Superabsorbent cellulosic fiber

Abstract

A modified cellulosic fiber having superabsorbent properties is described. The modified fiber of the invention has a fibrous structure substantially identical to the cellulosic fiber from which it is derived. The modified fiber is a water-swellable, water-insoluble fiber that substantially retains its fibrous structure in its expanded, water-swelled state. The modified fiber is a sulfated and crosslinked cellulosic fiber having a liquid absorption capacity of at least about 4 g/g. In one embodiment, the modified fiber is an individual, crosslinked, sulfated cellulosic fiber. In another aspects, the invention provides a rollgood that includes the modified fiber, absorbent composites and articles that include the modified fiber, and methods for making the modified cellulosic fiber.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:  
     
         1 . A modified cellulosic fiber, comprising a sulfated cellulosic fiber crosslinked to an extent to render the fiber substantially insoluble in water.  
     
     
         2 . The fiber of  claim 1  having a liquid absorption capacity of at least about 4 g/g.  
     
     
         3 . The fiber of  claim 1 , wherein the average degree of sulfate substitution is from about 0.1 to about 2.0.  
     
     
         4 . The fiber of  claim 1 , wherein the average degree of sulfate substitution is from about 0.2 to about 1.0.  
     
     
         5 . The fiber of  claim 1 , wherein the average degree of sulfate substitution is from about 0.3 to about 0.5.  
     
     
         6 . The fiber of  claim 1 , wherein the cellulosic fiber is a wood pulp fiber.  
     
     
         7 . Individual, water-swellable, water-insoluble, intrafiber crosslinked, sulfated cellulosic fibers.  
     
     
         8 . The fibers of  claim 7  having a liquid absorption capacity of at least about 4 g/g.  
     
     
         9 . The fibers of  claim 7 , wherein the average degree of sulfate substitution is from about 0.1 to about 2.0.  
     
     
         10 . The fibers of  claim 7 , wherein the average degree of sulfate substitution is from about 0.2 to about 1.0.  
     
     
         11 . The fibers of  claim 7 , wherein the average degree of sulfate substitution is from about 0.3 to about 0.5.  
     
     
         12 . The fibers of  claim 7 , wherein the cellulosic fibers are wood pulp fibers.  
     
     
         13 . The fibers of  claim 7 , wherein the fibers are crosslinked with a crosslinking agent selected from the group consisting of a urea-based crosslinking agent, a polycarboxylic acid crosslinking agent, an aldehyde crosslinking agent, a dialdehyde crosslinking agent, and mixtures thereof.  
     
     
         14 . The fibers of  claim 13 , wherein the crosslinking agent is applied to the fibers in an amount from about 0.01 to about 8.0 percent by weight based on the total weight of fibers.  
     
     
         15 . The fibers of  claim 13 , wherein the crosslinking agent is applied to the fibers in an amount from about 0.02 to about 5.0 percent by weight based on the total weight of fibers.  
     
     
         16 . A rollgood comprising the fibers of claims  1  or  7 .  
     
     
         17 . The rollgood of  claim 16  further comprising another fiber.  
     
     
         18 . The rollgood of  claim 17 , wherein the other fiber is at least one of fluff pulp fibers, crosslinked cellulosic fibers, cotton fibers, CTMP fibers, and synthetic fibers.  
     
     
         19 . The rollgood of  claim 16  further comprising an absorbent material.  
     
     
         20 . The rollgood of  claim 16  further comprising a binder material.  
     
     
         21 . An absorbent article comprising the rollgood of  claim 16 .  
     
     
         22 . An absorbent composite comprising the fibers of claims  1  or  7 .  
     
     
         23 . The composite of  claim 22  further comprising another fiber.  
     
     
         24 . The composite of  claim 23 , wherein the other fiber is at least one of fluff pulp fibers, crosslinked cellulosic fibers, cotton fibers, CTMP fibers, and synthetic fibers.  
     
     
         25 . An absorbent article comprising the fibers of claims  1  or  7 .  
     
     
         26 . The article of  claim 25 , wherein the article is at least one of an infant diaper, an adult incontinence product, and a feminine care product.  
     
