WO2007013858A1

WO2007013858A1 - Method & apparatus for producing fiber yarn

Info

Publication number: WO2007013858A1
Application number: PCT/SG2006/000208
Authority: WO
Inventors: Wee Eong Teo; Kazutoshi Fujihara; Seeram Ramakrishna
Original assignee: National University Of Singapore
Priority date: 2005-07-25
Filing date: 2006-07-25
Publication date: 2007-02-01

Abstract

A method for producing a fiber yarn comprising the step of electrospinning a fiber into a non-solvent contained within a receptacle, the receptacle comprising an outlet conduit to allow non-solvent to flow therefrom, wherein the dimensions of the outlet conduit are such that as non-solvent flows therefrom said yarn is formed therein from said electrospun fiber.

Description

METHOD & APPARATUS FOR PRODUCING FIBER YARN

Technical Field

The present invention generally relates to the fabrication of electrospun fiber yarns and to apparatuses used in their manufacture.

Background

Textile fabrics have been used in various industrial applications, such as protective cloth, sports wear and apparel cloths. They can be chemically functionalized to achieve desired properties such as higher hydrophobicity, higher moisture absorption, excellent draping, ease of stain removal, anti-microbial activity, etc. In order to enhance these functionalities, the fiber surface area to volume ratio has been increased by reducing the fiber diameter.

In industrial scale manufacture, there are difficulties associated with producing smaller diameter fibers. To date, most fibers used in industry are limited to fiber diameters of more than 2μm.

Electrospinning is a relatively easy and simple method to produce smaller diameter continuous fibers, that is, fibers of diameters in the nanometer to sub- micron size range. In electrospinning, a charge of about 5 to about 30 kV is applied by an electrode to a polymer solution. The charged polymer solution is separated at a defined distance from a collector, which is also charged with an opposite polarity to the first electrode. Hence, a static electric field is established between the charged polymer solution and the collector to thereby form a Taylor Cone therebetween. The Taylor Cone forms due to the competing forces of the static electric field and the polymer solution's surface tension. Assuming that the concentration of the polymer in solution is sufficiently high to cause molecular chain entanglement, a fiber is drawn from the tip of the Taylor cone onto the collector.

The charged polymer solution is usually ejected from a nozzle of a spinneret to form a jet which is deposited onto the oppositely charged collector. While the jet travels from the nozzle to the collector, the solvent of the polymer solution evaporates so that a polymer fiber is left to accumulate on the collector. The charge on the fibers eventually dissipates into the surrounding environment. The fibers may have a diameter between about 50 nanometers to about 10 microns A problem associated with known electrospinning techniques is that as the non-woven fibers are so small and fragile, it can often be very difficult to wind the yarn on a roll. This is particularly the case for electrospun yarns being produced on an industrial scale. There is a need to provide a method of producing electrospun fiber yarns that overcomes, or at least ameliorates, one or more of the disadvantages described above .

There is a need to provide a method of producing continuous yarn from electrospun fibers on an industrial scale.

There is a need to provide a method for continuously producing yarn from electrospun fibers which is undertaken on such a scale that it may be commercially viable.

Summary

According to a first aspect, there is provided a method for producing a fiber yarn comprising the step of electrospinning a fiber into a non-solvent contained within a receptacle, the receptacle comprising an outlet conduit to allow non-solvent to flow therefrom, wherein the dimensions of the outlet conduit are such that as non- solvent flows therefrom, flow conditions of said non- solvent within said receptacle form said yarn.

Advantageously, the non-solvent provides a support for the electrospun fibers and thereby inhibits breakage of said fibers. According to a second aspect, there is provided a method for producing a fiber yarn comprising the step of rotating a non-solvent about an axis as a fiber is electrospun from a charged polymer solution and dispensed into said rotating non-solvent to thereby form said fiber yarn.

Advantageously, the rotation of said fibers causes said fibers to twist and thereby form a yarn.

Advantageously, the rotation of said fibers during their formation within said non-solvent allows the formed yarn to be wound on a roller without becoming tangled.

According to a third aspect, there is provided a fiber yarn made in a method comprising the step of electrospinning a fiber into a non-solvent contained within a receptacle, the receptacle comprising an outlet conduit to allow non-solvent to flow therefrom, wherein the dimensions of the outlet conduit are such that as non- solvent flows therefrom, flow conditions of said non- solvent within said receptacle form said yarn.

According to a fourth aspect, there is provided a fiber yarn made in a method comprising the step of rotating a non-solvent about an axis as an electrospun fiber is dispensed into said rotating non-solvent to thereby produce said fiber yarn. According to a fifth aspect, there is provided a fiber yarn manufacturing apparatus for making fiber yarn, the apparatus comprising: a non-solvent receptacle for containing non-solvent therein, said non-solvent being at least partially insoluble to a polymer solution; a nozzle disposed above the non-solvent for dispensing a jet of charged polymer solution into said non-solvent; and an outlet conduit extending from said receptacle to allow non-solvent to flow therefrom, wherein the dimensions of the outlet conduit are such that as non-solvent flows therefrom, flow conditions of said non-solvent within said receptacle form said yarn.

