Patent Application
20150165667
The present disclosure generally relates to a slot die for electrospinning polymeric fiber.
The process of electrospinning is well known in the art as represented in U.S. Pat. Nos. 2,158,416; 4,043,331; 4,044,404; 4,143,196; 4,287,139; 4,323,525; 4,432,916; 4,689,186; 6,641,773; and 8,178,030, each of which is incorporated herein by this reference. Electrostatic spinning, also referred to in the art as electro spinning or espinning, involves a charged polymer moving towards a charged or grounded surface. The fibers produced by electrospinning have submicron or “nano” diameters and their resultant fabrics have been found to be useful in the filtration, medical, and textile areas. These fibers with their dense packed yet porous structure can effectively be used for gas or fluid separation or absorption.
Electrospun polymeric fiber can be derived from a melt, solution, or dispersion. For example, the melt, solution, or dispersion can be discharged through a small charged orifice, such as a needle, towards a target wherein the needle and target have opposing electrical charges. The target (also sometimes referred to as the collector) includes a collection surface, which may be of a variety of materials and shapes, as will be understood by those skilled in the art. When an electric potential is placed on the melt, solution, or dispersion, and as the charge attempts to move to ground (i.e., the target or collector), one or more jets can be produced from which the fiber is drawn. A needle or small orifice typically produces a single jet, which can produce fiber at a rate of about 0.1 g/hr. Throughput of this type of electrospinning apparatus is usually very low. This process produces long fibers with a relatively narrow range of fiber diameters in the micron to submicron range. When fibers are allowed to accumulate on the collection surface, they produce a nonwoven fabric, also referred as a mat. Such apparatus for electrospinning from a single orifice and producing a single jet are represented by U.S. Pat. No. 8,178,030B2, and U.S. Pub. Nos. 2003/0215624A1, 2009/0032475A1, 2010/0233812A1, and 2011/0082565A1, each of which is incorporated herein by this reference.
Additional orifices can be added and banks of orifices in two-dimensional blocks or single lines may be used. Such apparatuses for producing multiple jets from multiple orifices are represented by U.S. Pat. No. 7,980,838B2; U.S. Pub. Nos. 2007/022563A1; 2008/0241297A1; and 2008/0277836A1, and European Patents EP 1,967,617A1; 1,975,284A2; and 1,992,721, each of which is incorporated herein by this reference. However, one issue of the multiple orifices producing multiple jets is the repulsion between the multiple jets due to the jets having the same or similar electric charge. The repulsion between the jets can cause bending, as well as possible suppression of the jets; thus, jet stability suffers, resulting in one or more of erratic spinning, less uniform deposition of fibers, a wider range of fiber diameters, and fiber breakage.
One or more jets can also be generated from the same orifice by increasing the electrical potential between the charged source (dispersion, solution, or melt) and the collector. The increase in electric potential increases the throughput proportionately, but at the expense of jet stability since the jets are mutually repulsive.
Another technique in the art is to electrospin from a charged free surface. A charge is placed on the dispersion, solution, or melt and free surface electrospinning occurs from a wire, a cylinder turning in a trough, or the like. At points of perturbation on the surface of the dispersion, solution, or melt, jets may form. An advantage of this approach is that multiple stable jets may be formed so that higher, more uniform throughputs may be obtained.
For free surface electrospinning, the ejection volumes are dependent upon, for example, but not limited to: 1) the viscosity of the dispersion, solution, or melt; 2) the distance from the dispersion source to the collection surface; 3) solvent properties; 4) the rate of loading or covering of the wire or cylinder of the spinning apparatus; or 5) the voltage. These factors also affect the thickness of the mat and the desired fiber diameters, so optimization of these parameters is required. The equipment for free surface electrospinning from a trough or wire process has been commercially developed for solution and dispersion electrospinning and lab, pilot, and commercial sized units are available. Lab units have also been developed for melt electrospinning Apparatuses for electrospinning from free surfaces are known in the art and are represented by: US Pat. Nos. 7,967,588B2 and 8,231,822B2; U.S. Pub. Nos. 2009/014547A1 and 2010/0272847A1; European Patents EP 1,673,493B1 and 2,059,630B1; and International Patent Publications WO 2008/028428A1 and 2009/049566A2, each of which is incorporated herein by this reference.
Further exemplary discussion of materials and methods as disclosed herein is provided in U.S. provisional patent application No. 61/917,511, filed Dec. 18, 2013 and U.S. provisional patent application No. 61/950,252, filed Mar. 10, 2014, which are both incorporated herein by reference in their entireties.