     
         27 . An absorbent article comprising a liquid pervious topsheet, a liquid impervious backsheet attached to the topsheet, and an absorbent member intermediate the topsheet and backsheet, wherein the absorbent member comprises the fibers of claims  1  or  7 .  
     
     
         28 . An absorbent article comprising a liquid pervious topsheet, a liquid impervious backsheet attached to the topsheet, and an absorbent member intermediate the topsheet and backsheet, wherein the absorbent member comprises the rollgood of  claim 16 .  
     
     
         29 . A method for making cellulosic fibers, comprising crosslinking sulfated cellulosic fibers to render the fibers substantially water-insoluble.  
     
     
         30 . The method of  claim 29 , wherein crosslinking sulfated cellulosic fibers comprises treating sulfated cellulosic fibers with an amount of a crosslinking agent sufficient to render the crosslinked fibers substantially water insoluble.  
     
     
         31 . The method of  claim 30 , wherein the amount of crosslinking agent ranges from about 0.01 to about 8.0 percent by weight crosslinking agent based on the total weight of fibers.  
     
     
         32 . The method of  claim 30 , wherein the crosslinking agent is selected from the group consisting of a urea-based crosslinking agent, a polycarboxylic acid crosslinking agent, an aldehyde crosslinking agent, a dialdehyde crosslinking agent, and mixtures thereof.  
     
     
         33 . The method of  claim 30 , wherein the crosslinking agent is applied to the fibers as an aqueous alcoholic solution.  
     
     
         34 . The method of  claim 29 , wherein the sulfated cellulosic fibers have an average degree of sulfate substitution of from about 0.1 to about 2.0.  
     
     
         35 . The method of  claim 29  further comprising baling the crosslinked, sulfated fibers.  
     
     
         36 . The method of  claim 29  further comprising forming the crosslinked, sulfated fibers into a rollgood.  
     
     
         37 . A method for making cellulosic fibers, comprising the steps of: 
 reacting cellulosic fibers with a sulfating agent to provide sulfated fibers;    applying a crosslinking agent to the sulfated fibers; and    curing the crosslinking agent to provide crosslinked, sulfated cellulosic fibers.    
     
     
         38 . The method of  claim 37 , wherein the sulfating agent comprises sulfuric acid.  
     
     
         39 . The method of  claim 37 , wherein the sulfating agent comprises a solution of sulfuric acid in an organic solvent.  
     
     
         40 . The method of  claim 37 , wherein the organic solvent is an alcohol is selected from the group consisting of isopropanol, propanol, and butanol.  
     
     
         41 . The method of  claim 40 , wherein the ratio of sulfuric acid to alcohol is about 2.4:1 by mole.  
     
     
         42 . The method of  claim 37  further comprising treating the sulfated fibers with a neutralizing agent prior to crosslinking.  
     
     
         43 . The method of  claim 42 , wherein the neutralizing agent comprises a base.  
     
     
         44 . The method of  claim 42 , wherein the neutralizing agent comprises a multivalent metal salt.  
     
     
         45 . The method of  claim 44 , wherein the metal salt is selected from the group consisting of cerium nitrate, magnesium sulfate, and aluminum sulfate.  
     
     
         46 . The method of  claim 37 , wherein the crosslinking agent is selected from the group consisting of a urea-based crosslinking agent, a polycarboxylic acid crosslinking agent, an aldehyde crosslinking agent, a dialdehyde crosslinking agent, and mixtures thereof.  
     
     
         47 . The method of  claim 37 , wherein the crosslinking agent is applied to the fibers as an aqueous alcoholic solution.  
     
     
         48 . The method of  claim 37 , wherein the cellulosic fibers are reacted with the sulfating agent at a temperature of about 4° C.  
     
     
         49 . The method of  claim 37  further comprising swelling the fibers prior to reacting the fibers with the sulfating agent.  
     
     
         50 . The method of  claim 49 , wherein swelling the fibers comprises treating the fibers with a swelling agent selected from the group consisting of acetic acid, acetic anhydride, and mixtures thereof.  
     
     
         51 . The method of  claim 50  further comprising removing excess swelling agent prior to reacting the fibers with the sulfating agent.  
     