According to a sixth aspect, there is provided a fiber yarn manufacturing system comprising: a receptacle for containing non-solvent therein; and a rotator capable of rotating the non-solvent about an axis, wherein in use, a fiber is electrospun from a charged polymer solution and dispensed into said rotating non- solvent to produce said fiber yarn.

Definitions

The following words and terms used herein shall have the meaning indicated: The term "electrospun fiber yarn" is to be interpreted broadly to include any yarns that have been formed from fibers that had been electrospun. Such fibers may have diameters from the nanometer to the sub-micron scale. The term "polymer solution" is to be interpreted broadly to include any solution comprising one or more polymer, copolymer or polymer blend dissolved in a solvent and which comprises a concentration of polymers that is capable of being electrospun. Exemplary polymers include, but are not limited to, poly (vinylidenefluoride) , poly (vinylidene fluoride-co-hexafluoropropylene) , polyacrylonitrile, poly (acrylonitrile-co-methacrylate) , polymethylmethacrylate, polyvinylchloride, poly (vinylidenechloride-co-acrylate) , polyethylene, polypropylene, nylon series such as nylonl2 and nylon-4,6, aramid, polybenzimidazole, polyvinylalcohol, cellulose, cellulose acetate, cellulose acetate butylate, polyvinyl pyrrolidone-vinyl acetates, poly (bis- (2-methoxy- ethoxyethoxy) ) phosphazene (MEEP) , poly (ethylene imide) , poly (ethylene succinate), poly (ethylene sulphide), poly (oxymethylene-oligo-oxyethylene) , poly (propyleneoxide) , poly (vinyl acetate), polyaniline, poly (ethylene terephthalate) , poly (hydroxy butyrate) , poly (ethylene oxide), SBS copolymer, poly (lacticacid) , polypeptide, biopolymer such as protein, pitch series such as coal-tar pitch and petroleum pitch. Copolymers and blends of the above polymers may be used. Exemplary polymer solutions for electrospinning fibers are disclosed in US Patent Nos. 6,790,528, 6,616,435, 6,713,011, 4,043,331 and 4,878,908.

The term "non-solvent" is to be interpreted broadly to include any liquids that, at least partially, do not dissolve the polymer of the fiber. In some embodiments, the non-solvent is water.

The term "vortex-like manner" is to be interpreted broadly to include a spiral motion of non-solvent within a receptacle, wherein spiral motion of the mass of the non- solvent tends to draw the non-solvent towards its center. The term "composite yarn" is to be interpreted broadly to include any yarn that may be made from a mixture of polymer solutions.

Unless specified otherwise, the terms "comprising" and "comprise", and grammatical variants thereof, are intended to represent "open" or "inclusive" language such that they include recited elements but also permit inclusion of additional, unrecited elements.

As used herein, the term "about", in the context of concentrations of components of the formulations, typically means +/- 5% of the stated value, more typically +/- 4% of the stated value, more typically +/- 3% of the stated value, more typically, +/- 2% of the stated value, even more typically +/- 1% of the stated value, and even more typically +/- 0.5% of the stated value.

Throughout this disclosure, certain embodiments may be disclosed in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 ^• to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

Disclosure of Optional Embodiments

Exemplary, non-limiting embodiments of a method of producing a fiber yarn comprising the step of electrospinning a fiber into a non-solvent contained within a receptacle, the receptacle comprising an outlet conduit to allow non-solvent to flow therefrom, wherein the dimensions of the outlet conduit are such that as non- solvent flows therefrom, flow conditions of said non- solvent within said receptacle form said yarn.

The dimensions of the outlet conduit may be such that it aids in the rotation of said non-solvent contained within said receptacle. The rotating may be such that said non-solvent is caused to flow in a vortex-like manner. Advantageously, the spiral motion of the non- solvent flowing in a vortex-like manner promotes twisting of the fiber and thereby assists in the formation of the yarn. The method may comprise the step of removing said formed fiber yarn from said non-solvent. Removal of the fiber yarn from the non-solvent allows it to be wound on a roller.

The method may comprise the step of injecting multiple jets of said charged polymer solution into said rotating non-solvent to form multiple fibers. Advantageously, the rotation of said non-solvent causes said formed multiple fibers to form a single fiber yarn. In one embodiment, multiple jets of different types of charged polymer solutions may be injected into said rotating non-solvent to form multiple fibers. These fibers may be twisted by the rotating non-solvent to form a single composite fiber yarn.

The method may comprise the step of injecting a jet of said charged polymer solution into said non-solvent, wherein said jet is projected from at least one spinneret selected from the group consisting of a uniaxial spinneret, a co-axial spinneret, a bi-capillary spinneret and a multi-capillary spinneret. The method may comprise the step of using water as the non-solvent.

The method may comprise the step of applying an electrical ground to said non-solvent during electrospinning of said polymer solution. The electrical ground provides an electrical pathway to dissipate the electric charge of the formed fiber present in the non- solvent .

The method may comprise the step of providing one or more additives in said non-solvent selected from the group consisting of sugars, amino acids, proteins, growth factors, vitamins, hormones, cytokines, coloring dye, binders and cells. These additives may therefore be adsorbed or encapsulated on the surface of the formed fibers to thereby enhance the functionality of the yarn.

