WO2018162950A1

WO2018162950A1 - Apparatus and method for the production of fine fibers

Info

Publication number: WO2018162950A1
Application number: PCT/IB2017/051318
Authority: WO
Inventors: Haydn KRIEL; Megan Patricia COATES; Anton Eugene Smit; Donna-Leigh VAN STADEN
Original assignee: The Stellenbosch Nanofiber Company (Pty) Ltd
Priority date: 2017-03-07
Filing date: 2017-03-07
Publication date: 2018-09-13

Abstract

An apparatus and method for the production of fine fibers by electrospinning are provided. The apparatus includes a collector electrode and a plurality of spinning electrodes spaced apart therefrom. Each spinning electrode is provided by a loose and unattached rotatable element supported in a receptacle capable of containing a polymer solution to partly submerge the rotatable element. The polymer solution is applied to an exposed surface of each rotatable element by causing it to rotate in the polymer solution. In use, fine fibers form when an electric field of sufficient magnitude is generated between the spinning electrode and collector electrode. Nanofiber materials of variable composition are produced at high production rates by controlling one spinning parameter of one or more of the spinning electrodes independently of the other spinning electrodes in the apparatus.

Description

APPARATUS AND METHOD FOR THE PRODUCTION OF FINE FIBERS

FIELD OF THE INVENTION

This invention 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.

BACKGROUND TO THE INVENTION

Very fine fibres, 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.

Electrostatic spinning of fibres 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 0.5-4 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.

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 fibre that is left behind. The formed fibres are then collected on a counter or collector electrode, typically in the form of a nonwoven web. The collected fibres are usually quite uniform and can have fibre diameters of several micrometers, down to as low as 5 nm.

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. Fibres 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 needle-based electrospinning process is 0.05 g to 0.1 g of fibre per hour per needle. At this rate, production of a nanofibre web with a planar density of 80 g/m² at a rate of 5 m²/s will require a minimum of 14,400,000 needles.

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.

A system with a significantly high throughput, known as NanoSpider, is described in international patent application publication number WO05024101 . In this system the fibre 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.

International patent application publication number WO 2006131081 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 fibres. 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.

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. 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 (ie more rings arranged in longer row) 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.

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 a trough 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. 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.

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 web is 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. In this specification "polymer solution" or "spinning solution" shall have their widest meaning and include polymer melts. The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. 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.

SUMMARY OF THE INVENTION

In accordance with the invention, there is provided an apparatus for the production of fine fibers by electrospinning which includes a collector electrode and a plurality of spinning electrodes spaced apart therefrom, each spinning electrode provided by a loose (unattached) rotatable element supported in a receptacle capable of containing a polymer solution to partly submerge the rotatable element and which is applied to an exposed surface of each rotatable element by causing it to rotate in the polymer solution and wherein each rotatable element has an operative surface from which fine fibers form when an electric field of sufficient magnitude is generated between the spinning electrode and collector electrode and characterized in that at least one spinning parameter of one or more of the spinning electrodes is controllable independently of the other spinning electrodes.

A further feature provides for the at least one spinning parameter to be an adjustable characteristic of one or more of the polymer solution, spinning electrode and apparatus which affects the production of fine fibers by electrospinning; for the at least one spinning parameter to be one or more of: a temperature of the polymer solution, a flow rate of the polymer solution to the spinning electrode, a level of the polymer solution in the receptacle, a formulation of the polymer solution, a speed of rotation of the rotatable element, a voltage applied between the collector electrode and spinning electrode by a voltage source, a current applied between the collector electrode and spinning electrode and a distance between the operative surface of the rotatable element and the collector electrode.

Still further features provide for each spinning electrode to be controllable independently of the other spinning electrodes; and for each spinning electrode to be individually replaceable.

Yet further features provide for the rotatable element of each spinning electrode to be of the same or a different preselected size; for the rotatable element of each spinning electrode to be of the same or a different preselected shape and for the rotatable element of each spinning electrode to be of the same or a different preselected texture.

An even further feature provides for the receptacle of each spinning electrode to be of the same or a different preselected shape or configuration. Further features provide for the apparatus to include a support for the spinning electrodes; for a plurality of actuators to be arranged to individually move one or more of the spinning electrodes relative to the collector electrode or relative to the other spinning electrodes to independently control the distance between the operative surface of the rotatable element and the collector electrode and the distance between the spinning electrodes; for the support to be configured to provide individual reciprocal movement or individual circular movement to each of the spinning electrodes.

Still further features provide for each spinning electrode to be provided with a wiping device operable to wipe off fine fibers that form on the receptacle in use; for each spinning electrode to be provided with a tap mechanism operable to contact the rotatable element to break the surface tension and create a point of high charge density for jet initiation of polymer solution on the surface thereof; for each spinning electrode to have a light source associated therewith for lighting the fine fibers that form in use; for each spinning electrode to have a UV radiation source for directing UV radiation at either or both of the polymer solution and fine fibers that form in use; for each spinning electrode to have a source of vibration, preferably a sonicator, for vibrating the polymer solution in the receptacle; for each spinning electrode to have a gas feed directed through at least one gas outlet in a preselected direction or pattern; and for gas composition, temperature and flow rate to be controllable for each spinning electrode.

