Method and apparatus for the production of fine fibers

Abstract

NOT VISIBLE DUE TO STATUS OF PATENT

Description

[0001] METHOD AND APPARATUS FOR THE PRODUCTION OF FINE FIBERS

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority from South African provisional patent application number 2023 / 11607 filed on 19 December 2023, which is incorporated by reference herein.

[0004] FIELD

[0005] This disclosure relates to an apparatus and method for the production of fine fibers, particularly, but not exclusively, very fine fibers of the general nature often referred to as nanofibers, from various polymers, polymer blends, ceramic precursor mixtures and metal precursor mixtures.

[0006] BACKGROUND

[0007] Very fine fibers, often referred to as nanofibers, are useful in a wide variety of applications, including filter media, tissue-engineering scaffold structures and devices, nanofiber-reinforced composite materials, sensors, electrodes for batteries and fuel cells, catalyst support materials, wiping cloths, absorbent pads, post-operative adhesion preventative agents, smart textiles as well as in smart materials to be used in the medical field.

[0008] Electrostatic spinning of fibers was, it appears, first described in US Patent 692,631. In principle, a droplet of polymer solution or melt is placed in a strong electric field giving rise to the repulsion between the induced like-charges in the droplet competing with the surface tension of the liquid. When a sufficiently strong electric field is applied (typically 0.5-7 kV / cm), the electrostatic forces can overcome the surface tension of the fluid and a jet of polymer solution or melt is ejected from the droplet.

[0009] Electrostatic instability leads to rapid, chaotic whipping of the jet, leading, in turn, to fast evaporation of any solvent as well as a stretching and thinning of the polymer fiber that is left behind. The formed fibers are then collected on a counter or collector electrode, typically in the form of a nonwoven web. The collected fibers are usually quite uniform and can have fiber diameters of several micrometers, down to as low as 5 nm.

[0010] The technical barriers to manufacturing large quantities of nanofibers by electrospinning include low production rates. One general method of production utilises multiple passages such as may be provided by multiple needles. On average, solution-based electrospinning, using needle spinnerets, have solution throughput rates on the order of 1 ml per hour per needle. Fibers with diameters in the range of 50 to 100 nm are typically spun from solutions with relatively low concentrations, typically 5-10 wt% depending on polymer type and molecular weight. This means that, assuming a polymer density of around 1 g / ml, the typical solids throughput rate of a needlebased electrospinning process is 0.05 g to 0.1 g of fiber per hour per needle. At this rate, production of a nanofiber web with a planar density of 80 g / m2at a rate of 5 m2 / s will require a minimum of 14,400,000 needles.

[0011] In addition, electrical field interference between the different needles limits the minimum separation between them and furthermore, continuous operation of needle-based spinnerets requires frequent cleaning of the needles as polymer deposits tend to block the spinnerets. The overall result is that the production of industrial volumes becomes almost prohibitively expensive for most commodity applications like filtration and absorbent textiles.

[0012] US 6,713,011 , teaches that spinning rates may be somewhat improved where the spinnerets or needles used for introducing fluid into an electric field are placed apart from each other.

[0013] A system with a significantly high throughput, known as NanoSpider, is described in international patent application publication number W02005024101. In this system the fiber forming polymer solution is contained in a dish and a partly exposed conductive cylinder is slowly rotated in it to form a thin layer of solution on its surface. A counter-electrode is placed 10-20 cm above the cylinder and hundreds of jets initiate off the surface of the cylinder and electrospin onto the target.

[0014] International patent application publication number W02006131081 describes a follow up type of NanoSpider technology in which the conductive cylinders are replaced by axially mounted rotatable cylindrical structures presenting multiple "discharge" surfaces from which solution is to be discharged to form the polymer fibers. The arrangement is somewhat complex and the cylindrical structures must be somewhat costly due to the large diameter rings and the drive required to rotate them.

[0015] Similarly, US 3,994,258 discloses a series of large, captive, rotating rings arranged end-to-end forming a primary electrode with a pair of counter-electrodes on either side of the rings. This arrangement too is complex, cumbersome and probably expensive. From a practical perspective, the apparatus will be difficult, or impossible, to implement. The rings are of very large diameter, 200 mm - 1000 mm, resulting in two competing disadvantages: they need to be rotated fairly rapidly to prevent excessive drying of the polymer solution, but rapid rotation will result in the solution being flung off. The use of "strippers" acting on the surface of the rings is unlikely to be very effective and leads to the further problem of the stripped deposits changing the concentration of the polymer solution. This all goes to make consistent results difficult, if not impossible, to achieve.

[0016] The apparatus in US 3,994,258 will be difficult to scale up or down due to its complexity. The ring arrangement can only be made longer (i.e. more rings arranged in longer rows) but there is a practical limit to the length of the counter-electrodes and width of the supporting band. Also, it will be difficult to rearrange or replace the rings as they are mounted (fixed) between three rollers.

