Solution Spinning of Fibers

Abstract

A technique for forming fibers (e.g., nanofibers, microfibers, etc.) from an aqueous spinning solution is provided. Through careful control over the nature and relative concentration of the components in the solution, fibers can be formed that remain relatively water resistant. To help accomplish these unique features, a pH-sensitive polymer is employed in the spinning solution that is generally soluble in water at a certain pH value, yet generally insoluble in water at a different pH value. This property allows for selective adjustment of the pH both before and after spinning to control the water-solubility of the polymer as desired.

What is claimed is: 
     
         1 . A method for forming fibers from an aqueous spinning solution, wherein the spinning solution contains a pH-sensitive polymer and a solvent that includes water, wherein the pH-sensitive polymer is generally soluble in water at a first pH level and generally insoluble in water at a second pH level, the method comprising spinning the solution into fibers while at the first pH level and selectively adjusting the pH of the fibers during and/or after spinning so the pH is at the second pH level. 
     
     
         2 . The method of  claim 1 , wherein pH-sensitive polymers constitute from about 30 wt. % to about 90 wt. % of the solution and solvents constitute from about 10 wt. % to about 60 wt. % of the solution. 
     
     
         3 . The method of  claim 1 , wherein the pH-sensitive polymer is an acidic polymer. 
     
     
         4 . The method of  claim 3 , wherein the acidic polymer contains carboxylic functional groups. 
     
     
         5 . The method of  claim 4 , wherein the acidic polymer is a (meth)acrylic acid polymer. 
     
     
         6 . The method of  claim 3 , wherein the first pH level is about 5 or more and the second pH level is less than about 5. 
     
     
         7 . The method of  claim 1 , wherein the pH-sensitive polymer is a basic polymer. 
     
     
         8 . The method of  claim 7 , wherein the pH-sensitive polymer contains amine functional groups. 
     
     
         9 . The method of  claim 7 , wherein first pH level is about 5 or less and the second pH level is greater than about 5. 
     
     
         10 . The method of  claim 1 , wherein the spinning solution further contains a pH modifier. 
     
     
         11 . The method of  claim 10 , wherein the pH modifier is removed from the fibers during and/or after spinning. 
     
     
         12 . The method of  claim 10 , wherein the pH modifier has a boiling point in water of from about 10° C. to about 50° C. at atmospheric pressure. 
     
     
         13 . The method of  claim 1 , wherein water constitutes about 50 wt. % or more of the solvents in the spinning solution. 
     
     
         14 . The method of  claim 1 , wherein the spinning solution is generally free of organic solvents. 
     
     
         15 . The method of  claim 1 , wherein the spinning solution further contains a hydrophilic polymer that is generally soluble in water at the first pH level and the second pH level. 
     
     
         16 . The method of  claim 1 , wherein the fibers are formed by centrifugal spinning. 
     
     
         17 . A nanofiber formed according to the method of  claim 1 . 
     
     
         18 . A microfiber formed according to the method of  claim 1 . 
     
     
         19 . A nonwoven web comprising fibers formed according to the method of  claim 1 . 
     
     
         20 . A fiber that is formed from an aqueous spinning solution, the fiber containing one or more pH-sensitive polymers that are generally soluble in water at a first pH level and generally insoluble in water at a second pH level and optionally one or more hydrophilic polymers that are generally soluble in water at the first pH level and the second pH level, and wherein the pH-sensitive polymers constitute about 50 wt. % or more of the polymer content of the fiber and the hydrophilic polymers constitute less than about 50 wt. % of the polymer content of the fiber. 
     
     
         21 . The fiber of  claim 20 , wherein the fiber is a nanofiber or microfiber. 
     
     
         22 . A composite that comprises the fiber of  claim 20  in combination with additional fibers. 
     
     
         23 . A nonwoven web comprising the fiber of  claim 20 . 
     
     
         24 . A laminate comprising the nonwoven web of  claim 23  and layer of a melt-spun nonwoven web, film, strands, or combination thereof. 
     
     
         25 . An absorbent article comprising an absorbent core positioned between a liquid-permeable layer and a substantially liquid-impermeable layer, wherein the absorbent core, liquid-permeable layer, the liquid-impermeable layer, or a combination thereof, comprise the nonwoven web of  claim 23 . 
     
     
         26 . A wipe comprising the nonwoven web of  claim 23 .