MX2010013924A - Process for improved electrospinning using a conductive web. - Google Patents

Abstract

A process for producing a composite conductive fibrous material is provided which includes the steps of providing a conductive fibrous web and supporting the conductive fibrous web with a nonconductive support member. A polymer stream is provided and a voltage is established between the conductive fibrous web and the polymer stream. In this manner, the polymer stream is attracted to the conductive web. Nanofibers are produced by the polymer stream and collected on the conductive web.

Description

PROCESS FOR IMPROVED ELECTROYLATING USING A CONDUCTOR TISSUE Background of the Invention There are many advantages to using very fine fibers, such as nanofibers, in a myriad of applications. Nanofibers with large surface to volume ratios have many potential applications in fields such as protective garments, filtration, sensors, drug delivery systems and in medical applications. While different processes are capable of manufacturing nanofibers, a readily available process is electro-spinning.

Electro-spinning refers to a technology that produces fibers from a polymer solution or μ? molten polymer between fluid dynamics, electrically charged surfaces and electrically charged liquids. In general, a typical electro-spinning apparatus useful for spinning nanofibers from a polymer solution includes a spinner such as a metal needle, a syringe and a syringe pump, a high-voltage power supply, and a metal collector. which is connected to ground. The polymer solution, which typically includes a polymer and a solvent, has been loaded into a syringe and is propelled to the tip of the needle by the pump of the syringe so that a drop is formed at the tip of the needle. An electrode such as a stainless steel wire can be placed inside the syringe and can be used to charge the polymer solution. When the polymer solution inside the syringe is charged, the droplet is drawn into the grounded collector and stretched in a configuration commonly known as a Taylor cone. As the jet of solution flows from the tip of the needle to the grounded collector, the jet is stretched and the solvent in the polymer solution evaporates. As the jet of the solution reaches the harvester connected to ground, the electric forces cause a whipping effect that results in the nanofibers being scattered over the collector. A material, such as a non-woven fabric, can be placed between the collector and the tip of the needle to collect the nanofibers.

Many publications are available that fully describe the electro-spinning process and its control variables, such as, for example, viscosity of the solution, the distance between the tip of the spinner and the collector, the voltage and conductivity of the solution.

Even though the electro-spinning process described above can produce nanofibers repeatedly, some aspects of the process are undesirable. For example, nanofibers can be difficult to separate from the collector. Additionally, it is important to properly manage the electrical charges that impact the polymer jet to obtain optimum fiber formation. While non-conductive textile fabrics have been used to collect the nanofibers and eliminate the problems related to the separation of the nanofibers from the grounded collector, the dielectric nature of the textile fabrics can interfere with the stability of the polymer jet and negatively Impact fiber formation. A solution is desired to address these as well as other problems.

Synthesis of the Invention In accordance with an embodiment of the present invention, a process for producing a conductive fibrous composite material is described. The process generally includes the steps of providing a conductive fibrous web and supporting the conductive fibrous web with a non-conductive support member. A voltage is established between the conductive fibrous web and a polymer jet such that the polymer jet is attracted to the conductive fibrous web. The nanofibers are produced from the polymer jet and collected on the conductive fibrous web.

The present invention also encompasses a process for producing a composite conductive fibrous material wherein the conductive fibrous web is connected to ground and a jet of electrically charged polymer is attracted to the conductive web.

Brief Description of the Drawings A complete and authoritative description of the present invention, including the best mode thereof, addressed to one of ordinary skill in the art, is pointed out more particularly in the remainder of the specification, which refers to the accompanying figures in which : Figure 1 is a simplified schematic representation of a process in accordance with an embodiment of the present invention; Figure 2 is a simplified schematic representation of a process in accordance with another embodiment of the present invention; Y Figure 3 is a photo-micrograph of a material produced by an embodiment of the present invention.

The repeated use of reference characters in the present specification and drawings is intended to present the same or analogous features or elements of the invention.

Detailed Description of Representative Incorporations Reference will now be made in detail to several embodiments of the invention, one or more examples of which are noted below. Each example is provided by way of explanation, not limitation of the invention. It will be apparent to those of ordinary skill in the art that modifications and variations may be made in the present invention without departing from the scope or spirit of the invention. For example, features illustrated or described as part of an embodiment may be used in another embodiment to produce yet another embodiment. It is the intention that the present invention cover such modifications and variations.