[0017] In our international patent publication number WO 2009 / 156822 we describe an improvement of the electrospinning process in which a multitude of operatively semi-submerged elements are supported on the bottom of an elongate receptacle or tray or another support member and wherein a facility is included for causing polymer solution to be applied to the exposed surfaces of the loose elements by causing them to roll in the polymer solution so that they become coated with a thin layer of polymer solution on their surfaces. This overcomes the limitations imposed by the NanoSpider's pivoted cylinder design as the application of multiple loose (i.e. un-pivoted) rolling elements simultaneously allows for the concurrent use of different-sized rolling elements, more optimal utilisation of spin equipment area through denser packing of rolling elements, and also gives an additional degree of freedom in the rolling element's manoeuvrability and conversely more freedom in the design possibilities for the equipment. The specification of that application is incorporated in its entirety herein by reference. Application of the described method and apparatus revealed a number of limitations. Firstly, the apparatus is large and cumbersome to clean and maintain. Furthermore, production rate did not increase with an increase in the footprint of the spinning electrodes. Instead, an increase in the number of spinning electrodes in a single support member led to a reduced production rate, as well as a reduction in the uniformity of fine fibers produced. Experiments with this system and apparatus revealed that spacing the spinning electrodes apart from each other lead to an improvement of performance of the method and apparatus. This surprising finding led to an apparatus and method as described in our international publication number WO 2018 / 162950.

[0018] In our international patent publication number WO 2018 / 162950 we describe an improvement of the electrospinning process described in international patent publication number WO 2009 / 156822 in which a multitude of operatively semi-submerged loose elements are supported within individual receptacles and wherein a facility is included for causing polymer solution to be applied to the exposed surfaces of the loose elements by causing them to roll in the polymer solution so that they become coated with a thin layer of polymer solution on their surfaces. This overcomes certain limitations imposed by the multitude of elements supported together within an elongate receptacle or tray as the individual receptacle design eliminates negative effects of abutting rotating elements. It was therefore, surprisingly, found that spacing the spinning electrodes apart from each other resulted in an improvement of the rate production. The apparatus and method described in international patent publication number WO 2018 / 162950 is limited in that for every individual receptacle added, a plurality of accompanying components, such as solution supply route, voltage, and rotation connection are required. Furthermore, manufacturing, cleaning, maintenance, and in line troubleshooting is negatively affected with this apparatus and method. The specification of that application is incorporated in its entirety herein by reference.

[0019] A number of parameters are known to affect the production of fine fibers by electrospinning. These shall be termed spinning parameters in this specification and this term shall have its widest meaning and include all parameters which may have an effect on electrospinning.

[0020] Generally with the prior art apparatuses described above, these spinning parameters are typically preselected and the apparatus is designed and operated for the parameters to achieve uniformity over the entire apparatus. For example, the spinning parameters for electrospinning from the needles of needle-based spinnerets are usually controlled together and a homogenous environment is provided in which the multiple needles are operated under similar conditions to ensure that homogenous fine fibers and non-woven webs are formed. However, uniformity is not always ideal, particularly when production requires two or more different polymer solution types electrospun into fine fibers on the same collector electrode with intimate blending of the fibers. Similarly, uniformity is not ideal for a blend of two or more different average fiber diameters from the same polymer solution type.

[0021] In this specification "polymer solution" or "spinning solution" shall have their widest meaning and include polymer melts. The preceding discussion of the background is intended only to facilitate an understanding of the present disclosure. It should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge in the art as at the priority date of the application.

[0022] SUMMARY

[0023] In accordance with an aspect of the disclosure there is provided an apparatus for the production of fine fibers by electrospinning comprising: a counter electrode; an elongate receptacle capable of containing a polymer solution in use; a spinning electrode spaced apart from the counter electrode, the spinning electrode including a plurality of loose rotatable elements supported within the elongate receptacle, partly submerged in the polymer solution in use, arranged along a single axis; and a rotation means configured to exert a rotational force on the loose rotatable elements to cause rotation thereof around a rotational axis within the polymer solution in use such that polymer solution is applied to an operative surface of each rotatable element and electrospinning jets form from the operative surfaces when an electric field of sufficient magnitude is generated between the spinning electrode and the counter electrode; wherein the elongate receptacle is configured to receive the plurality of loose rotatable elements therein arranged in a single row and abutting each other.

[0024] The elongate receptacle may have a width dimensioned to receive a single rotatable element and a length dimensioned to receive the row of rotatable elements, wherein the width ranges between 101 % to 140% of a diameter of the rotatable element across the rotatable element’s rotational axis.

[0025] The rotatable elements may be configured to roll in a uniform direction. The rotatable elements may be of a uniform size arranged along a single, shared axis. The rotatable elements may be configured to rotate around the shared axis. The rotational force may be uniformly exerted on each rotational element.

[0026] The apparatus may further include a fluid supply configured to introduce and optionally also remove the polymer solution into and from the elongate receptacle.

[0027] The rotation means may comprise one or more rods abutting the rotatable elements, wherein the rods may be configured to rotate. The rotation means may include a pair of rods on which the rotatable elements are supported. At least one of these rods may be configured to rotate to cause the rotatable elements to rotate, preferably, both rods may be configured to rotate.

[0028] The rotation means may alternatively include a means for tilting the elongate receptacle from side to side to cause the rotatable elements to roll therein. The rotation means may alternatively include an endless belt abutting the rotatable elements, wherein the belt may be configured to extend around at least two pulleys, and may be driven to move. The apparatus may further include a power source which may be configured to operate the rotation means. The rotatable elements may include at least a component that is magnetic or may include a magnetic element, and the rotation means may then include a magnetic field generating means configured to cause the rotatable elements to rotate under the influence of changing magnetic fields.

[0029] The rotatable elements may have a diameter within the range of from 1 mm to 300mm in diameter across the rotational axis. Furthermore, the rotatable elements may have a diameter within the range of from 5mm to 30mm in diameter across the rotational axis.

[0030] The apparatus may further include a wiping device operable to wipe off fine fibers that form on the elongate receptacle in use.