While advancements in producing multiple stable jets from free surface electrospinning have been made, there are still several shortcomings, such as uniformity of the deposited fiber and the characteristics of the fiber and the derived nonwoven fabrics. Furthermore, being able to control a variety of compositions and allowing for different polymeric preparations (e.g., that may not be electrospun on other electrospinning apparatuses) would be very desirable attributes. Thus, a need exists for processes and apparatuses that address various deficiencies or that would create additional benefits, including the deficiencies and benefits described above.
The present disclosure generally relates to processes and apparatuses for high-throughput electrospinning of nonwoven materials. One aspect of the present disclosure involves a process of generating a substantially uniform electric field along and about the slit of a slot die, and “electrospinning” a polymeric solution, dispersion, suspension, and/or melt (collectively and individually referred to herein as “polymeric preparation”) from the slit through the substantially uniform field to a collector. Another aspect involves purposeful generating of a non-uniform electric field along and about the slot die slit. According to another aspect of the present disclosure, an apparatus is provided, comprising a slot die having a spinning edge with a slit. The slot die can be shaped to generate, according to some embodiments, a uniform, and according to some embodiments a purposefully non-uniform, electric field along and about the spinning edge when voltage is applied to the polymeric preparation and/or slot die. According to one embodiment, the spinning edge can be curved, defining at least one arc. The curved spinning edge can have a radius of curvature of at least 1 cm, and in one embodiment, between 5 and 100 cm inclusive. According to one embodiment, the curved spinning edge comprises a slit having a width (e.g., 90° perpendicular to the direction of the slit) between 0.01 and 10 mm, inclusive. The apparatus can further comprise one or more of a reservoir for holding the polymeric preparation, a collector installed a distance away from the slot die, a power source to apply a voltage difference between the slot die and the collector, and a delivery mechanism or pathway to supply the polymeric preparation to the slot die.
Additional features, advantages, and embodiments of the disclosure may be set forth or may be apparent from consideration of the following detailed description, drawings, and claims. Moreover, it is to be understood that both the foregoing summary of the disclosure and the following detailed description are exemplary and intended to provide further explanation without limiting the scope of the disclosure as claimed.
A full and enabling disclosure, including the best mode thereof, directed to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, which makes reference to the following figures.
a-3f are illustrations of a representative segment of a first embodiment of a slot die in accordance with the disclosure.
g-3l are illustrations of an enclosed slot die according to
a-4g are illustrations of a representative segment of a second embodiment of a slot die in accordance with the disclosure.
h-4m are illustrations of an enclosed slot die according to
a-5f are illustrations of a representative segment of a third embodiment of a slot die in accordance with the disclosure.
g-5l are illustrations of an enclosed slot die according to
a-8d are illustrations of a representative segment of a fourth embodiment of a slot die in accordance with the disclosure.
The present disclosure will now be described more fully hereinafter with reference to the accompanying figures, in which some, but not all embodiments of the disclosure are shown. Similar or identical features of the embodiments are provided with like reference numbers. Indeed, the disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Each example is provided by way of explanation of the disclosure, and is not intended to be limiting of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. For instance, features illustrated or described as part of one embodiment can be used in the context of another embodiment to yield a further embodiment. Thus, it is intended that the present disclosure covers modifications and variations that come within the scope of the disclosed embodiments and their equivalents.
The present disclosure is directed to an apparatus 11 and process for electrospinning polymeric preparation 9 (i.e., polymeric solution, dispersion, suspension, or melt) into fibers for the formation of non-woven sheets, membranes, tubes, and coatings with the potential for multiple other applications and forms. In particular, the present disclosure is directed to high throughput electrospinning of nanofibers formed from spinning a polymeric preparation 9 from a slot die 10 so shaped and configured as to result in a substantially uniform electric field formed along the spinning edge 12 when high voltage is applied across the slot die 10 or polymeric preparation 9 and collector 15 of the electrospinning apparatus 11.
One aspect of the disclosure provides for an even distribution of polymeric preparation 9 to the edge of a slit 16. Jet stability can be controlled by slit edge shape, gap width, applied voltage, or a combination of these parameters. Jet stability can be controlled and adjusted accordingly to produce espun sheets with different physical and mechanical properties. When a sufficiently strong electric field is formed when voltage is applied to the slot die and the sharpness of the die sharp edge 34 is sufficiently sharp to provide suitable perturbation, Taylor cones are formed and electrospinning jets 14 of the polymeric preparation 9 erupt from the slit 16 in the slot die 10. The jets 14 travel from the slit 16 of the slot die 10 toward a grounded or oppositely charged collector 15 to form a solid nonwoven material. In one embodiment, the disclosure focuses on slot dies in general and, in particular, the impact of the slot die's shape on the electric field uniformity to optimize electrospinning output.