In one embodiment, the rotating fluid flow may be created by the step of allowing said rotating solvent to be removed from said receptacle. The outlet conduit may be dimensioned such that as said non-solvent flows therefrom, said non-solvent flows in a vortex-like manner within said receptacle.

In one embodiment, to create the vortex, the outlet conduit has a diameter of about 5mm to about 20mm, about 10mm to about 20mm, about 15mm to about 20mm, about 5mm to about 10mm, about 5mm to about 15mm. In one embodiment, to create the vortex, the height of the non-solvent above the outlet conduit is about 100 mm to about 200 mm, about 120 mm to about 200 mm, about 140 mm to about 200 mm, about 160 mm to about 200 mm, about 180 mm to about 200 mm, about 100 mm to about 180 mm, about 100 mm to about 160 mm, about 100 mm to about 140 mm, about 100 mm to about 120 mm. In one embodiment, the height of water as non- solvent in a receptacle above a 5 mm diameter outlet conduit having a diameter of 350 mm is maintained at a level between about 100 to about 200 mm to create the vortex. It will be appreciated that the above disclosed embodiments are exemplary and that the creation of the vortex may be dependent on the viscosity of the non- solvent used, the head pressure of the non-solvent (ie the level of non-solvent above the outlet conduit) and possibly the shape and dimensions of the receptacle. A mathematical model for the theoretical formation of a vortex of a non-compressible fluid is known in the art. For example, Transport Phenomena, Bird et al, Chapter 3, John Wiley & Sons, 1960 provides a general discussion of vortex fluid flows and in particular pages 108-111 disclose a mathematical model for prediction of a vortex depth in an agitated tank. Vortices in agitated tanks have also been experimentally investigated in other literature such as Memoirs of the Faculty of Engineering, Kyoto University, Vol. XVII, No. Ill, July 1955 by S Nagata et al. Although these are idealized fluid flow models they can function as an approximation of vortex fluid flow in a receptacle. The creation of a vortex may ultimately be verified empirically.

In one embodiment, the rotating fluid flow may be created by the step of pumping non-solvent into a receptacle to cause said non-solvent to rotate therein. In use, said pump pumps non-solvent into said receptacle via a non-solvent inlet provided within said receptacle. Advantageously, the dimension of said non-solvent inlet and the pressure exerted by said pump causes said non- solvent to flow in a vortex-like manner within said receptacle.

In one embodiment, to create the vortex, the non- solvent is pumped substantially tangential to the surface of the non-solvent at a speed selected from the group consisting of about 5 m/s to about 15 m/s, about 8 m/s to about 15 m/s, about 10 m/s to about 15 m/s, about 10 m/s to about 14 m/s, and about 11 m/s to about 13 m/s.

The method may comprise the step of providing a funnel disposed within said receptacle such that said formed fiber is emitted from the outlet conduit located in said receptacle via the spout of said funnel, wherein the funnel is dimensioned such that it promotes the creation of the vortex-like fluid flow within the receptacle.

In one embodiment, to create the vortex, the funnel outlet has a diameter of about 5mm to about 20mm, about 10mm to about 20mm, about 15mm to about 20mm, about 5mm to about 10mm, about 5mm to about 15mm.

More advantageously, the spout of the funnel acts as a guide to guide the formed yarn into the hole and thereby be ejected from the receptacle.

In one embodiment, the charged polymer solution may be selected from the group consisting of polylactide, polycaprolactone, poly (glycolic acid), polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyesters, polyamides, polyimides, polyethylenes, polyolefins, polypropylenes, poly (vinyl alcohols), polyacrylonitriles, polycarbamides, polyurethanes and mixtures thereof. Copolymers, polymer melts and blends of the above polymers may also be used. In one embodiment, the solution to be electrospun may be ceramic precursors. A method of electrospinning ceramic precursors without polymer additives is disclosed in ""Direct Electrospinning of Ultrafine Titania Fibres in the Absence of Polymer Additives and Formation of Pure Anatase Titania Fibres at Low Temperatures' , Son et al , Nanotechnology, 11, (2006) p439-443.

The method may comprise the step of selecting the diameter of said fiber yarn by varying any one or more of the following: (i) the feedrate of said charged polymer solution into said non-solvent; (ii) the number of spinnerets used to inject said charged polymer solution into said non-solvent; (iii) the diameter of said charged polymer solution that is injected by a spinneret into the non-solvent; and (iv) the size of a hole provided in said receptacle containing said rotating non-solvent.

The fiber yarn may be at least one of a solid fiber yarn, hollow fiber yarn, tubular fiber yarn and a twisted fiber yarn. The method may comprise the step of providing an auxiliary electrode to a jet of said polymer solution as it is electrospun into said non-solvent, wherein said auxiliary electrode distorts the electrostatic field of said jet of polymer solution to thereby cause it to rotate about an axis as it enters said non-solvent. The use of the auxiliary electrodes controls the flight path of the charged electrospinning jet. It will be appreciated that the actual spinning jet may be unstable and therefore the "rotation" is not necessarily about a fixed axis. A description of the effects of an auxiliary electrode on the flight of an electrospun jet is disclosed in M review on electrospinning design and nanofibre assemblies' , W. E. Teo and S Ramakrishna, Nanotechnology, 17 (2006) p89-106.