Generally speaking, the present invention is broadly directed to a process for producing a composite conductive fibrous material that includes a conductive fibrous web upon which the nanofibers can be spun. The term "nanofibers" generally refers to fibers of very small diameter that have an average diameter no greater than about 1000 nanometers (nm) and a proportion aspect (the ratio between length and width) greater than 50. Nanofibers they are generally understood to have an average fiber diameter in the range of about 10 to about 1000 nanometers. In instances where the particles are present and heterogeneously distributed over the nanofibers, the average diameter of a nanofiber can be measured using known techniques (for example, image analysis tools coupled with an electron microscope), but excluding the parts of a fiber that are substantially enlarged by the presence of added particles relative to the free particle portions of the fiber.

In general, many processes are capable of forming a suitable conductive fabric for use in the present invention. In particular, conductive fibrous fabrics such as textiles, which are generally considered to be flexible materials comprising a network of natural or artificial fibers, are suitable for use in the present invention. Textiles are often categorized as woven materials or non-woven materials. Generally, the term "woven fabric" is used to refer to a sheet or fabric of material formed by the weaving, weaving, crocheting or knotting of long fibers together. Useful fibers in woven materials include wool, silk, natural fibers such as hemp and jute, and mineral fibers such as those fibers of asbestos, basalt, glass and composite materials. Metal fibers and synthetic fibers such as polyester, acrylic, nylon, and polyurethane fibers are also used in woven textiles.

The term "non-woven fabric" generally refers to a sheet or fabric of material having a structure of individual fibers or threads that are between placed, but not in an identifiable manner as in a woven fabric. Examples of suitable non-woven fabrics include, but are not limited to, tissue tissues, spun and bonded fabrics such as spunbond fabrics and blown and bonded fabrics, hydroentangled fabrics, carded and bonded fabrics, and the like. The term "meltblown fabrics" generally refers to a non-woven fabric that is formed by a process in which a molten thermoplastic material is extruded through a plurality of thin, usually circular, capillaries such as converging melted fibers. high velocity gas jets (e.g., air) that attenuate the fibers of molten thermoplastic material to reduce its diameter, which may be of microfiber diameter. The meltblown fibers are then transported by the high speed gas jet and deposited on a collecting surface to form a randomly dispersed meltblown fabric. The term "spunbond" generally refers to a non-woven fabric that contains a small diameter substantially of continuous fibers. The fibers are formed by the extrusion of a molten thermoplastic material from a plurality of usually circular capillaries of a spinner with the diameter of the extruded fibers then being rapidly reduced as, for example, extruded and / or other well-known spinning mechanisms and united. Non-woven fabrics are generally formed in a continuous process. The terms "machine direction" or "MD" typically refer to the direction in which a material is produced. On the other hand, the term "cross machine direction" or "CD" generally refers to the direction perpendicular to the machine direction.

The basis weight of the non-woven fabrics can generally vary, such as from about 0.1 grams per square meter (gsm) to about 120 grams per square meter. In some additions from about 0.5 grams per square meter to about 70 grams per square meter, and in some additions, from about 1 gram per square meter to about 35 grams per square meter. Once formed, the non-woven fabrics can be incorporated into sheets or can be used as a single layer.

As used herein, the term "conductive fabric" generally refers to a fabric having an electrical surface resistance that is less than 1 x 106 ohms / square. The term "non-conductive" generally refers to a material having an electrical surface resistance that is equal to or greater than 1 x 106 ohms / square. The electrical surface resistance (designated "ps") is a measure of a material's ability to conduct an electric current. The electrical surface resistance is determined by the following formula: ps = y L I Where the pa is determined by the ratio of DC voltage drop (designated "U") per unit length (designated "L") to the surface current designated as ls) per unit of width (designated D) . The resulting resistance of the material is expressed in ohms per square.