An electrospinning apparatus 11 is illustrated schematically in
The polymeric preparation (i.e., solution, dispersion, suspension, and/or melt) used to produce fibers can have a viscosity of between 1 and 200,000 cP. This polymeric preparation can be pumped through a pathway network 19 such as a tube, hose, vessel or the like and provided to the slot die 10 and thus the spinning edge 12 at a rate of between 0.1 and 5000 milliliters per hour per centimeter length of slit, or at a rate of 10 and 500 milliliters per hour per centimeter length of slit. In one embodiment, the polymeric preparation 9 can be supplied to the spinning edge 12 in a uniform manner across the slit length pneumatically, hydraulically, mechanically, or by gravity. In order to encourage uniform fiber spinning in accordance with at least one embodiment of this disclosure, it is important to provide a uniform distribution of polymeric preparation 9 across the die spinning edge 12, which will be discussed in more detail below.
Materials to be electrospun into fibers according to the methods disclosed herein include dextran, alginates, chitosan, polyvinylpyridine compounds, cellulosic compounds, cellulose ether, hydrolyzed polyacrylamides, polyacrylates, polycarboxylates, polyethylene oxide, polyethylene glycol, polyethylene imine, polyvinylpyrrolidone, polyacrylic acid, poly(methacrylic acid), poly(vinyl alcohol), poly(vinyl alcohol) 12% acetyl, hydroxylpropyl cellulose, cellulose acetate, cellulose nitrate, alginic ammonium salts, pullulan, xanthan gum, polyurethanes (DSM (Bionate, Carbosil, Pursil), Lubrizol® (TG-500, SP-93A-100, tecophilic product line), AdvanSource® (C55D, C80A, and Hydrothane)), polystyrene, polymethacrylates, Teflon®, polyvinylidene fluoride, perfluoroalkoxy, fluorinated ethylene propylene, polytetrafluoroethylene, polyacrylonitrile, nylons, PEBAX®, polycarbonates, polyethylene terephthalate, polyesters, polyamides, poly(amic acid), polyimide, polylactic acid, polyglycolic acids, blends or copolymers of polylactic acid and polycglycolic acid, polyvinyl chloride, polycaprolactone, polyaniline, and blends and copolymers thereof.
The above solutions and dispersions of polymers may be combined with various additives and modifiers such as silver, calcium carbonate, hyaluronic acid and the like to produce beneficial modifications and features in the electrospun fibers.
As illustrated in
In one embodiment, the slot dies 10 (10, 10′, 10″) may be comprised of a conducting material such as gold, brass, copper, silver, steel, platinum or other metal and alloys thereof. In other embodiments, the slot dies 10 (10, 10′, 10″) could be totally or partially comprised of non-metal or non-conducting materials such as plastics, ceramics, etc. As illustrated in
a-4m illustrate electrospinning slot dies 10 (10, 10′) unique to the present disclosure with a spinning edge 12 having a radius of curvature “r”. The spinning edge 12 may have a sharp edge 34 as shown in
In one embodiment, the cavity 28 may comprise a divergent section 29 and convergent section 30. The divergent section 29 expands from a smaller length (l′) beginning at the end of the flow channel 26 to a larger length (l), the cord length of the slit. The convergent section 30 narrows from a larger width (W) to a smaller slit width (w). The purpose of the fluid pathway network 21 of the present disclosure can be to provide the polymeric preparation 9 to the die slit with as much uniformity as possible along the length (L) of the slit, and a variety of other (non-depicted) pathway networks may be utilized as will be understood by those skilled in the art.
According to one embodiment of the present disclosure, as depicted by
One goal of the design of the slot die, in accordance with at least one embodiment of the present disclosure is to create, as much as possible, a uniform electric field along the spinning edge 12. According to some embodiments of the present disclosure (see, e.g.,
In one embodiment, a die with multiple slits and/or multiple single slit slot dies either in series or in parallel may be used without departing from the disclosure.