The method may comprise the step of agitating the non-solvent in a receptacle to cause it to rotate about the axis .

The method may comprise the step of rotating a receptacle containing said non-solvent to cause said non- solvent to rotate about the axis.

Brief Description Of Drawings

The accompanying drawings illustrate a disclosed embodiment and serve to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

Fig. 1 is a schematic diagram of a first disclosed apparatus for forming fiber yarn from electrospun fiber.

Fig. 2 is a schematic diagram of a second disclosed apparatus for forming fiber yarn from electrospun fiber.

Fig. 3 is a schematic diagram of multiple spinnerets being used to form a single fiber yarn in accordance with a disclosed embodiment.

Fig. 4A is an SEM image at 400Ox magnification of poly (vinylidene fluoride) electrospun fiber yarn formed in a method of the disclosed embodiment.

Fig. 4B is an SEM image at 300Ox magnification of a cross-sectional view of the fiber yarn of Fig. 4A.

Fig. 4C is an SEM image at 200Ox magnification of poly (caprolactone) electrospun fiber yarn formed in a method of the disclosed embodiment.

Fig. 4D is an SEM image at 300Ox magnification of a cross-sectional view of the fiber yarn of Fig. 4C.

Fig. 5 is an SEM image at 50Ox magnification of the twisted poly (caprolactone) fiber yarn formed in a method of the disclosed embodiment.

Fig. 6 is a photograph diagram of a tape-like electrospun fiber yarn drawn at a speed of 1 m/min without vortex in the non-solvent.

Fig. 7 is an SEM image at 80Ox magnification of a tape-like electrospun fiber yarn drawn at a speed of 1 m/min without vortex in the non-solvent. Fig. 8 is a schematic diagram of a third disclosed apparatus for forming fiber yarn from electrospun fiber. Disclosure of Detailed Embodiment

Fig. 1 shows a schematic diagram of an apparatus 100 for forming a fiber yarn according to a disclosed embodiment. The apparatus 100 comprises a non-solvent receptacle in the form of container 3 for containing non- solvent in the form of water which is insoluble to a charged polymer solution which is electrospun to form a fiber. The container 3 is disposed about a vertical axis as shown by arrow 20. As will be described further below, non-solvent present in the container 3 is made to rotate in the direction of arrow 22 about the axis 20 to allow the non-solvent to flow in a vortex fluid flow 10 within the container 3. As will be further described below, the vortex fluid flow 10 twists the fibers which are electrospun into the non-solvent to thereby form a fiber yarn 14.

A spinneret 1 having a nozzle IA is disposed above the container 3 to electrospin a fiber into the non- solvent of the container 3. Electrospinning is a known processes and is described in the literature, for example in Fong, H.; Reneker, D. H.; J. Polym. Sci., Part B, 37 (1999), 3488, and in US Patent Nos. 6,616,435, 6,713,011, 4,043,331, 4,878,908 and 6,790,528. A high voltage 2 of about 5 to 50 kV is applied to the spinneret to charge the polymer solution contained therein. Electrospinning occurs as a jet 5 of the charged polymer solution is dispensed from the nozzle IA into the rotating non- solvent of the container 3. After dispensation of the jet 5 from the nozzle IA, the solvent of the charged polymer solution evaporates to thereby form a fiber which deposits as a fiber mesh 8 on the surface of the rotating non-solvent disposed within the container 3. The apparatus also has an outlet conduit in the form of a hole 9 located in the bottom of the container 3. The hole is disposed on the axis 20 and is dimensioned such that a vortex fluid flow 10 is created within the container 3 as non-solvent is emitted from the hole 9 under gravity.

The high voltage 2 is also applied to a ring-shaped electrode 7 disposed between the spinneret 1 and top of the container 3 to thereby distort the electrostatic field surrounding the polymer jet 5 as it is emitted from the nozzle IA. Distortion of the electrostatic field surrounding the polymer jet 5 promotes rotation of the polymer jet 5 about the axis 20 within the electrostatic field defined by the ring-shaped electrode 7 as it forms fiber and enters the non-solvent.

To aid in the formation of the polymer jet 5, the non-solvent is grounded to establish a static electric field between the spinneret 1 and container 3 and to thereby form a Taylor Cone therebetween. The grounded non-solvent also allows for an electrical pathway to dissipate the electric charge of the formed fiber mesh 8 present in the non-solvent.

When the fiber mesh 8 is deposited on the surface of the non-solvent just before it is drawn into a hole 9 at the bottom of the container 3, other substances such as salt, nano-particles, cells, proteins, vitamins, sugar, etc, may be added on top of the fiber mesh 8 such that the substance gets encapsulated or mixed with the fibers as it is drawn into a fiber yarn 14. Other chemicals such as, but not limited to, sugars, amino acids, proteins, growth factors, vitamins, hormones, cytokines, coloring dye, binders may be added to the non-solvent such that the fiber yarn 14 is automatically coated during the drawing process. In this embodiment, the container 3 is cylindrical in shape but it will be appreciated that the container 3 can be of any shape.

The vortex fluid flow 10 is created in the non- solvent to facilitate formation of the fiber yarn 14 from the fiber mesh 8 that is deposited on the surface of the non-solvent.