In accordance with a second aspect, there is provided a spinning electrode for use in an apparatus as described above and which includes a receptacle with a loose (unattached) rotatable element supported therein and wherein the receptacle is capable of containing a polymer solution to partly submerge the rotatable element and which is applied to an exposed surface of each rotatable element by causing it to rotate in the polymer solution and wherein the receptacle includes at least one inlet and at least one outlet for a polymer solution or reagent, characterised in that at least one spinning parameter of the spinning electrode is controllable. Further features of this aspect provide for the spinning electrode to include at least one inlet and at least one outlet which permits gas to be directed therethrough; for the receptacle to have multiple polymer solution or reagent inlets and outlets; for multiple gas inlets and multiple gas outlets at or near a periphery of the receptacle to be included; for the gas outlets to be orientatable in different, preferably user selectable, directions; for the spinning electrode to include a light source orientatable in a user selectable direction; for the spinning electrode to include a source of UV radiation; for the spinning electrode to include a source of heat; for the spinning electrode to include a source of vibration for a polymer solution contained in the receptacle; for the spinning electrode to include a wiping device operable to wipe away fibers formed on the receptacle; for a tap mechanism to be operable to contact the rotatable element to break the surface tension and create a point of high charge density for jet initiation of polymer solution on the surface thereof; for a drive to be included and configured to rotate the rotatable element at a user selectable speed; for a level sensor to be included and configured to sense the level of polymer solution in the receptacle and a valve associated with each polymer solution or reagent inlet for controlling the flow of polymer solution or reagent into the receptacle.

Still a further feature provides the at least one outlet of the receptacle to be operatively above the at least one inlet to the receptacle for controlling the level of polymer solution in the receptacle. In accordance with a third aspect of the invention, there is provided a method for the production of fine fibers by electrospinning by applying an electrical field between a collector electrode and a plurality of spinning electrodes spaced apart therefrom, each spinning electrode including a loose (unattached) rotatable element supported in a receptacle containing a polymer solution to partly submerge the rotatable element; rotating each rotatable element in its 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 rotating element from which fine fibers form when an electric field of sufficient magnitude is generated between the spinning electrode and collector electrode, and characterized in that at least one spinning parameter of one or more of the spinning electrodes is controlled independently of the other spinning electrodes.

A further feature of this aspect provides for the at least one spinning parameter to include one or more of a temperature of the polymer solution, a flow rate of the polymer solution into the receptacle, a level of the polymer solution in the receptacle, a formulation of the polymer solution, a speed of rotation of the rotatable element, a voltage applied between the collector electrode and spinning electrode, a current applied between the collector electrode and spinning electrode and a distance between the operative surface of the rotatable element and the collector electrode.

Still further features provide the rotatable element of each spinning electrode to be selected to have the same or a different size, the same or different shape and to have the same or a different texture; and for the receptacle of each spinning electrode to be selected to have the same or a different shape or configuration.

Yet further features provide for the method to include supporting the spinning electrodes spaced apart and such that they are individually moveable relative to either or both of the collector electrode and the other spinning electrodes; for each spinning electrode to be moved in a reciprocal or circular movement; for the reciprocal or circular movement of each spinning electrode to be the same or different; and for the method to include illuminating the fine fibers formed by each spinning electrode in use; for the method to include directing UV radiation at either or both of the polymer solution and the fine fibers that form in use; for the method to include vibrating the polymer solution contained in each receptacle; for the method to include directing a gas feed to each spinning electrode in a one or more user selectable directions; and for the method to include controlling one or all of the gas composition, temperature and flow rate fed to each spinning electrode.

In accordance with a fourth aspect, there is provided a control system for controlling spinning parameters in an apparatus as described above comprising:

a processor and a memory configured to provide computer program instructions to the processor to execute the function of the following components:

a spinning parameter determining component for determining at least one spinning parameter of one or more spinning electrode; and

an output component for adjusting the at least one spinning parameter of one or more of the spinning electrodes independently of the other spinning electrodes. Further features of this aspect provides for the control system to include an input component for selecting inputs to the spinning parameter determining component based on one or more of a formulation of the polymer solution, a user-selectable average production rate range of fine fibers and a user selectable average diameter range of the fine fibers produced; and for the control system to include a feedback component which receives feedback about the production of fine fibers and provides instructions to the spinning parameter determining component.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings: Figure 1 is a schematic perspective illustration of one form of implementation of the invention;

Figure 2 is a schematic illustration of a spinning electrode; Figure 3 is a schematic illustration showing a spinning electrode positioned on a movable platform for shunting the spinning electrode;

Figure 4 is a schematic illustration of fixture points for positioning spinning electrodes on a support; Figure 5 is a schematic illustration of a control system for controlling spinning parameters;

Figures 6a illustrates an example of the coverage of foil in an open bath;

Figure 6b illustrates an example of the coverage of foil with three cups;

Figure 7 is a top view of a first arrangement of elements in an example of varying spinning configurations and parameters; and

Figure 8 is a top view of a second arrangement of elements in an example of varying spinning configurations and parameters.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

An apparatus is provided for the production of fine fibers by electrospinning. The apparatus includes a collector electrode and a plurality of separate spinning electrodes spaced apart therefrom. Each spinning electrode is provided by a loose (unattached) rotatable element supported in a receptacle capable of containing a polymer solution to partly submerge the rotatable element. The plurality of spinning electrodes are spaced apart from each other so that they generally do not abut each other. The degree or pattern of spacing may be selected to achieve optimal electrospinning conditions for each of the specific polymer or spinning solutions contained in the receptacles of the spinning electrodes. The spinning electrodes may be spaced in any predetermined pattern or patterns and may be moved or adjusted as will become apparent.

The polymer solution is applied to an exposed surface of each rotatable element by causing it to rotate in the polymer solution. An appropriate facility is included in the apparatus for causing polymer solution to be applied to the exposed surfaces of the rotatable elements by causing them to rotate in the polymer solution so that they become coated with a thin layer of polymer solution on their surfaces. 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. Typical means for fixing or mounting include axle, gears or rollers which hold a rotating element captive against movement other than rotation. Thus, for example, the electrode of the NanoSpider is mounted on an axle while the ring electrodes of US 3,994,258 are mounted between rollers and cannot be moved other than to be rotated. Elements which are not loose cannot simply be removed from an apparatus by picking them up, and conversely cannot simply be replaced by putting another in its place.

Rolling of such loose rotatable elements can be promoted by a support member or members inside the receptacle or receptacles. Alternatively, a support plate or the like provided below each spinning electrode can be moved relative to the elements to cause them to rotate with such movement, typically, in this variation being reciprocal to-and-fro movement or a circular motion.