The electrical surface resistance is generally measured in accordance with the test of the American Society for Testing and Materials (ASTM) number D 257-99. With respect to the present invention, the electrical surface resistance can be measured using a resistance meter that is available from Trek, Inc., (from Medina, New York or online at www.trekinc.com) and which is designated as Trek Model 152. A variety of probes can be used with the Trek Model 152 Surface Resistance Meter, including point-to-point probes, two-point probes, or concentric ring probes. Specific instructions for measuring surface resistance using the Model 152 Trek apparatus can be found in the Trek Application Note number 1005 entitled "Surface Resistance and Surface Resistance Measurements Using a Concentric Ring Probe Technique", also available from The Trek, Inc. The electrode voltage test for the measurement probe can be selected as either 10 volts or 100 volts, and should be used over 10 volts. Before testing, samples should be conditioned at a relative humidity of 50% and at a temperature of 25 degrees Celsius for eight hours.

An exemplary electro-spinning apparatus 10 for spinning a polymer solution is shown schematically in Figures 1 and 2. The electro-spinning apparatus 10 includes a spinner 12 which is held in place by a spinner support 14. A solution of Polymer 16, which has been located in a syringe 18, is urged to the tip of the spinner 12 by a pump 20 or other suitable mechanism. The spinner 12 and the syringe 18 can be formed of metal, glass or other material which is suitable for use in an electro-spinning apparatus.

A conductive fibrous web 24 can be placed over an appropriate distance from the tip of the spinner 12. A non-conductive backing 26 is placed behind the conductive fibrous web 24 to hold the conductive fibrous web 24 in a suitable position during spinning. Various materials can be used as non-conductive support, including ceramic, cardboard, wood, etc. The conductive fibrous web 24 can, in selected embodiments, be secured to the non-conductive backing 26 using a releasable mechanism or adhesive fastening systems.

A voltage is established between the conductive fibrous web 24 and the polymer solution 16. In some embodiments, the conductive fibrous web can be ground and the polymer solution can have a positive charge. In other incorporations, both the conductive fibrous fabric and the polymer solution can be positively charged, but with enough difference between the charges for a voltage to be established that causes the polymer solution to flow into the conductive fibrous fabric. In still other additions, the polymer solution can make ground and a positive charge can be applied to the conductive fibrous web. Such a configuration can assist in electro-spinning materials that degrade or lose desirable properties when subjected to a positive electrical charge.

The voltage can be established in various ways, such as, for example and as shown in Figure 1, energy supplies 22 and 28 which can be electrically connected to the polymer solution 16 and the conductive fibrous web 24, respectively. Alternatively, the power supply 28 may be in electrical communication with the fabric 24 through a connector, device or other mechanism. The voltage established between the conductive fibrous web and the charged polymer jet may be in the range of 10-100 kV, even though the use of voltages, outside this range, may be apriate. The voltage selected will depend on the configuration of the equipment, the selection of the polymer, as well as other variables. In some embodiments, voltages such as 10-40 kV or 50-80 kV may be adequate.

Figure 2 illustrates a fibrous web 24 being unwound from or wound to a roller 30 which is electrically connected to ground 32. The fibrous web 24 can be moved through the non-conductive backing 26 using a conventional unwind / roll mechanism suitable for use with an electro-spinning device. A direct connection to ground can be attached to the conductive fibrous web 24.

The electrical and mechanical forces on the polymer solution 16 are sufficient to form a drop on the tip of the spinner 12 and draw a stream of electrified liquid from the drop. As the jet of polymer solution flows from the tip of the spinner 12 to the conductive fibrous web 24, the solution jet is stretched and the solvent in the polymer solution evaporates. The resulting fibers are deposited on the conductive fibrous web 24.

A wire (not shown) inside the syringe 18 can be used as an electrode to charge the polymer solution. The polymer solution can also be charged by loading the spinner 12 or the syringe 18.

Other electro-spinning systems, including systems having multiple spinners, may be used in accordance with the present invention. Numerous sources of voltage can be provided to control the voltage applied to two or more groups of spinners.

A wide variety of polymer solutions are suitable for use in the present invention. For example, such polymers include, but are not limited to, polyolefins, polyethers, polyacrylates, polyesters, polyamides, polyimides, polysiloxanes, polyphosphazines, vinyl homopolymers and copolymers, as well as naturally occurring polymers such as cellulose, cellulose ester, gums natural and polysaccharides. Solvents which are known to be useful in dissolving the above polymers for the electro-spinning solution include, but are not limited to, alkanes, chloroform, ethyl acetate, tetrahydrofuran, dimethyl formamide, dimethyl acetamide, dimethyl sulfoxide, acetonitrile, acetic acid, formic acid, ethanol, propanol, and water.

