Superabsorbent cellulosic fiber and method of making same

Abstract

The present invention relates to superabsorbent cellulose fiber including cellulose and at least one ethylenically unsaturated monomer. The invention also relates to a method of producing the superabsorbent fiber, and absorbent articles including the superabsorbent fiber.

1 - 29 . (canceled)  
   
   
       30 . A method of making a superabsorbent cellulosic fiber, comprising: 
 preparing an aqueous solution comprising an ethylenically unsaturated monomer containing at least one acidic group, and cross-linking agent;    contacting the cellulosic fibers and the aqueous solution;    treating the fiber while under an inert atmosphere with free radical initiator; and    recovering the grafted cellulosic fiber.    
   
   
       31 . The method of  claim 30 , wherein contacting the cellulosic fibers and aqueous solution comprises suspending the cellulosic fibers in an aqueous solution of ethylenically unsaturated monomer and cross-linking agent having a consistency of about 6.0 wt %.  
   
   
       32 . The method of  claim 30 , wherein the cellulose fibers are caustic treated fibers having an a-cellulose content of at least 90%.  
   
   
       33 . The method of  claim 30 , wherein the cellulose fiber is derived from one or more component selected from the group consisting of cotton linters, bagasse, kemp, flax, grass, and combinations and mixtures thereof.  
   
   
       34 . The method of  claim 30 , wherein the ethylenically unsaturated monomer is one or more monomers having the formula:  
     
       
         
         
             
             
         
       
     
     where R represents hydrogen, methyl, or ethyl.  
   
   
       35 . The method of  claim 34 , wherein the ethylenically unsaturated monomer is one or more monomers selected from the group consisting of acrylic acid, methacrylic acid, ethacrylic acid, α-chloroacrylic acid, α-cyanoacrylic acid, vinylsulfonic acid, acryamidopropanesulfonic acid, crotonic acid, α-acryloxypropionic acid, sorbic acid, isocrotonic acid and alkali metal salts itaconic acid, and ammonium salts, and a mixture of thereof.  
   
   
       36 . The method of  claim 35 , wherein the ethylenically unsaturated monomer is one or more monomers selected from the group consisting of acrylic acid, methacrylic acid, and mixtures thereof.  
   
   
       37 . The method of  claim 30 , wherein the cross-linking agent includes polyfunctional groups capable of polymerizing in the presence of a free radical initiator, or optionally capable of reacting with carboxyl and hydroxyl groups of the neighboring monomers simultaneously.  
   
   
       38 . The method of  claim 37 , wherein the cross-linking agent is selected from the group consisting of diacrylates and dimethacrylates of ethylene glycol, bisacrylamides, epoxy acrylates, allylamines, polyepoxides, epoxy silanes, methacryloxy or acryloxy silanes, aminosilanes, and mixtures thereof.  
   
   
       39 . The method of  claim 38 , wherein the cross-linking agent is a mixture of a bisacrylamide and at least one of polyepoxides or methacryloxy silanes.  
   
   
       40 . The method of  claim 30 , wherein the free radical initiator is selected from the group consisting of potassium persulfate, ammonium persulfate, sodium persulfate, alkali-metal persulfates, hydrogen peroxide, ammonium cerium nitrate, 2,2′-azobis-(2-amidinopropane) hydrochloride, and mixtures thereof.  
   
   
       41 . The method of  claim 30 , whereby the fiber has a grafting efficiency of ethylenically unsaturated monomer on cellulose of greater than about 75%.  
   
   
       42 . The method of  claim 30 , wherein the fibers have a cross-linking density of less than about 20%.  
   
   
       43 . The method of  claim 30 , wherein the fibers have a dry density of at least about 0.04 g/cm 3 .  
   
   
       44 . The method of  claim 30 , wherein the fibers have a centrifuge retention of more than about 4 g saline/g fiber.  
   
   
       45 . The method of  claim 30 , wherein the fibers have a free swell of at least about 10 g saline/g fiber.  
   
   
       46 . The method of  claim 30 , wherein the fibers have a grafting efficiency of greater than about 85%.  
   
   
       47 . The method of  claim 30 , wherein when the superabsorbent fiber is incorporated into an absorbent core, the absorbent core has a third insult acquisition time of less than about 25 seconds.  
   
   
       48 . The method of  claim 30 , wherein superabsorbent fiber has absorbent retention efficiency of from about 0.65 to about 0.99, the absorbent retention efficiency being represented by the following equation.  
       Absorbent retention efficiency (%)=Absorbency Under Load/Retention Under Load×100  
   
   
       49 . The method of  claim 30 , wherein when the superabsorbent fiber is incorporated into an absorbent core, the absorbent core has an absorbency efficiency of from about 0.56 to about 0.95, the absorbency efficiency being represented by the following equation.  
       Absorbent efficiency (%)=Absorbency Under Load/Absorbent Capaity×100  
   
   
       50 . The method of  claim 30 , wherein contacting the cellulosic fibers and the aqueous solution comprises suspending the cellulosic fibers in the aqueous solution.  
   
   
       51 . The method of  claim 30 , wherein contacting the cellulosic fibers and the aqueous solution comprises spraying the aqueous solution onto the cellulosic fibers.  
   
   
       52 . The method of  claim 31 , wherein the cellulosic fibers are present in the aqueous solution of ethylenically unsaturated monomer and cross-linking agent at a consistency of about 5%.  
   
   
       53 . The method of  claim 31 , wherein the excess aqueous solution of ethylenically unsaturated monomer and cross-linking agent is removed to obtain cellulosic fibers with a consistency of between about 8 to 35 wt.% based upon the total weight of the fiber and the aqueous solution.  
   
   
       54 . The method of  claim 30 , wherein contacting the cellulosic fibers and aqueous solution comprises spraying an aqueous solution of ethylenically unsaturated monomer and cross-linking agent onto the fiber to obtain fiber with a consistency of between about 8 to 35 wt.% based on the total weight of the fiber and the aqueous solution.  
   
   
       55 - 66 . (canceled)