The rotatable elements may be of any suitable material and may have a preselected size, shape and texture on its surface. The elements may be the same or different in each of the individual spinning electrodes. The elements may be rounded and most commonly circular when viewed in at least one direction. They can be spheres, cylinders or intermediate ellipsoidal shapes. In a very simple embodiment of the present invention, the rotatable elements are solid spheres or balls made from a solvent-resistant plastic. These can easily be picked up, removed, replaced or added to the apparatus. They are inexpensive and available in a wide variety of sizes.

Electrospinning is achieved by applying an electrical field between the collector electrode and the plurality of spinning electrodes spaced apart from the collector electrode. The plurality of spinning electrodes may extend generally parallel to the collector electrode or in a curvilinear or other pattern or configuration relative to the collector electrode. An operative surface of the loose rotatable elements of each spinning electrode is coated with a polymer solution and an electric field of sufficient magnitude is generated between the spinning and collector electrodes to cause the formation of fine fibres in the space between the electrodes.

In the embodiment illustrated in Figure 1 , loose rotatable elements (1 ), in this embodiment spheres, are each supported in a cup-shaped receptacle (3). Each rotatable element (1 ) and cup- shaped receptacle (3) defines, in effect, is a spinning electrode (4). The cups (3) may be filled with the same or a different polymer solution and the loose spheres are each supported in a partially submerged fashion on a drive facility. In this embodiment a pair of parallel, spaced rollers (not shown) forms the drive facility for each cup. Operating the rollers causes each sphere (1 ) to roll in the polymer solution causing a thin layer of polymer solution to form on the exposed surfaces of the spheres.

A power source (7) applies a high voltage to the spinning electrodes (4) and the collector electrode (9) that is generally parallel to it but spaced apart from the spinning electrodes (4). The high voltage applied to each of the spinning electrodes (4) is individually or independently controlled. The power source (7) has a number of output channels each having an individually or independently configurable output voltage for one or more of the spinning electrodes. Electrical contact with the polymer solution carried on the exposed surfaces of the spheres is maintained by way of an electrode, in each cup (3).

The production of fibers is controlled, in particular by controlling the voltage applied between the primary and counter electrodes, such that multiple electrospinning jets (1 1 ) erupt from the surfaces of the spheres under influence of the high voltage that is applied. The apparatus offers the ability to move the cups into different patterns or configurations to so alter the electric field between individual spinning electrodes and the collector electrode.

Further according to this embodiment, a plurality of gas jets (13) are provided about the periphery of each cup (3). These direct air or other gases in the direction of the counter electrode (9). The air or gas can be used in a number of ways. An important function is to assist in quick drying of the fibres, thus enhancing process efficiency and fibre quality. The jets can also be directed to produce a vortex about the fibres to twist them before reaching the counter electrode. Still further, gases which react with the fibres can also be used to change or modify characteristics of the fibres. Clearly, different gas and jet configurations can be used with each cup.

Generally the apparatus operates along lines that are well-known to those skilled in the art and further detail of which need not be included herein. It is, however, to be noted that the apparatus includes a support and drive means for the plurality of spinning electrodes. The support may be in the form of a tray with a plurality of seats or receiving formations for spinning electrodes. The tray may be mounted on a pair of rails configured to support the tray in a horizontal or other operating condition. The rollers in the cups of the spinning electrodes may be rotated by any suitable drive means either directly or indirectly by means of drive shaft which transmits its rotational motion to the rollers in the cups. For example, one or more drive shafts may be provided underneath the support. A motor may be connected to a first end of the shaft and may be configured to rotate the shaft about a bearing. One or more pulley belts may be provided on the drive shaft and may be arranged to transmit the rotary motion of the drive shaft to the rollers inside the receptacles of the spinning electrodes.

A spinning electrode (27) is shown in more detail in Figure 2 and includes a spherical rotatable element or ball (45) mounted within a receptacle or cup (47) with a cavity (48) for polymer solution. A pair of rollers (49) are located within the receptacle for rotating the ball (45). In this embodiment, the receptacle has an inlet (51 ) and an outlet (53) for a polymer solution or reagent. The outlet (53) is provided operatively above the inlet (51 ) in the cup (47) by means of an overflow tube (55) which controls the level of solution within the receptacle. A high voltage connection point (57) is provided for an electrode rod (not shown), that extends into the polymer solution held in the receptacle (47) and applies a high voltage to the entire spinning electrode (27) in use. The overflow tube (55) is in fluid communication with an outlet port member (61 ). The inlet to the receptacle is in fluid communication with an inlet port member (63).The rollers (49) may be connected to a drive mechanism which rotates the rollers. The receptacle may have multiple polymer solution or reagent inlets and outlets, in this manner one or more reagents may be introduced into the receptacle before, during or after electrospinning. One or more pumps may be associated with each of the inlets for pumping a polymer solution or reagent into the receptacle. The receptacles of the spinning electrodes preferably have a periphery which is complementary to the shape of the rotatable elements so that a minimal amount of the surface of the spinning solution is exposed to the collector electrode to increase the production rate and yield of fine fibers by electrospinning. Figure 3 shows a method of independent shunting or circular motion of an individual spinning electrode (4) by mounting it on a platform (97) that is movable independently of a support for the plurality of spinning electrodes in an apparatus. The platform (97) has a rod (101 ) which is moved to transmit the shunting movement to the platform and spinning electrode. The shunt parameters such as speed and orbital radius can be pre-selected to allow different nanofiber coating profiles onto the collector surface. The platform defines a slot (99) in which the spinning electrode (4) is adjustably secured. The position of the spinning electrode (4) within the slot can be adjusted to adjust the orbital radius of the circular motion. Alternatively, a different size of platform (or turn table) can also be used to adjust the orbital radius of the circular motion. Figure 4 is a schematic illustration of the positions for spinning electrodes on a support (105). The support has multiple receiving formations or fixture points for positioning spinning electrodes. Some of the receiving formations are in the form of elongate grooves (109) in which the spinning electrodes may be slideably or releasably received for adjusting the position of the spinning electrodes on the support to change the pattern and configuration of spinning electrodes on the support. The grooves (109) are spaced radially outward and the length of the grooves spaced further from the centre of the support are longer than those closer to the centre. The support (105) allows for spinning electrodes to be grouped close together or to be in an expanded arrangement in which the spinning electrodes are spaced further apart from each other. The support also allows for individual positioning of one spinning electrode relative to the other spinning electrodes. Apertures (107) for ambient air or atmosphere are provided within the support. The grooves (109) allow the spinning electrodes to be repositioned at a new position before or during electrospinning. The repositioning may be achieved with various types of actuators such as a robotic arms for example. Importantly, at least one spinning parameter of one or more of the spinning electrodes is controllable independently of the other spinning electrodes. The operating conditions of each spinning electrode can thus be individually controlled to ensure optimal fibre formation from the polymer solution in the receptacle of a particular spinning electrode which may be the same or different to the polymer solution contained in one or more of the other receptacles. A spinning parameter is a parameter known to affect the production of fine fibers by electrospinning. It is an adjustable characteristic, feature or component of the apparatus, particularly the spinning electrode as well as of the polymer solution in use.

