Liquid ammonia explosion treatment of wood fibers

Abstract

A process of forming improved cellulosic fibers, fibrous compositions containing cellulosic fibers, and absorbent articles comprising such compositions are disclosed. In the process, liquid ammonia penetrates cellulosic fibers in a pressurized environment, and when the pressure is released, an explosive process produces cellulosic fibers having unique structure and properties. The high pressure liquid ammonia treatment introduces a significant curl into the fiber and introduces a smooth, soft, silky feel to the fiber not present in conventional cellulosic fibers. Such fibers are particularly useful in tissue, wipes, distributive layers, fiber mats, filter papers, and other porous articles.

What is claimed is:  
     
         1 . A process comprising: 
 providing a cellulosic fibrous material, said fibrous material having been processed such that the lignin content has been reduced therein;    charging a vessel with a composition comprising said cellulosic fibrous material;    charging the vessel with ammonia at a pressure sufficient to cause the ammonia to penetrate cellulosic fibers in the cellulosic fibrous material; and    rapidly depressurizing the fibrous material.    
     
     
         2 . The process of  claim 1 , wherein the vessel is charged with ammonia at a pressure sufficient to cause the ammonia to penetrate crystalline and amorphous portions of at least some cellulosic fibers.  
     
     
         3 . The process of  claim 1 , wherein, after charging the vessel with ammonia, the ammonia and fibrous material are retained in the vessel for a period of time ranging from about 0.5 to about 30 minutes.  
     
     
         4 . The process of  claim 1 , wherein the ammonia and cellulosic fibrous material are present in a weight ratio of ammonia to cellulosic fibrous material of from about 1:1 to about 8:1.  
     
     
         5 . The process of  claim 1 , wherein the cellulosic fibrous material is in an aqueous mixture prior to saturation with ammonia.  
     
     
         6 . The process of  claim 5 , wherein the aqueous mixture comprises about 10 to about 80 weight percent fibers.  
     
     
         7 . The process of  claim 1 , wherein the pressure ranges from about 100 to about 300 psi.  
     
     
         8 . The process of  claim 1 , wherein the lignin content in the cellulosic fibrous material has been eliminated through a pulping process.  
     
     
         9 . A cellulosic fiber made according to the process of  claim 1 .  
     
     
         10 . A disposable absorbent product comprising the fiber of  claim 9 .  
     
     
         11 . A cellulosic fiber having a curl index of greater than 0.2; and a Wet Curl Value of at least 0.2.  
     
     
         12 . The fiber of  claim 11 , wherein the fiber has a curl index from about 0.2 to about 0.4.  
     
     
         13 . The fiber of  claim 11 , wherein the fiber is formed from wood, cotton, straw, grass, cane, reed, bamboo, stalks with bast fibers, leaf fibers or a combination thereof.  
     
     
         14 . The fiber of  claim 13 , wherein the fiber comprises wood.  
     
     
         15 . A fiber-containing web or fabric comprising the fiber of  claim 11 .  
     
     
         16 . A disposable absorbent product comprising the fiber of  claim 11 .  
     
     
         17 . A disposable absorbent product comprising a cellulosic fiber, wherein the fiber has a curl index of greater than 0.2.  
     
     
         18 . The disposable absorbent product of  claim 17 , wherein the fiber has a curl index from about 0.2 to about 0.4.  
     
     
         19 . The disposable absorbent product of  claim 17 , wherein the product is a diaper, adult incontinent product, bed pad, catamenial device, wound dressing, surgical cape, surgical drape or tissue-based product.  
     
     
         20 . The disposable absorbent product of  claim 17 , wherein the product is a handsheet.  
     
     
         21 . The disposable absorbent product of  claim 17 , wherein the product comprises: 
 a topsheet;    a backsheet; and    an absorbent structure positioned between the topsheet and the backsheet, wherein the absorbent structure comprises said fiber.