Useful conductive fibers in fibrous tissues include carbon fibers and metallic fibers. Suitable carbon fibers include fibers made entirely of carbon or fibers containing only enough carbon such that the fibers are electrically conductive. The carbon fibers can be used which are formed of a polyacrylonitrile polymer (PAN). Such carbon fibers are formed by heating, oxidation, and carbonized polyacrylonitrile polymer (PAN) fibers, polyacrylonitrile-based carbon fibers (PAN) can be widely available from companies such as Toho Tenax America, Inc., of Rockwood , Tennessee. Other raw materials used to make carbon fibers include rayon and pitch oil. Suitable conductive fibrous fabrics that include carbon conductive fibers, such as SGL C25, are available from Technical Fiber Products Ltd. (of Newburgh, New York).

Suitable metallic fibers can include silver, copper, and aluminum fibers, etc. Such conductive fibers can have a variety of suitable lengths and diameters. Conductive polymer fibers can be used and include fibers made of conductive polymers as well as polymer fibers containing a conductive material or impregnated with a conductive material. Metal-coated polymer fibers and mixtures of these various conductive fibers may also be useful in the present invention.

The conductive fibers can be combined with other fibers such as natural or synthetic cellulose fibers including, but not limited to, cotton, abaca, flax, esparto, straw, jute hemp, or fibers obtained from deciduous and coniferous trees, including fibers of soft wood and hard wood fibers. Synthetic fibers such as rayon, polyolefin fibers, polyester fibers, polyvinyl alcohol fibers, bicomponent sheath and core fibers, multi-component binder fibers, and the like can also be combined with the conductive fibers. Recycled fibers can also be used in combination with conductive and non-conductive fibers. The amount of conductive fibers within the fabric can be selected based on various design criteria, such as the type of fiber and the end use of the fabric.

The conductive fabric can contain a substantial amount of pulp fibers and can be made using a process for making tissue. For example, in one embodiment, the conductive fibers can be combined with pulp and water fibers to form an aqueous suspension of fibers which is then deposited on a porous surface to form a conductive tissue. The conductivity of such fabric can be controlled by selecting particular conductive fibers, locating the fibers in particular locations within the fabric and controlling various other factors and variables. For example, the conductive fibers can be incorporated into a fabric including non-conductive fibers such that the fabric is electrically conductive in at least one zone. As such, the fibrous web may be made such that it is capable of conveying an electrical current in the machine direction (MD) or in the cross machine direction (CD), or in any suitable combination of directions. The conductivity of the fibrous web can vary depending on the type of conductive fibers incorporated in the fabric, the amount of conductive fibers incorporated in the fabric, and the manner in which the conductive fibers are placed, concentrated or oriented on the fabric.

A variety of binders including water and soluble organic polymers can be used to bind the various fibers in a fabric. Such binders are widely available and are commonly known.

As described above, the fibrous webs made in accordance with the present invention can be used in numerous applications, such as, for example, in protective garments, odor control applications, filtration, electrical applications such as sensors, drug delivery systems and other medical applications. Protective clothing includes, but is not limited to, absorbent articles such as diapers, underpants, adult incontinence garments and female care. Other protective garments include medical gowns, wound coverings, sterile wraps, face masks, surgical gloves, etc. The materials of the present invention are also useful for many other types of products, including, but not limited to, wipes, filtration media, absorbent pads, electrostatic fabrics, etc.

And emplos In each of the following examples, a wet-laid carbon fiber non-woven fabric was used as the conductive fibrous web 24. Specifically, a substrate of 17 grams per square meter of base weight designated as Optimat® Grade 20304A obtained from Technical Fiber Products Ltd. (from Newburgh, New York). The Optimat® Grade 20304A is formed from carbon fibers that have lengths from 6 millimeters to 12 millimeters with an average diameter of seven microns. The carbon fibers are bonded with an insoluble cross-linked polyester binder.

In each example, a grounded wire was attached to the carbon non-woven fabric to effectively ground the carbon non-woven fabric. Each nonwoven carbon conductive fabric was maintained in a stationary position by a non-conductive cardboard support. The distance between the tip of the spinner and the conductive non-woven fabric was between 10 and 20 centimeters.