A first spinning parameter is a temperature of the polymer solution. Different polymer solutions may require different operating temperatures for electrospinning that is based on their respective formulations. Temperature is known to affect the solubility of polymers in solution, for example, and the temperature required for the electrospinning of different polymer solutions varies. Furthermore, temperature control of a spinning electrode allows for electrospinning of polymer melts. Each spinning electrode may be provided with its own source of heat that can be individually controlled.

A flow rate of the polymer solution to a receptacle of a spinning electrode is a further individually controllable spinning parameter of the apparatus. The flow rate refers to the rate at which the polymer solution flows or is pumped into the receptacle which may be adjusted depending on the volatility and other properties of the solvents or reagents present in the polymer or spinning solution. The flow rate may be controlled by an appropriate control valve provided in an inlet in fluid communication with the receptacle.

A level of the polymer solution in the receptacle is a spinning parameter that may be controlled to accommodate different types and sizes of rotatable elements and to achieve optimal submersion of the rotatable element so that the surfaces of the rotatable elements are sufficiently covered with polymer solution when rotated therein to ensure efficient electrospinning. A level sensor may be included in each individual spinning electrode which is configured to sense the level of polymer solution in the receptacle to provide feedback to a user. Each spinning electrode may also include a control valve in each polymer solution or reagent inlet for controlling the flow of polymer solution or reagent into the receptacle. An appropriate overflow mechanism may be provided to maintain a level of polymer solution in a receptacle. For example, an outlet may be positioned operatively above an inlet to the receptacle for controlling the level of polymer solution in the receptacle. The outlet may configured to provide a weir over which excess polymer solution flows into the outlet to maintain a preselected level of polymer solution in the receptacle. Accordingly, the height of the outlet or weir is adjustable to vary the level of polymer solution in each receptacle as required. A formulation of the polymer solution is a spinning parameter of one or more of the spinning electrodes that is controllable independently of the other spinning electrodes. Composite or intimately blended nanofiber webs that include different types and compositions of polymer can be formed by spinning different polymer solutions and or melts from different spinning electrodes at the same time with the apparatus.

A further spinning parameter of a particular spinning electrode that may be independently controllable is a speed of rotation of the rotatable element which is individually selectable based on the type of polymer solution and the fine fibre production requirements for the particular web to be formed on the collector electrode.

Different polymer solutions have different surface tensions, viscosities and charging characteristics and thus further spinning parameters that must be individually controllable for each spinning electrode which may contain different or the same polymer solutions include: a voltage applied between the collector electrode and spinning electrode by a voltage source; a current applied between the collector electrode and spinning electrode; and a distance between the operative surface of the rotatable element and the collector electrode. All of these particular parameters affect the electric field present between the collector electrode and each spinning electrode and directly affect the electrospinning process.

Each spinning electrode is controllable independently of the other spinning electrodes and each spinning electrode is individually replaceable so that if one of the spinning electrodes malfunctions or is in need of repair or replacement it can be removed and/or replaced without substantially affecting the production of fine fibers from the remaining spinning electrodes. An appropriate releasable coupling may be provided for releasing the spinning electrode from the apparatus.

The apparatus is versatile in that it has user selectable components and configurations to optimise electrospinning for a variety of polymer solutions and to enable it to produce different nanofiber webs or materials. For example, the rotatable element of each spinning electrode may be the same or a different preselected size or preselected shape and the rotatable element of each spinning electrode may be of the same or a different preselected texture. Similarly, the receptacle of each spinning electrode may be of the same or a different preselected shape or configuration and may be selected based on the size and shape of the rotatable element or the appropriate volume of polymer solution to be contained in the receptacle.

The apparatus includes a support such as a tray for the spinning electrodes. The spinning electrodes may be in any appropriate orientation relative to the collector electrode so that electrospinning may occur vertically, horizontally or at an angle. The support may be planar or curved and the collector electrode may also be planar or curved. In this manner a constant distance and thus electric field may be generated between the plurality of spinning electrodes and collector electrode or a gradient or variable electric field strength may be provided between the spinning electrodes and collector electrode as required. A plurality of actuators may be included and arranged to individually move one or more of the spinning electrodes relative to the collector electrode or relative to the other spinning electrodes to independently control and adjust the distance between the operative surface of the rotatable element and the collector electrode and the distance between the spinning electrodes. Additionally, the pitch of individual spinning electrodes relative to the collector electrode may also be adjusted.

The support or tray may include movable platforms for each individual spinning electrode which is configured to provide individual reciprocal movement or individual circular movement to each of the spinning electrodes.