In the apparatus 100, in addition to the hole 9, the rotator also comprises pumping non-solvent under pressure into the container to thereby promote vortex fluid flow formation. The rotator further comprises a liquid conduit 18 which is disposed adjacent to the surface of the container 3 to emit pressurized non-solvent which has been pumped by pump 11. The pressurized non-solvent is tangentially introduced onto the surface of the non- solvent within container 3 in the rotating direction 22 of the vortex fluid flow 10. The inlet of the pump 11 is connected to a non-solvent feed tank 13, disposed at the bottom of container 3, for feeding non-solvent into the container. The speed of the vortex fluid flow 10 is controlled by the rate at which non-solvent is pumped into the container 3. An opening 12 at the side of container 3 near the top is used to discharge any excess non-solvent to feed tank 13 so as to maintain the level of non-solvent in container 3. This excess non-solvent is recycled back to container 3 from feed tank 13 via pump 11 and liquid conduit 18.

The non-solvent that flows out through hole 9 flows into feed tank 13 and is recycled back to container 3 via pump 11 and liquid conduit 18.

The fiber yarn 14 is drawn from hole 9 located at the bottom of container 3. It is guided by a guide 19 to a roller 15. As the roller 15 rotates, it winds the drawn fiber yarn 14 onto it. An example of a fiber yarn 14 formed according to this embodiment is seen from Figs. 4A and 4B.

The vortex fluid flow 10 causes the fiber to twist while it is resident in the container 3. The twisting of the fiber produces a yarn 14.

Fig. 2 shows a schematic diagram of an apparatus 100' having a number of technical features that are the same as the apparatus 100 described above which are indicated by the same reference numeral but with a prime symbol (')• However, unlike the apparatus 100, the apparatus 100' does not have a ring electrode 7 but it does further comprise a funnel 16' disposed within the container 3' such that the inlet 16A' of the funnel 16' is disposed directly below the spinneret to receive the fiber mesh 8' therein. The outlet 16B' of the funnel 16' extends through the hole 9' . The funnel 16' is used to aid in the creation of the vortex fluid flow 10' such that the vortex fluid flow 10' extents into hole 9' . In this way, the fiber mesh 8' is assisted to be drawn into the vortex fluid flow 10' and thereby twist and form the fiber yarn 14.

Fig. 3 is a schematic diagram of the apparatus of Fig. 1 wherein multiple spinnerets (IA, IB, 1C, ID) are used to form a single fiber yarn 14 from respective polymer jets (5A, 5B, 5C, 5D) . It will be appreciated that by using multiple spinnerets (IA, IB, 1C, ID) , it is possible to use different polymer solutions in each spinneret to form a single fiber yarn 14 made up of a mixture of fibers. This is particularly advantageous because it permits the formation of fibers having different functionalities or morphologies. Additionally, by varying the number of polymer jets, it is possible to vary the diameter of the yarn 14. To form a hollow fiber, a filament in the form of a flexible rod 17 is passed through hole 9 at the bottom of container 3 to cause fiber yarn 14 to form around the flexible rod 17. An example of a tubular fiber yarn can be seen from Fig. 4D showing a SEM image at 300Ox magnification .

Finer diameter electrospun fiber yarns or single electrospun fibers are drawn individually from different containers and collected into a central container where there is a rapid vortex such that a few electrospun fiber yarns or electrospun fibers are twisted together.

A higher feedrate of polymer solution to spinneret 1 or using multiple spinnerets (Fig. 3) during electrospinning may yield higher production of continuous electrospun fiber yarn 14. The use of multiple spinnerets may result in a hollow yarn, as seen in Fig. 4, when a vortex is created in the container 3. As the formed fibers are sucked into the vortex fluid flow 10, a hollow space is created in the middle of the yarn 14 due to the spiral forces of the vortex fluid flow 10. The hollow yarn 14 forms due to evaporation of the non- solvent from the core of the yarn. Alternatively, or in addition to, the flexible rod or filament 17 (refer to Fig. 3) may be used to form the hollow fiber as described above.

The diameter of the fiber yarn 14 is able to be varied by:

(i) varying the feedrate to the spinneret 1; (ii) the number of spinnerets 1 used; (iii) where multiple fibers are used to form the yarn, the diameter of the electrospun fibers that make up the fiber yarn 14; and (iv) the speed at which the non-solvent exits through the hole 9 located at the bottom of the container 3.

Fig. 8 shows a schematic diagram of an apparatus 100" having a number of technical features that are the same as the apparatus 100 described above, which are indicated by the same reference numeral but with an end quotation symbol (") . However, unlike the apparatus 100, the apparatus 100" does not have a ring electrode 7, vortex fluid flow 10, pump 11, opening 12 and liquid conduit 18.

If the vortex fluid flow 10 does not extend through the hole 9" located in the bottom of container 3", or if there is no vortex fluid flow 10, it may be possible to draw the fiber yarn 14" from the hole 9" located in the bottom of container 3" through the use of a barbed stick (not shown) to initiate the fiber yarn 14" drawing process. The barbed stick may be used to latch onto the electrospun fiber mesh 8" on the surface of the non- solvent so as to draw the fiber yarn 14" through the hole 9" located at the bottom of the container 3" after which normal drawing process may proceed.

