Apparatus and Method for Elevated Temperature Electrospinning

Abstract

Elevated temperature electrospinning apparatus comprises a pump upstream of or containing a resistance heater, means to shield applied electrostatic field from the resistance heater, and a temperature modulator for modulating temperature in the spinning region.

What is claimed is: 
     
         1 . Apparatus for elevated temperature production of non-woven fabric from thermoplastic polymer or thermoplastic polymer nanoclay nanocomposite, neat or in solution and requiring elevated temperature for dissolving in an acceptable solvent, said apparatus comprising a resistance heater for melting the polymer or nanocomposite or maintaining the polymer or nanocomposite in solution in acceptable solvent; a pump upstream of or containing the resistance heater for causing dispensing of said melted polymer or nanocomposite or elevated temperature solution; a droplet forming passageway for receiving said polymer or nanocomposite melt or elevated temperature solution and having one or more outlet orifices for providing one or more droplets of melted polymer or nanocomposite or elevated temperature solution at the one or more outlet orifices; a guiding chamber having an inlet side in fluid communication with the outlet orifice(s); a collection surface at a rear side of the guiding chamber for receiving elongated fibers of polymer or nanocomposite and collecting them as a non-woven fabric; and a high voltage source in electrical communication with the droplet forming passageway to provide an electric charge in the droplet(s) emitting therefrom to overcome the surface tension of a droplet to produce a jet of melted polymer or nanocomposite or elevated temperature solution in the guiding chamber giving rise to unstable flow through the guiding chamber to the collection surface manifested by a series of electrically induced bending instabilities and flashing off of any solvent during passage of polymer or nanocomposite to the collection surface and production of elongated fibers of polymer or nanocomposite and deposit of these on the collection surface so as to form the non-woven fabric. 
     
     
         2 . The apparatus of  claim 1  where the electrical communication of the high voltage source is shielded from the resistance heater to prevent induced voltage in the resistance heater and where a temperature modulator is provided for the guiding chamber to adjust cooling of the fiber being formed to provide against premature solidification and to provide against induction of relaxation of molecular orientation, and to potentiate flashing off of any solvent, without affecting the bending instabilities causing fiber elongation. 
     
     
         3 . The apparatus of  claim 1  which is for batch operation, said apparatus comprising the following elements:
 (a) a syringe having an inlet for introduction into the syringe of solid meltable thermoplastic polymer or solid meltable thermoplastic polymer nanoclay nanocomposite or solution of thermoplastic polymer or thermoplastic polymer nanoclay nanocomposite requiring elevated temperature for dissolving, and an outlet for dispensing of melted thermoplastic polymer or nanocomposite or elevated temperature solution, 
 (b) a heating chamber in heat exchange communication with the syringe to supply heat to the syringe to melt polymer or nanocomposite or maintain polymer or nanocomposite in solution within the syringe, 
 (c) droplet forming passageway having an inlet in fluid communication with the outlet of the syringe and one or more outlet orifices for providing one or more droplets of polymer or nanocomposite melt or elevated temperature solution at the one or more outlet orifices; 
 (d) a pump upstream of the inlet of the syringe for causing the syringe to dispense melted polymer or nanocomposite or elevated temperature solution to the droplet forming passageway, 
 (e) a guiding chamber having inlet side in fluid communication with the orifice outlet(s); 
 (f) a collection surface at a rear end of the guiding chamber; and a high voltage source in electrical communication with the droplet forming passageway to provide an electric charge in the droplet(s) emitting therefrom to overcome the surface tension of a droplet to produce a jet of melted polymer or nanocomposite or elevated temperature solution in the guiding chamber giving rise to unstable flow through the guiding chamber to the collection surface manifested by a series of electrically induced bending instabilities and flashing off of any solvent, during passage to the collection surface, and production of elongated fibers of the polymer or nanocomposite which are deposited on the collection surface where they are collected as a non-woven fabric. 
 
     
     
         4 . The apparatus of  claim 1  which comprises at least one of the following elements (h), (i) and (j):
 (h) a temperature modulator for the guiding chamber to adjust cooling of the fiber being formed to provide against premature solidification and to provide against induction of relaxation of molecular orientation and to potentiate flashing off of any solvent, without affecting the bending instabilities causing fiber elongation, 
 (i) a controller for controlling temperature in the heating chamber, a heating coil in the heating chamber, and shielding for the heating coil inside the heating chamber to prevent induced voltage in the heating coil from the electric charge supplied by the high voltage source so that induced voltage will not affect or damage the controller, 
 (j) the heating chamber being constructed of material comprising a substance that provides both thermal and electrical insulation. 
 
     
     
         5 . The apparatus of  claim 4  which includes a modulator for the temperature of the collection surface to provide annealing of fibers deposited on the collection surface to provide fibers on the collection surface with properties that do not change with time and have increased molecular orientation. 
     