Each individual spinning electrode may be provided with one or more further components that affect the electrospinning process. Each spinning electrode may be provided with a tap mechanism operable to contact the rotatable element to break the surface tension and create a point of high charge density for jet initiation of polymer solution on the surface thereof. This is 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 spheres then leads to automatic splitting of the first jet (or jets) into multiple jets, which ideally spread to the other spheres through a synergistic inductive effect that is frequently observed in multi-cup 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. Each spinning electrode may include its own source of heat such as a heater or appropriate heating element for heating the polymer solution. Furthermore, each spinning electrode may be provided with a wiping device operable to wipe off fine fibers that form on the receptacle in use.

Each spinning electrode may have a light source associated therewith for lighting the fine fibers that form in use to enable visualisation of the production of fine fibres to provide feedback to a user. The light source may be orientatable in a user selectable direction and may be an adjustably mounted LED light for example. Each spinning electrode may have a UV radiation source 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.

Each spinning electrode may have a source of vibration, preferably a sonicator, for vibrating the polymer solution in the receptacle. The vibration being 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 each receptacle, or at least some receptacles, could be made of, or covered in, or have a conductive material. This permits that the electrostatic field around each cup can 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 focussing effect. Each spinning electrode may have a gas feed directed through at least one gas outlet or nozzle provided at or near the spinning electrode and directed in a preselected direction or pattern. Accordingly each spinning electrode may have at least one inlet and at least one outlet which permits gas to be directed therethrough. 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 orientatable in different, preferably user selectable, directions. The gas composition, temperature and flow rate in respect of the one or more gas feeds associated with a spinning electrode may be individually controllable for each spinning electrode.

Each spinning electrode may have its own drive configured to rotate the rotatable element at a user selectable speed. In this manner the apparatus may include multiple drives. Alternatively two or more spinning electrodes may be coupled to a single drive to obtain the same user selectable speed of rotation of the rotatable elements as may be required for two or more of the spinning electrodes. Any suitable drive for the rollers on which the rotatable element may be supported can be used, including, for example, a sprocket and chain drive, and a pneumatic or hydraulic drive. The rotatable element could also be supported on an endless belt located within the receptacle which causes it to rotate with the result described above.

A method for the production of fine fibers by electrospinning is provided which may be implemented with the apparatus described above. At a first step an electrical field is applied between a collector electrode and a plurality of spinning electrodes spaced apart therefrom. Each spinning electrode includes a loose (unattached) rotatable element supported in a receptacle containing a polymer solution to partly submerge the rotatable element. At a next step, each rotatable element is rotated in its receptacle so that the polymer solution is applied to an exposed surface of each rotatable element. A thin layer of polymer solution is thus formed on an operative surface of the rotating element from which fine fibers form between the each spinning electrode and the collector electrode when an electric field of sufficient magnitude is generated between the spinning electrode and collector electrode. The method is characterized in that at least one spinning parameter of one or more of the spinning electrodes is controlled independently of the other spinning electrodes. The spinning parameters that are independently controlled include one or more of a temperature of the polymer solution, a flow rate of the polymer solution into the receptacle, a level of the polymer solution in the receptacle, a formulation of the polymer solution, a speed of rotation of the rotatable element, a voltage applied between the collector electrode and spinning electrode, a current applied between the collector electrode and spinning electrode and a distance between the operative surface of the rotatable element and the collector electrode.

The method also includes selecting individual configurations for each spinning electrode. The rotatable element of each spinning electrode may be selected to have the same or a different size, the same or different shape and to have the same or a different texture and the receptacle of each spinning electrode may be selected to have the same or a different shape or configuration.

The method also includes supporting the spinning electrodes spaced apart and such that they are individually moveable relative to either or both of the collector electrode and the other spinning electrodes. Also, each spinning electrode may be moved in a reciprocal or circular movement and the reciprocal or circular movement of each spinning electrode may be the same or different. 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.

In order to implement the above method, a control system (201 ) shown in Figure 5 is provided for controlling spinning parameters in an apparatus (203) as described above. The control system (201 ) includes a processor (205) and a memory (207) configured to provide computer program instructions (209) to the processor (205) to execute the function of the components of the control system. The control system (201 ) includes a spinning parameter determining component (21 1 ) for determining at least one spinning parameter of one or more spinning electrode. After the appropriate or selected spinning parameter of a spinning electrode has been determined by the spinning parameter determining component (21 1 ), it instructs the output component (213) to adjust the at least one spinning parameter of one or more of the spinning electrodes of the apparatus (203) independently of the other spinning electrodes. An input component (215) with an appropriate user interface may also be provided for selecting inputs to the spinning parameter determining component (21 1 ). As described above, the spinning parameters may be the applied voltage, applied current, spinning element rotation speed, distance between spinning electrode and the collector electrode, humidity, temperature, gas flow rate. Further spinning parameters may include the tapping and wiping frequency. The input may be in the form of a particular protocol that has been designed for a specific type of polymer solution or a desired polymer fiber characteristic or average production rate range. In this manner the input will be based on one or more of a user-selectable formulation of the polymer solution, a user- selectable average production rate range of fine fibers and a user-selectable average diameter range of the fine fibers produced.

The control system (201 ) may also include a feedback component (217) which receives feedback about the production of fine fibers by the apparatus (203) based on information received from sensors and the like and provides instructions to the spinning parameter determining component (21 1 ) to determine the spinning parameters of one or more of the spinning electrodes. The spinning electrode may, for example, include resistive sensing to determine the voltage drop across and the current between each individual spinning electrode and the collector electrode. The current is thus a form of feedback provided to the feedback component. The current indicates whether electrospinning is occurring at the specific spinning electrode and whether a sufficient number of jets that form fibers are present. If a lower current is measured than a predetermined threshold current, the voltage applied to the specific spinning electrode may be increased, the rate of rotation of the rotatable element adjusted or any other appropriate spinning parameter or configuration of the apparatus may be adjusted. A thickness or density distribution sensor can be provided at the collector surface to sense the production rate and thickness or density distribution or web quality of the fine fibers that collect on the collector. This can be used as feedback for the feedback component.