Post-treatment of Fiber yarn The formed fiber yarn 14, after passing through the hole 9, is able to be passed through a series of blowers and/or heating elements (not shown) to dry the fiber yarn before collecting on the roller 15.

The fiber yarn is also able to be mechanically twisted and/or braided after it is drawn out from the hole 9 of the container 3 before being wound onto a roller 15. Examples

Non-limiting examples of the invention will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

Example 1 - Yarn drawn into the vortex using a single spinneret

The apparatus of Fig. 1 was used on this experiment. A hole (9) with a diameter of 5 mm located in the bottom of the container (3) having a diameter of 35cm was filled with water as the non-solvent. The water flowed from the hole (9) under gravity to create the vortex fluid flow (10) of the water. Water was dispelled from the container (3) into the feed tank (13) . The pump (11) recycled the water back to the container (3) via liquid conduit (18) at a pump speed of 900 1/hr. The diameter of liquid conduit (18) is 15 mm.

The polymer solution was prepared by dissolving Polyvinylidene fluoride-co-Hexafluoropropylene (PVDF-co- HFP) (M_w 455,000) from Aldrich of St. Louis, Missouri, United States of America in a mixture of 40% dimethylacetamide and 60% acetone before being heated to 60⁰C. The concentration of PVDF-co-HFP in solution was 0.12g/ml.

Electrospinning was carried using a high voltage power supply (2) from Gamma High Voltage Research Inc of Ormond Beach, Florida, United States of America. A voltage of 12kV was applied to the polymer solution. A kd Scientific syringe pump was used to provide constant feedrates of lml/hr, 2ml/hr, 5ml/hr, 8ml/hr, 12ml/hr to the spinneret (1) . The inner diameter of the spinneret nozzle (IA) was 0.21 mm. The continuous yarn collection timing without breakage was noted up to 1 minute for the different feedrates.

The properties of the yarn produced in this experiment are tabulated in Table 1.

Table 1. Properties of electros un fiber arn

Fig. 4A is an SEM image at 400Ox magnification of the poly (vinylidene fluoride) electrospun fiber yarn formed using a feedrate of 5ml/hr. Fig. 4B is an SEM image at 300Ox magnification of a cross-sectional view of the fiber yarn of Fig. 4A. It can be seen from Fig. 4A and Fig. 4B that a micro-sized diameter fiber yarn was produced from nano-sized diameter fibers.

Example 2 - Yarn drawn into the vortex using single spinneret with a funnel below

The apparatus of Fig. 2 was used on this experiment. A funnel (16') with an outlet (16B') having a diameter of 6 mm was located at the bottom of container (3') having a diameter of 24cm such that the outlet (16B') extended from the hole (9')- The container (3') was filled with water as the non-solvent. The funnel (16') aided in the creation of the vortex fluid flow (10') in the container (3') and allowed the fiber yarn (14') to be drawn from the funnel outlet (16B' ) easily.

Water was dispelled from the container (3') into the feed tank (13'). The pump (H') recycled the water back to the container (3') via liquid conduit (18') at a pump speed of 900 1/hr. The diameter of liquid conduit (18') is 15 mm.

The polymer solution was prepared by dissolving Polycaprolactone (PCL) (M_n 80000) from Aldrich of St Louis, Missouri, United States of America in a mixture of 80% dichloromethane and 20% N,N-dimethylformamide. The concentration of PCL in solution was 0.14g/ml.

Electrospinning was carried out by connecting a high voltage power supply from Gamma High Voltage Research HV Inc of Ormond Beach, Florida, United States of America. A voltage of 1OkV was applied to the polymer solution. A kd Scientific syringe pump was used to provide constant feedrates of lml/hr, 2ml/hr, 5ml/hr, 10ml/hr to the spinneret (I' ) • The inner diameter of the spinneret nozzle (IA' ) was 0.21 mm.

The properties of the yarn produced in this experiment are tabulated in Table 2.

Table 2. Properties of electrospun fiber yarn with funnel

Comparing the data of Table 2 with that of Table 1 for Example 1 above, it can be seen that the use of the funnel allows an increase in the take-up speed for forming the yarn. Example 3 - Yarn drawn into the vortex using multiple spinnerets to fabricate hollow yarn

The apparatus (100') of Fig. 2 with five spinnerets was used in this experiment. A funnel (16' ) with an outlet (16B' ) having a diameter of 6 mm was located at the bottom of container (3') having a diameter of 24cm such that the outlet (16B') extended from the hole (9'). The container (3') was filled with water as the non-solvent. Water was dispelled from the container (3' ) into the feed tank (13'). The pump (H') recycled the water back to the container (3') via liquid conduit (18') at a pump speed of 900 1/hr. The diameter of liquid conduit (18' ) is- 15 mm. The polymer solution was prepared by dissolving Polycaprolactone (PCL) (M_n 80000) from Aldrich of St Louis, Missouri, United States of America in a mixture of 75% chloroform and 25% methanol. The concentration of PCL in solution was 8wt%. Electrospinning was carried out by connecting a high voltage power supply from Gamma High Voltage Research HV Inc of Ormond Beach, Florida, United States of America. A voltage of 1OkV was applied to the polymer solution. A kd Scientific syringe pump was used to provide a constant feedrate of 15ml/hr to five spinnerets arranged around the vortex fluid flow (10') on the surface of the water. The inner diameter of -the nozzle (IA') of each of the spinnerets used here is 0.21 mm.