An electro-spinning apparatus as schematically shown in Figure 1 was used to apply the nanofibers to a conductive non-woven fabric. In all the examples, a high voltage load of between 10 and 25 kV was applied to the polymer solution to initiate electro-spinning.

In each example, a stable droplet was held at the tip of the spinner by pressure. In Examples 1, 2, and 3, a syringe pump was used to apply pressure to the polymer solution to maintain a stable drop at the end of the blunt tip gauge needle 20 which was placed inside and supported by an aluminum block. In Examples 4 and 5, a hydrostatic pressure system was used to maintain an appropriate amount of polymer solution at the tip of the needle. The hydrostatic pressure system differs from the syringe pump in that it provides improved control over the electro-spinning process, reduced material waste and provides increased safety when operating the apparatus.

In Example 1, a solution of de-ionized water, MU-4 and DMF was prepared. The MU-4 solution is a cationic acrylonitrile acrylic copolymer that is available in 27 percent by weight in a water solution from Bostik, Inc. (of auwatosa, Wisconsin) as product # LX-7170-03. The reported relative molar mass (Mr) of MU-4 is around 250,000. The degree of re-agent N, -dimethylformamide (DMF) was purchased from Aldrich Chemical Co., Inc. (of Milwaukee, Wisconsin), which was added to the MU-4 solution such that DMF comprises 16% by weight of the total polymer solution. A voltage between 10 and 25 kV was applied to the aluminum block as the syringe pump moves the polymer solution to the tip of the needle.

As seen in Figure 3, the nanofibers produced show good distribution and uniformity. Fibers of relative sizes of the polymer were compared to fibers of smaller sizes of non-woven fabric of conductive carbon. When compared to fabrics of longer carbon fibers, the smallest electro-spun fibers appear in the range from submicron diameters to a few microns in diameter.

In Example 2, beads of the AQ 38S polymer were added to the DMF such that the resulting polymer solution constitutes 42 percent by weight of the DMF. The AQ 38S polymer is a sulfopolyester available from Eastman Chemical Co. (of Kingsport, Tennessee) having a relative molar mass (Mr) of about 8,000. The dissolution was achieved by the mechanical agitation of the solution. The set-up of Example 1 was used for Examples 2 and 3. In Example 3, polydimethylaminoethyl methacrylate (PDMAEMA) was obtained from Polysciences, Inc. (of Warrington, Pennsylvania) as a 20 percent by weight solution in tert. -butanol. The relative molar mass of the polydimethylaminoethyl methacrylate polydimethylaminoethyl methacrylate (PDMAEMA) is about 50,000.

In Examples 4 and 5, the polymer solution was contained in a glass pipette that was connected to a nylon support. A tungsten wire was electrically connected to a high-voltage power supply and supplied horizontally through the support to charge the solution. All the connections were hermetic to prevent pressure filtration. Needle valves and a flow meter were attached to the remaining outlet of the nylon support, which allows precise pressure to be applied to the solution loaded inside the pipette.

In Example 4, polyhydroxyethyl methacrylate (PHEMA) obtained from Aldrich Chemical Co. Inc. (of Milwaukee, Wisconsin) having a relative molar mass (Mr) of about 300,000 was added to the DMF such that the resulting polymer solution constitutes 30 percent by weight of the DMF. The dissolution was achieved by the mechanical agitation of the solution. In Example 5, polyethylene oxide (PEO) was obtained from Polysciences, Inc. (of Warrington, Pennsylvania) having a Mr of 300,000 and added to PHMB (polyhexamethylene biguanide) in a ratio of 10.0 to 0.9. The polyhexamethylene biguanide was purchased from Arch Chemicals, of Norwalk, CT as the registered Cosmocilkmark CQ _ The deionized water was added to the PEO / PHMB so that the final polymer solution constituted 6 percent by weight of water.

The materials formed in each example showed good distribution and uniformity of the nanofibers on the conductive non-woven fabric. Therefore, the materials formed by the process of the present invention will be suitable for using a wide variety of applications including, but not limited to commercial, medical and personal applications such as, for example, conductive garments, devices and components of devices and filtration of gases and liquids.