The control system allows for individual control of one or more of the spinning electrodes to adjust spinning parameters ahead of or during production of fine fibers by electrospinning using the apparatus described herein.

EXAMPLES

Example 1

The following example demonstrate the efficiency of electrospinning when the polymer solution is contained in receptacles (cups) of spinning electrodes instead of having a plurality of loose (unattached) rotatable elements supported in a large open bath in which a significantly larger surface area of the polymer solution is exposed to the collector electrode.

Polycaprolactone (PCL) was dissolved in a suitable solvent. This solution was electrospun using 3 spherical elements, in this example glass marbles, in an open bath and 3 receptacles, in this example cups, respectively. These two configurations were compared with respect to production rate, expressed as fiber-mat-mass per active spinning surface area per hour (kg/m²/hr), the average fiber diameter (incl. STDEV and variance) and coverage/fiber deposition area (m²). Fibers were deposited onto aluminium foil coated on a drum (diameter 160 mm, length 400 mm) that was rotated (drum surface speed 4000mm/s) above the elements with an element to drum distance of 130mm. The elements were rotated at 0.5mm/s surface speed. The current was limited to 0.1 mA in all experiments and the ambient conditions were controlled within a temperature and relative humidity range of 22-23°C and 54-55%. The voltage was applied accordingly to allow consistent spinning (the open bath would not spin below 85kV potential over 130mm spinning distance) and for the current to be limited to 0.1 mA (to allow comparison between the two configurations). As-spun fiber mats were removed and then immediately weighed to determine production rates.

Results and discussion:

Spinning from the open bath required higher applied voltage (+65;-20kV) to yield the same current (0.1 mA) as when spinning from the cups at +60;-20kV. Spinning from the open bath had the tendency to produce electrical discharge due to the slightly higher electric field strength (below which spinning was not consistent).

The comparative production rates can be seen in Table 1 . The cups showed the greatest production rate being roughly four times greater than with the open bath. The average fiber diameters are shown in Table 2. The cups produced significantly lower average fiber diameters with better uniformity compared with the open bath.

Table 1 : Production rate comparison

Table 2: Average fiber diameter comparison

The results for the comparison of the coverage/fiber deposition area are shown in Table 3. The coverage of the foil was poorest in the case of the open bath producing three strips of fiber mats spaced far apart (Figure 6a). The cups obtained total coverage (Figure 6b).

Table 3: Coverage comparison

The following examples demonstrate the versatility in the type of materials that can be produced with individual control of spinning parameters and configurations of a particular spinning electrode in one apparatus.

Example 2

This example relates to a method of electrospinning two different spin solution formulations from the same electrospinning apparatus to yield an intimate binary mixture of nanofibers of these two materials. The formulations, denoted solution formulation 1 and solution formulation 2, are fed to two rows each containing three cups in the cup configuration as shown in Figure 7. The common spinning parameters are in the range shown in Table 4 and the independently controlled spinning parameter in Table 5. A binary nanofiber sheet can be produced to specifically yield two types of nanofiber materials intimately blended with the fiber diameter, blend ratio and density controlled by the independent cup spinning parameters.

Table 4

o ut on ow rate m m n cup . .

Example 3 Example 3 relates to a method of electrospinning two different spin solution formulations from the same electrospinning apparatus to yield a gradient mixture of fine fibers of the two materials, where one nanofiber material comprises the top layer, both nanofibers comprise an intimately blended middle layer, and the second nanofiber material comprises the bottom layer. The formulations, denoted solution formulation 1 and solution formulation 2, are fed to two rows each containing three cups in the cup configuration as shown in Figure 7. The common spinning parameters are in the range shown in Table 5 and the independently controlled spinning parameter in Table 6 below.

The protocol is as follows:

The HV for formulation 1 is turned on, while the HV for formulation 2 is off. Formulation 1 is electrospun for 30 minutes, whereupon the HV for formulation 2 is turned on. Both formulations are electrospun for 30 minutes, whereupon the HV for formulation 1 is turned off. Formulation 2 is then electrospun for 30 minutes. A nanofiber sheet can be thus produced to specifically yield two types of nanofiber materials with the one nanofiber material comprising the top layer, an intimately blended middle layer of both materials, and the second nanofiber material comprising the bottom layer with the fiber diameter, blend ratio and density controlled by the independent cup spinning parameters. Example 4

Example 4 describes a method to electrospin two different spin solution formulations from the same electrospinning apparatus to yield an intimate binary mixture of nanofibers of these two materials, in the case where one formulation requires heating to prevent precipitation of the polymer. The formulations, denoted solution formulation 1 and solution formulation 2, are fed to two rows each containing three cups in the cup configuration as shown in Figure 8. The common spinning parameters are in the range shown in Table 6 below and the independently controlled spinning parameter in Table 7 below. A binary nanofiber sheet can be produced to specifically yield two types of nanofiber materials intimately blended that would not otherwise be able to be electrospun to the same collector due to the different solution temperatures required.

Table 6

The apparatus of the invention is more versatile than prior art apparatuses and allows more effective control of the spinning process. The use of a plurality of receptacles thus permits close control of the spinning process by allowing the conditions pertaining to individual spinning electrodes to be individually controlled and by allowing additional features, such as one or more gas jets, a heat source, a UV source, a wiping device, a light source and the like to be associated with each individual spinning electrode. The advantage offered by the apparatus of the invention is that each spinning electrode can be individually controlled with respect to its height relative to the collector electrode, level of spinning solution, direction and speed of rotation of the rotatable elements, and operating electrical potential and temperature and other parameters described herein. The operating conditions of each spinning electrode can thus be individually controlled to ensure optimal fibre formation from the spinning solution in that receptacle.