Other properties of the non-woven mat can be controlled, altered, or improved in accordance with this disclosure. These include but are not limited to: fiber diameter, porosity, fiber uniformity, total spinning width, fiber quality, fiber orientation, air flow, air permeability, cellular ingrowth, cellular attachment, surface area, tensile strength, max load, elasticity, opacity, pore size, and bubble point. Various such properties of interest in a non-woven mat are described, for example, in U.S. Pat. No. 8,262,979 and U.S. Pat. Publication Nos. 2013/0268062 A1, 2013/0053948 A1, and 2013/0197664 A1, which are incorporated herein by reference in their entireties.
a-4g illustrate a slot die 10′ that has a spinning edge 12 with a smaller radius of curvature compared to the slot die 10 of
In some embodiments, the slot dies 10 (10, 10′, 10″) may comprise shoulder sections 20 that extend between and connect the edges of the slit 16 and the curved corners 32. The shoulder sections 20 may be curved or straight and may range in length from 1 mm to 10 m, inclusive, from 1 cm to 1 m, inclusive, or in one embodiment, from 1 cm to 30 cm, inclusive. In accordance with alternative embodiments of the disclosure, the shoulder sections 20 can be otherwise shaped, positioned, arranged, and/or omitted without departing from the disclosure.
In some embodiments of the disclosure, the curved spinning edge 12, the shoulder sections 20, and curved corners 32 affect Taylor cone stability. Different spinning edge 12, shoulder section 20 and corner 32 geometries can, according to the present disclosure, effect varying degrees of non-uniformity (and uniformity) of the electric field, thus affecting the Taylor cone stability differently. When a jet 14 is formed and spinning from a slot die 22 (
In one embodiment, the slot dies 10 (10, 10′, 10″) may comprise two half portions 54 with identical features illustrated in
Table 1 below illustrates how certain properties can be affected in accordance with at least one embodiment of the present disclosure.
20-95
±10-50%
Polyurethane (PU) was electrospun using a flat slot die design similar to slot die 22 as illustrated in
Polyurethane (PU) was electrospun using the radius slot die 10 as illustrated in
PU was electrospun using a die design incorporating a flat edge (with a spinning edge having no radius of curvature) and rounded/curved corners as shown in
There were two noticeable differences between the two sheets produced by the dies with different gap widths. The 0.012″ gap die produced an espun PU sheet with 0.4 inches more usable width. However, this was also accompanied by significantly more surface defects. These types of surface defects are usually attributed to jet instability. It appears the larger gap width is responsible for both of these differences. The larger gap would allow for larger jets and/or more jets, depending upon the voltage which was set high for this example. The increased mat width is believed to be due to the greater number of jets and the increased number of jets would also lead to greater repulsion between the jets, and thus may lead to “walking” of the jets wherein the jets move along the spinning edge. This action causes entanglement between the jets as well as broken fibers that can both lead to surface defects. Controlling the spinning parameters in conjunction with the gap width can allow for various sheet widths and densities to be produced.
While in certain aspects of the current disclosure, the goal is to maximize the stability and control of the Taylor cones or jets in order to achieve more uniform fibers and electrospun fabric, certain embodiments of the present disclosure are for the control and utilization of induced instability for the purposes of creating fibers with lower aspect ratios or lengths, more broken fibers and surface defects on the electrospun fabric, as understood from the previous description, by manipulating various aspects of the slot die (e.g., the slit width, the curvature of the spinning edge and/or the corners) in accordance with principles described above. The ability to control the stability of the electric field and subsequently the stability of the Taylor cones or jets formed at the face of the slot die is key in controlling the uniformity of the fibers and resulting electrospun fabric. While most potential applications benefit from increased uniformity, there are certain applications where induced defects and differences in uniformity are important.
The foregoing description generally illustrates and describes various embodiments of the present disclosure. Regarding the values provided in the above discussions, those values may be approximate, such as in other embodiments that are like the above-disused embodiments. It will, however, be understood by those skilled in the art that various changes and modifications can be made to the above-discussed construction of the present disclosure without departing from the spirit and scope of the disclosure as disclosed herein, and that it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as being illustrative, and not to be taken in a limiting sense. Furthermore, the scope of the present disclosure shall be construed to cover various modifications, combinations, additions, alterations, etc., above and to the above-described embodiments, which shall be considered to be within the scope of the present disclosure. Accordingly, various features and characteristics of the present disclosure as discussed herein may be selectively interchanged and applied to other illustrated and non-illustrated embodiments of the disclosure, and numerous variations, modifications, and additions further can be made thereto without departing from the spirit and scope of the present disclosure as set forth in the appended claims.
This application claims the benefit of U.S. Provisional Application No. 61/917,511, filed Dec. 18, 2013, and U.S. Provisional Application No. 61/950,252, filed Mar. 10, 2014. The entire disclosures of U.S. Provisional Application No. 61/917,511, filed Dec. 18, 2013, and U.S. Provisional Application No. 61/950,252, filed Mar. 10, 2014, are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61917511 | Dec 2013 | US | |
| 61950252 | Mar 2014 | US |
