2 L measuring cylinder of hexane. The yarn was passed through the solvent and equals 1 dip. The yarn passed 0.5 m down through the solvent, then 0.5 m back to the surface of the solvent. This was done twice in each cylinder meaning a total contact length of 2 m of solvent / yarn interaction. Sample B had 45% oil as its total mass.

[0199] Sample C was thoroughly washed in a large amount (i.e., through 8 metres) of hexane. Specifically, the spool of yarn was passed through a 4 x 2 L measuring cylinder of hexane. Sample C had 3 % oil as its total mass.

[0200] Example 3 - extraction process

[0201] Supercritical carbon dioxide acts as a second solvent in this production system.

[0202] A sample of each UHMWPE yarn was placed within a cellulose thimble. This thimble was placed inside an extraction vessel (0.5L) and the vessel was sealed. The extraction vessel was filled with carbon dioxide (food grade) and heated to 100 bar and 80C. This allowed the carbon dioxide to reach a supercritical phase.

[0203] Once, the pressure and temperature had been achieved a flow of carbon dioxide (at the same pressure and temperature) was passed through the vessel (20 g / min). This continued for a total of 30 minutes after which time the flow of carbon dioxide was stopped, and the vessel depressurized (6 bar per minute) and the vessel returned to room temperature.

[0204] After this, each sample of UHMPWE yarn was assessed for mass loss via this extraction process.

[0205] Via the scCO2route, sample A had lost 51% of its initial mass. Sample B had lost 3% of its mass and sample C had lost 1% of its mass.

[0206] Example 4 - solvent recovery process

[0207] Several 500 g samples of UHMWPE and oil yarn wound on porous bobbins were placed on a spindle (Figure 4, top), inserted into an extraction vessel, and the vessel was sealed. The extraction vessel was filled with carbon dioxide (food grade) and heated above 50 °C and above 100 bar. This allowed the carbon dioxide to reach a supercritical phase.

[0208] Once the pressure and temperature had been achieved, a flow of carbon dioxide (at the same pressure and temperature) was passed through the vessel at 100-1000 g / min. This continued for a total of 120 minutes after which time the flow of carbon dioxide was stopped, the vessel was depressurized (2 bar per minute), and the vessel returned to room temperature. The spindle with porous bobbins was removed from the vessel, showing dried UHMWPE yarn (figure 4, bottom). After this, samples of UHMPWE yarn were assessed for mass loss via this extraction process.

[0209] Via the scCO2route, samples consisted of <0.5% of the total mass as oil (Figure 5). The extracted oil was recovered at >95% yield from the CO2vessel. The recovered oil was shown by mass spectrometry to be unaffected by the process (Figure 3) and fully recyclable.

[0210] CO2washed yarn was drawn following established protocols and analyzed by tensile testing. The final yarn washed with CO2showed tensile properties (Figure 7) equal to yarn washed with a petroleum-based solvent (Figure 6). An example of the properties reached for washed UHMWPE yarn is given in Figure 6. The tensile properties of a CO2washed sample are shown in Figure 7. Note the average tenacity of >30 g / den, the initial modulus of >1200 g / den, and the strain at peak of >2%. These are typical target values for UHMWPE yarn, that have been reached comfortably using the novel CO2-based extraction process.

[0211] Conclusion

[0212] These experiments demonstrate that supercritical CO2can be used to successfully extract mineral oil from UHMWPE and produce equivalent yarn, leading to a significant reduction in harmful solvent usage and environmental impact to produce yarn as compared to known techniques using hexane washing.

Claims

CLAIMS1 . A method of producing a polymer yarn, comprising:(i) dissolving the polymer in a first solvent to form a solution;(ii) extruding the solution to form gel fibres comprising the polymer and the first solvent;(iii) extracting the first solvent using supercritical or subcritical carbon dioxide, wherein the extracted first solvent is captured for re-use; and(iv) drawing the fibres to form the polymer yarn following extraction of the first solvent using the supercritical or subcritical carbon dioxide.

2. The method according to claim 1 , wherein the first solvent is extracted using supercritical carbon dioxide (scCO2).

3. The method according to claim 2, wherein extracting the first solvent consists of use of scCO2.

4. The method according to any one of claims 1 to 3, wherein the polymer is an Ultra High Molecular Weight Polyolefin.

5. The method according to any one of claims 1 to 4, wherein the polymer is Ultra High Molecular Weight Polyethylene (UHMWPE).

6. The method according to any one of claims 1 to 5, wherein the first solvent is nonpolar.

7. The method according to any one of claims 1 to 6, wherein the first solvent is mineral oil, decalin, tetralin, naphthalene, dodecane, paraffin oil, benzene, toluene, xylene, dichlorobenzene and / or trichlorobenzene.

8. The method according to any one of claims 1 to 7, wherein the extracted first solvent is captured as a liquid for re-use.

9. The method according to any one of claims 1 to 8, wherein the first solvent is mineral oil.

10. The method according to any one of claims 1 to 9, wherein the first solvent is extracted at a temperature of greater than about 31 °C, a pressure greater than about 74 bar, and / or a flow rate greater than about 1 g I min.11 . The method according to claim 10, wherein the temperature is above about 50°C, the pressure is above about 100 bar, and / or the flow rate is above about 100 g / min.

12. The method according to any of claims 1 to 11 , wherein the step of extracting the first solvent comprises:(a) inserting the gel fibres into one or more extraction vessels;(b) passing the supercritical or subcritical carbon dioxide through the gel fibres; and(c) separating the gel fibres from the supercritical carbon dioxide.

13. The method according to any one of claims 1 to 12, wherein the extracted first solvent is captured for re-use in step (i) and / or the supercritical or subcritical carbon dioxide is also recycled.

14. The method according to any one of claims 1 to 13, wherein the polymer yarn is sterile.

15. The method according to any one of claims 1 to 14, wherein the polymer yarn is alkane- free.

16. The method according to any one of claims 1 to 15, wherein the polymer yarn is colourless, non-resorbable and / or non-toxic.

17. The method according to any one of claims 1 to 16, wherein the solution is extruded through a spinneret to form continuous gel fibres and / or the gel fibres are cooled and / or solidified prior to extraction of the solvent.

18. The method according to any one of claims 1 to 17, wherein 90% or more of the first solvent is extracted from the gel fibre during step (iii).

19. A polymer yarn obtainable by the method according to any one of claims 1 to 18.

20. A medical implant comprising the polymer yarn according to claim 19, optionally wherein the implant is a suture, cable, implantable valve, vascular graft, or mesh.

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