It is also possible to spin different solutions simultaneously by filling the receptacles with different solutions. In particular, it is now possible to spin polymer melts and conventional polymer solutions, or combinations of melts and/or solutions together. This allows blending of materials at a fibre level to obtain different desirable characteristics. In particular, a more intimate blend of materials can be obtained due to the relative positions which the cups may take with respect to each other. Using the process for manufacturing a yarn described in WO 2008/062264, it will be possible to obtain high quality, high volume, blended yarns.

Importantly, as mentioned above, the spinning electrodes can be moved into any suitable configuration. Their spacing and relative positions and heights can thus be adjusted to optimise production for the specific spinning solution or solutions being used. Spinning electrodes can also be moved, removed, replaced or added during spinning without having to stop the process.

The apparatus and process permits easy moving or shunting of cups during spinning as inertia has a negligible effect on the relatively small volume of spinning solution and primary electrode. The spinning electrodes of the invention can thus be continually moved to optimise spinning or blending. Prior art apparatus cannot be so easily moved without the spinning solution spilling, and those using large rotating electrodes with large spin solution baths, like the Nanospider, would have severe difficulties overcoming the inertia of such a large, rotating object without disrupting the process.

One further major advantage of the apparatus is the lack of spinning solution between the cups. It has been found that certain polymer solutions are easier to spin, and/or spin at much higher rates, with the apparatus of the invention. Although not yet fully understood, it is surmised that the exposed surface of the polymer solution in prior art apparatuses creates counteractive or interfering electrostatic field effects between the coated primary electrode and counter electrode. By selectively exposing the surface of the solution to the counter electrode, dramatic increases in productivity can be obtained and fibres produced from certain polymer solutions from which it was previously not possible to effectively produce these.

The use of receptacles has the further advantage that much dead volume of spinning solution is avoided. This ensures better economic viability and also reduces the surface area of solution available to evaporation and precipitation of contaminants. The application of multiple rotating elements simultaneously allows for the concurrent use of different-sized elements, more optimal utilisation of spin equipment area through denser packing of rotatable elements, and also gives an additional degree of freedom in the rotatable element's manoeuvrability and conversely more freedom in the design possibilities for the equipment. It will be understood that numerous different arrangements are possible within the scope of this invention without departing from the scope hereof. In particular, numerous variations are possible to the shape and configuration of the rotatable elements and the manner in which they are supported and rotated. Thus, for example, the rotatable elements may be basically cylindrical, although maybe ellipsoidal. If desired, the elements could also have textured surfaces which may include a multiplicity of small projections. It will also be understood that different materials, including glass, metal, and polymer, or combinations of these, can be used to make the rotating elements.

The rotatable elements can have a rolling diameter anywhere within in the range of from about 1 mm to about 300 mm, preferably 1 mm to about 200 mm, more preferably, 1 mm to about 100 mm, and generally between about 3 mm and about 30 mm. It will also be appreciated that the collector electrode (the counter electrode) can have any suitable configuration.

It will also be appreciated by those skilled in the art that a plurality of spinning electrodes may be grouped into clusters and that the spinning electrodes in a cluster may have the same spinning parameters and configurations and be controlled as a unit in the apparatus which is independent from the other spinning electrodes or clusters.

The method and apparatus of the invention allows for high throughput spinning without the difficulties associated with the use of needles. This is achieved by creating what can possibly be described as a solid, bubble-like surface. The coated elements simulate bubbles on the surface of a polymer spinning solution, as disclosed in WO 2008/125971 , but have the advantage that they do not burst, causing destructive splatter, and maintain a constant geometry leading to better process control, predictability and uniformity. Throughout the specification and claims unless the contents 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 which includes a collector electrode and a plurality of spinning electrodes spaced apart therefrom, each spinning electrode provided by a loose rotatable element supported in a receptacle capable of containing a polymer solution to partly submerge the rotatable element and which is applied to an exposed surface of each rotatable element by causing it to rotate in the polymer solution and wherein each rotatable element has an operative surface from which fine fibers form when an electric field of sufficient magnitude is generated between the spinning electrode and collector electrode and characterized in that at least one spinning parameter of one or more of the spinning electrodes is controllable independently of the other spinning electrodes.

2. An apparatus as claimed in claim 1 , wherein the at least one spinning parameter is one or more of: a temperature of the polymer solution, a flow rate of the polymer solution to the spinning electrode, a level of the polymer solution in the receptacle, a formulation of the polymer solution, a speed of rotation of the rotatable element, a voltage applied between the collector electrode and spinning electrode by a voltage source, a current applied between the collector electrode and spinning electrode and a distance between the operative surface of the rotatable element and the collector electrode.

3. An apparatus as claimed in claim 1 or claim 2, wherein each spinning electrode is controllable independently of the other spinning electrodes.

4. An apparatus as claimed in any one of the preceding claims, wherein each spinning electrode is individually replaceable.

5. An apparatus as claimed in any one of the preceding claims, wherein the rotatable element of each spinning electrode is the same or a different preselected size, the same or different preselected shape and the same or a different preselected texture.

6. An apparatus as claimed in any one of the preceding claims, wherein the receptacle of each spinning electrode is of the same or a different preselected shape or configuration.

7. An apparatus as claimed in any one of the preceding claims, further including a support for the spinning electrodes and a plurality of actuators arranged to individually move one or more of the spinning electrodes relative to the collector electrode or relative to the other spinning electrodes to independently control the distance between the operative surface of the rotatable element and the collector electrode and the distance between the spinning electrodes.

8. An apparatus as claimed in claim 7, wherein the support is configured to provide individual reciprocal movement or individual circular movement to each of the spinning electrodes.

9. An apparatus as claimed in any one of the preceding claims, wherein each spinning electrode is provided with a wiping device operable to wipe off fine fibers that form on the receptacle in use.

10. An apparatus as claimed in any one of the preceding claims, wherein each spinning electrode is provided with a tap mechanism operable to contact the rotatable element to break the surface tension and create a point of high charge density for jet initiation of polymer solution on the surface thereof.