Fig. 4C is an SEM image at 200Ox magnification of the poly (caprolactone) electrospun fiber yarn collected at a speed of 63 m/min in this experiment. The diameter of the yarn is 50 μm

Fig. 4D is an SEM image at 300Ox magnification of a cross-sectional view of the fiber yarn of Fig. 4C. It can be seen that a hollow fiber yarn was produced by using multiple spinnerets.

Example 4 - Yarn drawn without the use of vortex The apparatus (100") of Fig. 8 was used in this experiment .

A hole (9") with a diameter of 1 mm was located in the bottom of the container (3") having a diameter of 24cm filled with water as the non-solvent. Water was dispelled from the container (3") into the feed tank (13") .

The polymer solution was prepared by dissolving

Polycaprolactone (PCL) (M_n 80000) from Aldrich of St Louis,

Missouri, United States of America in a mixture of 90% chloroform and 10% methanol. The concentration of the PCL in solution was 0.12g/ml.

Electrospinning was carried out by connecting a high voltage power supply from Gamma High Voltage Research HV Inc of Ormond Beach, Florida, United States of America. A voltage of 1OkV was applied to the polymer solution. A kd Scientific syringe pump was used to provide a constant feedrate of lml/hr to the spinneret (1") . The inner diameter of the spinneret nozzle (IA") used was 0.21 mm.

Fig. 6 is a photograph diagram of a tape-like electrospun fiber yarn drawn at a speed of 1 m/min formed in this experiment.

Fig. 7 is an SEM image at 80Ox magnification of a tape-like electrospun fiber yarn drawn at a speed of

1 m/min formed in this experiment. It can be seen that the yarn consists of an intricate array of interconnecting fibers, which provides the yarn with enhanced strength.

It will also be appreciated from Fig. 6 and Fig. 7 that a thicker yarn is able to be spun in the absence of a vortex. Furthermore, although a vortex fluid flow is absent in this example, it will be appreciated that the non-solvent acts as a support for the fiber yarn (14") to prevent or inhibit it from breakage. Additionally, as the fibers are removed from the hole (9"), non-solvent is drawn down into the hole (9") and assists in pushing the fibers together to thereby form the yarn (14") .

Applications

Fiber yarns produced by an embodiment described herein can be used for a variety of purposes such as, but not limited to, production of composites, filtration media, gas separation, sensors or biomedical engineering. Moreover, such fiber yarns can be used in the healthcare industry as tissue scaffolds whereby the fiber yarns impart desired mechanical strength. Furthermore, fibers with diameters from the nanometer to sub-micron scale that impart desired properties can be electrospun together to form fiber yarns for the textile industry.

Advantageously, the formation of a vortex within the non-solvent assists in twisting the electrospun fibers and thereby forms the yarn.

Advantageously, the non-solvent provides a support for the fibers as they are electrospun to prevent or inhibit them from breakage. Advantageously, even in embodiments where there is no vortex, drawing the fibers through the outlet conduit promotes formation of the yarn by drawing the fibers together by the flow regime within the receptacle as non- solvent passes through the outlet conduit. Advantageously, the use of a vortex enables production of an electrospun yarn at relatively high rates

(ie about 57 m/min to about 16 m/min from the above examples) . This is particularly useful for large-scale manufacturing of the yarn. Advantageously, the absence of the vortex enables production of an electrospun yarn at lower rates (ie about 1 m/min) , which is particularly useful when additives are to be added to the yarn. The slower production rate results in a longer residence time within the receptacle which allows a greater time for adsorption when an additive to be adsorbed is present in the non-solvent.

It will also be appreciated that additives may be added onto the fiber mesh formed in the non-solvent. The advantage of adding additives onto the mesh is that the additives are encapsulated unto the yarn as it is formed.

It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims. For example, it will be appreciated that in embodiments other than that described in the detailed description herein, the non-solvent may be mechanically agitated or the container may be rotated to cause non- solvent to rotate within the container and thereby promote formation of the vortex fluid flow.

Claims

1. A method for producing a fiber yarn comprising the step of electrospinning a fiber into a non-solvent contained within a receptacle, the receptacle comprising an outlet conduit to allow non-solvent to flow therefrom, wherein the dimensions of the outlet conduit are such that as non-solvent flows therefrom and wherein flow conditions of said non-solvent within said receptacle form said yarn.

2. A method as claimed in claim 1, comprising the step of rotating the non-solvent about an axis during said electrospinning so that said fiber is dispensed into said rotating non-solvent to form said fiber yarn.

3. A method according to claim 2, wherein said rotating . causes said non-solvent to flow in a vortex-like manner.

4. A method according to claim 1, comprising the step of removing said formed fiber yarn from said non- solvent.

5. A method according to claim 1, wherein said electrospinning comprises the step of injecting at least one charged polymer solution jet into said non-solvent.

6. A method according to claim 5, wherein multiple jets of said charged polymer solution are injected into said non-solvent.

