Apparatus and Method for Producing Electrospun Fibers

Abstract

An apparatus for making electrspun fibers comprises a collector that may be submerged in a coagulation bath. The collector may be automatically movable between a first position and a second position, wherein at least a portion of the collected fibers are submerged in a coagulation bath in the first position and spaced apart from the coagulation bath in the second position. The collector may be a rotating collector. A process for making electrospun fibers comprises electrospinning a dispersion and collecting a plurality of electrospun fibers, followed by submerging the collected fibers in a coagulation bath.

1 . A process for making fibers comprising:
 providing a starting material comprising an organic polymer;   dissolving the starting material in a polar solvent to create a dispersion;   electrospinning the dispersion by providing an electric charge on droplets of the dispersion to produce a j et of polymer and provide a plurality of electrically induced bending instabilities and/or whipping motions;   collecting a plurality of the jets as fibers; and   submerging the plurality of fibers into a coagulation bath as they are collected.   
   
   
       2 . The process of  claim 1 , wherein the organic polymer used in the providing step is cellulose. 
   
   
       3 . The process of  claim 1 , wherein the polar solvent used in the dissolving step comprises lithium chloride and N,N-dimethylacetamide. 
   
   
       4 . The process of  claim 1 , wherein the polar solvent is sufficiently volatile to substantially dissolve during the electrospinning step. 
   
   
       5 . The process of  claim 1 , wherein the electrospinning step is carried out in an electric field between about 1.0 kV/cm to about 4.0 kV/cm at a flow rate between about 0.03 ml/min. and about 0.05 ml/min. 
   
   
       6 . The process of  claim 1 , wherein the fibers are nanofibers comprising diameters between about 100 nm and 300 nm. 
   
   
       7 . The process of  claim 1 , wherein the fibers comprise a degree of crystallinity between about 1% and about 40%. 
   
   
       8 . The process of  claim 1 , wherein the fibers comprise a substantially amorphous form of cellulose exhibiting an X-ray diffraction pattern comprising at least two 2θ values selected from about 7.0 degrees and about 17.8 degrees. 
   
   
       9 . The process of  claim 1 , wherein the fibers comprise a repeat unit conforming to the general formula: 
     
       
         
         
             
             
         
       
     
     in random positions and orientations. 
   
   
       10 . The process of  claim 1 , wherein the coagulation bath comprises at least one of water and alcohol for removing residual solvent without dissolving the fibers. 
   
   
       11 . The process of  claim 1 , wherein the fibers are collected on a rotating collector and the rotating collector is submerged into a coagulation bath on a periodic basis. 
   
   
       12 . The process of  claim 1 , further comprising heating the rotating collector to temperatures ranging between about 70° C. and 110° C. 
   
   
       13 . The process of  claim 12 , further comprising shielding a voltage collector for supplying an electric charge from heating. 
   
   
       14 . The process of  claim 1 , wherein the collector comprises a cellulose filter media. 
   
   
       15 . A process for making cellulose nanofibers comprising:
 providing a starting material comprising cellulose;   dissolving the starting material in a polar solvent unreactive with cellulose to create a dispersion;   electrospinning the dispersion by providing an electric charge on droplets of the dispersion to produce a charged jet of polymer and provide a plurality of electrically induced bending instabilities and/or whipping motions;   collecting a plurality of the charged jets as substantially amorphous non-derivatized cellulose nanofibers on a rotating collector; and.   submerging the rotating collector comprising the plurality of substantially amorphous non-derivatized fibers into a coagulation bath on a periodic basis.   
   
   
       16 . The process of  claim 15 , wherein the fibers are submerged in the coagulation bath at regular intervals between about 1 and about 3 seconds. 
   
   
       17 . An apparatus for making fibers through electrospinning comprising:
 a chamber for receiving a dispersion;   a pump upstream of the chamber for dispensing the dispersion;   a syringe for receiving the dispersion from the pump, the syringe comprising an opening sized to providing droplets of the dispersion;   a voltage supplier in electrical communication with the syringe to provide an electric charge in the droplets emanating from the opening to produce a plurality of charged jets and provide a plurality of electrically induced bending instabilities and/or whipping motions;   a collector for receiving and collecting the charged jets as non-woven fibers, the collector automatically movable between a first position and a second position, wherein at least a portion of the collected fibers are submerged in a coagulation bath in the first position and spaced apart from the coagulation bath in the second position.   
   
   
       18 . The apparatus of  claim 17 , wherein the collector comprises a rotating collector. 
   
   
       19 . The apparatus of  claim 18 , wherein the rotating collector is submerged in the coagulation bath on a periodic basis. 
   
   
       20 . The apparatus of  claim 17 , further comprising a heating chamber constructed of an electrically and thermally insulating material, the heating chamber positioned to heat the dispersion as it travels through the syringe. 
   
   
       21 . The apparatus of  claim 20 , wherein the heating chamber is shielded from the voltage supplier. 
   
   
       22 . The apparatus of  claim 17 , further comprising a heating gun for heating the collector. 
   
   
       23 . The apparatus of  claim 17 , further comprising a motor for driving the collector.