[0031] The apparatus may further include a tap mechanism operable to contact at a surface of the polymer solution to break surface tension thereof and create a point of high charge density for jet initiation of polymer solution on the surface thereof.

[0032] The apparatus may further include a light source for lighting the fine fibers that form in use.

[0033] The apparatus may further include a UV radiation source for directing UV radiation at either or both of the polymer solution and fine fibers that form in use.

[0034] The apparatus may further include a source of vibration for vibrating the polymer solution in the elongate receptacle. The source of vibration may be a sonicator.

[0035] The apparatus may further include a gas feed directed through at least one gas outlet in a preselected direction or pattern.

[0036] A further aspect of the disclosure provides for a method for the production of fine fibers by electrospinning comprising the steps of: applying an electric field between a counter electrode and a spinning electrode spaced apart therefrom, wherein the spinning electrode is provided by a plurality of loose rotatable element arranged in a single row and abutting each other, supported in an elongate receptacle capable of containing a polymer solution to partly submerge the rotatable elements in use; rotating each rotatable element within the elongate receptacle so that the polymer solution is applied to an exposed surface of each rotatable element to form a thin layer on an operative surface of the rotatable element from which electrospinning jets form when an electric field of sufficient magnitude is generated between the spinning electrode and counter electrode. The elongate receptacle may have a width dimensioned to receive a single rotatable element and a length dimensioned to receive the row of rotatable elements, wherein the width ranges between 101 % to 140% of a diameter of the rotatable element across the rotatable element’s rotational axis.

[0037] The rotatable elements may be rotated in a uniform direction. The rotatable elements may be of a uniform size arranged along a single, shared axis. The rotatable elements may be rotated around the shared axis. The rotational force may be uniformly exerted on each rotational element.

[0038] The method may include a step of introducing and optionally also removing the polymer solution into and from the elongate receptacle through a fluid source.

[0039] Rotating each rotatable element may be achieved by rotating one or more rod abutting the rotatable elements. Alternatively rotating each rotatable element may be achieved by tilting the elongate receptacle. Alternatively rotating each rotatable element may be achieved by driving an endless belt abutting the rotatable elements. A power source may be configured to rotate the rotatable elements.

[0040] The rotatable elements may include at least a component that is magnetic or a magnetic element, and a facility may be included for causing polymer solution to be applied to the exposed surfaces of the rotatable elements by causing them to rotate in the polymer solution which may include a magnetic field generating means configured to cause the rotatable elements to rotate under the influence of changing magnetic fields.

[0041] The rotatable elements may have a diameter within the range of from 1 mm to 300mm in diameter across the rotational axis. Furthermore, the rotatable elements may have a diameter within the range of from 5mm to 30mm in diameter across the rotational axis.

[0042] The method may include a step of wiping off fine fibers that form on the elongate receptacle in use. The method may further include a step of contacting a surface of the polymer solution to break surface tension thereof and creating a point of high charge density for jet initiation of polymer solution on the surface thereof. The method may further include a step of lighting the fine fibers that form in use. The method may further include a step of directing UV radiation at either or both of the polymer solution and fine fibers that form in use. The method may include a step of vibrating the polymer solution in the elongate receptacle. The method may further include a step of directing gas through at least one gas outlet in a preselected direction or pattern. Embodiments of the technology will now be described, by way of example only, with reference to the accompanying drawings.

[0043] BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In the drawings:

[0045] Figure 1 is a front view of an apparatus for the production of fibers by electrospinning;

[0046] Figure 2 is a front view of a portion of the apparatus of Figure 1 ;

[0047] Figure 3 is a side view of a portion of the apparatus of Figure 1 ;

[0048] Figure 4 is a top view of a portion of the apparatus of Figure 1 ;

[0049] Figure 5 is a graph showing normalised production rate per row of elements and average percentage standard deviation of the density uniformity for a line, planar, and point source;

[0050] Figure 6 is a top view of a prior art apparatus for the production of fine fibers by electrospinning; and

[0051] Figure 7 is a perspective view of a prior art apparatus for the production of fine fibers by electrospinning.

[0052] DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

[0053] An apparatus is provided for the production of fine fibers by electrospinning. The apparatus comprises a counter electrode, an elongate receptacle, a spinning electrode, and a rotation means. The elongate receptacle is capable of containing a polymer solution in use. The spinning electrode is spaced apart from the counter electrode, and the spinning electrode includes a plurality of loose rotatable elements supported within the elongate receptacle, partly submerged in the polymer solution in use, arranged side-by-side in a single row. The rotatable elements thus abut each other, or be substantially abutting, and may share an axis along the row. The rotatable elements may be spheres and may be of a uniform size or differing sizes. The rotatable elements may be constructed from glass, such as marbles, or of a solvent-resistant plastic or polymeric material, or any other suitable material.

[0054] The rotation means is configured to exert a rotational force on the loose rotatable elements to cause rotation thereof within the polymer solution such that polymer solution is applied to an operative surface of each rotatable element and electrospinning jets form from the operative surfaces when an electric field of sufficient magnitude is generated between the spinning electrode and the counter electrode. The polymer solution may also be referred to as a “spinning solution” and may include any suitable liquid or polymer solution or melt. “Electrospinning jets” refer to liquid droplets which are electrified to generate a jet, which can be dried to form fine fibers.

[0055] In the present disclosure, reference to fine fibers produced by electrospinning may be understood to mean electrospinning jets which dry to form fine fibers. Reference to the fine fibers may be understood to refer to fine fibers in any stage of this process, and may be understood to extend to the electrospinning jets, which are substantially liquid jets, as well as fine fibers which may be dried.