1 1 . An apparatus as claimed in any one of the preceding claims, wherein each spinning electrode has a light source associated therewith for lighting the fine fibers that form in use.

12. An apparatus as claimed in any one of the preceding claims, wherein each spinning electrode has a UV radiation source for directing UV radiation at either or both of the polymer solution and fine fibers that form in use.

13. An apparatus as claimed in any one of the preceding claims, wherein each spinning electrode has a source of vibration, preferably a sonicator, for vibrating the polymer solution in the receptacle.

14. An apparatus as claimed in any one of the preceding claims, wherein each spinning electrode has a gas feed directed through at least one gas outlet in a preselected direction or pattern.

15. An apparatus as claimed in claim 14, wherein the gas composition, temperature and flow rate is controllable for each spinning electrode.

16. A spinning electrode which includes a receptacle with a loose rotatable element supported therein and wherein the receptacle is capable of containing a polymer solution to partly submerge the rotatable element and which is applied to an exposed surface of each rotatable element by causing it to rotate in the polymer solution and wherein the receptacle includes at least one inlet and at least one outlet for a polymer solution or reagent, characterised in that at least one spinning parameter of the spinning electrode is controllable.

17. A spinning electrode as claimed in claim 16, further including at least one inlet and at least one outlet which permits gas to be directed therethrough.

18. A spinning electrode as claimed in claim 16 or claim 17, wherein the receptacle includes multiple polymer solution or reagent inlets and outlets.

19. A spinning electrode as claimed in any one of claims 16 to 18, wherein the receptacle is provided with multiple gas inlets and multiple gas outlets at or near a periphery of the receptacle.

20. A spinning electrode as claimed in claim 19, wherein the gas outlets are orientatable in different, preferably user selectable, directions.

21 . A spinning electrode as claimed in any one of claims 16 to 20 which includes a light source orientatable in a user selectable direction.

22. A spinning electrode as claimed in any one of claims 16 to 21 which includes a source of UV radiation.

23. A spinning electrode as claimed in any one of claims 16 to 22 which includes a source of heat.

24. A spinning electrode as claimed in any one of claims 16 to 23 which includes a source of vibration for a polymer solution contained in the receptacle.

25. A spinning electrode as claimed in any one of claims 16 to 24 which includes a wiping device operable to wipe away fibers formed on the receptacle.

26. A spinning electrode as claimed in any one of claims 16 to 25 which includes a tap mechanism operable to contact the rotatable element to break the surface tension and create a point of high charge density for jet initiation of polymer solution on the surface thereof.

27. A spinning electrode as claimed in any one of claims 1 6 to 26 which includes a drive configured to rotate the rotatable element at a user selectable speed.

28. A spinning electrode as claimed in any one of claims 16 to 27 which includes a level sensor configured to sense the level of polymer solution in the receptacle and a valve associated with each polymer solution or reagent inlet for controlling the flow of polymer solution or reagent into the receptacle.

29. A spinning electrode as claimed in any one of claims 16 to 28, wherein the at least one outlet of the receptacle is operatively above the inlet to the receptacle for controlling the level of polymer solution in the receptacle.

30. A method for the production of fine fibers by electrospinning by

applying an electrical field between a collector electrode and a plurality of spinning electrodes spaced apart therefrom, each spinning electrode including a loose rotatable element supported in a receptacle containing a polymer solution to partly submerge the rotatable element;

rotating each rotatable element in its 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 rotating element from which fine fibers form when an electric field of sufficient magnitude is generated between the spinning electrode and collector electrode,

and characterized in that at least one spinning parameter of one or more of the spinning electrodes is controlled independently of the other spinning electrodes.

31 . A method as claimed in claim 30 in which the at least one spinning parameter includes one or more of a temperature of the polymer solution, a flow rate of the polymer solution into the receptacle, a level of the polymer solution in the receptacle, a formulation of the polymer solution, a speed of rotation of the rotatable element, a voltage applied between the collector electrode and spinning electrode, a current applied between the collector electrode and spinning electrode and a distance between the operative surface of the rotatable element and the collector electrode.

32. A method as claimed in claim 30 or claim 31 which includes selecting the rotatable element of each spinning electrode to have the same or a different size, the same or different shape and to have the same or a different texture.

33. A method as claimed in any one of claims 30 to 32 which includes selecting the receptacle of each spinning electrode to have the same or a different shape or configuration.

34. A method as claimed in any one of claims 30 to 33 which includes supporting the spinning electrodes spaced apart and such that they are individually moveable relative to either or both of the collector electrode and the other spinning electrodes.

35. A method as claimed in any one of claims 30 to 34 which includes moving each spinning electrode in a reciprocal or circular movement.

36. A method as claimed in claim 35, wherein the reciprocal or circular movement of each spinning electrode is the same or different.

37. A method as claimed in any one of claims 30 to 36 which includes illuminating the fine fibers formed by each spinning electrode in use.

38. A method as claimed in any one of claims 30 to 37 which includes directing UV radiation at either or both of the polymer solution and the fine fibers that form in use.

39. A method as claimed in any one of claims 30 to 38 which includes vibrating the polymer solution contained in each receptacle.

40. A method as claimed in any one of claims 30 to 39 which includes directing a gas feed to each spinning electrode in a one or more user selectable directions.

41 . A method as claimed in claim 40, which includes controlling one or all of the gas composition, temperature and flow rate fed to each spinning electrode.

42. A control system for controlling spinning parameters in an apparatus as claimed in any one of claims 1 to 16, comprising:

an output component for adjusting the at least one spinning parameter of one or more of the spinning electrodes independently of the other spinning electrodes.

43. A control system as claimed in claim 42 which includes an input component for selecting inputs to the spinning parameter determining component based on one or more of a formulation of the polymer solution, a user-selectable average production rate range of fine fibers and a user selectable-average diameter range of the fine fibers produced.

44. A control system as claimed in claim 42 or claim 43 which includes a feedback component which receives feedback about the production of fine fibers and provides instructions to the spinning parameter determining component.