     
         6 . The apparatus of  claim 1  which is for continuous melt electrospinning operation, and for production of non-woven fabric from thermoplastic polymer or thermoplastic polymer nanoclay nanocomposite, comprising a hopper for containing and feeding chunks of thermoplastic polymer or thermoplastic polymer nanoclay nanocomposite; an extruder for receiving the polymer or nanocomposite from the hopper and conveying, melting and pumping the polymer or nanocomposite to produce a flow of polymer or nanocomposite melt therefrom; a melt pump for receiving the melted polymer or nanocomposite from the extruder and for maintaining the melted condition of the polymer or nanocomposite melt by means of electric resistance heating and providing a melt output; a header for receiving the melt output and distributing it to multiple nozzles for forming droplets of polymer or nanocomposite melt; a guiding chamber for receiving the output of the nozzles, a collection surface at a rear end of the guiding chamber; and a high voltage source in electrical communication with the nozzles to provide an electric charge in the droplets emitting therefrom to overcome the surface tension of a droplet to produce a jet of polymer or nanocomposite melt giving rise to unstable flow through the guiding chamber to the collection surface manifested by a series of electrically induced bending instabilities during passage to the collection surface and production of elongated fibers of the polymer or nanocomposite which are deposited on the collection surface where they are collected as a non-woven fabric, a shield for the header and nozzles to prevent induced voltage in the melt pump from the electric charge supplied by the high voltage source; and an infrared heater for the guiding chamber to adjust cooling of the fiber formed therein to provide against premature solidification and to provide against induction of relaxation of molecular orientation, without affecting the bending instabilities causing fiber elongation. 
     
     
         7 . A method for melt electrospinning production of non-woven fabric from meltable thermoplastic polymer or meltable thermoplastic polymer nanoclay nanocomposite, said method comprising the steps of
 (a) melting thermoplastic polymer or nanocomposite in a melting zone,   (b) moving the thermoplastic polymer or nanocomposite through the melting zone by a force supplier upstream of or in the melting zone,   (c) forming droplets from the melted polymer or nanocomposite,   (d) providing an electric charge on the droplets to overcome the surface tension of a droplet to produce a jet of melted polymer or nanocomposite and provide unstable flow involving a plurality of electrically induced bending instabilities/whipping motions and elongation of and production of polymer or nanocomposite fibers,   (e) collecting of the elongated fibers to form a non-woven fabric.   
     
     
         8 . The method of  claim 7  additionally comprising at least one of the following steps (f) and (g):
 (f) providing a temperature for the polymer or nanocomposite being subjected to electrically induced bending instabilities/whipping motions and fiber elongation so as to provide against premature solidification and to provide against induction of relaxation of molecular orientation without affecting the electrically induced bending instabilities, 
 (g) shielding to prevent induction of voltage in the melting zone. 
 
     
     
         9 . The method of  claim 8  comprising the additional step of annealing the collected fibers to impart stability and molecular orientation. 
     
     
         10 . A method for high temperature solution electrospinning of non-woven fabric from thermoplastic polymer or thermoplastic polymer nanoclay nanocomposite that is not dissolvable at room temperature in an acceptable solvent, said method comprising the steps of:
 (a) homogenizing the polymer or nanocomposite in solvent in an elevated temperature zone to form a solution of the polymer or nanocomposite in the solvent;   (b) maintaining the solution at a temperature sufficient for maintaining dissolution in a second elevated temperature zone;   (c) moving the solution through the second elevated temperature zone by a force supplier upstream of or at the second elevated temperature zone;   (d) forming droplets of the solution moved through the second elevated temperature zone;   (e) providing an electric charge on the droplets to overcome the surface tension of a droplet to produce a jet of polymer on-nanocomposite solution and provide unstable flow involving a plurality of electrically induced bending instabilities/whipping motions and flashing off of solvent and elongation of and production of polymer or nanocomposite fibers;   (f) collecting the fibers to form a non-woven fabric.   
     
     
         11 . The method of  claim 10  additionally comprising at least one of the following steps (g) and (h):
 (g) providing a temperature for the polymer or nanocomposite and solution thereof being subjected to electrically induced bending instabilities/whipping motions and fiber elongation to provide against premature solidification and to provide against induction of relaxation of molecular orientation and potentiate flashing off of solvent, without affecting the electrically induced bending instabilities, 
 (h) shielding to prevent induction of voltage in the second elevated temperature zone. 
 
     
     
         12 . The method of  claim 11 , comprising the additional step of annealing the collected fibers to impart stability and molecular orientation. 
     
     
         13 . A fiber formed from a polymer, wherein a temperature in a droplet forming passageway that the polymer passes through to form droplets is above 215° C. 
     
     
         14 . The fiber of  claim 13 , wherein the polymer is a meltable thermoplastic polymer. 
     
     
         15 . The fiber of  claim 14 , wherein the meltable thermoplastic polymer is selected from the group consisting of rubber, polycarbonate, polystyrene, poly(methyl methacrylate), poly(lactic acid), polyethylene terephthalate, polybutylene terephthalate, nylon 6, polypropylene, polyethylene, and nylon 6,6.