[0056] The counter electrode may serve as a collector electrode configured to collect electrospun fibers. Additionally or alternatively the counter electrode may be connected to or be near a collector electrode.

[0057] The rotatable elements are loose (unattached) elements, wherein the term “loose” is used to denote elements that are not fixed or mounted in any way. Elements that are loose can simply be removed from a support means, such as the elongate receptacle in this apparatus, by picking them up, and can be replaced by putting another in its place. The rotatable elements may be made of any suitable material and may have a preselected size, shape, and surface texture.

[0058] The rotatable elements may be configured to roll in a uniform direction around the shared axis. In alternate embodiments, the rotatable elements may be configured to roll independently from each other, possibly in different directions, and at different rotational velocities or speeds. The rotational force exerted by the rotation means on the rotatable elements is uniformly applied to the rotatable elements, such that each element experiences the same force. The rotatable elements are arranged in a row, within the elongate receptacle, to make up the spinning electrode. A row may comprise as few as three rotatable elements, although many more rotatable elements may be included in a row. For example, a row may include fifteen or more rotatable elements. In use, the rotatable elements abut each other in the single row. The term “abut” is used to denote a close proximity between the loose rotatable elements, and includes instances where the two or more rotatable elements touch each other, and also extends to instances where the two or more rotatable elements are separated slightly by a distance of between 0% and 40% of a radius of one or both of the rotatable elements, more particularly, where the two or more rotatable elements are separated slightly by a distance of between 0% and 5% of a radius of one or both of the rotatable elements. This radius is a measure of a distance from an outer surface of the rotatable element to the axis of rotation thereof.

[0059] The elongate receptacle has a length suitable to accommodate the row of the rotatable elements and a width to accommodate a diameter of each rotatable element wherein the diameter is measured across a rotational axis of the rotatable element. The width of the elongate receptacle is such that side walls thereof are in close proximity to the sides of the rotatable elements in order to limit the area of surface of the polymer solution that is exposed. In particular, the width ranges between 101 % to 140% of a diameter of the rotatable element measured across the rotatable element’s rotational axis. More particularly, the width of the elongate receptacle may range from between 101% to 120% of a diameter of the rotatable element measured across the rotatable element’s rotational axis. When the rotatable element is held or located within the elongate receptacle and positioned therein such that the rotational axis of the rotatable element is substantially in the center of the width of the elongate receptacle, a distance from an external surface of one or more rotatable elements held within the elongate receptacle and a side wall of the elongate receptacle is between 0% to 40% of a radius of the rotatable element, in particular, a radius which extends from a rotational axis to an external surface of the rotatable element. More particularly, the distance from an external surface of one or more rotatable elements held within the elongate receptacle and a side wall of the elongate receptacle is between 0% to 5% of the radius of the rotatable element.

[0060] In embodiments of the apparatus which include rotatable elements of differing sizes or dimensions, the width of the elongate receptacle may vary to accommodate each different sized rotatable element. In such an embodiment, side walls of the elongate receptacle may be sinuous to account for this varying width.

[0061] The apparatus further includes a fluid source or inlet connected to the elongate receptacle to introduce the polymer solution into the elongate receptacle. Additionally, or alternatively, the apparatus may have an inlet and an outlet to introduce and remove the polymer solution from the elongate receptacle. In alternate embodiments, the apparatus may include a plurality of fluid sources. The rotation means may comprise any suitable means of exerting a rotational force on the rotatable elements. In one embodiment, the rotation means comprises one or more rods abutting the rotatable elements. The rods are configured to rotate, and rotation of the rods causes the abutting rotatable elements to rotate. In a further embodiment, the rotational means may comprise a means for tilting the elongate receptacle. By tilting the elongate receptacle to a predetermined angle, the rotatable elements held within the elongate receptacle experience a rotational force as a result of the gravitational shift. This tilting therefore results in the rotation of the rotatable elements. In a further embodiment, the apparatus includes an endless belt, held within the elongate receptacle, abutting the loose rotatable elements. The endless belt is configured to stretch between two or more pulleys at opposite ends of the elongate receptacle such that the belt rotates around the pulleys in a continuous rotation. The endless belt rotates, and rotation thereof causes a rotational force to be exerted on the abutting rotatable elements. In any of these or further embodiments, the apparatus includes a power source configured to provide power to, and operate, the rotation means.

[0062] In a further, alternate embodiment, the rotatable elements may include at least a component therein that is magnetic or comprises a magnetic element. In such an embodiment, the rotation means may comprise a magnetic field generating means configured to cause the rotatable elements to rotate under the influence of changing magnetic fields.

[0063] The rotatable elements may have a diameter within the range of 1mm to 300mm in diameter measured across a rotational axis thereof. The rotational axis of the rotatable elements refers to the axis around which each rotatable element may rotate, and the diameter measured across the rotational axis therefore means the straight distance between any two points on opposing sides of an external surface of the rotatable element which passes through the rotational axis. Similarly, reference to a rotational radius, or radius, of a rotatable element refers to a distance measured between a rotational axis of a rotatable element and an external surface of the rotatable element. Preferably, the rotatable elements may have a diameter within the range from 5mm to 30mm in diameter measured across a rotational axis.

[0064] The rotatable elements are rounded and most commonly circular when viewed in at least one direction. They may be spheres, cylinders or intermediate ellipsoidal shapes. In one embodiment, the rotatable elements are spherical, or substantially spherical, in shape. In a simple embodiment of the present disclosure, the rotatable elements are solid spheres or balls, having a 25mm diameter measured across the rotational axis, made from a solvent-resistant plastic or polymeric material. The apparatus may include further components to facilitate or improve the production of fine fibers by electrospinning. These further components include a wiping device, operable to wipe off fine fibers that form on the elongate receptacle in use.