     
         52 . The method of  claim 37 , wherein reacting the fibers with a sulfating agent comprises adding the fibers to an alcoholic solution of the sulfating agent.  
     
     
         53 . The method of  claim 52 , wherein the fibers are cooled to about 4° C. prior to adding the fibers to the alcoholic solution of the sulfating agent.  
     
     
         54 . The method of  claim 52 , wherein the alcoholic solution of the sulfating agent is cooled to about 4° C. prior to the addition.  
     
     
         55 . The method of  claim 37 , wherein the sulfating agent is reacted with the fibers at a temperature of about 4° C.  
     
     
         56 . The method of  claim 42  further comprising separating the sulfated fibers from excess sulfating agent prior to treating the sulfated fibers with the neutralizing agent.  
     
     
         57 . The method of  claim 42  further comprising washing the sulfated fibers with alcohol solution prior to treating the sulfated fibers with the neutralizing agent.  
     
     
         58 . The method of  claim 37 , wherein the cellulosic fibers further comprise magnesium sulfate.  
     
     
         59 . The method of  claim 37 , wherein the sulfating agent further comprises magnesium sulfate.  
     
     
         60 . The method of  claim 40 , wherein the alcoholic solution of the sulfating agent further comprises magnesium sulfate.  
     
     
         61 . A method for making cellulosic fibers, comprising the steps of: 
 swelling dry cellulosic fibers with a swelling agent to provide swelled fibers;    separating excess swelling agent from the swelled fibers;    reacting swelled cellulosic fibers with a sulfating agent to provide sulfated fibers;    separating excess sulfating agent from the sulfated fibers;    treating the sulfated fibers with a neutralizing agent to provide fibers suitable for crosslinking;    applying a crosslinking agent to the sulfated fibers; and    curing the crosslinking agent to provide crosslinked, sulfated cellulosic fibers.    
     
     
         62 . The method of  claim 61 , wherein the dry cellulosic fibers comprise never-dried cellulosic fibers solvent exchanged with an alcohol.  
     
     
         63 . The method of  claim 61 , wherein the swelling agent is selected from the group consisting of acetic acid, acetic anhydride, and mixtures thereof.  
     
     
         64 . The method of  claim 61 , wherein the sulfating agent comprises sulfuric acid.  
     
     
         65 . The method of  claim 61 , wherein the sulfating agent comprises a solution of sulfuric acid in an alcohol.  
     
     
         66 . The method of  claim 65 , wherein the ratio of sulfuric acid to alcohol is about 2.4:1.  
     
     
         67 . The method of  claim 65 , wherein the alcohol comprises isopropanol.  
     
     
         68 . The method of  claim 61 , wherein the neutralizing agent comprises sodium hydroxide.  
     
     
         69 . The method of  claim 61 , wherein the crosslinking agent is applied to the fibers as an aqueous alcoholic solution.  
     
     
         70 . The method of  claim 61 , wherein the cellulosic fibers are reacted with the sulfating agent at a temperature of about 4° C.  
     
     
         71 . The method of  claim 61 , wherein the cellulosic fibers are reacted with the sulfating agent for a period of time from about 10 to about 60 minutes.  
     
     
         72 . The method of  claim 61  further comprising washing the sulfated fibers with an alcohol solution prior to treating the sulfated fibers with the neutralizing agent.  
     
     
         73 . The method of  claim 61 , wherein the sulfating agent further comprises magnesium sulfate.  
     
     
         74 . The product obtainable by the process of  claim 29 .  
     
     
         75 . The product obtainable by the process of  claim 37 .  
     
     
         76 . The product obtainable by the process of  claim 61 .  
     
     
         77 . An absorbent core for an absorbent article, comprising a sulfated cellulosic fiber crosslinked to an extent to render the fiber substantially insoluble in water, wherein the core has a liquid absorption capacity of at least about 22 g/g.  
     
     
         78 . An absorbent core for an absorbent article, comprising individual, water-swellable, water-insoluble, intrafiber crosslinked, sulfated cellulosic fibers, wherein the core has a liquid absorption capacity of at least about 22 g/g.