Although the invention has been described in detail with respect to the specific embodiments thereof, it will be appreciated by those skilled in the art to achieve an understanding of the foregoing that alterations, variations and equivalents of these additions can be easily conceived. Therefore, the scope of the present invention should be evaluated as that of the appended claims and any equivalents thereof.

Claims (19)

R E I V I N D I C A C I O N S

1. A process for producing a composite conductive fibrous material comprising the steps of: provide a conductive fibrous tissue with a first potential; supporting the conductive fibrous tissue with a non-conductive support member; providing a polymer stream with a second potential which is different from the first potential so that the polymer stream is attracted to the conductive fibrous tissue; produce the nanofibers from the polymer stream; Y collect the nanofibers on the conductive fibrous tissue.

2. The process as claimed in clause 1, characterized in that the first potential is zero and the second potential is a positive charge.

3. The process as claimed in clause 2, characterized in that the difference between the first potential and the second potential creates a voltage greater than lOkV.

. The process as claimed in clause 3, characterized in that the difference between the first potential and the second potential creates a voltage greater than 40kV.

5. The process as claimed in clause 1, characterized in that the second potential is zero and the first potential is a positive charge.

6. The process as claimed in clause 5, characterized in that the difference between the first potential and the second potential creates a voltage greater than lOkV.

7. The process as claimed in clause 6, characterized in that the difference between the first potential and the second potential creates a voltage greater than 40kV.

8. The process as claimed in clause 1, characterized in that the polymer stream is formed of polyolefins, polyethers, polyacrylates, polyesters, polyamides, polyimides, polysiloxanes, polyphosphazines, vinyl homopolymers and copolymers, naturally occurring polymers such as cellulose , cellulose ester, natural gums and polysaccharides and mixtures thereof.

9. The process as claimed in clause 1, characterized in that the conductive fibrous fabric includes conductive fibers comprising carbon fibers, metallic fibers, conductive polymeric fibers, metal coated fibers or mixtures thereof.

10. The process as claimed in clause 9, characterized in that the conductive fibrous fabric includes the conductive carbon fibers having an average length of from about 1 millimeter to about 12 millimeters.

11. The process as claimed in clause 9, characterized in that the conductive fibrous tissue includes carbon fibers that are formed of acrylonitrile.

12. The process as claimed in clause 1, characterized in that the conductive fibrous fabric is a non-woven fabric.

13. The process as claimed in clause 1, characterized in that the conductive fibrous tissue is a non-woven fabric.

14. A process for producing a composite conductive fibrous material comprising the steps of: provide a conductive fibrous tissue; supporting the conductive fibrous tissue with a non-conductive support member; provide a polymer stream; establish a voltage between the conductive fibrous tissue and the polymer stream so that the polymer stream is attracted to the conductive fibrous tissue, - produce nanofibers from the polymer stream; Y collect the nanofibers on the conductive fibrous tissue.

15. The process as claimed in clause 14, characterized in that the step of establishing a voltage between the conductive fibrous tissue and the polymer stream creates a voltage greater than 10kV.

16. The process as claimed in clause 15, characterized in that the step of establishing a voltage between the conductive fibrous tissue and the polymer stream creates a voltage greater than 40kV.

17. A filter that includes the conductive compound made according to the process as claimed in clause 1.

18. A protective garment that includes the conductive compound made according to the process as claimed in clause 1.

19. A process for producing a composite conductive fibrous material comprising the steps of: provide a conductive fibrous fabric comprising carbon fibers, - support the conductive fibrous tissue with a non-conductive support; provide an electrically charged polymer stream; grinding the conducting fibrous nonwoven fabric so that the charged polymer stream is attracted to the conductive fibrous tissue; produce nanofibers from the charged polymer stream; Y collect the nanofiber on the conductive fiber fibrous tissue. SUMMARIZES A process for producing a conductive fibrous composite material is provided which includes the steps of providing a conductive fibrous tissue and supporting the conductive fibrous tissue with a non-conductive support member. A polymer stream is provided and a voltage is established between the conductive fibrous tissue and the polymer stream. In this way, the polymer stream is attracted to the conductive fabric. The nanofibers are produced by the polymer stream and collected on the conductive fabric.