[0065] Furthermore, a tap mechanism may be included. The term “tap mechanism” is used to refer to any mechanisms configured to tap, touch, or contact, a surface of an object or liquid. In the present disclosure, the tap mechanism is operable to contact a surface of the polymer solution to break surface tension thereof and create a point of high charge density for jet initiation of a polymer solution on the surface thereof. This may be necessary to initiate jet formation on the spheres by physically contacting the wetted surface. The result is the formation of a sharp tipped liquid protrusion on the liquid surface as the tapping mechanism, which may be a robotically controlled rod made of glass or any other type of chemically resistant material moves away again, for example. One or more jets then erupt from that point. The high charge on the rotatable elements then leads to automatic splitting of the first jet (or jets) into multiple jets, which ideally spread to the other rotatable elements through a synergistic inductive effect that is frequently observed in electrospinning, without further intervention from outside. Such an initiation could also be performed in many other ways involving some physical deformation of the liquid layer on a sphere.

[0066] A light source may further be included, to light the fine fibers that form in use. This is to enable visualisation of the production of fine fibers to provide feedback to a user. The light source may be orientated in a user selectable direction and may be an adjustably mounted LED light, for example.

[0067] Furthermore, a UV radiation source may be included, for directing UV radiation at either or both of the polymer solution and fine fibers that form in use. The UV radiation may be used for in situ sterilisation of fibers formed or to react UV sensitive reactants to form a desired product in the fine fibers.

[0068] A source of vibration, such as a sonicator, may also be included, for vibrating the polymer solution in the elongate receptacle. The vibration is useful for dissolving polymers and / or for disrupting the stability of the surface and lowering solution viscosity of the polymer solution so that a lower voltage may be applied to result in electrospinning. Furthermore, the rim of the elongate receptacle could be made of, or covered in, or have a conductive material. This permits the electrostatic field around a rim of the elongate receptacle to be altered by, for example, pulsing an electrical potential through the rim or holding it at a different, or similar, electrical potential to the spinning solution to have a focusing effect.

[0069] An even further feature that may be included in the apparatus is a gas feed directed through at least one gas outlet in a preselected direction or pattern. The gas feed may be directed through at least one gas outlet or nozzle provided at or near the spinning electrode and directed in a preselected direction or pattern. It is preferred for multiple gas inlets and multiple gas outlets at or near a periphery of the receptacle to be included. The gas outlets may be orientated in different, preferably user selectable, directions. The gas composition, temperature and flow rate in respect of the one or more gas feeds associated with the spinning electrode may be controllable. The gas may be used in a number of different ways. Importantly, the gas may be used to facilitate quick drying of the fibers, which enhances process efficiency and fiber quality.

[0070] A method for the production of fine fibers by electrospinning is provided, which may be implemented with the apparatus described above. The method comprises the steps of applying an electrical field between a counter electrode and a spinning electrode spaced apart therefrom, wherein the spinning electrode includes a plurality of loose rotatable elements arranged in a single row and abutting each other, supported in an elongate receptacle capable of containing a polymer solution to partly submerge the rotatable elements in use; rotating each rotatable element around the shared axis within the elongate receptacle so that the polymer solution is applied to an exposed surface of each rotatable element to form a thin layer on an operative surface of the rotatable element from which fine fibers form when an electric field of sufficient magnitude is generated between the spinning electrode and counter electrode.

[0071] The loose, i.e. unattached, rotatable elements may be rotated in a uniform direction or in different directions. Where the rotatable elements are of the same size, they may be rotated around a shared axis. The rotational force may be exerted uniformly on each rotational element.

[0072] The method further includes the step of introducing polymer solution into the elongate receptacle, through a fluid source. Additionally, or alternatively, the method may include the step of removing the polymer solution from the elongate receptacle through an outlet.

[0073] The step of rotating each rotatable element is achieved by any one of: rotating one or more rods abutting the rotatable elements, tilting the elongate receptacle, or rotating an endless belt abutting the rotatable elements, wherein a power source is configured to power any one of these means of rotating the rotatable elements. Alternatively, the step of rotating each rotatable element is achieved by exerting a magnetic field on the rotatable elements, in an embodiment where the rotatable elements include at least a component that is magnetic or comprises a magnetic element.

[0074] The method further includes illuminating the fine fibers formed by each spinning electrode in use; directing UV radiation at either or both of the polymer solution and the fine fibers that form in use; vibrating the polymer solution contained in each receptacle; directing a gas feed to each spinning electrode in a one or more user selectable directions; and controlling one or all of the gas composition, temperature and flow rate fed to each spinning electrode.

[0075] The term “plurality” as used herein is used to denote more than one article. In particular, and as used in the present description, reference to a plurality of rotatable elements or spinning electrodes provides for more than one rotatable element or spinning electrodes.

[0076] Figures 1 to 4 illustrate an example embodiment of the above-described apparatus for the production of fine fibers by electrospinning, which may be used to carry out the above-described method.