7. A method according to claim 5, wherein the at least one charged polymer solution jet is ejected from a nozzle of a spinneret selected from the group consisting of a uniaxial spinneret, a co-axial spinneret, a bi-capillary spinneret and a multi- capillary spinneret.

8. A method according to claim 1, comprising the step of using water as the non-solvent.

9. A method according to claim 1, comprising the step of applying an electrical ground to said non-solvent during electrospinning of said polymer solution.

10. A method according to claim 1 comprising the step of providing one or more additives in said non- solvent selected from the group consisting of sugars, amino acids, proteins, growth factors, vitamins, hormones, cytokines, coloring dye, binders and cells.

11. A method according to claim 1, wherein said yarn is removed from the outlet conduit.

12. A method according to claim 11, comprising the step of providing a funnel disposed within said receptacle such that said formed yarn is emitted from the outlet conduit via the spout of said funnel .

13. A method according to claim 2, wherein said rotating fluid flow is created by the step of pumping a non-solvent stream into the non-solvent contained within said receptacle, said non-solvent stream being projected at a substantially tangential angle relative to the surface of the non-solvent contained within said receptacle.

14. A method according to claim 1, wherein said fiber is a polymer fiber.

15. A method according to claim 14, wherein said polymer of said polymer fiber is selected from the group consisting of polylactide, polycaprolactone, poly (glycolic acid), polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyesters, polyamides, polyimides, polyethylenes, polyolefins, polypropylenes, poly (vinyl alcohols), polyacrylonitriles, polycarbamides, polyurethanes, polymer melts, polymer blends, copolymers of said polymer and mixtures thereof.

16. A method according to claim 1, wherein said fiber is a ceramic precursor.

17. A method according to claim 5, comprising the step of selecting the diameter of said fiber yarn by varying any one or more of the following: (i) the feedrate of said charged polymer solution into said non-solvent; (ii) the number of spinnerets used to inject said charged polymer solution into said non- solvent; (iii) the diameter of the fiber that is dispensed into the non-solvent; and (iv) the size of outlet conduit.

18. A method according to claim 1, wherein said fiber yarn is at least one of a solid fiber yarn, hollow fiber yarn, tubular fiber yarn and a twisted fiber yarn.

19. A method according to claim 5, comprising the step of providing an auxiliary electrode to said at least one jet of said charged polymer solution as it is electrospun into said non-solvent, wherein said auxiliary electrode distorts the electrostatic field of said jet of charged polymer solution to thereby cause it to rotate generally about an axis as it enters said non-solvent.

20. A method as claimed in claim 2, comprising the step of agitating the non-solvent in a receptacle to cause it to rotate about the axis.

21. A method as claimed in claim 2, comprising the step of rotating a receptacle containing said non- solvent to cause said non-solvent to rotate about the axis.

22. A fiber yarn made in a method comprising the step of electrospinning a fiber into a non-solvent contained within a receptacle, the receptacle comprising an outlet conduit to allow non-solvent to flow therefrom, wherein the dimensions of the outlet conduit are such that as non-solvent ^■ flows therefrom, flow conditions of said non-solvent within said receptacle form said yarn.

23. A fiber yarn made in a method comprising the step of rotating a non-solvent about an axis as an electrospun fiber is dispensed into said rotating non-solvent to thereby produce said fiber yarn.

24. A fiber yarn manufacturing apparatus for making fiber yarn, the apparatus comprising: a non-solvent receptacle for containing non- solvent therein, said non-solvent being at least partially insoluble to a polymer solution; a nozzle disposed above the non-solvent for dispensing a jet of charged polymer solution into said non-solvent; and an outlet conduit extending from said receptacle to allow non-solvent to flow therefrom, wherein the dimensions of the outlet conduit are such that as non-solvent flows therefrom, flow conditions of said non-solvent within said receptacle form said yarn.

25. An apparatus as claimed in claim 24, wherein said outlet conduit is dimensioned such that in use, said non-solvent rotates about the axis to form said fiber yarn.

26. An apparatus as claimed in claim 24, comprising a non-solvent inlet disposed within said receptacle and a pump in fluid communication with said non- solvent inlet, wherein in use, said pump pumps non- solvent into said receptacle via said non-solvent inlet.

27. An apparatus as claimed in claim 24, comprising an auxiliary electrode disposed between a spinneret and the top of said receptacle, wherein said auxiliary electrode distorts the electrostatic field of a jet of charged polymer solution to thereby cause it to rotate generally about an axis as it is electrospun into said non-solvent.

28. An apparatus as claimed in claim 24, comprising a funnel disposed within said receptacle such that in use, said yarn is emitted from the outlet conduit via the spout of said funnel.

29. An apparatus as claimed in claim 24, comprising a roller disposed below outlet conduit located in the bottom of said receptacle.

30. A fiber yarn manufacturing system comprising: a receptacle for containing non-solvent therein; and a rotator capable of rotating the non-solvent about an axis, wherein in use, a fiber is electrospun from a charged polymer solution and dispensed into said rotating non-solvent to produce said fiber yarn.

31. A method for producing a fiber yarn comprising the step of rotating a non-solvent about an axis as a fiber is electrospun from a charged polymer solution and dispensed into said rotating non- solvent to thereby form said fiber yarn.