[0077] In the embodiment illustrated in Figure 1 , an apparatus (1) is provided for the production of fine fibers by electrospinning. The apparatus (1) comprises a counter electrode (13), a spinning electrode (5), an elongate receptacle (7), and a rotation means, provided for by rods (15). The counter electrode (13) may be, for example, a collector electrode, or may be at or near a collector surface. The spinning electrode (11) includes a plurality of loose, rotatable elements (5) arranged in a row within the elongate receptacle (7). The elongate receptacle (7) contains a polymer solution (23), which partially submerges the rotatable elements (5). When the rotatable elements (5) roll within the elongate receptacle, the polymer solution (23) covers the rotatable elements such that an operative surface thereof is coated with polymer solution (23). When a voltage of sufficient magnitude is applied between the spinning electrode (5) and the counter electrode (13) electrospinning jets (29) are then formed on the operative surface of the rotatable elements (5), which extend to the counter electrode (13). The electrospinning jets (29) ultimately form the fine fibers that are deposited on the counter electrode (13) or collector surface.

[0078] The rods (15) are configured to rotate. A motor (21), drive shaft (19) and gear mechanism (17) are provided to facilitate this rotation of the rods (15). The rods (15) are positioned within the elongate receptacle (7) such the rotatable elements (5) are supported on the rods (15). Rotation of the rods (15) therefore facilitates and causes rotation of the rotatable elements (5). The rods may be constructed from stainless steel, glass, acetal, or other suitable non-reactive material that is fit for purpose. The rods may be coated, textured or surface treated so as to facilitate sufficient friction to cause the rotatable elements to rotate in the polymer solution.

[0079] A power source (27) applies high voltage to the spinning electrode (11) and the counter electrode (13) that is generally parallel to the spinning electrode (11) but spaced apart therefrom. This voltage is applied by way of an electrode which is included in the elongate receptacle (7), which is in contact with the polymer solution. An elongate receptacle support (9) includes a port for plugging in a high voltage connection to apply this voltage to the elongate receptacle (7).

[0080] The elongate receptacle (7) of the apparatus (1) is supported by the elongate receptacle support (9), which in this embodiment, includes two stands which raise and support the elongate receptacle (7). In further embodiments, the apparatus includes three or more stands, wherein a middle stand is configured to connect two elongate receptacles together, to form a single, continuous elongate receptacle. The elongate receptacle (7) is configured to contain a polymer solution (23), and therefore the elongate receptacle (7) is sealed such that a fluid can be retained therein. The elongate receptacle (7) is generally shaped or configured in a channel or trough shape, having a base and four side walls extended from the base to create the trough shape. In alternate embodiments, the elongate receptacle may be of any other suitable shape or configuration. The elongate receptacle may be constructed from plastic, metal, or any other suitable material, and may be constructed by three-dimensional printing, machining, or moulding, in the case of construction from plastic. The rotatable elements (5) are held within the elongate receptacle (7) in a row. The walls of the elongate receptacle (7) are high enough so that an upper portion of each rotatable element (5) is partially exposed. A width of the elongate receptacle (7) is such that the side walls thereof are in close proximity to the sides of the rotatable elements (5) in order to limit the area of surface of the polymer solution (23) that is exposed. In this embodiment, the polymer solution (23) is introduced into the elongate receptacle (7) through a solution inlet (26) which is in fluid communication with a solution reservoir (25). In further embodiments, the solution inlet and / or the solution reservoir may be incorporated into the elongate receptacle support (9) of the apparatus. The level of the polymer solution is regulated by the solution inlet. A solution outlet may be included in the apparatus to assist with management of the level of polymer solution. A solution outlet may also be used for completely draining the elongate receptacle for cleaning thereof, or for changing the type of polymer solution held therein. The level of the solution may be regulated such that the rotatable elements (5) held within the elongate receptacle (7) are at least partially submerged therein.

[0081] The elongate receptacle (7) may, in some embodiments, include an overflow outlet at a predetermined height, such that the level of the polymer solution therein is maintained at a desired level. If the polymer solution is introduced into the elongate receptacle at a greater rate than is required for electrospinning, then the excess polymer solution may flow out the overflow outlet and be recirculated to be stored in the solution reservoir or reintroduced into the elongate receptacle via the inlet.

[0082] The rods (15) are fitted within the elongate receptacle (7) through apertures at each end of the elongate receptacle (7), as shown in Figures 2 and 3. The rods (15) are positioned within the elongate receptacle (7) along the base thereof.

[0083] As shown in Figure 2, the elongate receptacle (7) may be any suitable or required length. This length of the elongate receptacle (7) will determine how many rotatable elements (5) may be placed into the elongate receptacle (7). The rotatable elements (5) are removably and loosely placed within the elongate receptacle (7) in a row, along a single, shared axis. A row of rotatable elements (5) is made up of at least three rotatable elements (5).

[0084] As shown most clearly in Figure 3, the rotatable elements (5) are placed into the elongate receptacle (7), atop a rotation means. In this embodiment, the rotation means includes two rods or shafts (15) which run along a length of the elongate receptacle (7), at a bottom surface thereof. The rotatable elements (5) abut and are supported by the rods, such that rotation of the rods results in movement of the rotatable elements (5). In particular, rotation of the rods (15) exerts a rotational force on the rotatable elements (5) which then also rotate, uniformly, around a single axis. In this embodiment, the rods (15) are configured to rotate in a single direction such that the rotatable elements (5) rotate in the opposite direction. As is indicated in Figure 3, in this embodiment the rods (15) rotate in a clockwise direction viewed from the side perspective depicted. As such, the rotatable elements are rotated in a counter-clockwise direction.

[0085] In a further embodiment the rods are radiused along the length thereof, such that each rotatable element is locatable within a radiused portion and lateral movement of the rotatable element is prevented. This may also be achieved by the inclusion of protrusions or flanges at predefined positions of the rods, such that each rotatable element is located between at least two protrusions, spaced apart such that the rotatable elements abut each other.

[0086] In a further embodiment the walls of the elongate receptacle may curve inwards and include radiused cut-outs complementary to the rotatable elements, in which the rotatable elements locate. This configuration ensures that the surface area of the polymer solution held within the elongate receptacle is reduced. As illustrated in Figure 4, the elongate receptacle (7) has a width configured to accommodate the rotatable elements.

[0087] Other than the configuration of the apparatus, the separate components of the apparatus which are known in the art operate along lines that are well-known to those skilled in the art and further detail of which need not be included herein. Despite operating in a substantially conventional or known manner, the novel configuration of the apparatus provides a surprising increase in rate or production of fine fibers and efficiency of the apparatus which could not be predicted from prior art or conventional apparatuses.

[0088] A method for the production of fine fibers by electrospinning is provided which may be implemented with the apparatus described above. A first step of the method is application of an electrical field between a counter electrode and a spinning electrode spaced apart therefrom. Each spinning electrode includes loose (unattached) rotatable elements supported in an elongate receptacle containing a polymer solution to partly submerge the rotatable elements. The rotatable elements are arranged along a single shared axis within the elongate receptacle. A further step of the method involves rotation of the rotatable elements within the elongate receptacle, through use of a rotation means. The rotation step results in the polymer solution being applied to an exposed surface of each rotatable element to form a thin layer on an operative surface of the rotatable element from which electrospinning jets form when an electric field of sufficient magnitude is generated between the spinning electrode and counter electrode.

[0089] The step of rotation of the rotatable elements involves an application of a rotational force thereon, such that the rotatable elements are rotated in a uniform direction around the shared axis. The rotational force is exerted uniformly on each rotational element.

[0090] The method further includes the step of introducing polymer solution into the elongate receptacle, through a fluid source. In the illustrated embodiment, the polymer solution is introduced through a solution inlet in fluid communication with the elongate receptacle.

[0091] The step of rotating each rotatable element is achieved by any one of: rotating one or more rods or shafts abutting the rotatable elements, tilting the elongate receptacle, or rotating an endless belt abutting the rotatable elements, wherein a power source is configured to power any one of these means of rotating the rotatable elements. Alternatively, the step of rotating each rotatable element is achieved by exerting a magnetic field on the rotatable elements, in an embodiment where the rotatable elements include at least a component that is magnetic or comprises a magnetic element. The method further includes illuminating the fine fibers formed by the spinning electrode in use; directing UV radiation at either or both of the polymer solution and the fine fibers that form in use; vibrating the polymer solution contained in each receptacle; directing a gas feed to each spinning electrode in a one or more user selectable directions; and controlling one or all of the gas composition, temperature and flow rate fed to each spinning electrode.

[0092] Figure 5 is a graph which illustrates results from a comparison of the apparatus of the disclosure with prior art apparatuses. A description hereof requires a brief description of the prior art apparatuses.

[0093] An embodiment of a first prior art apparatus, such as the apparatus described in W02009 / 156822, for the production of fine fibers by electrospinning is illustrated in Figure 6. The apparatus comprises a counter electrode spaced apart from an electrode containing a plurality of rotating elements held within a tray, partially submerged in a polymer solution. This apparatus is defined as having a planar source of rotating elements and is identified in Figure 5 as such. The apparatus includes a spinning electrode containing a plurality of rotating elements arranged in multiple rows, wherein each rotating element may be spaced apart from each other or may alternatively abut each other. Different embodiments of the planar source apparatus may include multiple rows or rotating element, such as that illustrated in Figure 5 having 33 rotating elements (or “balls”) arranged in three rows. Alternatively, a single row, having as an example, 11 balls, may be provided. Further, the tray may include much fewer balls, such as 3 as illustrated in Figure 5, in a single row within the tray. Such an apparatus is limited in that production rate is not linearly related to the footprint of the rotating element. The arrangement of rotating element is such that fiber production is fairly unpredictable and is not uniform for each rotating element present in the apparatus. For example, jet formation, and subsequent fiber production, on rotating elements positioned on an inner portion of the support tray, surrounded by other rotating elements, is constrained. Conversely, rotating elements on an outer edge of the tray have a higher production rate. Furthermore, this large tray setup of the apparatus means that the apparatus is large and cumbersome to clean, set up and dismantle. Therefore, it was observed that certain disadvantages of this apparatus arose as a result of the positioning of the rotatable elements, abutting each other.

[0094] A further prior art apparatus such as the apparatus described in WO 2018 / 162950, which sought to address the shortcomings of the planar source apparatus is provided for by point source electrospinning. An embodiment of such an apparatus is illustrated in Figure 7. In such an apparatus, the rotating elements do not abut each other and therefore it is expected that production rates would be improved in comparison with production rates observed in the aforementioned prior art apparatus. The apparatus comprises a counter electrode with multiple rotating elements spaced apart therefrom, wherein each rotating element is held within a separate receptacle. This allows for independent adjustment of different parameters of each receptacle and rotating element. This apparatus is identified as “point source” in Figure 5. This apparatus provided benefits over the first prior art apparatus in that the individual receptacles are grouped together in a set number to allow for easy assembly. A benefit of this approach is that normalised production rates are increased, when compared to the planar source, as is indicated in Figure 5. However, the average percentage standard deviation in density uniformity of the fiber web that is formed is substantially higher than that observed in production rate from apparatuses utilising a planar source.

[0095] In light of the evolution of the first prior art apparatus to the second prior art apparatus, it would seem counterintuitive to resort to placing rotating elements in a single receptacle, abutting each other, when the approach of moving towards separate receptacles as used in the second prior art apparatus sought to address issues observed in the first prior art apparatus. However, experiments conducted using the apparatus of the present disclosure revealed a surprising increase in production rate of fine fibers produced using this apparatus. Furthermore, uniformity and predictability of the fibers produced improved with the apparatus of the present disclosure. These results are indicated in Figure 5, wherein the apparatus of the present disclosure is identified as “line source”. The results indicated in the graph show the normalised production rate per row of elements and the average percentage standard deviation of the density uniformity of the web of electrospun fibers.

[0096] In comparison to the above-described planar source, the line source of the present disclosure may be comparatively smaller which may improve ease of handling and use. In comparison to the point source, the line source of the present disclosure may comprise fewer components, such as fluid sources and mechanical parts, thereby reducing time required for assembly and cleaning. Adjacent rows of line sources of the present disclosure may contain different polymer solutions, to blend different polymer nanofibers into one material.

[0097] In use, polymer solution is introduced into the elongate receptacle of the apparatus. The rotation means is powered such that the spinning electrode rotates within the polymer solution and polymer solution is applied to an exposed, operative surface of the spinning electrode. An electrical field is applied between the counter electrode and the spinning electrode. Upon generation of an electric field of sufficient magnitude between the spinning electrode and counter electrode, fine fibers are formed in the space between the electrodes. The foregoing description has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the technology to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure.

[0098] The language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the present disclosure be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the present disclosure is intended to be illustrative, but not limiting, of the scope of any accompanying claims.

[0099] Finally, throughout the specification and any accompanying claims, unless the context requires otherwise, the word ‘comprise’ or variations such as ‘comprises’ or ‘comprising’ will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Claims

CLAIMS:1 . An apparatus for the production of fine fibers by electrospinning comprising: a counter electrode; an elongate receptacle capable of containing a polymer solution in use; a spinning electrode spaced apart from the counter electrode, the spinning electrode including a plurality of loose rotatable elements supported within the elongate receptacle, partly submerged in the polymer solution in use, arranged along a single axis; and a rotation means configured to exert a rotational force on the loose rotatable elements to cause rotation thereof around a rotational axis within the polymer solution in use such that polymer solution is applied to an operative surface of each rotatable element and electrospinning jets form from the operative surfaces when an electric field of sufficient magnitude is generated between the spinning electrode and the counter electrode; wherein the elongate receptacle is configured to receive the plurality of loose rotatable elements therein arranged in a single row and abutting each other.

2. The apparatus as claimed in claim 1 , wherein the elongate receptacle has a width dimensioned to receive a single rotatable element and a length dimensioned to receive the row of rotatable elements, wherein the width ranges between 101% to 140% of a diameter of the rotatable element measured across the rotatable element’s rotational axis.

3. The apparatus as claimed in any one of the preceding claims, including a fluid supply configured to introduce the polymer solution into the elongate receptacle and to remove the polymer solution from the elongate receptacle.

4. The apparatus as claimed in any one of the preceding claims, wherein the rotation means includes one or more rods abutting the rotatable elements, wherein the rods are configured to rotate.

5. The apparatus as claimed in any one of claims 1 to 3, wherein the rotation means includes one or both of: a means for tilting the elongate receptacle, an endless belt abutting the rotatable elements, wherein the belt is configured to extend around at least two pulleys and is driven to move,6. The apparatus as claimed in any one of claims 1 to 3, wherein the rotatable elements include at least a component that is magnetic or includes a magnetic element, and wherein therotation means includes a magnetic field generating means configured to cause the rotatable elements to rotate under the influence of changing magnetic fields.

7. The apparatus as claimed in any of the preceding claims, including a power source configured to operate the rotation means.

8. The apparatus as claimed in any one of the preceding claims, wherein the rotatable elements have a diameter within the range of from 1 to 300mm in diameter measured across the rotational axis.

9. The apparatus as claimed in any one of the preceding claims, including a wiping device operable to wipe off fine fibers that form on the elongate receptacle in use.

10. The apparatus as claimed in any one of the preceding claims, including a tap mechanism operable to contact at a surface of the polymer solution to break surface tension thereof and create a point of high charge density for jet initiation of polymer solution on the surface thereof.

11. The apparatus as claimed in any one of the preceding claims, including a light source for lighting the fine fibers that form in use.

12. The apparatus as claimed in any one of the preceding claims, including a UV radiation source for directing UV radiation at either or both of the polymer solution and fine fibers that form in use.

13. The apparatus as claimed in any one of the preceding claims, including a source of vibration for vibrating the polymer solution in the elongate receptacle.

14. The apparatus as claimed in any one of the preceding claims, including a gas feed directed through at least one gas outlet in a preselected direction or pattern.

15. A method for the production of fine fibers by electrospinning comprising the steps of: applying an electrical field between a counter electrode and a spinning electrode spaced apart therefrom, wherein the spinning electrode includes a plurality of loose rotatable elements arranged in a single row and abutting each other, supported in an elongate receptacle capable of containing a polymer solution to partly submerge the rotatable elements in use; rotating each rotatable element within the elongate receptacle so that the polymer solution is applied to an exposed surface of each rotatable element to form a thin layer on an operativesurface of the rotatable element from which electrospinning jets form when an electric field of sufficient magnitude is generated between the spinning electrode and counter electrode.